NAVAIR 00-80T-112 NATOPS INSTRUMENT FLIGHT MANUAL (15 NOVEMBER 2006)

NAVAIR 00-80T-112

19.3.3 Aileron Roll

Begin the maneuver from straight-and-level flight after obtaining the desired airspeed. Smoothly increase the pitch

attitude with the wings level and as directed by the applicable NATOPS flight manual. Start a roll in either direction

and adjust the rate of roll so that, when inverted, the wings will be level as the fuselage dot of the miniature aircraft

passes through the horizon bar. Continue the roll and recover in a nose-low, wings-level attitude (Figure 19-10). The

entire maneuver should be accomplished by reference to the attitude indicator. The rate of roll should be constant and

continuous throughout the maneuver.

19.3.4 Loops

Advance the power and lower the nose to attain a desired entry airspeed compatible with aircraft performance. Refer

to the attitude indicator and smoothly raise the nose to the horizon with the wings level. Upon reaching the horizon,

increase back-pressure, ensuring sufficient g’s are applied to pull the aircraft up through the vertical and over the top

of the loop without exceeding aircraft limitations (Figure 19-11).

Bear in mind that some attitude indicators reverse themselves by controlled precession as the aircraft passes through

a vertical attitude. It is essential that the aircraft wings are level prior to and after this reversal. An easy method of

keeping the wings level is to keep the bank pointer centered at the top of the attitude indicator prior to reversal and

then keeping it centered at the bottom after reversal. Be alert to recognize and then disregard the attitude indications

during this short period of controlled precession.

As the airspeed decreases in the pullup, pitch control may become less effective and further backpressure may be

required to maintain constant g force. As the airspeed drops to the point where the g can no longer be maintained in

the control region without stalling, release some backpressure.

90° OF ROLL

INVERTED

RECOVERY

A BEGIN ROLL

Figure 19-10. Aileron Roll

19-9

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NAVAIR 00-80T-112

90° OF ROLL

RECOVER

A INVERTED (NOSE SLIGHTLY BELOW

HORIZON, BEGIN ROLLOUT)

(NOSE LOW)

Figure 19-12. Immelmann Recovery

Ensure sufficient backpressure remains to fly the aircraft through the top of the loop with a safe margin of airspeed

above the stall. In some aircraft, rudder application may be necessary to maintain balanced flight throughout the

maneuver.

After passing through the inverted attitude at the top of the loop, gradually increase the backpressure as the airspeed

increases. Recover from the resultant dive, being alert for controlled precession on the attitude indicator as the aircraft

passes through the vertical attitude. Keep the aircraft wings level throughout the maneuver, being careful not to

exceed any aircraft limitations.

Note

Considering varying load conditions with resultant accelerated stall speeds

and feel/buffet changes, reference to the angle of attack indicator in aircraft

so equipped is recommended during critical segments of the loop.

19.3.5 Immelmann

The Immelmann (Figure 19-12) is executed in the same manner as the first half of a loop followed by a half roll to

an upright attitude. Maintain inverted flight through the top of the maneuver until just before the fuselage dot of the

miniature aircraft passes through the horizon bar. Release backpressure upon approaching the horizon and roll to an

upright level attitude. Do not reduce power until the maneuver is completed.

19.3.6 Half Cuban Eight

The Half Cuban Eight is the first half of a loop with a rollout from the inverted nosedown attitude, resulting in a 180_

heading change. It differs from the Immelmann turn in that the rollout is in a nose-low attitude rather than a level

attitude. This maneuver is practiced to develop the pilot’s confidence in the attitude indicator (Figure 19-13).

19-11

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NAVAIR 00-80T-112

CHAPTER 20

Unusual Attitudes

20.1

INTRODUCTION

An unusual attitude is an aircraft attitude occurring inadvertently (Figure 20-1). It may result from one factor or a

combination of several factors such as turbulence, distraction of cockpit duties, instrument failure, inattention, spatial

disorientation, etc. In most instances, these attitudes are mild enough for the pilot to recover by reestablishing the

proper attitude for the desired flight condition and resuming a normal cross-check.

Techniques of recovery should be compatible with the severity of the unusual attitude, the characteristics of the

aircraft, and the altitude available for the recovery. The procedures outlined in this chapter are not designed to recover

from controlled tactical maneuvers. They are applicable to unusual attitudes wherein recovery can be accomplished

before entering areas of critical aerodynamics peculiar to a specific type of aircraft.

1. Decreasing the angle of bank in a dive should assist pitch control.

2. Increasing the angle of bank in a climb may assist pitch control.

3. In most aircraft, a decrease of angle of attack is an acceptable recovery technique (near zero g), and in some

aircraft this is the only acceptable technique, as an increase of bank will aggravate the recovery (refer to

applicable NATOPS flight manual).

4. Power and drag devices used properly will assist airspeed control.

Figure 20-1. Unusual Attitude

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NAVAIR 00-80T-112

20.2

ATTITUDE INTERPRETATION

Normally, an unusual attitude is recognized in one of two ways: an unusual attitude picture on the attitude indicator

or unusual performance on the performance instruments. Regardless of how the attitude is recognized, verify an

unusual attitude exists by comparing control and performance instrument indications prior to initiating recovery on

the attitude indicator. This precludes entering an unusual attitude as a result of making control movements to correct

for erroneous instrument indications. During this process, the attitude must correctly be interpreted. Additional

attitude indicating sources (standby attitude indicator, copilot attitude indicator, etc.) should be used. If there is any

doubt as to proper attitude indicator operation, recovery should be made using attitude indicator inoperative

procedures.

The following techniques will aid aircraft attitude interpretation on the attitude indicator:

1. For attitude indicators with a single bank pointer and bank scale at the top, the bank pointer can be considered

a sky pointer. It always points up and should be in the upper half of the case. Rolling toward the bank pointer

to place it in the upper half of the case will correct an inverted attitude.

2. For those attitude indicators with the bank scale at the bottom, rolling in the direction that will place the pitch

reference scale right-side up will correct an inverted attitude (Figure 20-2).

Ease of pitch interpretation varies with the type of attitude indicator installed. Attitude indicators having pitch

reference scales in degrees and grey/black attitude spheres can easily be interpreted for climb or dive indications. For

those aircraft not so equipped, the airspeed indicator, altimeter, or vertical speed indicator generally present the most

easily interpreted indications of a climb or a dive. Attitude interpretation is a skill that must be highly developed by

practice in flight or on the ground in simulators or with mockups.

20.3

RECOVERY PROCEDURES

Unusual attitudes are generally classified as nose high or nose low. Each has distinct recovery techniques that are

generally applicable to all aircraft. Refer to the NATOPS flight manual for specific recovery procedures.

20.3.1 Nose-High Recovery

Factors to consider in nose-high recoveries are pitch attitude and airspeed. If the pitch attitude is not extreme and

airspeed is not approaching the stall ranges, recovery can be considered to be a normal nose-high attitude.

To recover from a normal nose-high unusual attitude, use power as necessary, and smoothly lower the nose toward

the level flight attitude. As the nose approaches the level flight attitude, level the wings and readjust power as

necessary.

If the pitch attitude is extreme or airspeed is approaching the stall range, recovery can be considered to be for an

extreme nose-high attitude.

To recover from an extreme nose-high unusual attitude, roll the aircraft in the shortest direction toward the wingover

position. As the nose falls through the horizon, level the wings and raise the nose to the level flight attitude. Use power

as necessary throughout the recovery.

Note

For swept-wing aircraft, the wingover recovery method is not acceptable.

Instead, a decrease in angle of attack (zero g) is used until sufficient

airspeed is gained to prevent an accelerated stall or spin condition. For

further information, consult the applicable NATOPS flight manual.

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NAVAIR 00-80T-112

20.3.2 Nose-Low Recovery

Factors to be considered in recovering from nose-low unusual attitudes are altitude and g loading during pullout. If

altitude permits, avoid rolling pullouts, as allowable stresses in an angle of bank are considerably lower than those

allowed in a wings-level pullout.

To recover from a nose-low unusual attitude, roll to a wings-level upright position, then raise the nose to the level

flight attitude. Adjust power and/or drag devices as appropriate.

During unusual attitude recoveries, the pilot should coordinate the amount of bank and power used with the rate at

which airspeed and pitch are being controlled. Bank and power used must be compatible with aircraft and engine

characteristics.

Note

For helicopters encountering blade stall, in a nose-high attitude, collective

pitch (power) must be reduced before applying attitude corrections. To

avoid blade stall when recovering from steep diving attitudes, reduce

collective pitch and bank attitude before initiating a pitch change. In all

cases, avoid abnormal positive g loads; prevent negative g loads and

inverted flight.

20.3.3 Partial Panel Unusual Attitudes

With an inoperative attitude indicator, successful recovery from unusual attitudes depends greatly on pilot proficiency

and early recognition of attitude indicator failure. For example, attitude indicator failure should immediately be

suspected if control pressures were applied for a turn without corresponding attitude indicator changes. Another

example would be satisfactory performance instrument indications that contradict the picture on the attitude indicator.

20.3.3.1 Recovery Procedures — Partial Panel

Should an unusual attitude be encountered with an inoperative attitude indicator, determine whether the aircraft is

in a climb or a dive by reference to the airspeed, altimeter, and vertical speed indicators.

If nose low, roll to center the turn needle and recover from the dive. Adjust power and/or drag devices as appropriate.

If nose high, use power as required. Apply controls as necessary to decrease the aircraft g to not less than zero g. After

reaching level flight and if the aircraft is in a turn, smoothly roll to center the turn needle; reversal of the altimeter

and vertical speeds tends to indicate passage of a level flight attitude. (Refer to the appropriate NATOPS flight manual

for detailed aircraft limitations.)

As the level flight attitude is approached, as indicated by the decrease in rate of change of airspeed and altitude, a

correction will be required to prevent chasing the vertical speed indicator. For example, in recovery from a nose-low

unusual attitude, once the turn needle has been centered, back stick pressure is applied until the performance

indicators show the approach of level flight. Because of the slight lag inherent in these instruments, the pilot should

anticipate the performance instruments and apply opposite pressure as the indicators show the approach of the level

flight attitude. Failure to do so will usually result in the progressing from one unusual attitude to another (in this

example, from nose low to nose high).

Spatial disorientation may become severe during the recovery from

unusual attitudes with an inoperative attitude indicator. Extreme attitudes

may result in an excessive loss of altitude and possible loss of aircraft

control; therefore, the pilot should decide upon an altitude at which

recovery attempts will be discontinued and the aircraft abandoned.

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NAVAIR 00-80T-112

CHAPTER 21

VHF Omnidirectional Range (VOR)

21.1

INTRODUCTION

The VHF Omnidirectional Range (VOR) is a radio facility that eliminated many of the difficulties previously

encountered when navigating with the radio compass. VOR course information is not affected by weather or other

factors common to ADF. With a course indicator, it is possible to select and precisely fly any 1 of 360 courses to or

from a VOR.

21.2

EQUIPMENT AND OPERATION

21.2.1 Equipment

TheVORprovides360coursesthatradiatefromthestationlikespokesfromthehubofawheel.Thesecourses,known

as radials, are identified by their magnetic bearing from the station; thus, regardless of heading, an aircraft on the 90_

radial is physically located due east of the station. Flying to the station on this radial, the magnetic course is 270_.

As the transmitting equipment is in the VHF band, the signals are free of atmospheric disturbances but subject to

line-of-sight reception. Reception range varies according to the altitude of the aircraft (Figure 21-1).

Figure 21-1. Radials

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NAVAIR 00-80T-112

21.2.1.1 Principle of Operation

The transmission principle of the VOR is based on the creation of a phase difference between two signals. One of

these signals, the reference phase, is omnidirectional and radiates from the station in a circular pattern. The phase of

this signal is constant throughout 360_. The other signal, the variable phase, rotates uniformly at 1,800 rpm, which

causes its phase to vary at a constant rate.

Magnetic north is used as the baseline for electronically measuring the phase relationship between the reference and

variable phase signals. At magnetic north, the signals are exactly in phase; however, a phase difference exists at any

other point around the station. This phase difference is measured electronically by the aircraft receiver and displayed

on the navigation instruments (Radio Magnetic Indicator [RMI], course indicator, etc.) (Figure 21-2).

21.2.1.2 Control Panel

Typical VOR control panels contain a power switch, frequency selector knobs, a frequency window, and a volume

control (Figure 21-3).

The VHF navigation frequency band is as follows:

1. ILS — 108.1 to 111.9 MHz (odd tenths).

2. VOR — 108.0 to 117.95 MHz.

Figure 21-2. Signal Phase Angle Relationship

ORIGINAL

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NAVAIR 00-80T-112

Figure 21-3. Control Panel

Since a large portion of the frequency band overlaps into the VHF communication band (108.0 to 135.9 MHz), the

VOR receiver may be used as a secondary VHF communication receiver.

The volume control knob controls the level of the signals going into the headset only. It has no effect on the signal

reception of the VOR receiver.

21.2.2 Operation

21.2.2.1 Tuning

To tune the VOR equipment, flip the power switch ON, select the desired frequency, and identify the station. The

station identification may be a three-letter Morse code, a recorded voice, or a combination of both. The voice

announcement alternates with the usual Morse code identification. If no air/ground communications facility is

associated with the VOR, the phrase “UNATTENDED VOR” (VORTAC) precedes the station name. Positively

identify the selected station. Through human error or equipment malfunction, it is possible that the station intended

to be selected is not the one being received. This may occur as the result of failing to select the correct frequency or

failure of the receiver to channel to the new frequency.

After identifying the VOR station, an unreliable signal can be identified on the instrument (refer to specific aircraft

NATOPS). Some VOR stations transmit Transcribed Weather Broadcasts (TWEBs), Hazardous In-Flight Weather

Advisory Service

(HIWAS), Airmen’s Meteorological Information

(AIRMETs), Significant Meteorological

Information (SIGMETs), and possibly communications from air traffic control.

Note

During periods of maintenance, the coded identification is removed.

21-3

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NAVAIR 00-80T-112

After the set is tuned, check the bearing pointer, Course Deviation Indicator (CDI), and TO-FROM indicator for

proper operation. The bearing pointer should point to the magnetic bearing to the station. The CDI should center when

this bearing is set in the course selector window, and the TO-FROM indicator should indicate TO.

