Navigation System

WCS Computer

The WCS or weapon control system computer and CSDC use several alignment routines stored on a magnetic tape to perform the necessary computations to align the INS.

These stored alignment routines in the WCS computer are called SMAL single mode alignment program. When alignment is initiated, the routines are loaded in the computer’s destructive readout memory from magnetic tape.

This process is called “tape read-in” and is represented by an M on the TID. During the alignment of the IMU platform, the WCS communicates with the CSDC to address specific CSDC navigation routines.

IMU Platform Alignment

When alignment mode is selected, the IMU platform first erects to a coarse alignment with the help of accelerometer output and gives an aircraft heading that represents the angular displacement from true north. This displacement is referred to as wander angle. The CSDC sends inertial velocity data to the WCS during the alignment process.

The second stage – fine alignment – uses the precise measurement of gyroscope drift to calculate the aircraft’s true heading. This is possible because of the Earth’s rotation. At no point of alignment, is the magnetic heading used, and the whole process relies only on the sensing of the non-inertial movement of the platform within the 3D space.

The WCS calculates terms for platform alignment corrections and estimates the value of the wander angle, then sends this data to the CSDC. The CSDC uses these correction terms in the CSDC inertial equations to generate pulses for the platform torquing that are then transmitted to the IMU. The CSDC in return receives velocity information from the IMU and sends this new inertial velocity data to the WCS alignment program, upon which the cycle repeats. The exchange of data continues until INS is entered.

The leveling process of the platform is achieved by the CSDC generating torquing pulses based on IMU accelerometer off-level indications being sent to the IMU by the CSDC. With each data exchange, the WCS calculates an error value (delta) between the values of the previous and current wander angle. This delta is largest at the beginning of the alignment and smallest at the end of alignment.

The alignment is finished when the delta is near zero and near zero velocity is sensed along the platform X and Y axes. Variable factors required to align the platform are continuously calculated, updated, and saved as calibration data. When the alignment is complete, the system is ready to enter INS. The last used calibration data and wander angle are stored in the CSDC upon entry into INS. When in INS, the WCS accepts the velocity and position data and the wander angle from the CSDC.

Navigation Modes

Three navigation data mode sources are used for general navigation:

1. INS - The primary navigation mode set by the RIO once IMU alignment is complete. The IMU is the primary sensor supplying velocity data that is used to compute all inertial outputs. The IMU is the source for roll and pitch data.

2. IMU/AM - A backup mode that can either be selected by the RIO or is automatically entered when the CSDC determines the IMU inertial velocity data is unreliable. In this mode, true airspeed from the CADC and stored or entered winds are combined to provide ground speed and true heading for general navigation. The IMU is the source for pitch and roll.

3. AHRS/AM - An even further degraded mode that can be either selected by the RIO or automatically entered when the CSDC detects a total INS failure. Heading in this mode is derived from magnetic heading plus entered or stored magnetic variation (MAG VAR). This heading, TAS from the CADC, and entered or stored wind are used for general navigation. The AHRS is the source of pitch and roll.

Navigation Computations

The CSDC and the WCS are aware of the selected navigation mode. The CSDC sends the WCS navigation data parameters (TAS from the CADC, latitude and longitude, inertial velocities, true heading, etc.) required to support general navigation calculations. The WCS uses stored and input navigation data (based on the current navigation mode) to perform the required navigational computations. The WCS also performs additional computations so that the crew is provided with:

• Current latitude and longitude
• Attitude
• Heading true and magnetic
• Own ground speed and ground track
• Ability to store and display three waypoints, a fixed point (FP), an initial point (IP), a surface target (ST), a home base (HB), a defended point, and a hostile area
• Range, bearing, command course, command heading, and time-to-go to a selected destination point
• Calculated wind speed and direction
• Calculated magnetic variation
• Continuous monitoring of the status of the unit, and in case of failure inform the crew with advisory lights and appropriate acronyms displayed on the TID
• Backup navigation modes in case of partial system failure
• Backup present position

Displays

Navigation information is displayed on the TID, HSD, multiple display indicator (MDI), HUD, and VDI, depending on the mode selected by the pilot and RIO. If an IMU or navigation computer failure occurs, two backup modes are available: IMU airmass (IMU/AM) or AHRS airmass (AHRS/AM).

Navigational Controls

To control the INS, use the navigation control and data readout panel and the computer address panel. See Tactical Information Display (TID) and Associated Controls and Associated Controls and Computer Address Panel (CAP) for a more detailed description.