Note

Although the RMI is used with the course indicator in the accompanying

text and illustrations, the Bearing-Distance-Heading Indicator (BDHI)

display of bearing information is identical.

21.2.2.2 VOR/DME Paired Frequencies

Distance Measuring Equipment (DME) consists of airborne and ground equipment, usually co-located. The DME

provides distance (and in some systems groundspeed) information only from the ground facility. DME operates in

the Ultrahigh Frequency (UHF) band; however, its frequency can be “paired” with VOR or Instrument Landing

System (ILS) or Localizer (LOC) frequencies. The receiving equipment in most aircraft provide for automatic DME

selection through a coupled VOR/lLS receiver. Selection of the appropriate VOR or ILS frequency automatically

tunes the DME. Some equipment then allows the user to manually tune another VOR/ILS frequency and keep the

DME paired to the previously selected VOR/ILS frequency. The UHF/VHF paired frequency chart can be found in

the Flight Information Handbook.

21.3

PROCEDURES

21.3.1 Proceeding Direct to Station

To proceed directly to the station, turn the aircraft in the shorter direction to place the bearing pointer under the top

index of the RMI. Set the bearing read under the head of the bearing pointer into the course selector window. If this

does not center the CDI exactly, rotate the course set knob until the CDI does center. Maintain this course to the station.

If either the compass card or the bearing pointer is inoperative, the course indicator may be used to determine the

bearing to the station by rotating the course set knob until the CDI centers and TO is read in the TO-FROM indicator.

The magnetic bearing from the aircraft to the station then appears in the course selector window (Figure 21-4).

21.3.2 Course Interceptions

Course interceptions are performed in most phases of instrument navigation. The equipment used varies, but an

intercept heading must be flown that results in an angle or rate of intercept sufficient to solve a particular problem.

Rate of intercept, seen by the pilot as bearing pointer or CDI movement, is a result of the following factors:

1. The angle at which the aircraft is flown toward a desired course (angle of intercept).

2. True airspeed and wind (groundspeed).

3. Distance from the station.

The angle of intercept is the angle between the heading of the aircraft (intercept heading) and the desired course.

Controlling this angle by selection and/or adjustment of the intercept heading is the easiest and most effective way

to control course interceptions. Angle of intercept must be greater than the degrees from course, but should not exceed

90_. At 90_, rate of intercept is the maximum possible. Within this limit, adjust to achieve the most desirable rate

of intercept.

When selecting an intercept heading, the key factor is the relationship between distance from the station and degrees

from the course. Each degree, or radial, is 1 nm wide at a distance of 60 nm from the station. Width increases or

decreases in proportion to the 60 nm distance. For example, 1_ is 2 nm wide at 120 nm and 1/2 nm wide at 30 nm.

For a given groundspeed and angle of intercept, the resultant rate of intercept varies according to the distance from

the station.

ORIGINAL

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NAVAIR 00-80T-112

When selecting an intercept heading to form an angle of intercept, consider the following factors:

1. Degrees from course.

2. Distance from the station.

3. True airspeed and wind (groundspeed).

21.3.3 Inbound Procedures

To intercept a radial while flying to a station, a number of varying methods may be employed. Generally, setting up

a 45_ angle of intercept is recommended; 30_ angle of intercept is equally correct, as is the double the angle off the

bow method if the number of radials to be crossed is not in excess of 45. The double-the-angle-off-the-bow method

is described in detail in Chapter 22, as is the timed distance method for radial changes in excess of 45_.

21.3.3.1 RMI Only

Inbound course interceptions utilizing only the RMI are described in detail in Figure 21-5. The essential element is

to visualize the problem utilizing the RMI center as the station and the tail of the bearing pointer as the present aircraft

position. Then a pilot can visualize the new radial that the pilot wants to intercept as is done in Tactical Air Navigation

(TACAN) point to point. As distances are not known, a standard 45_ angle of intercept is recommended. It is

important to disregard aircraft heading until the intercept heading is computed. Then, turn in the shortest direction

to that heading.

21.3.3.2 RMI and CDI

Inbound course interceptions utilizing RMI and CDI are described in detail in Figure 21-6. Essentially these can be

accomplished exactly as under RMI only with the additional aid of using the CDI in the final phase.

21.3.3.3 CDI Only

Inbound course interceptions utilizing the CDI only are described in detail in Figure 21-7. The essential element is

to visualize the problem on an RMI or on any compass card and then proceed as under RMI and CDI. Some CDIs

do not have heading pointers and some VOR sets do not employ a bearing pointer. In these cases, it is essential to

disregard aircraft heading until the intercept heading is determined. Then, turn in the shortest direction to that heading

(utilizing a timed turn if all compass cards are inoperative).

21.3.4 Outbound Procedures — Immediately After Station Passage

Intercepting courses immediately after station passage does not require large intercept angles. Because of radial

convergence, actual aircraft displacement from course is relatively small compared to bearing pointer or CDI

indications. For example, a 30_ off-course indication when 2 nm from the station represents approximately 1 nm off

course.

Paralleling the desired outbound course while allowing the bearing pointer or CDI to stabilize is acceptable. If this

method is utilized, proceed as outlined below for outboard course interceptions.

Continuing to turn to intercept the outbound course may be preferred in order to expedite the intercept. This method

is described in Figure 21-8.

Utilize the RMI or CDI as available. Use an angle or intercept equal to the number of degrees of radial change desired;

however, to prevent overshooting, do not turn more than 45_ beyond the heading required to parallel course.

ORIGINAL

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NAVAIR 00-80T-112

Inbound Procedural Steps — RMI Only

1. Tune and identify the VOR station.

The bearing pointer will then point to the magnetic course to the station as it appears on the RMI;

heading has nothing to do with the radial the aircraft is on. The aircraft can be visualized on the tail of the

bearing pointer with the station at the center of the RMI.

2. Determine intercept heading.

Determine which radial the aircraft is on by noting the tail of the bearing pointer. Determine the required

direction of turn to the new radial. An intercept angle is formed when the head of the bearing pointer is

between the desired course and the top index of the RMI.

3. Determine and set in the new course.

4. Turn in the shortest direction to the intercept heading.

Set up a 45-degree, 30-degree, or double-the-angle-off-the-bow intercept.

5. Maintain the intercept heading until a lead point is reached, then complete the intercept.

Lead point depends on bearing pointer rate of movement and the time required to turn on course.

Figure 21-5. Inbound Course Interception (RMI Only) (Sheet 2 of 2)

ORIGINAL

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NAVAIR 00-80T-112

INTERCEPT

COMPLETED

Inbound Procedural Steps — Course Indicator and RMI

1. Tune and identify the VOR station.

The bearing pointer will function as described in Figure 21-5.

2. Set the desired inbound course in the course selector window and check for a TO indication.

3. Determine intercept heading as described in Figure 21-5.

4. Turn in the shortest direction to the intercept heading.

The CDI heading pointer should be positioned on the upper half of the CDI when established in the

intercept heading. Both the heading pointer and course bar must be on the same side of the CDI while

intercepting the desired course. The CDI heading pointer should be deflected in a manner that

corresponds to the angle of intercept.

5. Maintain the intercept heading until a lead point is reached, then complete the intercept.

Lead point depends on bearing pointer/CDI rate of movement and the time required to turn on course.

Figure 21-6. Inbound Course Interception (Course Indicator and RMI) (Sheet 2 of 2)

ORIGINAL

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NAVAIR 00-80T-112

Inbound Procedural Steps — Course Indicator Only

1. Tune and identify the VOR station.

2. Center the CDI with TO in the TO-FROM indicator.

Note the course displayed in the course selector window and visualize on any compass card a bearing

pointer pointing to the course displayed and the desired inbound radial.

3. Determine an intercept heading using RMI only procedures.

4. Set the desired inbound course in the course selector window and check for a TO indication.

5. Turn to the intercept heading.

Turn in the shortest direction to the intercept heading. If a CDI heading pointer is installed, ensure the

pointer is positioned in the upper half of the CDI when established on the intercept heading.

Note

If all compass cards are inoperative, make a timed turn to the intercept heading using

the magnetic compass.

6. Maintain the intercept heading until a lead point is reached, then complete the intercept.

Lead point depends on the CDI rate of movement and the same required to turn on course.

Figure 21-7. Inbound Course Interception (CDI Only) (Sheet 2 of 2)

ORIGINAL

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NAVAIR 00-80T-112

FROM

INTERCEPT

COMPLETED

Outbound Procedural Steps Immediately After Station Passage — Course Indicator and RMI

1. Tune and identify the VOR station.

This should already be accomplished.

2. Turn in the shortest direction to a heading that will parallel or intercept the outbound course.

Turning to parallel the desired outbound course is acceptable. Continuing the turn to an intercept heading

may be preferable to expedite the intercept. If turning immediately to intercept, utilize an angle of

intercept equal to the number of degrees or radial desired, not to exceed 45 degrees.

3. Set the desired course in the course selector window and check for FROM indication.

4. Turn to an intercept heading, if not previously accomplished.

5. Maintain the intercept heading until a lead point is reached, then complete the intercept.

Lead point depends on bearing pointer/CDI rate of movement and the time required to turn on course.

Figure 21-8. Course Interception Immediately After Station Passage (Course Indicator and RMI) (Sheet 2 of 2)

ORIGINAL

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NAVAIR 00-80T-112

Outbound Procedural Steps — RMI Only

1. Tune and identify the VOR station.

2. Determine which radial the aircraft is on by noting the tail of the bearing pointer.

Determine the direction of turn to the new radial.

3. Determine and set in the new course.

4. Turn to the intercept heading in the direction determined in step 2.

Set up a 45-degree, 30-degree, or double-the-angle-off-the-bow intercept.

5. Maintain the intercept heading until a lead point is reached, then complete the intercept.

Lead point depends on bearing pointer rate of movement and the time required to turn on course.

Figure 21-9. Outbound Course Interception — Away from the Station (RMI Only) (Sheet 2 of 2)

21.3.5 Outbound Procedures

To intercept a radial while flying from a station, several methods may be employed. Whereas a 45_ angle of intercept

is recommended, a 30_ angle of intercept or the double the angle off the bow (as described in Figure 21-16) may be

used.

21.3.5.1 RMI Only

Outbound radial interceptions utilizing only the RMI are described in detail in Figure 21-9. The essential element is

to visualize the problem utilizing the RMI center as the station and the tail of the bearing pointer as the present aircraft

position. Then a pilot can visualize the new radial that the pilot wants to intercept as is done in TACAN point to point.

As distances are not known, the pilot can picture the aircraft at the middle of the bearing pointer with the desired point

of interception at the outer edge of the compass card.

21.3.5.2 RMI and CDI

Outbound radial interception utilizing RMI and CDI are described in detail in Figure 21-10. Essentially, these can

be accomplished exactly as described in paragraph 21.3.5.1 with the additional aid of using the CDI in the final phase.

21.3.5.3 CDI Only

Outbound radial interceptions utilizing the CDI only are described in detail in Figure 21-11. The essential element

is to visualize the problem on an RMI or on any compass card and then proceed as under RMI and CDI. Some CDIs

do not have a heading pointer, and some VOR sets do not employ a bearing pointer. In these cases, it is essential to

disregard aircraft heading until the intercept heading is determined. Then turn in the shortest direction to that heading

(utilizing a timed turn if all compass cards are inoperative).

ORIGINAL

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NAVAIR 00-80T-112

21.3.6 Completing the Intercept

After the intercept heading has been established, adjustments may be required to achieve a more desirable angle

or rate of intercept. As the aircraft approaches course, determine a lead point for turning because of turn radius.

A properly selected lead point will result in the turn being completed as the course is intercepted. Lead point is

determined by comparing bearing pointer/CDI movement (rate of intercept) to the time required to turn to

course. Whenever the CDI is fully deflected, monitor the bearing pointer to detect unusually slow or fast rates

of intercept. Remember that the CDI remains fully deflected until the aircraft is within 10_ of course. As CDI

movement can be accurately compared with angle of intercept displayed by the heading pointer, use the course

indicator for completing intercepts whenever possible. If it is obvious that the lead point selected will result in

undershooting the desired course, reduce the angle of bank or roll out of the turn and resume the intercept. If the

lead point selected results in an overshoot, continue the turn and roll out with an intercept heading. Aircraft is

on course when CDI is centered and/or the bearing pointer points to the desired course. Complete turn to course

with a correction applied for known wind.

21.3.7 Estimating Drift Correction

After completing the turn to course with the CDI centered, maintain heading until the CDI indicates deviation from

the selected course. At the first indication of course deviation, turn toward the CDI to reintercept course. Follow the

same procedure used for a normal course interception and consider the same factors (i.e., degrees from course,

distance from the station, True Airspeed [TAS], and wind). After returning to course from a deviation caused by wind,

reestimate the drift correction and increase or decrease the one previously held. To keep the CDI centered, make

further corrections from this new heading. When close to the station, the CDI may show a rapid movement from the

on-course indication because of radial convergence; however, actual course deviation is probably small, especially

if wind drift has been solved. Avoid overcorrecting in this situation.

To maintain a course to the station using only the RMI, maintain heading until the bearing pointer shows a deviation

from the desired course. To return to course, use normal course interception procedures. The aircraft is back on course

when the desired course is again shown under the head of the bearing pointer. If you have applied the correct wind

drift, the pointer should continue to point to the desired course. If the pointer moves toward the top index, the drift

correction is too small; if it moves away from the top index, it is too large.

To maintain an outbound course, use outbound course interception procedures. Apply corrections to keep the desired

course under the tail of the bearing pointer. After applying a wind drift correction outbound and the tail of the pointer

moves toward the top index, the drift correction is too large; if it moves away from the top index, the drift correction

is too small (Figure 21-12).

21.3.8 Homing

After the VOR station is tuned, the VOR bearing pointer will point to the magnetic bearing of the selected station.

To home to the station, turn the aircraft to place the head of the bearing pointer under the top index. By keeping the

bearing pointer under the index, the station will always be directly ahead of the aircraft. As homing does not

incorporate wind drift correction, in a crosswind, the aircraft follows a curved path to the station. Homing is not an

approved IFR procedure and, therefore, should be used only when close to the station (Figure 21-13).

21-17

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NAVAIR 00-80T-112

FROM

Outbound Procedural Steps — Course Indicator Only

1. Tune and identify the VOR station.

2. Set the desired outbound course in the course selector window.

3. Turn to an intercept heading.

Determine direction of turn as in RMI only by visualizing the intercept on any compass card.

4. Maintain the intercept heading until a lead point is reached, then complete the intercept.

Lead point depends on the CDI rate of movement and the time required to turn on course.

Figure 21-11. Outbound Course Interception (CDI Only) (Sheet 2 of 2)

21.3.9 Time-Distance Check

To compute time and distance from an omnirange, first turn the aircraft to place the bearing pointer on the nearest

90_ index. Set the bearing read under the head of the bearing pointer into the course selector window. If this does not

center the CDI exactly, rotate the course set knob until the CDI does center. Note the time and maintain heading. When

the CDI shows a definite displacement from center, set a 10_ bearing change in the course window by rotating the

course set knob in the direction of CDI movement. Check that the CDI has moved over the heading pointer. Maintain

heading until the CDI recenters. Note elapsed time, and apply the following formulas:

Time in seconds between bearings

+ Minutes to station.

Degrees of bearing change

TAS or groundspeed in nm per minute times minutes from the station will give distance. Expressed as a formula, this

is:

* TAS

minutes from the station = nm from the station.

*If known, groundspeed should be substituted for TAS.

For example, if it requires 2 minutes to fly a 10_ bearing change at a TAS of 360 knots, you are:

120 seconds

+ 12 minutes from the station.

10 degrees

360 knots

12 = 72 nm from the station.

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ORIGINAL

NAVAIR 00-80T-112

The time from the station is easily calculated provided a 10_ bearing change is flown and the elapsed time for the

bearing change is noted in seconds. The time from the station in minutes is determined by counting off 1 decimal point

from the elapsed time for the bearing change; thus, if it requires 75 seconds to fly a 10_ bearing change, the aircraft

is 7.5 minutes from the station.

Determining the TAS in nm per minute can be easily approximated by referring to indicated Mach, if available. For

example, Mach 0.6 equals approximately 6 nm per minute; Mach 0.7 equals 7 nm per minute, etc. (Figure 21-14).

There are several other methods for determining time and distance from a radio station. If it is a station to be passed

abeam, the conventional bow and beam bearing method utilized for visible bearings in navigation may be used

(Figure 21-15). The double the angle on the bow method, similar to the same system discussed for intercepting a

bearing, may also be used (Figure 21-16). More often, however, the pilot will be in a situation where the pilot desires

time/distance from a station that is the destination. If no specific course or bearing is required for the approach, it is

suggested one be selected suitable for the double-the-angle-on-the-bow interception, or one 10_ off your inbound

track for the 30_ turn method (explained in paragraph 21.3.10), and request clearance to approach on that bearing.

The 30_ turn method of time/distance check is preferable because it requires very little alteration of heading; however,

it may or may not be accurate in an unknown wind situation.

21.3.10 30° Method

This method (Figure 21-17) is begun when tracking toward station. To start the check, turn 30_ right or left and note

the time (to 1 second). Hold this new heading. If the VOR had read zero before the turn, it should now read 330_ or

30° relative. If drift correction was being held, it should now read 330_ or 30_ relative, plus or minus that correction.

This heading should be maintained on the remote compass or RMI until the needle of the VOR has moved 10_ toward

the wingtip position. Note the exact time, turn toward the station, and track to the station. The time from this second

turn to the station will be three times the time between turns.

The distance to the station is also three times the distance between turns. (Compute the time/distance at groundspeed

if groundspeed is known, or at the TAS if groundspeed is not known.)

There are two minor precautions to observe in connection with the 30_ turn method. First, determine drift before starting.

If the pattern is flown under conditions of no wind and there is a wind blowing the aircraft off course, the results obtained

will not be accurate. In fact, if the needle does not progress toward the wingtip at all, the aircraft is drifting to the other

side of the station entirely.

The accuracy of time and distance checks is governed by the existing wind, the degree of bearing change, and the

accuracy of timing. The number of variables involved causes the result to be an approximation; however, by flying

an accurate heading and checking the time and bearing closely, you can get a reasonable estimate of time and distance

from the station.

Time and distance checks using only the course indicator employ the same principles. First, rotate the course set knob

until the CDI centers, then turn to a heading 90_ from the bearing in the course window. After completing this turn,

rotate the course set knob to recenter the CDI and accomplish the time and distance check as previously described.

For VOR time-distance checks using the RMI only, refer to ADF time-distance check in Chapter 23.

21.3.11 Station Passage

The cone of confusion is encountered just before passing over the VOR station. As the width of the cone varies with

altitude, the actual time spent in the cone varies according to altitude and groundspeed. As the aircraft enters the cone

of confusion, the bearing pointer may swing from side to side, the CDI will reflect the bearing pointer movement,

the TO-FROM indicator may fluctuate between TO and FROM, and the course warning flag may appear. For timing

purposes, station passage occurs when the TO-FROM indicator makes the first positive change to FROM. After the

bearing pointer stabilizes, the CDI resumes its normal indications.

When making course changes over a VORTAC and range is available, the pilot may begin the turn just before station

passage so as to roll out on the desired outbound course.

21-23

ORIGINAL

NAVAIR 00-80T-112

21.3.12 Holding

(Figures 21-18, 21-19, 21-20, 21-21, 21-22, 21-23, and 21-24.)

1. When holding at a VOR station, pilots should begin the turn to the outbound leg at the time of the first complete

reversal of the TO-FROM indicator.

2. Patterns at the most generally used holding fixes are depicted on appropriate charts. Pilots are expected to hold

in the pattern depicted unless specifically advised otherwise by Air Traffic Control (ATC).

3. ATC clearance requiring that an aircraft be held at a holding point where the pattern is not depicted will include

the following information:

a. General holding instructions.

(1) The direction to hold from holding point. (The direction to hold with relation to the holding fix will be

specified as one of eight general points of the compass [i.e., north, northeast, east, etc.].)

(2) Holding fix.

(3) On (specified) radial course, magnetic bearing airway number of jet route.

(4) Outbound leg length in nm, if DME is to be used.

(5) Left turns, if nonstandard pattern is to be used.

Figure 21-17. 30° Turn Method of Time/Distance Check

21-27

ORIGINAL

NAVAIR 00-80T-112

When the inbound course is toward the NAVAID and

the fix distance is 10 nm and the leg length is 5 nm,

then the end of the outbound leg will be reached

when the DME reads 15 nm.

END OUTBOUND LEG

NAVAID

15 nm

DME FIX

10 nm

When the inbound course is away from the NAVAID

and the fix distance is 28 nm and the leg length is

8 nm, then the end of the outbound leg will be reached

when the DME reads 20 nm.

28 nm

20 nm

DME FIX

NAVAID

END OUTBOUND LEG

Figure 21-24. DME Holding

(6) Time to expect further clearance.

b. Detailed holding instructions: Same as a (1), (2), and (3) above with following additions to (4) and (5):

(1) or minute(s) if DME is not to be used.

(2) or right turns if standard pattern is to be used.

Holding pattern airspace protection is based on the following procedures. They are the only procedures for

entry and holding recommended by the Federal Aviation Administration (FAA).

a. Entry procedures.

(1) Descriptive terms.

(2) Airspeed (maximum) — Refer to Flight Information Publications (FLIP) general planning.

(3) Entry.

(a) Parallel Procedure — Parallel holding course, turn left, and return to holding fix or intercept holding

course. (Also called left turn.)

(b) Teardrop procedure — Proceed on outbound track of 30_ (or less) to holding course, turn right to

intercept holding course.

Note

Text and illustration are standard pattern, turns are opposite for nonstandard

pattern.

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ORIGINAL

NAVAIR 00-80T-112

(4) Timing.

Note

The initial outbound leg should be flown for 1 minute or 1-1/2 minutes

(appropriate to altitude). Timing for subsequent outbound legs should be

adjusted as necessary to achieve proper inbound leg time.

(a) Outbound timing begins over or abeam the fix, whichever occurs later. If the abeam position cannot

be determined, start timing when turn to outbound is completed.

(5) Distance Measuring Equipment (DME).

(a) DME holding is subject to the same entry and holding procedures except that distances (nm) are used

in lieu of time values. The outbound course of a DME holding pattern is called the outbound leg of

the pattern. The length of the outbound leg will be specified by the controller. The end of the

outbound leg is determined by the DME reading.

(6) Pilot action.

(a) Cross holding fix initially at or below maximum holding airspeed. Effect speed reduction within 3

minutes prior to estimated initial time over the holding fix.

(b) Make all turns during entry and while holding at: (1) 3_ per second, (2) 30_ bank angle, or (3) 25_

bank angle (provided a flight director system is used), whichever requires the least bank angle.

(d) Determine entry turn from aircraft heading upon arrival at the holding fix. Plus or minus 5_ in

heading is considered to be within allowable good operating limits for determining entry.

(e) Advise ATC immediately if any increased airspeed is necessary due to turbulence, icing, etc., or if

unable to accomplish any part of the holding procedures. After such higher speeds are no longer

necessary, operate according to the appropriate published holding speed and notify ATC.

Note

Airspace protection for turbulent air holding is based on a maximum of 280

Knots Indicated Airspeed (KIAS) or Mach 0.8, whichever is lower.

Considerable impact on traffic flow will result when turbulent air holding

patterns are used; thus, pilot discretion will ensure their use is limited to

bona fide conditions/requirements.

(7) Nonstandard holding pattern — Fix end and outbound end turns are made to the left. Entry procedures

to a nonstandard pattern are oriented in relation to the 70_ line on the holding side just as in the standard

pattern.

When holding at a fix, and instructions are received specifying the time of departure from the fix, the pilot

should adjust the flightpath within the limits of the established holding pattern in order to leave the fix at the

exact time specified. After departing the holding fix, normal speed is to be resumed with respect to other

governing speed requirements, such as terminal area speed limits, specific ATC requests, etc. Where the fix

is associated with an instrument approach, and timed approaches are in effect, a procedure turn shall not be

executed unless the pilot advises ATC, as aircraft holding is expected to proceed inbound on final approach

directly from the holding pattern when approach clearance is received.

ORIGINAL

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NAVAIR 00-80T-112

6. Radar surveillance of outer fix holding pattern airspace areas.

a. Whenever aircraft are holding at an outer fix, ATC will usually provide radar surveillance of the outer fix

holding pattern airspace area, or any portion of it, if it is shown on the controller’s radarscope.

b. The controller will attempt to detect any holding aircraft that stray outside the holding pattern airspace area

and will assist any detected aircraft to return to the assigned airspace area.

c. Many factors could prevent ATC from providing this additional service, such as workload, number of

targets, precipitation, ground clutter, and radar system capability. These circumstances may make it

unfeasible to maintain radar identification of aircraft or to detect aircraft straying from the holding pattern.

The provision of this service depends entirely upon whether the controller believes to be in a position to

provide it and does not relieve a pilot of the pilot’s responsibility to adhere to an accepted ATC clearance.

21.3.12.1 Wind Correction Techniques

21.3.12.1.1 Crosswind Correction

After entering the holding pattern, the pilot should compensate for wind in order to arrive at an outbound position

from which a turn inbound will place the aircraft on the holding course.

This is normally accomplished by utilizing a larger drift correction on the outbound leg.

21.3.12.1.2 Headwind or Tailwind Corrections

After completing the first circuit of the holding pattern, adjust the time outbound as necessary to provide the desired

inbound time. For example, if the inbound leg was 30 seconds too long, subtract 30 seconds from the outbound leg.

In extreme wind conditions, even though the turn inbound is initiated when abeam the station, the inbound leg may

exceed the 1 or 1-1/2 minute limit. In this case only is the pilot authorized to exceed the time limit inbound.

21.3.12.1.3 Meeting an Expected Further Clearance Time (EFC)

The holding pattern may be shortened (never lengthened) as required to meet the Expected Further Clearance Time

(EFC). Planning to meet the EFC should be based on the point of departure from the holding pattern. Two factors to

consider in planning are the length of time required to make the two turns and the inbound leg time compared to the

outbound leg.

21.3.12.2 Approaches

A limited number of VOR instrument approaches utilizing a VORTAC facility have been approved for use for

TACAN equipped aircraft. These procedures are identified by the phrase “or TACAN” printed adjacent to the name

of the procedure (e.g., VOR or TACAN Rwy 17). Approaches designated as VORTAC may be executed by aircraft

using either TACAN or VOR with DME; DME is required. Approaches designated VOR/DME shall be executed by

aircraft utilizing VOR with DME, and both the VOR and DME are required.

The approach procedures discussed in this section are for basic instruction

only. Consult the latest Aeronautical Information Manual/Federal Aviation

Regulation (AIM/FAR) for detailed procedures.

21.3.12.3 Transition to the Initial Approach Fix (IAF)

Published routes on the terminal chart provide a course and distance from the en route structure to the Initial Approach

Fix (IAF). If other than a published routing is used, ensure it does not exceed the operational limitation of the

Navigation Aid (NAVAID). Limitations according to type NAVAID, aircraft altitude, and range from the facility are

published in FLIP.

21-33

ORIGINAL

NAVAIR 00-80T-112

Before reaching the IAF, review the approach chart, recheck the weather at destination and alternate, and obtain

clearance for the approach.

An IAF may be approached from directions not favorable to intercepting the initial approach course upon arrival at

the fix. When this occurs, and prior approach clearance has been received, the pilot must maneuver to intercept the

initial approach course. Preapproach intercept maneuvers should be accomplished as follows:

1. Turn at the IAF in the shortest direction to intercept the initial approach course.

2. Begin descent from the Initial Penetration Altitude (IPA) when established on a segment of the published

approach.

3. If holding is not required, reduce to penetration airspeed or below before crossing the IAF.

21.3.12.4 High-Altitude Approach Procedures

21.3.12.4.1 Non-DME Teardrop Approach

After crossing the IAF, turn in the shorter direction toward the penetration course. Set the altimeter in accordance with

FLIP procedures. Start descent when the aircraft is over or abeam the fix, headed in the direction of the penetration

course. Correct to course using

“immediately after station passage interception” procedures described in

paragraph 21.3.4. Some penetrations include altitude restrictions for a specified number of miles. In these cases,

intercept the outbound course and descend as depicted on the approach chart. Before reaching the penetration turn

altitude, set the inbound course in the course selector window. Recheck the altimeter and the minimum altitude for

completion of the penetration turn.