The desired operation mode, alignment mode, and destination point can be selected at the navigation control and data readout panel. The CAP allows entering navigation data and the selected information to be displayed on the TID. The CATEGORY switch on the lower end of the panel determines the function of the MESSAGE button. The categories used for navigation are NAV and TAC DATA. The STBY and READY advisory lights on the navigation control and data readout panel indicate the status of the alignment program and navigation system.

Failure indicators for the main components of the navigation system are on the caution/advisory light panels in both cockpits, however, the NAV COMP and IMU indicators are only present on the RIO cockpit caution/advisory light panel.

The pilot displays (HUD, VDI, and HSD) and the RIO multiple display indicator are controlled with either the pilot display control panel or the multiple display indicator control panel.

Note: For detailed information on CAP operation, refer to Computer Address Panel (CAP).

Navigation Category

If the CATEGORY switch is in NAV, the following matrix appears in the MESSAGE windows:

OWN
A/C
TACAN
FIX
STORED
HDG
ALIGN
RDR
FIX
VIS
FIX
WIND
SPD HDG
FIX
ENABLE
MAG
VAR
(HDG)

Each window has a designated button. Pressing this button tells the WCS computer which function of the matrix to use. If OWN AC, WIND, or MAG VAR is pressed, data can be entered and displayed for each.

Own-aircraft airspeed and magnetic heading are displayed on the TID. If own-aircraft data file is hooked using the TID cursor, heading will be magnetic. If OWN AC button was selected (hooked) via the CAP, own-aircraft true heading, speed (groundspeed), altitude, or course can be displayed on the TID by depressing the appropriate prefix button:

• LAT or LONG button will display own-aircraft latitude and longitude.
• SPD button displays ground speed and magnetic course.
• True airspeed and true heading are displayed when the HDG prefix button is depressed.
• Altitude is displayed on the left TID readout (right is blank) when the ALT button is used.
• When pressing the WIND button, the TID displays present wind speed (left readout) and magnetic direction (right readout).
• The MAG VAR button is used for displaying and entering magnetic variation (MAG VAR).

In order to change own-aircraft lat, long, true heading, or altitude, press the according prefix button followed by the desired quantity. During entry, the data is displayed on the upper middle readout on the TID. At the same time, existing data is being displayed on the two lower readouts. If new data is correct, the RIO can press the ENTER button and the new values will appear on the readout.

To change wind data entry, press the WIND button, then either the SPD or HDG prefix button and the appropriate numbers: knots (0 to 512) for speed or degrees (000 to 359) for magnetic direction. The multiple display indicator data readout of WIND direction is always displayed as true.

Note: In the INS mode, wind is calculated and updated continuously. The manual entry of wind is ignored by the wind calculations even though the system accepts the entry.

Depressing the MAG VAR button displays alternating values of computed MAG VAR (vC) and manual MAG VAR (vM) on the left readout and displays magnetic heading (MH) on the right readout. The two values alternate every 2 seconds. On the CAP sign/direction buttons, plus (+) corresponds to east variation and minus (-) to west variation.

For manual MAG VAR, press the MAG VAR button. Press HDG, E, or W, the angle in degrees and tenths, and ENTER. Tenths of a degree must be entered even if zero. The TID displays including the NAV GRID will shift appropriately. Computed MAG VAR is constantly calculated in the AWG-9 by comparing the IMU’s true heading with the magnetic heading from AHRS. This difference is saved as computed MAG VAR. The table below shows the MAG VAR source used by the computer for displays and CAP entries.

Computed MAG VAR and manual MAG VAR are compared by the AWG-9 computer. If they differ by a certain value, the acronym MV will alternate with the IN or IM navigation mode acronym on the TID and HSD. The acronym is cleared when the difference falls below 5°.

If the selection of AHRS/AM occurs and no update (or re-entering of the same value) occurs last vC will be used.

Note: When operating in SLAVED or COMP mode near a magnetic disturbance, such as aboard a carrier, the MV acronym should be expected to appear.

The table below shows error source analysis and response to the MV acronym appearing in flight.

Tactical Data Category

If the CATEGORY switch is in TAC DATA, the following matrix appears in the MESSAGE windows:

WAY
PT
1
HOME
BASE
WAY
PT
2
DEF
PT
WAY
PT
3
HOST
AREA
FIX
PT
SURF
TGT
IP
PT
TO
PT

The functions in this category have a TID symbol each, except the PT to PT FUNCTION. When pressing any one of these MESSAGE buttons, the TID symbol brightens and the activated MESSAGE push button illuminates, indicating a successful hook. The RIO can then use the functions for which hooking was required. Data regarding the hooked point can be displayed on the TID by pressing the according prefix button. Additionally, the latitude, longitude, and altitude of the hooked point can be entered by pressing either the LAT, LONG, or ALT button followed by the desired numbers. Like before, existing data is being displayed on the two lower readouts. If the new data is correct, the RIO can press the ENTER button and the new values will appear on the readout.

Navigational Caution Lights

In addition to the NAV COMP, AHRS, and IMU lights mentioned above, the RIO caution/advisory panel contains two other advisory lights, C&D HOT and AWG-9 COND, that are indirectly related to navigation system operation. Illumination of either or both of these lights could mean degraded navigation operation and would require further investigation of the WCS.

Radar Altimeter System (AN/APN-194)

The radar altimeter is a low-altitude (0 to 5,000 feet), pulsed, range-tracking radar that measures the surface or terrain clearance below the aircraft. Altitude information is obtained by radiating a short-duration RF pulse from the transmit antenna to the Earth’s surface and measuring elapsed time until RF energy returns through the receiver antenna. The altitude is continuously presented to the pilot on an indicator dial in feet AGL. If either Landing or Take off mode is selected on the PDCP, radar altitude is displayed on the HUD from 0 to 1,400 feet.

The radar altimeter can operate in two modes. In the search mode, the system successively examines increments of range until the complete altitude range is searched for a return signal. When a return signal is detected, the system switches to the track mode and tracks the return signal to provide continuous altitude information.

If the radar altimeter drops out of the track mode, an OFF flag appears and the pointer is hidden by a mask. The altimeter will remain inoperative until a return signal is received, at which point the altimeter will display altitude above ground again. Reliable system operation in the altitude range of 0 to 5,000 feet permits close altitude control at minimum altitudes. The system will operate normally in bank angles up to 45° and in climbs or dives except when the reflected signal is too weak.

The system includes a height indicator (altimeter), a test light on the indicator, a low-altitude warning tone, a radar receiver-transmitter under the forward cockpit, and two antennas (transmit and receive), one on each side of the IR fairing, in the aircraft skin. During descent, the warning tone is heard momentarily when the aircraft passes through the altitude set on the limit index. When the aircraft is below this altitude, the red low-altitude warning light on the indicator will stay on.

Note: If radar altitude is unreliable, only the OFF flag is present.

The radar altimeter has a minimum warmup time of 3 minutes. During warmup, failure indications and erroneous readouts should be disregarded.

Radar Altimeter

The only controls for the system are on the Radar Altimeter on the pilot instrument panel. The indicator displays radar altitude above the Earth’s surface on a single-turn dial that is calibrated from 0 to 5,000 feet in decreasing scale to provide greater definition at lower altitudes. The control knob in the lower left corner of the indicator is a combination power switch, self-test switch, and positioning control for the low-altitude limit bug.

Altimeter BIT

To energize the self-test circuitry press and hold the control knob and the green test light will illuminate, the indicator will read 100 ±10 feet, and the HUD altitude scale should read approximately 100 feet. If the indicator passes below the altimeter limit bug setting, the aural and visual warnings are triggered. To resume normal operation simply release the control knob again.

Low-Altitude Audio Warning

A low-altitude 1,000-Hz tone provides an aural warning, modulated at two pulses per second, lasting for 3 seconds. The tone is played to both crew members when the aircraft descends below the altitude set on the low-altitude limit bug.

Navigation System Integration

Navigational Modes

Three navigational modes exist in the F-14:

1. Inertial Navigation Mode (INS)

   • Achieved by the INS, employing the IMU (and PSU) and the CSDC.
   • Provides the flight crew with own-aircraft position, velocity, attitude, and heading information.

2. Inertial Measurement Unit/Airmass Mode (IMU/AM)

   • Serves as a backup navigation mode.
   • Entry into this mode permanently degrades INS platform heading alignment.

3. AHRS/Air Mass Mode (AHRS/AM)

   • Utilizes the AHRS attitude and heading information in place of the IMU.
   • Serves as an additional backup mode if both INS and IMU/AM modes fail.