Perform the penetration turn as published. If it appears the course will not be intercepted upon completion of the

penetration turn, roll out with an intercept to the inbound course. Normally, a 30_ to 45_ intercept angle is sufficient;

however, vary the angle as necessary depending upon groundspeed, displacement from course, and range from the

station.

Descend from the altitude specified for completion of penetration turn when on the inbound course. Before reaching

the Final Approach Fix (FAF), configure the aircraft for landing in accordance with the flight manual. Cross the FAF

at the published altitude, start timing, intercept the final approach course, and report to the controlling agency.

Note

The time-distance tables published in the approach charts are based on

groundspeed; therefore, TAS and the existing wind must be considered in

order to accurately determine the time from the final approach fix to the

missed approach point.

Descend to the Minimum Descent Altitude (MDA) so that visual references for landing may be acquired as soon as

practical. Comply with any published altitude restrictions between the final approach fix and Missed Approach Point

(MAP). The descent to the MDA should be completed before reaching the missed approach point. Descent below

MDA is authorized when visual reference with the runway environment is sufficient to complete the landing. Part

VII discusses landing from a straight-in or circling approach.

The MDA should not be confused with the weather minimums for the approach being flown. The weather minimums

indicate the ceiling and visibility required before the approach may be started (reference OPNAV 3710.7 series,

Chapter 5, Approach Criteria for Multipiloted Aircraft). The MDA indicates the minimum altitude Mean Sea Level

(MSL) to which the aircraft may be flown. Use Runway Visual Range (RVR) for the visibility minimum when

available. The RVR is found in the landing minimums block next to the MDA (Figure 21-25).

ORIGINAL

21-34

NAVAIR 00-80T-112

Perform the missed approach when:

1. Visual reference with the runway environment at the missed approach point is insufficient to complete the

landing.

2. Instructed by the controlling agency.

3. A safe landing is not possible.

21.3.12.4.2 Dual-Facility Approaches

This type of approach may use dual VOR, ADF, or a combination of the two facilities. Figure 21-26 illustrates one

type of dual-facility approach. With dual navigational receivers, this type of approach offers a few advantages over

the non-DME teardrop approach. The pilot can maintain course on one facility and monitor his progress by reference

to the second facility. Normally, the distance between the IAF and FAF is published in the profile view of the approach

chart. If the pilot is position oriented, the pilot can better approximate the time available to configure the aircraft for

the final approach.

With only a single VOR (or ADF) receiver, this type of approach may require a high degree of pilot proficiency. In

the illustration, a pilot flying this approach would have to retune the VOR several times in order to intercept and

maintain course and, at the same time, determine the aircraft position in relation to the intersection(s). Consider

weather, aircraft equipment, and pilot proficiency when planning a dual-facility approach.

Note

Dual receivers are required when an intersection (formed by a radial from

another facility) is used as a step-down fix between the final approach fix

and missed approach point.

21.3.12.5 Low-Altitude Approach Procedures

The reduction of airspace and the predominant use of the procedure turn are two factors that distinguish the Low- (AL)

from the High-Altitude Approach (JAL). Pilots of high-performance aircraft that have an operational requirement

to use the low-altitude charts (AL) should maneuver at airspeeds compatible with the depicted procedure. Category

E will be depicted on low-altitude (AL) procedures only where an operational requirement exists. Procedure turns

are discussed under paragraph 21.3.12.6. Some low-altitude VOR (or ADF) approaches do not use the procedure turn

(Figure 21-27). The guidance concerning transition found preceding high-altitude approach procedures also applies

to low-altitude approach procedures.

21.3.12.5.1 Straight-In Approaches

A straight-in approach is an instrument approach conducted by proceeding over the FAF at the prescribed altitude and

continuing inbound on the final approach course to the airport without making a Procedure Turn (PT). When issued

a clearance for a straight-in approach while conducting a timed approach from a holding fix, when the initial approach

published on the Instrument Approach Procedure (IAP) is designated NoPT (procedure turn not required), or when

ATC radar vectors to a final approach position are provided, the pilot shall not make a procedure turn unless the pilot

so advises ATC and an appropriate clearance is received. Some instrument approach procedures specifically prohibit

use of a procedure turn (Figure 21-27).

An aircraft cleared to a holding fix, other than the IAF, then subsequently cleared for a straight-in approach (even if

the aircraft has not yet entered holding) is expected by ATC to proceed to the IAF via the holding fix to commence

the approach. If route of flight directly to the IAF is desired, it should be so stated by the controller. If doubt exists,

contact ATC to determine the correct route of flight.

ORIGINAL

21-36

NAVAIR 00-80T-112

When operating on an unpublished route or while being radar vectored when an approach clearance is received, the

pilot shall maintain the last assigned altitude: unless a different altitude is assigned by ATC or until the aircraft is

established on a segment of a published route or instrument approach procedure. Descend from the initial approach

altitude to the next altitude depicted after established on the initial approach course. If there is insufficient time to

intercept course and comply with the first altitude restriction, before starting the approach, request ATC clearance

to maneuver for a favorable alignment with the initial approach course. Before reaching the FAF, configure the aircraft

for landing in accordance with the applicable NATOPS flight manual. At the FAF, start the time, intercept the final

approach course, and call the controlling agency, if required.

If no FAF is depicted, treat the point of interception of the final approach course as the FAF.

Note

The time-distance tables published in the approach charts are based on

groundspeed; therefore, TAS and the existing wind must be considered to

determine accurately the time from the final approach fix to the missed

approach point.

Descend to the MDA so that visual references for landing may be acquired as soon as practical. Comply with any

published altitude restriction between the FAF and missed approach point. Descent below MDA is authorized when

visual reference with the runway environment is sufficient to complete the landing. Perform the missed approach

when:

1. Visual reference with the runway environment at the missed approach point is insufficient to complete the

landing.

2. Instructed by the controlling agency.

3. A safe landing is not possible.

21.3.12.6 Procedure Turns (PT)

A Procedure Turn (PT) is a maneuver that is designed to place the aircraft on an inbound course to the FAF. Further,

it provides for descent to the FAF altitude and affords the pilot time to establish the final approach configuration. A

procedure turn is normally associated with the low-altitude approach (AL); however, it may be included as a part of

the High-Altitude Approach (JAL) procedure (Figures 21-28 and 21-29).

21.3.12.6.1 Entry

Initial entry for a procedure turn may be accomplished as described under paragraph 21.3.12, or may be made by the

aircraft turning in the shortest direction to proceed outbound. On U.S. Government charts, a barbed arrow indicates

the direction or side of the outbound course on which procedure turn is made. Headings are provided for course

reversal using the 45 degree type procedure turn; however, the point at which the turn may be commenced and the

type and rate of turn is left to the discretion of the aircrew. Some of the options are the 45 degree procedure turn, the

racetrack pattern, the teardrop procedure turn, or the 80/260 degree course reversal. Some procedure turns are

specified by procedural track. These turns must be flown exactly as depicted.

When the approach procedure involves a procedure turn, a maximum speed of not greater than 200 knots Indicated

Airspeed (IAS) should be observed from first overheading the course reversal IAF through the procedure turn

maneuver to ensure containment within the obstruction clearance area.

21-39

ORIGINAL

NAVAIR 00-80T-112

On the outbound leg, the aircraft shall not exceed the protected airspace depicted. At the completion of the outbound

leg, course reversal may be accomplished by utilizing the 90-270 method, the depicted procedure turn headings, or

any other method that safely reverses course and keeps the aircraft on the Procedure Turn (PT) side of the approach

course within the protected airspace. If on a teardrop approach, at the completion of outbound timing, turn in the

shortest direction toward the inbound course.

When nonstandard distances are specified, adjust timing in order to comply with the depicted procedure. The standard

procedure turn length is 10 nm (15 nm on terminal charts where Category E minimums are published). For those

procedure turns prescribed from a DME fix, adhere to published distance restrictions in lieu of timing.

21.3.12.6.2 Descent

Initiate descent from the initial approach altitude to the published procedure turn altitude when the aircraft is abeam

the fix or wings level outbound, whichever occurs last. Start descent from procedure turn altitude to final approach

fix altitude when the aircraft is headed inbound on the inbound course. If a teardrop is performed from a fix without

outbound course guidance, descend from procedure turn altitude when the aircraft is on course inbound.

Before reaching the final approach fix, configure the aircraft for landing in accordance with the NATOPS flight

manual. At the final approach fix, note the time, make the mandatory position report, and intercept the final approach

course to the airfield. If no FAF is depicted, treat the point at which the aircraft has intercepted the inbound course

as the FAF.

Note

The time-distance tables published on the approach charts are based on

groundspeed; therefore, TAS and the existing wind must be considered in

order to determine accurately the time from the final approach fix to the

missed approach point.

Descend to the MDA so that visual references for landing may be acquired as soon as practical. Comply with any

published altitude restriction between the FAF and missed approach point. Descent below MDA is authorized when

visual reference with the runway environment is sufficient to complete the landing and the Visual Descent Point

(VDP) has been reached.

Perform the missed approach when:

1. Visual reference with the runway environment at the missed approach point is insufficient to complete the

landing.

2. Instructed by the controlling agency.

3. A safe landing is not possible.

21.3.12.7 Approaches from Holding

21.3.12.7.1 Holding Type Approach

When executing an approach that specifies a holding pattern in lieu of a procedure turn, the pilot must fly the holding

pattern and does not retain the option of executing a procedure turn or teardrop (Figure 21-30). When established in

holding and cleared for the approach, the pilot may start the descent from any position in the pattern. The aircraft will

be configured for landing prior to reaching the FAF.

21.3.12.7.2 Holding Pattern Located on the Initial Approach Course

When cleared to hold in a pattern depicted on the approach plate on the initial approach course, and subsequently

cleared for the approach, the pilot may depart holding from any position and need not return to the holding fix. Pilots

may intercept the teardrop or procedure turn course directly and commence descent from IAF altitude immediately.

They may also remain in the holding pattern to dissipate excessive altitude power to proceeding outbound on the

procedure turn or teardrop course (Figure 21-29).

ORIGINAL

21-42

NAVAIR 00-80T-112

CHAPTER 22

Tactical Air Navigation (TACAN)

22.1

INTRODUCTION

Although VHF Omnidirectional Range (VOR) was a great improvement over earlier navigation systems, a gap still

existed in information presented to the pilot. The Tactical Air Navigation (TACAN) system was developed to fill this

gap by providing the pilot with information needed for precise, geographical orientation within TACAN range.

TACAN added a continuous display of range information to the course information already available. Distance

Measuring Equipment (DME), an integral part of TACAN, provides continuous slant range distance information.

Like VOR, TACAN provides 360 courses radiating from the station. In addition, because TACAN ground equipment

is compact and relatively easy to transport, it provides for greater versatility in beacon installation and mobility than

the VOR system (Figure 22-1).

22.2

EQUIPMENT AND TRANSMISSION PRINCIPLES

TACAN operates in the Ultrahigh Frequency (UHF) (1000 MHz) band. The TACAN system has a total of 126

two-way channels. Suffixes X or Y are used for discrimination between the sets, totaling 252 possible channels.

Air-to-ground frequencies (DME) for these channels are in the 1025 to 1150 MHz range; associated ground-to-air

frequencies are in the 962 to 1024 MHz and 1151 to 1213 MHz ranges. Channels are spaced at 1-MHz intervals in

these bands.

MAGNETIC

BEARING TO

STATION 090°

Figure 22-1. Determining Aircraft Position by TACAN

22-1

ORIGINAL

NAVAIR 00-80T-112

22.2.1 Ground Equipment

The ground equipment consists of a rotating type antenna for transmitting bearing information and a

receiver-transmitter (transponder) for transmitting distance information. The TACAN identifies itself aurally through

international Morse code every 35 seconds. Permanent TACAN ground stations are usually dual-transmitter equipped

(one operating and one on standby), fully monitored installations that automatically switch to the standby transmitter

when a malfunction occurs. The ground monitor (set to alarm at any radial shift of ±1_) is usually located in the base

control tower or approach control and sets off a light and buzzer to warn the groundcrew when an out-of-tolerance

condition exists. Anytime TACAN reception is suspected or bearing/distance unlock conditions are encountered in

flight, a pilot can check on the status of the ground equipment by calling Air Traffic Control (ATC). When ground

equipment is undergoing repairs that might cause it to transmit erroneous signals, its identification must be silenced;

therefore, always listen for identification signals during flight (Figure 22-2).

22.2.1.1 TACAN Signal Pattern

The signal pattern for bearing information is formed by varying the nondirectional pattern sent from the stationary

central element of the antenna. This is done by rotating a cylinder around the central element of the antenna at

15 revolutions per second (rps) (Figure 22-3, part A). A metal wire embedded vertically in the plastic cylinder distorts

the radiated signal into a cardioid (heart-shaped) pattern, and its rotation causes the cardioid pattern to also revolve

at 15 rps. This resulting rotating pattern is referred to as the course pattern. From this, the aircraft receives a 15

cycles-per-second (cps) amplitude modulation. This means that the strength of the signal goes from maximum to

minimum and back to a maximum at the rate of 15 cps.

Another larger cylinder, with nine wires in it, is mounted around the central element and the smaller cylinder and also

rotates at 15 rps. This is the fine antenna that superimposes nine lobes on the already-formed course pattern. This

forms a 135 cps signal (Figure 22-3, part B).

Figure 22-2. TACAN Ground Beacon Antenna

ORIGINAL

22-2

NAVAIR 00-80T-112

Figure 22-3. TACAN Antenna Pattern

To determine the aircraft position in bearing from the station, a phase angle must be measured electronically. To

measure the phase angle, a fixed reference is established. This fixed reference is a 15-cps nondirectional pulse signal

normally referred to as the main reference bearing pulse. One main reference pulse occurs with each revolution of

the antenna. In addition to the main reference pulse, eight auxiliary reference pulses also occur during one revolution

of the ground beacon antenna; therefore, a reference pulse occurs each 40_ of antenna rotation (360_ = 9 pulses).

The airborne equipment electronically measures the time lapse between the main reference pulse and the maximum

amplitude (signal strength) of the 15-cps rotating signal pattern. This determines the aircraft bearing from the station

within a 40_ sector. Then, the time lapse between the auxiliary reference pulses and the maximum amplitude of the

135-cps signal is measured to determine the aircraft position within the 40_ sector. The accuracy of this measurement

determines the position of the aircraft relative to the station within ±1_ (Figure 22-4).

22.2.1.2 Distance Measuring Equipment (DME)

Distance is determined with TACAN equipment by measuring the elapsed time between transmission of interrogating

pulses of the airborne set and reception of corresponding reply pulses of the ground station. The aircraft transmitter

starts the process by sending out the distance interrogation pulse signals. Receipt of these signals by the ground station

receiver triggers its transmitter, which sends out the distance reply pulse signals. These pulses require approximately

12 microseconds round trip travel time per nm of distance from the ground beacon. The range indicator displays

distance to the TACAN beacon in nm (Figure 22-5).

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NAVAIR 00-80T-112

As a large number of aircraft could be interrogating the same beacon, the airborne set must sort out only the pulses

that are replies to its own interrogations. Interrogation pulses are transmitted on an irregular, random basis by the

airborne set, which then searches for replies synchronized to its own interrogations. If the signals are interrupted, a

memory circuit maintains the last distance indication on the range indicator for approximately 10 seconds to prevent

the search operation from recurring. The searching process starts automatically whenever the airborne set is tuned

to a new beacon or when there is a major interruption in beacon signals. Depending upon the aircraft actual distance

from the beacon at the time, the searching process may require up to 22 seconds (Figure 22-6).

22.2.2 TACAN Characteristics

22.2.2.1 Bearing/Distance Unlock

TACAN bearing and distance signals are subject to line-of-sight restrictions. Because of the transmission/reception

principles, unlock (rotating of bearing pointer and/or range indicator) will occur if these signals are obstructed.

Temporary obstruction of TACAN signals can occur in flight when aircraft fuselage, wing, gear, external stores, or

wingmen get between the ground and aircraft antenna. Aircraft receiver memory circuits prevent unlock when signals

are obstructed for short periods (approximately 10 seconds for DME and 2 seconds for azimuth), but beyond this,

unlock occurs and will persist until the obstruction is removed and search cycles are completed. Unlock may occur

during procedure or penetration turns, or during maneuvers that cause the aircraft antenna to be obstructed for longer

than 2 to 10 seconds.

Figure 22-6. Slant Range Distance

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NAVAIR 00-80T-112

22.2.2.2 Azimuth Cone of Confusion

The structure of the cone of confusion over a TACAN station is considerably different from other navigational aids.

The azimuth cone can be up to 100_ or more in width (approximately 15 nm wide at 40,000 feet). Indications on the

aircraft instruments make it appear even wider to the pilot. Approaching the TACAN station, usable azimuth

information is lost before the actual cone is reached, although actual azimuth unlock is prevented by the memory

circuit until after the aircraft is into the cone. After the cone is crossed and usable signals are regained, the search cycle

function (22 seconds for a full cycle) prior to regaining lock-on extends the unusable area beyond the actual cone.

22.2.2.3 DME Cone of Confusion

The DME cone is much narrower and is actually insignificant to TACAN operation as DME unlock should never

occur when crossing the station except for hovering or very slow aircraft. Faster aircraft should get through the DME

cone area regardless of altitude before unlock occurs. On crossing a TACAN station, the DME should decrease until

the center of the cone is reached, stop, then begin to show an increase as the signal is regained.

22.2.2.4 Range Indicator Fluctuations

Slight oscillations up to approximately 1/4 nm are normal for range indicator operation due to the pulses generated

by the transmit/receive function. When a usable signal is lost, the memory circuit maintains the indicated range for

approximately 10 seconds, after which unlock will occur unless usable signals are regained.

22.2.2.5 Erroneous TACAN Indications

Several forms of malfunction of airborne equipment or interference between ground stations can give false or

erroneous TACAN information to a pilot. These discrepancies are easier to recognize and guard against if the pilot

is aware they can occur.

22.2.2.5.1 40_ Azimuth Error Lock-On

As previously explained, the construction of the TACAN ground antenna is such that it transmits a series of nine signal

lobes (eight auxiliary and one main reference pulse) 40_ apart. With the airborne receiver working correctly, these

pulses lock on the airborne equipment with the main reference at 90_. With a weak airborne receiver, the main

reference pulse may slide over or miss the 90_ slot and lock on at one of the auxiliary positions. When this occurs,

azimuth indications will be 40_ or some multiple of 40_ in error. Rechanneling the airborne receiver to deliberately

cause unlock gives the set another chance to lock on properly. When VOR or ADF bearing information is available,

use it to verify the existence of suspected TACAN errors.

22.2.2.5.2 Adjacent Channel Interference

Adjacent channel interference occurs when an aircraft is in a position to receive TACAN signals from more than one

ground station on the same frequency. Normally, this occurs only at high altitudes when distance separation between

like frequencies is inadequate. DME, azimuth, or identification from either ground station may be received. This is

not a malfunction of either air or ground equipment, but a result of ground equipment location and aircraft position.

22.2.2.5.3 False or Incorrect Lock-On

False or incorrect lock-on indications in the aircraft can be caused by misalignment or excessive wear of the airborne

crystal selector assembly. Selection of a numbered TACAN channel activates a drum and wiper arrangement in the

aircraft black box, which rotates until the wiper contacts the proper crystal on the drum. These crystal contact points

are very small (pinhead size) and close together. Wear of this assembly or misalignment can cause the wiper to miss

the proper crystal and contact the wrong one, resulting in the wrong TACAN being tuned in, or the wiper can miss

contact entirely, resulting in constant unlock. When this occurs, rechanneling from the selected channel number and

back (preferably from the opposite direction than the original setting) sometimes results in proper channelization.

This is an airborne equipment malfunction.

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NAVAIR 00-80T-112

22.2.2.5.4 Precautionary Actions

Several precautionary actions should be taken by pilots to guard against in-flight use of erroneous navigation signals:

1. Always check the identification of any navigational aid station and monitor it during flight. Always utilize all

suitable navigation equipment aboard the aircraft and cross-check heading and bearing information.

2. Never overfly preplanned Estimated Times of Arrival (ETAs) without careful cross-check of navigational aids

and ground checkpoints.

3. Check Notices to Airmen (NOTAMs) and Flight Information Publications (FLIP) before flight for possible

malfunctions or limitations on navigational aids to be used.

4. Discontinue use of any suspected navigational aid and, if necessary, confirm aircraft position with radar or

other equipment.

Note

If there is a malfunction of the compass system or card, consider the

TACAN bearing information unreliable and merely advisory until verified

by radar or other navigational equipment.

22.2.3 TACAN Procedures

As TACAN presents bearing information in the same manner as VOR, use the same homing, proceeding direct, course

interception, and maintaining course procedures explained in Part 1 (VOR Navigation); however, with the addition

of range information, additional procedures have been devised to use TACAN to its full advantage. The remainder

of this chapter is devoted to those procedures that differ from VOR.

22.2.3.1 Tuning

The TACAN control panel (Figure 22-7) consists of a power switch, volume control, and channel selector. The power

switch has four positions: OFF, REC, T/R, and A/A. Selecting either the REC or T/R position turns on the set. (As

some TACAN sets require a warmup period in the REC position, before selecting the T/R position, refer to the

appropriate aircraft flight manual for instructions.) In the REC position, only bearing information and station

identification are available. In the T/R position, bearing/distance information and station identification are available.

After turning on the equipment, select the desired channel, adjust the volume, and identify the station. After

identifying the TACAN station, an unreliable signal can be identified on the instrument (refer to specific aircraft

NATOPS).

Tune and check the set before takeoff. After tuning, check the bearing pointer, Course Deviation Indicator/Horizontal

Situation Indicator (CDI/HSI) TO-FROM indicator, and range indicator for proper operation. The bearing pointer

should point to magnetic bearing to the station. The CDI/HSI should center when this bearing is set in the course

selector window, and the TO-FROM indicator should indicate TO. The range indicator should indicate the distance

to the station.

22.2.3.2 Groundspeed Check

A groundspeed check can be made while maintaining a course to or from a TACAN station; however, as a guide,

groundspeed checks should be performed only when the aircraft slant range distance is more than the aircraft altitude

divided by 1,000. For example, if the aircraft is at Flight Level (FL) 200, groundspeed checks should be performed

when beyond 20 nm. Checks made below 5,000 feet are accurate at any distance.

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NAVAIR 00-80T-112

1. VOLUME CONTROL

2. CHANNEL DISPLAY

3. POWER SWITCH

4. X/Y CHANNEL SELECTOR SWITCH

5. RIGHT KNOB SELECTS UNITS DIGITS

6. LEFT KNOB SELECTS 100 AND 10 DIGITS

7. AIR-TO-AIR (A/A)/AIR-TO-GROUND (A/G) SELECTOR SWITCH

Figure 22-7. TACAN Control Panel

To perform the groundspeed check, begin timing when the range indicator shows a whole number. After the

predetermined time has elapsed, check the range indicator and note the distance flown. Apply this information to the

following formula to determine groundspeed:

Distance flown

60 = Groundspeed elapsed time in minutes.

For precise computation, time for longer periods and solve the problem on a computer. To simplify computations,

use a 2-minute time check and multiply the distance traveled by 30; for a 3-minute time check, multiply distance by

20; for a 6-minute time check, multiply distance by 10 (Figure 22-8).

22.2.3.3 Station Passage

Because of the azimuth cone of confusion over the TACAN station, station passage is determined when the range

indicator stops decreasing. Flying directly over the station, the range indicator will stop decreasing when it indicates

the approximate aircraft altitude above the station in nm. One nm is equal to approximately 6,000 feet. For example,

an aircraft cruising at FL 300 is at an altitude of approximately 5 nm; therefore, the range indicator should stop

decreasing at approximately 5 nm when directly over a station at sea level. If the station elevation is 6,000 feet, the

indicated range over the station would be approximately 4 nm (Figure 22-9).

22.2.3.4 TACAN Arcs

Sometimes used during approaches and departures, a TACAN arc is flown around the station at a specific distance.

Some approaches require the entire final approach to be flown along an arc, using radials to determine the Final

Approach Fix (FAF) and the Missed Approach Point (MAP). On the other hand, an arc may be used to transition to

the FAF and the MAP. During departures, it may be necessary to fly an arc soon after takeoff to transition to a departure

radial. Arc instructions are given as “VIA (NUMBER OF MILES) MILE ARC (DIRECTION) OF (NAME OF

NAVAID).” Direction will be given as “ARC SOUTH” or “ARC EAST,” etc.

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NAVAIR 00-80T-112

22.2.3.5 Arc Interceptions

To intercept an arc from a radial, a turn of approximately 90_ is required to place the bearing pointer on the wingtip

with a range indication equal to the desired arc. Determine the direction to turn and the desired lead point. Lead point

will equal 0.5 percent of groundspeed (200 knots

.005 = 1 nm). Rollout heading is based on determining if the

aircraft is inside or outside of desired arc track. Detailed techniques for correcting to the arc are discussed under

paragraph 22.2.3.6.

22.2.3.5.1 Techniques for Determining Lead

When using 30_ of bank, an approximate lead point for the arc may be determined from the aircraft Groundspeed

(GS) or Mach. Groundspeed in nm per minute minus 2 represents the approximate lead (e.g., 6 nm per minute, use

4 nm lead). A Mach indicator may be used in the same manner to determine a no-wind lead point because 0.5 Mach

is approximately 5 nm per minute, 0.6 Mach is 6 nm per minute, etc. Lead points based on aircraft turn radius may

be approximated as follows: 1 percent GS = nm lead for 1-1/2_ per second rate of turn, 1/2 percent GS = nm

lead for 3_ per second rate of turn. For groundspeeds below 150 knots, 1/2 nm lead point is satisfactory (Figure 22-10).

22.2.3.6 Maintaining Arcs

In theory, it is a simple matter to maintain an arc. Under no-wind conditions, the aircraft will fly in an exact circle

around the station by maintaining a relative bearing of 90_ or 270_. In practice, a method for maintaining an arc is

to fly a series of short legs, keeping the bearing pointer on or near the wingtip position while maintaining the desired

range. With the bearing pointer on the wingtip and the aircraft at the desired range, maintain heading and allow the

bearing pointer to move 5_ to 10_ behind the wingtip position. This will cause the range to increase slightly. Next,

turn toward the station to place the bearing pointer 5_ to 10_ ahead of the wingtip, and maintain this heading until

the bearing pointer is again behind the wingtip.

During crosswind conditions, the reference point (wingtip) will change. If the wind is blowing the aircraft away from

the station, the reference point is ahead of the wingtip. If the wind is blowing the aircraft toward the station, the

reference point is behind the wingtip. While proceeding around the arc, the drift correction will constantly be

changing for a constant wind direction and velocity. As a guide, correct approximately 10_ to 20_ for each 1/2 mile

deviation from the desired arc. For example, under no-wind conditions, if the aircraft is 1/2 mile outside the arc and

the bearing pointer is on the wingtip, the aircraft should be turned approximately 20_ toward the station to return to

the arc. The actual amount of correction required for a given error varies. Factors to consider are the size of the arc,

groundspeed of the aircraft, whether the aircraft is inside or outside of the arc, etc. These variables are seen by the

pilot as rates of deviation. Establish a correction according to the rate of deviation and adjust as necessary according

to the rate of correction. Remember that the curve of small arcs is relatively sharp, and corrections from the inside

are assisted by the arc curving toward the aircraft. Conversely, the aircraft outside small arc requires larger corrections

because of the curvature away from the aircraft. Large arcs are easier to fly because of their flatter curve. High

groundspeeds require more pilot attention to maintain an arc because of higher rates of deviation and correction

(Figure 22-11).

22.2.3.7 Intercepting a Radial from an Arc

To intercept a radial from an arc, set the desired course in the course selector window as soon as practical. Monitor

the rate of bearing pointer movement while flying the arc, and remember that the interception angle will be

approximately 90_. Changing the lead point used for the arc interception from nautical miles to degrees is a technique

that can be used to determine an approximate lead point. Use the relationship that 1_ is 1 nm wide at 60 nm from the

station and its width increases or decreases in proportion to the distance. For example, with a 200-knot groundspeed

(using a 3_ per second rate of turn), a 1-nm lead point was used to intercept the 10-nm arc. Because 1_ of travel along

the 10 nm arc represents 1/6 nm, the lead point when intercepting a radial from the arc (no wind) would be 6_

(Figure 22-12).

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NAVAIR 00-80T-112

22.2.3.8 Technique of Navigating Point to Point

When an aircraft approaches a terminal area, air traffic control normally clears it to the holding fix or the initial

approach fix. This clearance may be to the station and out the radial, along an arc to a radial, or direct to the fix. If

cleared direct to the fix, the pilot may use a radar vector or point-to-point navigation.

A single TACAN providing bearing and distance information is sufficient for navigating directly to any fix (radial

and distance) within reception range of the station.

Basic navigation principles are used and include:

1. Establishing two fixes (aircraft and desired).

2. Connecting the fixes with a line.

3. Reading the heading to the desired fix.

The technique of applying these principles in the aircraft without cumbersome charts is simple. The key to this

technique is in learning to visually establish the aircraft and the desired fix on the compass card of a Radio Magnetic

Indicator (RMI) or similar type instrument (Figure 22-13). The following factors will aid in developing this ability:

1. The TACAN station is always at the center of the compass card. The compass card is merely a compass rose

around the station.

2. The fix having the greater distance is always established on its radial at the outer edge of the compass card.

3. The remaining fix is established along its radial at a point whose distance from the center of the card is

proportional to the distance represented by the outer edge of the compass card.

For example, assume an aircraft to be on the 180_ radial (indicated by the tail of the bearing pointer) at 60 nm. The

pilot desires to proceed direct to a fix located on the 90_ radial at 30 nm.

If not proceeding in the general direction of the fix, turn to a heading approximately halfway between the head of the

bearing pointer and the desired fix radial, then:

1. Establish the fix with the greater distance (60 nm) on the edge of the card at its radial (180_). The distance

represented from the center to the edge of the compass card is now 60 nm.

2. Establish the remaining fix (90_/30_) along the 90_ radial at a proportionate distance from the center (i.e.,

halfway).

3. Connect the two fixes with an imaginary line or with the aid of a pencil or other straight edge. Move the line

to the center of the compass card so that it is parallel to the original line.

4. Read the no-wind heading at the point where the second line crosses the compass card (30_). Always read

direction from the aircraft position to the desired fix. Turn to this heading and apply wind correction.

As the distance from the center to the edge of the compass card represents 60 nm, the diameter of the card provides

a 120-nm scale. The distance between the aircraft fix and the desired fix may be determined using this scale

(approximately 65 miles in the example). The Estimated Time En Route (ETE) to the desired fix may then be

determined by applying aircraft groundspeed. For better accuracy, repeat the entire technique occasionally while en

route (Figure 22-14).

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NAVAIR 00-80T-112

22.2.3.9 TACAN Holding

Holding is maneuvering an aircraft in relation to a navigational fix while awaiting further clearance. Initial entry for

TACAN holding is identical to that described earlier for VOR, except a TACAN DME fix is substituted for a VOR

as the holding fix. The standard no-wind holding pattern is flown by following a specified holding course inbound

to the holding fix, making a 180_ turn to the right, flying a heading outbound to parallel the holding course, and

making another 180_ turn to the right to intercept and follow the holding course to the fix. The length of the legs while

using TACAN is usually specified in nautical miles. Pilots should not confuse TACAN holding fix (radial/distance)

with the TACAN station when considering the direction of holding. As illustrated in Figure 22-15, the direction of

holding is relative to the 30-nm fix rather than the TACAN station. The direction of turn is not included for standard

holding patterns. While in the holding pattern, turns are initiated at the indicated range as published or issued by the

controller. To meet the expected approach time, the pattern may be shortened, but never lengthened. The inbound

course to the holding fix should be set in the course selector window. As the holding pattern may be a considerable

distance from the TACAN station, course corrections to intercept course prior to reaching the holding fix will be larger

than those normally used in VOR or ADF holding. For example, 6_ off course at 30 miles is a 3-mile course error,

whereas 6_ off course at 10 miles is only a 1-mile course error.

Figure 22-13. Visualize Problem after Turning to Computed Heading

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NAVAIR 00-80T-112

22.2.4 TACAN Approach Procedures

With range information available, many different types of penetrations are depicted on the approach charts. Some

TACAN approaches are relatively simple and involve only a straight-in flightpath along a radial. Others require

extensive planning and may involve intercepting an arc from a radial, a radial from an arc, or any combination of the

above to arrive at the final approach fix (Figure 22-16).

A limited number of VOR instrument approaches based on a VORTAC facility have been approved for use by

TACAN-equipped aircraft. These procedures are identified by the phrase “or TACAN” printed adjacent to the name

of the procedure (e.g., VOR TACAN Rwy 17). Approaches designated VORTAC may be executed by aircraft using

either TACAN or VOR with DME, but DME is required. Approaches designated VOR/DME may be executed by

aircraft utilizing VOR with DME, and the DME is required.

22.2.4.1 Transition to the Initial Approach Fix

Published routes on the terminal chart may provide a course and range from the en route structure to the Initial

Approach Fix (IAF). If a routing other than one published is used, ensure it does not exceed the operational limitation

of the Navigation Aid (NAVAID) being used. Limitations according to type NAVAID, aircraft altitude, and range from

the facility are published in FLIP. Before reaching the IAF, recheck the weather, review the approach chart, and obtain

clearance for the approach.

An IAF may be approached from directions not favorable to intercepting the initial approach course upon arrival at

the fix. When this occurs, and prior approach clearance has been received, the pilot must maneuver to intercept the

initial approach course. Preapproach intercept maneuvers should be accomplished as follows:

1. Turn at the IAF in the shortest direction to intercept the initial approach course.

2. Begin descent from the Initial Penetration Altitude (IPA) when established on a segment of the published

approach.

3. If holding is not required, reduce to penetration airspeed or below before crossing the IAF.

22.2.4.2 High-Altitude Penetration and Approach

When over the IAF, turn in the shorter direction toward the penetration course. Descent may be started when

established on a segment of the published approach. Crossing the arc forming the IAF is considered abeam. Intercept

the initial penetration course and fly the approach as depicted.

At or before reaching the FAF, configure the aircraft for landing in accordance with the NATOPS flight manual. At

the FAF, report to the controlling agency. Descend to the Minimum Descent Altitude (MDA) to acquire visual

references for landing as soon as practical. Comply with any published altitude restriction between the FAF and

missed approach point. The descent to the MDA should be completed before reaching the missed approach point.

Descent below MDA is authorized when visual reference with the runway environment is sufficient to complete the

landing and the Visual Descent Point (VDP) has been reached.

There are a few approaches that have the final approach course along an arc. On these approaches, the FAF and missed

approach point are designated by radials rather than range.

Perform the missed approach when:

1. Visual reference with the runway environment at the missed approach point is insufficient to complete the

landing.

2. Instructed by the controlling agency.

3. A safe landing is not possible.

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NAVAIR 00-80T-112

Example: Figure 22-17 illustrates a straight-in TACAN approach to RWY 34R (S-TAC-34R) that combines arc and

radial segments to arrive at the missed approach point. The published weather approach minimums are 300 feet and

3/4 of a mile.

Approach control will assign an initial approach fix altitude. After passing the initial approach fix, call “DEPARTING

THE INITIAL APPROACH FIX.” Also call “LEAVING THE ASSIGNED ALTITUDE,” unless you will be

maintaining altitude until the 130_ radial. Use a lead point based on aircraft turn radius to intercept the 23-nm arc

and the 157_ radial. Before the 5-nm final approach fix, reduce airspeed and establish the landing configuration.

Note the altitude restrictions. After intercepting the 157_ radial inbound, you have approximately 17.5 nm to descend

from 8,000 feet to the 680-foot MDA at the 1.5-nm missed approach point. Although the altitudes published on the

157_ radial at 9 nm, 5 nm, and 3.3 nm are minimum rather than mandatory altitudes, it is advantageous to be near

this altitude. The altitude loss in relation to the distance to travel is significant and may require a continual descent;

therefore, control airspeed so that the final approach configuration may be established not later than the FAF.

Call the controlling agency at the final approach fix (e.g., “EL TORO APPROACH CONTROL, BEEFEATER 301,

FINAL APPROACH FIX WITH GEAR”). You may add intentions as to landing or low approach to this call. Descend

to the 680-foot MDA. If a safe landing is not possible after reaching the missed approach point (1.5 nm), perform

the missed approach.

22.2.4.3 Low-Altitude Approach

The primary differences between the TACAN low-altitude approach (Figure 22-18) and the high-altitude penetration

and approach are the altitude loss and the length of the approach. Before crossing the IAF, establish the airspeed and

the configuration specified in the NATOPS flight manual for low-altitude maneuvering. Category E will be depicted

on low-altitude (AL) charts only when an operational requirement exists. The relatively short length of many

low-altitude approaches may require you to establish the final approach configuration during the transition to the IAF.

When operating on an unpublished route or while being radar vectored when an approach clearance is received, the

pilot shall maintain the last assigned altitude unless a different altitude is assigned by ATC or until the aircraft is

established on a segment of a published route or instrument approach procedure. If in holding, commence descent

as described previously under VOR. Descend from the IAF altitude when established on the initial approach course.

If there is insufficient time to intercept course and comply with the first altitude restriction before starting the

approach, request ATC clearance to maneuver for a favorable alignment with the initial approach course. At or before

reaching the final approach fix, configure the aircraft for landing in accordance with the NATOPS flight manual.

Descend to the MDA on the approach chart to acquire visual reference for landing as soon as practical. Comply with

any published altitude restriction between the FAF and missed approach point. Descent below MDA is authorized

when visual reference with the runway environment is sufficient to complete the landing and the Visual Descent Point

(VDP) has been reached. Perform the missed approach when:

1. Visual reference with runway environment at missed approach is insufficient to complete the landing.

2. Instructed by the controlling agency.

3. A safe landing is not possible.

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CHAPTER 23

ADF, UHF/ADF, Marker Beacons

23.1

AUTOMATIC DIRECTION FINDING (ADF)

The radio compass low-frequency receiver is capable of Automatic Direction Finding (ADF). Most direction finding

equipment will receive any frequency between 100 and 1750 kHz. Most other low-frequency receivers have a

frequency range of 190 to 1750 kHz. The en route supplement lists the location and frequency of the Low-Frequency

(LF) radio ranges and radio beacons. Those beacons coded SAB provide continuous weather information.

Both high- and low-altitude instrument approaches are found in the applicable terminal approach procedures books.

23.1.1 Automatic Direction Finding (ADF) Procedures

Whenever possible, use a nondirectional radio beacon. Commercial broadcasting stations should be used with caution

because some have highly directional radiation patterns. Also, they are not flight-checked for navigational use.

Positive identification of the commercial station being used is imperative.

The radio compass automatically determines the bearing to any radio station within its frequency and sensitivity

range. The radio compass also may be used as an auxiliary receiver for the reception of weather broadcasts and other

broadcast information.

The operation of a radio compass depends chiefly upon the characteristics of a loop antenna. A loop-receiving antenna

gives maximum reception when the plane of the loop is parallel to, or in line with, the direction of wave travel. As

the loop is rotated from this position, volume gradually decreases and reaches a minimum when the plane of the loop

is perpendicular to the direction of wave travel.

These characteristics of a loop antenna result from the fact that the receiver input from a loop antenna is the resultant

of the opposing voltages in the two halves of the loop. When current flows in a looped conductor, it must flow in

opposite directions in each half of the loop. This occurs when the plane of the loop is in line with the station. The fact

that one side of the loop is closer to the transmitter causes a slight delay between the time the radio wave reaches one

side and the time it reaches the other; therefore, there is a phase difference between the voltages induced in each half

of the loop. This causes a resultant current to flow through the transformer and creates a signal input to the receiver.

When the plane of the loop is parallel to the direction of wave travel, a maximum voltage is induced in the loop, and

the strength of the signals heard in the headset is also at a maximum. Conversely, when the plane of the loop is

perpendicular to the direction of wave travel, both sides of the loop are equidistant from the station, and the radio wave

reaches both sides of the loop at the same point in its cycle. The induced voltage is theoretically zero, and the strength

of the received signal is at a minimum. This position of the loop is called the null position.

The null position of the loop, rather than the maximum position, is used for direction finding; that is, a bearing is

obtained when the plane of the loop is perpendicular to the line on which the radio waves are traveling when they strike

the loop. The null position is preferred because it can be determined more exactly than the maximum. A 25_ rotation

from the maximum position changes total signal strength less than 10 percent, whereas a 25_ rotation from the

minimum or null position changes the signal strength 50 percent.

With the loop rotated to a null position, the radio station being received is on a line perpendicular to the plane of the

loop; however, the direction of the radio station from the aircraft may be either one of two directions 180_ apart. The

inability of the loop antenna to determine which of the two possible directions is correct is called the 180_ ambiguity

of the loop.

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ORIGINAL

NAVAIR 00-80T-112

The 180_ ambiguity is eliminated with a nondirectional or sensing antenna.

The loop antenna of the radio compass is automatically rotated to the null position when signals are being received

over both the sensing and loop antennas. The combination of signals energizes a phasing system that operates a motor

on the loop drive. As the motor turns, it rotates the loop. The bearing pointer is electrically synchronized and turns

with the loop, indicating the bearing to the station when the loop has stopped in the null position.

The loop antenna continuously positions itself to remain perpendicular to the station. As the loop antenna can move

about only one axis (i.e., it can turn but cannot tilt), an error is induced whenever the aircraft is in a banked attitude.

This is called dip error. The magnitude of this error depends on the position of the aircraft from the station, its altitude

and range, and the angle of bank used. Dip error is most noticeable when the aircraft is banked and the station is on

the nose or tail of the aircraft. The ADF bearing pointer should be considered as giving accurate bearings only in

wings-level flight.

23.1.1.1 Tuning

The radio compass is normally tuned for ADF operation. The ADF feature is used for ease of operation; however,

if reception of radio signals is poor due to static, thunderstorms, or distance from the stations, use Manual Direction

Finder (MDF) procedures described later in this section. Since most ADF receivers do not have a “flag” to warn the

pilot when erroneous bearing information is being displayed, the pilot should continuously monitor the

Non-Directional Beacon (NDB) identification (refer to specific aircraft NATOPS).

Note

See the appropriate Flight Information Publications (FLIP) en route for the

procedures peculiar to tuning foreign low-frequency stations.

ADF tuning:

1. Interphone control panel and radio compass filter switch as required.

2. Obtain control of the set.

3. Function switch — ANT position.

4. VOICE-CW switch — VOICE.

5. Select the frequency band.

6. Tune to the desired frequency for best audible signal. Under conditions of static and/or interferences, a weak

station can sometimes be tuned by using the LOOP position. When tuning in LOOP, an increase in volume will

generally be required.

7. Identify the station.

8. Function switch — COMP/ADF position.

9. Retune for maximum needle deflection on the tuning meter.

Tuning with the nonmetered radio control compass panel:

As this control panel does not incorporate a tuning meter, do fine tuning for ADF with the function switch in the ANT

position and the VOICE-CW switch in the CW position. Tune for minimum or zero modulated tone, return the

VOICE-CW switch to VOICE and the function switch to ADF, and reidentify the station.

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NAVAIR 00-80T-112

Note

Tuning for zero modulation is an accurate method of obtaining maximum

signal strength and can be used if difficulty is experienced determining

maximum needle deflection on the tuning meter. See Figure 23-1 for

volume effects on null width.

23.1.1.2 Course Interceptions

Inbound course interceptions may be done identically to those described in paragraph 21.3.3.1. An alternate method:

To determine the intercept heading, locate the bearing from the station that you are presently on, the bearing that you

want to intercept, and measure the angular difference. If the angular difference is less than 45_, turn toward the desired

bearing in the shortest direction with an angle of intercept equal to the computed angular difference. The time to the

station will be approximately equal to the time necessary to complete the intercept (Figure 23-2). If the angular

difference is greater than 45_, a series of time-distance check maneuvers (discussed under paragraph 23.1.1.5) may

be performed if distance/time to the station is unknown. The pilot may select any angular interception if timing is not

essential, 30_ to 45_ being generally sufficient (Figure 23-3).

23.1.1.3 Station Passage

23.1.1.3.1 ADF Procedure

When close to the station, the bearing pointer becomes unsteady and erratic due to the area of signal confusion. This

characteristic increases with altitude. Also, a small, lateral displacement from the desired course causes a large

off-course bearing indication. A bearing pointer deflection of 5_, when the aircraft is 10 miles from the station, means

that the aircraft has departed from the desired course approximately 1 nm, whereas the same 5_ displacement at 1

mile would represent a distance of approximately 600 feet. Do not chase the bearing pointer when it starts moving

rapidly to the side; instead, maintain a constant heading, as the station is very near.

Figure 23-1. Effects of Volume Control on Null Width

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NAVAIR 00-80T-112

Procedural Steps

1. Tune and identify station.

2. Determine the bearing from the radio beacon you are on (240_) by looking at the tail of the No. 2 needle.

3. Determine the bearing from the radio beacon you desire to intercept (210_).

Visualize this on your heading indicator.

4. Measure the angular difference (30_).

Since it is less than 45_, compute your intercept heading based on the number of degrees in the

computed angular difference (30_) and your present inbound course to the station (060_). The computed

intercept heading would be (090_). Since the bearing visualized on the heading indicator is to the right of

your present bearing, the 30_ is added to your inbound course.

5. Look at your aircraft heading and turn in the shortest direction to the computed intercept heading.

Start the clock.

6. Maintain the intercept heading until a lead point is reached, then complete the intercept.

Lead points depend on the No. 2 needle rate of movement.

Figure 23-2. Inbound Course Interception Less Than 45°

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NAVAIR 00-80T-112

Procedural Steps

1. Tune and identify the station.

2. Determine the bearing from the radio beacon you are on (240_) by looking at the tail of the No. 2 needle.

3. Determine an intercept heading.

a. Determine the bearing from the radio beacon you desire to intercept (330_). Visualize this on the

heading indicator.

b. Measure the angular difference (90_).

c. Since it is greater than 45_, compute your initial heading based on the present course to the station

(060_) and the figure 70_.

d. Since the shortest direction to the bearing is to the left, subtract 70_ from the present course to the

station. The computed initial Magnetic Heading (MH) is 350_.

e. Turn in the shortest direction to the computed initial MH.

4. Intercept sequence.

a. When intercepting the 270_ bearing, start the clock and maintain heading.

b. After completing 20_ of bearing shift, note the time, start the clock again, and turn the aircraft 20_

toward the radio beacon.

c. Continue with the 20_ time distance checks until a lead point is reached, then complete the intercept.

d. Lead points depend on the rate of movement of the No. 2 needle.

Note

If heading indicators are inoperative, the No. 2 needle will still point to the station. Utilize the magnetic

compass to determine bearings and make timed turns.

Figure 23-3. Inbound Course Interception Greater Than 45° (Timed Distance Method) (Sheet 2 of 2)

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NAVAIR 00-80T-112

Initial station passage is positively determined when the pointer moves through the wingtip position. This usually

occurs shortly after the aircraft has actually passed the station. Timing should begin that instant regardless of further

oscillations.

23.1.1.4 Outbound — Immediately After Station Passage

Turn to parallel the desired outbound course (compensate for wind). Maintain heading and allow the bearing pointer

to stabilize. Note the number of degrees between the tail of the bearing pointer and the desired course. To correct back

on course, use outbound course interception technique (Figure 23-4).

23.1.1.4.1 Outbound — Away from the Station

First, note the position of the bearing pointer tail. Then, on the compass card, look from the tail in the short direction

to the desired course. Any heading beyond the desired course is a no-wind intercept heading. Normally, 45_ beyond

the desired course is a good intercept heading as it also forms a 45_ or “average” angle of intercept; however, as in

inbound intercepts, consider the known factors of groundspeed and distance from the station when selecting an

intercept heading. Outbound procedures are essentially identical with those for VHF Omnidirectional Range (VOR)

— Radio Magnetic Indicator (RMI) only (Figure 21-9).

23.1.1.4.2 Completing the Intercept

After the intercept heading has been established, adjustments may be required to achieve a more desirable angle or

rate of intercept. As the aircraft approaches course, it is necessary to determine a lead point for turning because of

the radius of turn. The lead point will depend upon the rate of movement of the bearing pointer and the time required

to complete the turn to course. Factors affecting the lead point are groundspeed, distance from the station, intercept

angle, and rate of turn. Complete the turn to course, simultaneously applying a correction for known wind.

23.1.1.5 Time-Distance Check

It is possible to calculate the time and distance from the station using ADF.

23.1.1.5.1 ADF Procedures

After tuning the radio compass for ADF, note the position of the bearing pointer. The number of degrees the bearing

pointer is deflected from the wingtip position indicates the magnitude and direction of turn required to place the

pointer on the wingtip position. Turn to this predetermined heading. If the bearing pointer is not within 5_ of the

wingtip position after you have made the turn, make a corrective turn to place it on the wingtip. Note the exact time

at the completion of this turn, and maintain a constant heading until the pointer shows a bearing change of 5_ to 20_

(Figure 23-5).

23.1.1.6 Tracking

It is possible to maintain a course to or from a station using the radio compass bearing pointer, regardless of whether

the compass card is working properly or not, because the bearing pointer will point to the station and show the relative

bearing of the aircraft to the station.

23.1.1.6.1 Inbound

After completing a turn to course, maintain heading until the bearing pointer shows a deflection from the desired

course. Turn toward the pointer and beyond a sufficient number of degrees to return to course.

After reintercepting course with the correct wind drift correction applied, the pointer will continue to point to the

desired course and be displaced from the top index the number of degrees equal to the applied drift correction. If the

pointer moves toward the top index, the correction is too small; if it moves away from the top index, the correction

is too large (Figure 23-6).

23-7

ORIGINAL

NAVAIR 00-80T-112

Outbound Procedural Steps — ONLY

1. Tune and identify the station.

This should already be accomplished.

2. Turn in the shortest direction to a heading that will parallel or intercept the outbound course.

Turning to parallel the desired outbound course is always acceptable. Continuing the turn to an intercept

heading may be preferable when the bearing pointer is stabilized or when the pilot knows the aircraft

position in relation to the desired course. The effect that airspeed, wind, and magnitude of turn will have

on aircraft position during the turn to an intercept heading should be carefully considered.

3. Determine number of degrees off course.

Note the angular difference between the tail of the bearing pointer and the desired course.

4. Determine an intercept heading.

If a suitable intercept angle was not established during the initial turn, look from the tail of the bearing

pointer to the desired course. Any heading beyond the desired course is a no-wind intercept heading.

Turn in this direction an amount approximately equal to the number of degrees off course. Normally, to

avoid overshooting the course, do not use an intercept angle greater than 45_.

Note

On some aircraft, the RMI/Bearing-Distance-Heading Indicator (BDHI) bearing pointer does not have a tail.

In this case, turn to the magnetic heading of the desired course. Continue on the outbound magnetic heading

of the desired course until the bearing pointer stabilizes. Note the number of degrees the bearing pointer is

off the tail of the aircraft. This is the number of degrees off course. Any heading change in the direction toward

the head of the bearing pointer is a no-wind intercept heading. Turn in the direction of the head of the bearing

pointer an amount approximately equal to the number of degrees off course. Normally, to avoid overshooting

the course, do not use an intercept angle greater than 45_.

5. Turn to an intercept heading, if not previously accomplished.

6. Maintain the intercept heading until a lead point is reached, then complete the intercept.

Lead point depends on bearing pointer rate of movement and the time required to turn on course.

Figure 23-4. Course Interception Immediately After Station Passage (Sheet 2 of 2)

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NAVAIR 00-80T-112

23.1.1.6.2 Outbound

To maintain an outbound course, use outbound course interception procedures. Apply corrections to keep the desired

course under the tail of the bearing pointer. After applying a wind drift correction outbound, and the tail of the pointer

moves toward the top index, the drift correction is too large; if it moves away from the top index, the drift correction

is too small (Figure 23-7).

For ease of computation, it is desirable to use 10_ of bearing change. When the bearing pointer shows the desired

bearing change, again note the exact time. Turn immediately to place the bearing pointer under the top index and

maintain that course to the station. Determine the time to the station by applying the following formula:

Time in seconds between bearings

+ Minutes to station.

Degrees of bearing change

For example, if it requires 2 minutes (120 seconds) to fly a bearing change of 10_, the aircraft is:

120

10 = 12 minutes to the station.

The time from the station may also be calculated by using a short method based on the above formula, provided a

10_ bearing change is flown. If the elapsed time for the bearing change is noted in seconds and a 10_ bearing change

is made, the time from the station in minutes is determined by counting off 1 decimal point; thus, if it requires 75

seconds to fly a 10_ bearing change, the aircraft is 7.5 minutes from the station.

When the bearing pointer is moving rapidly or when several corrections are required to place the pointer on the

wingtip position, the aircraft is very close to the station. For all practical purposes, this can be considered station

passage.

The distance from the station may be computed by multiplying True Airspeed (TAS) or groundspeed (in miles per

minute) by the previously determined time in minutes. For example, if the aircraft is 4 minutes from the station, flying

at a TAS of 300 knots (or 5 nm per minute), the distance from the station is:

4 = 20 nm.

The preceding are methods of computing approximate time and distance. For increased accuracy, use only a small

amount of bearing change (about 10_) and correct for existing winds.

By flying a constant heading and checking the time and bearing progression closely, you can determine the estimated

time of arrival over the station, or the position and distance from a station not directly on the flightpath.

23.1.1.7 Homing

Homing is essentially keeping the nose of the aircraft pointed at the station while proceeding inbound. As homing

in a crosswind will result in a curved flightpath to the station, use it only for short distances (i.e., transition from one

radio facility to another in the immediate area) (Figure 23-8).

Note

Homing is not an accepted instrument procedure.

23.1.1.7.1 ADF Homing Procedures

Observe the position of the radio compass bearing pointer and turn in the shorter direction to place the head of the

bearing pointer under the top index of the compass card. Maintain this indication while proceeding to the station.

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NAVAIR 00-80T-112

23.1.2 UHF Nondirectional Radio Beacon (Homer)

The Ultrahigh Frequency (UHF) homer ground station transmits a continuous carrier in the frequency range of 275

to 287 MHz, modulated with a 1020-cycle tone for identification purposes. Some UHF homers also have a voice

capability. The power output is approximately 15 watts. The pilot of an aircraft equipped with UHF/ADF equipment

can determine the relative bearing of, and home on, the ground equipment. The airborne equipment extracts the

information from signals received by the aircraft UHF communications receiver. The relative bearing of the signal

source is indicated on a heading indicator. Best results are obtained under straight-and-level flight conditions

(Figure 23-9).

23.1.2.1 UHF/ADF Navigation Auxiliary Receivers

UHF/ADF navigation auxiliary equipment receives UHF signals from any UHF radio beacon operating in the range

of 265.0 to 284.9 MHz. The equipment operates on any 1 of 20 preset crystal-controlled channels. To determine the

preset channel from a known frequency, subtract the number 264 from the known frequency, disregarding the

decimal;. thus, 265.2 MHz will be channel 1, 280.4 MHz will be channel 16, etc. A separate crystal-controlled Guard

channel, operating on an alternate basis with the main receiver, is also available. This Guard channel is preset on an

assigned frequency of 243.0 MHz.

The equipment is primarily designed for use in normal automatic direction finding; however, it may also be used to

provide auxiliary or emergency voice reception if the normal radio receiver should fail. When functioning in the

normal automatic direction finding mode, this equipment operates with the UHF homing adapter equipment and the

appropriate needle on the course indicator or RMI. As the relationship between the navigation equipment and the

communications equipment will vary between types of aircraft, the pilot should refer to the applicable NATOPS flight

manual for more specific procedures.

Figure 23-5. Time-Distance Check

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ORIGINAL

NAVAIR 00-80T-112

Figure 23-9. Automatic Direction Finding Signal Pattern

23.1.2.2 UHF Homing Adapters

These systems are used with UHF transceivers as a navigational aid. They provide a continuous indication of the

approximate relative bearing of an RF signal source transmitted by another aircraft, surface craft, or ground station

on a frequency range of 225.0 to 399.9 MHz. The approximate relative bearing will be indicated by the appropriate

needle on the course indicator or RMI.

Whenever the function selector switch on the UHF control panel is set to the T/R or T/R+G position, the homing

equipment will automatically be placed in the standby condition. When this selector is set to ADF, the command

equipment is placed in circuit with the homing equipment, enabling the latter to receive the frequency selected by

the channel selector switch on the command set control panel. In the ADF position, the auxiliary guard receiving

capability will be lost.

23.1.2.3 Approach Procedures

ADF procedures for holding, high-altitude penetration and approach, procedure turn and approach, and missed

approach are the same as those for VOR (refer to Chapter 21) except that normal ADF interception procedures are

used. Remember, dip error in turns causes erroneous bearing indications; therefore, make all turns to predetermined

headings (Figures 23-10 and 23-11).

23.2

MARKER BEACONS

Marker beacons serve to identify a particular location in space along an airway or on the approach to an instrument

runway. This is done by means of a 75-MHz transmitter that transmits a directional signal to be received by aircraft

flying overhead. These markers are generally used in conjunction with low-frequency radio ranges and the Instrument

Landing System (ILS) as point designators. Four classes of markers are now in general use: Frequency Modulation

(FM), Low-Power Fan Marker (LFM), station location or Z-markers, and the ILS marker beacons.

ORIGINAL

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NAVAIR 00-80T-112

FM and LFM fan markers are keyed to indicate on which radio range course they are located. The radio range courses

are numbered clockwise beginning at true north with the north (or near north) course being designated No. 1. Fan

markers located on course number one are keyed to emit single dashes, those on course two, two dashes, etc. When

two fan markers are located on the same radio range course, the identification of the outermost marker is preceded

by two dots; thus, the identification of the outermost marker on a number one course is two dots and one dash.

The class FM fan markers are used to provide a positive identification of positions at definite points along the airways.

The transmitters have a power output of approximately 100 watts. Two types of antenna array are used with class FM

fan markers. The first type, generally referred to as the standard type, produces an elliptical-shaped pattern, which

at an elevation of 1,000 feet above the station is approximately 4 miles wide and 12 miles long. At 10,000 feet, the

pattern widens to approximately 12 miles wide and 35 miles long. (The long axis lies across the airway or radio range.)

The second array produces a dumbbell or boneshaped pattern, which at the “handle” is approximately 3 miles wide

at 1,000 feet. The boneshaped marker is preferred at approach control locations where timed approaches are used.

The class LFM or low-power fan markers have a rated power output of 5 watts and are usually located within 5 miles

of the radio range stations with which they are associated. The antenna array produces a circular pattern, which

appears elongated at right angles to the airway due to the directional characteristics of the aircraft receiving antenna.

The station location, or Z-marker, was developed to meet the need for a positive position indicator for aircraft

operating under instrument flying conditions to show the pilot when the aircraft was passing directly over a

low-frequency radio range station. The marker consists of a 5-watt transmitter and a directional antenna array that

is located on the range plot between the towers or the loop antennas.

ILS marker beacon information is included in paragraph 24.2.1.3.

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ORIGINAL

NAVAIR 00-80T-112

CHAPTER 24

Instrument Landing System (ILS)

24.1

INTRODUCTION

The Instrument Landing System (ILS) (Figure 24-1) is a precision approach system that provides azimuth and

glideslope information to the pilot. It consists of a highly directional localizer (course) and glideslope transmitter with

associated marker beacons, compass locators, and, at some sites, Distance Measuring Equipment (DME). The system

is automatically monitored and provides changeover to a standby localizer or glideslope transmitter when the main

system malfunctions.

The system may be divided functionally into three parts:

1. Guidance information: localizer, glideslope.

2. Range information: marker beacon, DME.

3. Visual information: approach lights, touchdown and centerline lights, runway lights.

24.2

EQUIPMENT AND OPERATION

24.2.1 Ground Equipment

24.2.1.1 Localizer Transmitter

Localizer transmitters are located approximately 1,000 feet beyond and to the side of the nonapproach end of the ILS

runway. The antenna is in line with the runway centerline. The 90- and 150-cycle signal patterns are radiated on

opposite sides of the extended runway centerline. The 150-cycle signal is on the right when looking at the runway

from the outer marker; the 90-cycle signal is on the left. The course is formed along the runway centerline extended

(toward outer marker) where the signals overlap and are of equal strength. This course is referred to as the front course.

The front course envelope is approximately 5_ wide, extending 2-1/2_ either side of the course centerline. Most

localizer transmitters also provide a signal pattern around the runway so that course signals also overlap in the

opposite direction, forming a back course. There are few published ILS back course approaches and a glideslope is

not provided for them.

CAUTION

Unless the aircraft ILS equipment includes reverse sensing capability,

when flying inbound on the back course it is necessary to steer the aircraft

in the direction opposite the needle deflection when making corrections

from off-course to on-course. This “flying away from the needle” is also

required when flying outbound on the front course of the localizer. Do not

use back course signals for approach unless a back course approach

procedure is published for that particular runway and the approach is

authorized by Air Traffic Control (ATC).

On aircraft without reverse sensing capability, selecting the front course on your Course Deviation Indicator (CDI)

will prevent the need to fly away from needle deflection. The CDI will deflect in the proper direction, whether you

are on a back course or outbound on a front course.

24-1

ORIGINAL

NAVAIR 00-80T-112

ILS localizer transmitters use the odd decimal VHF frequencies from 108.1 to 111.9 MHz (e.g., 110.3 MHz). The

localizer transmitter emits continuous identification in the form of a coded three-letter station identifier preceded by

the letter I (e.g., I-EMH). Some have voice transmission capabilities.

Note

Momentary localizer flag activity and course aberrations may be observed

when other aircraft cross over the localizer antenna or are in a position to

affect the radiated signal.

24.2.1.2 Glideslope

The Ultrahigh Frequency (UHF) glideslope transmitter, operating on 1 of the 20 ILS channels within the

frequency range 329.3 to 335.0 MHz, radiates its signals principally in the direction of final approach. Any

instrument indications of a glideslope at azimuths other than those within the angular width of the localizer

front course should be disregarded.

The glideslope transmitter is located between 750 and 1,250 feet from the approach end of the runway (down

the runway) and offset 400 to 600 feet from the runway centerline. It transmits a glideslope beam 1.4_ wide.

The glideslope projection angle is normally adjusted to 2.5_ to 3_ above horizontal so that it intersects the

middle marker at approximately 200 feet and the outer marker at approximately 1,400 feet above the runway

elevation.

In addition to the desired glideslope, false course and reversal in sensing will occur at vertical angles

considerably greater than the usable slope. The proper use of the glideslope requires that the pilot maintain

alertness as the glideslope interception is approached and interpret correctly the “fly-up” and “fly-down”

instrument indications to avoid the possibility of attempting to follow one of the higher angle courses.

Extreme caution should be used to avoid exceeding a deviation of one dot (or approximately one-half scale)

below the glideslope up to the middle marker and to avoid any deviation below the glideslope from the middle

marker to completion of landing.

The glideslope facilities provide a signal that flares from 18 to 27 feet above the runway; therefore, the

glideslope should not be expected to provide guidance completely to a touchdown point on the runway.

DME may be installed at the glideslope transmitter site. Range and the three-letter station identifier are

available through the Tactical Air Navigation (TACAN) receiver. Bearing information is not provided.

24.2.1.3 Marker Beacons

Marker beacons are very low-powered, 75-MHz transmitters located along the ILS final approach course to mark a

specific position. Normally, two marker beacons are used for this purpose, and they are depicted on the terminal chart

by the letters OM and MM (Outer Marker and Middle Marker).

An additional beacon called an Inner Marker (IM) may also be installed. The beacons are identified in the aircraft

visually (marker beacon light) and/or aurally depending on aircraft equipment. The reception area of the aural signal

is larger than that of the visual signal. Marker beacons are not installed for navigation purposes but merely to indicate

a fix on the localizer course.

The Outer Marker (OM) is normally located 4 to 7 miles from the end of the runway. Outer marker identification

consists of continuous dashes. Aurally, the dashes are comparatively low pitched (400 Hz). The published altitude

at the outer marker is what the altimeter should indicate when the aircraft is over the marker and on the glideslope;

however, there are no specific limits. The outer marker altitude may also be the procedure turn or glideslope

interception altitude.

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ORIGINAL

NAVAIR 00-80T-112

The Middle Marker (MM) is located approximately 3,500 feet from the runway and is identified by alternating dots

and dashes. The aural signal is comparatively high pitched (1,300 Hertz) and easily distinguished from the outer

marker signal. This is also the position where an aircraft on glidepath will be at an altitude of approximately 200 feet

above the elevation of the touchdown zone.

The IM, where installed, will indicate a point at which an aircraft is at a designated Decision Height (DH) for Category

II equipped aircraft on the glideslope between the middle marker and landing threshold. The IM is modulated at 3000

Hz and identified with continuous dots keyed at the rate of six dots per second.

24.2.1.4 Compass Locators

If installed, compass locators are placed at the marker beacon sites (usually only at the OM) as aids to navigation

around the ILS. They are low-powered nondirectional radio beacons operating between 200 and 415 kHz with a

reliable reception range of at least 15 nm; however, higher-powered, low-frequency nondirectional radio beacons

may be collocated with the marker beacons and used as compass locators. These generally carry transcribed weather

broadcast information.

On the approach chart, the radio data information box for the locator is broken at the top by the letter L. Within the

box are the frequency and the identification of the facility.

The locator identification consists of two letters. When installed at an outer marker, it will normally transmit the first

two letters of the three-letter ILS localizer identification. If installed at a middle marker, it will transmit the last two

letters. For example, with an ILS localizer identified by the letters I-FAT, the compass locator identification at the

outer marker is FA, and at the middle marker is AT. On the profile view of the approach chart, the locators are depicted

by the letters LOM or LMM (Locator Outer Marker or Locator Middle Marker).

During periods of routine or emergency maintenance, the coded identification (or code and voice, where applicable)

will be removed from ILS localizers but not from Non-Directional Beacon (NDB) compass locators or 75-MHz

marker beacons (Figure 24-1).

Note

ILS minimums, with all components operative, normally establish a DH

(decision height MSL) with a Height Above Touchdown (HAT) of 200 feet

and a visibility of one-half statute mile.

24.2.2 Airborne Equipment

The control panel for tuning the ILS localizer is the same as that used for VHF Omnidirectional Range (VOR) in most

aircraft. The glideslope receiver is automatically tuned when the localizer frequency is selected.

A course indicator is used in this chapter to illustrate procedures for flying ILS. The flight director display is illustrated

in Figure 24-3.

The radio magnetic indicator has no function with ILS frequencies; however, bearing information to other radio

facilities (compass locators, TACAN, etc.) can be of considerable value. All available navigation equipment should

be used when appropriate during any approach.

24.2.2.1 ILS Channel/Frequency

ILS are being commissioned utilizing all 20 channels allotted to ILS by International Civil Aviation Organization

(ICAO) in Aeronautical Telecommunications Annex 10. Aircraft equipment should be checked to ensure the

receiving capability of all channels.

ORIGINAL

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NAVAIR 00-80T-112

24.3

ILS PROCEDURES

24.3.1 Performing the ILS Approach

Information for planning an ILS and transitioning to it from other Navigation Aids (NAVAIDs) is found in the

terminal flight information publications (Figure 24-2). The approach should be considered in its entirety from en route

transition through landing or missed approach. Refer to other Flight Information Publications (FLIP) documents such

as Planning and the En Route IFR Supplement.

Pilots should tune the ILS receiver and identify and monitor the localizer identification signal as soon as practical

during the transition procedure. The course and glideslope indicators are reliable only when (1) their warning flags

are not displayed, (2) the localizer identifier is received, and (3) the aircraft is within the usable range of the

equipment. The localizer is considered reliable within 18 miles of the transmitter within 10_ or 10 miles within 35_

of the course centerline unless the published approach depicts a transition point at a farther distance. The glideslope

interception point and altitude are designated on the terminal chart; the glideslope is considered reliable within 10

miles of the transmitter, provided the aircraft is on the localizer course.

Before localizer interception, set the published front course in the course selector window so that the aircraft

heading/localizer relationship is displayed on the course indicator. The transition may require a large turn onto the

localizer course (e.g., a teardrop penetration or procedure turn). If the CDI indicates full-scale deflection (course

deviation 2-1/2_ or greater) during the latter portion of the turn, roll out with an intercept angle that will ensure

localizer interception prior to the glideslope intercept point. Normally a 30_ to 45_ intercept is sufficient; however,

groundspeed, distance from the localizer course, and final approach fix may require another intercept angle.

When the localizer is intercepted, maintain the published heading until the first movement of the CDI. The rate of

CDI movement will aid in estimating the force and direction of the wind. Heading corrections should be sufficient

to stop the CDI movement and return the aircraft to course. After returning to course, apply the drift correction

necessary to keep the CDI centered. Heading corrections should be reduced as the aircraft continues inbound

(increments of 5_ or less are usually sufficient).

The pilot should maintain the glideslope interception altitude, configure the aircraft for landing, and establish the final

approach airspeed before reaching the glideslope intercept point. Do not descend below glideslope interception

altitude if the CDI indicates full-scale deflection. Call the controlling agency at the final approach fix or as directed.

As the Glideslope Indicator (GSI) moves downward from its upper limits, prepare to intercept the glideslope. Slightly

before the GSI reaches the center position, establish a pitch attitude on the attitude indicator and a power setting that

will result in the vertical velocity and airspeed required to maintain the glidepath. The amount of pitch change

required will depend on the glideslope angle. One technique that may be used when intercepting the glideslope

(provided the final approach airspeed and configuration have been established) is to change the pitch attitude on the

attitude indicator the same number of degrees as the glideslope angle (i.e., normally 2-1/2_ to 3_).

The glideslope facility provides a path that flares from 18 to 27 feet above

the runway; therefore, the glidepath should not be expected to provide

guidance completely to a touchdown point on the runway.

Corrections are made using coordinated pitch and power changes. Normally pitch changes should result in vertical

velocity changes of less than 300 fpm. A 1_ pitch change on the attitude indicator is usually a sufficient amount of

correction to achieve a vertical velocity change of 200 to 300 fpm for groundspeeds between 120 and 180 knots.

As indicated in Figure 24-3, the size of the course and glideslope envelope reduces progressively throughout the

approach; therefore, the size of the pitch and bank corrections should be gradually reduced as the distance to

touchdown decreases.

24-5

ORIGINAL

NAVAIR 00-80T-112 NATOPS INSTRUMENT FLIGHT MANUAL (15 NOVEMBER 2006) - page 3