Inertial Navigation Mode

• INS mode should be entered following an alignment.
• READY light illuminates in GND and CVA alignment positions and stays on after launch in CAT alignment, indicating completion of alignment.
• If the INS mode is selected, both the STBY and READY lights will go out. However, if the INS mode is selected before the caret turns into a diamond, both the STBY and READY lights will illuminate, and the system will revert to the IMU/AM backup mode.

Outputs provided by IMU and CSDC in INS mode:

• Aircraft latitude and longitude

• Aircraft magnetic or true heading (depending on CAP prefix button selected)

• System altitude (barometric damped inertial altitude)

• Platform wander angle

• Velocity components (x, y, z)

• Vertical acceleration

• Aircraft magnetic heading is derived from the AHRS. If the AHRS fails, magnetic heading is derived by subtracting the MAG VAR from the true heading.

• The TID can display latitude, longitude, ground speed, ground track, true airspeed, wind (speed and direction), MAG VAR, altitude, and aircraft true or magnetic heading.

• The WCS computer makes calculations in true north coordinates for steering and uses the magnetic heading input from the AHRS to update the value.

• Wind is computed from the difference between inertial velocities and air mass velocities.

• The WCS and CSDC also provide the steering and cueing functions required for display to the flight crew.

• Destination or navigation points include waypoints 1, 2, or 3, fixed point, home base, surface target, and initial point, which may be designated by the DEST switch on the TID.

• Navigational points (latitude and longitude) can also be inserted by the RIO using the CAP or by datalink message (when on the deck) using either cable or the RF link.

• The course to set (heading to a selected navigational point), range, bearing, and time-to-go to a point are based on great circle calculations.

Note: If INS fails, the RIO should verify MAG VAR calculated and WIND data and update via manual entries as required.

IMU/AM Navigation Mode

• If a failure of the navigation computer section of the CSDC or certain failures in the IMU are detected, the IMU/AM mode is entered automatically.
• Failures are indicated by the STBY and READY lights illuminating and the NAV COMP light illuminating on the RIO CAUTION/ADVISORY panel.
• The switch to IMU/AM is indicated by the IN acronym on the TID and HSD changing to IM. The RIO should select IMU/AM on the NAV MODE switch to extinguish the STBY and READY lights.
• The IMU/AM mode can be entered manually by selecting IMU/AM with the NAV MODE switch.
• If the switch is turned off before selecting IMU/AM mode, the computer cannot enter the IMU/AM mode for approximately 3 to 5 minutes. During this time, the aircraft must remain stationary on the ground or in level unaccelerated flight.

Note: If an alignment past coarse exists with no NAV COMP failure and the RIO switches to IMU/AM, the READY light will flash, indicating that if the switch is not returned to INS within 5 seconds the INS mode cannot be re-entered without completing a new alignment.

• The WCS computer performs dead-reckoning navigation in the IMU/AM mode, using heading information from the IMU and true airspeed from the CADC.
• Wind can be applied by either using the wind last computed in the INS mode or wind data manually entered through the CAP.

Note: After entering the IMU/AM mode, check wind and MAG VAR values. If MV is in error, enter own-aircraft true heading. If winds are in error, update.

IMU Reset Procedure

1. NAV MODE switch - OFF, for a few seconds.
2. NAV MODE switch - IMU.
3. Fly straight and level for 5 minutes.
4. Verify IM acronym.

AHRS/Air Mass Mode

• The AHRS/AM mode is another backup mode for navigation. It uses the last known aircraft position, either from the last navigation computer value or by manual data entry from the RIO. It then extrapolates the present position of the aircraft.
• AHRS/AM mode is automatically selected if the IMU fails or by switching to AHRS/AM on the NAV MODE switch. An IMU failure is indicated by the STBY and READY status lights and the IMU advisory light illuminating. Additionally, the attitude status readout on the TID changes to AH.

WARNING: The navigation mode will not automatically switch to AHRS/AM upon an IMU failure when the navigation system is in IMU/AM mode with a failed IMU quantizer and NAV COMP advisory light illuminated. Because the VDIG/TID/DDD are displaying invalid IMU attitudes, the NAV MODE switch should be moved to AHRS/AM.

Note: Although the navigation mode automatically switches to AHRS when the IMU fails, the STBY and READY lights will remain on until the RIO selects AHRS/AM on the NAV MODE switch.

• When AHRS/AM is selected on the NAV MODE switch, the AHRS provides heading information required for DR navigation in place of the IMU platform and the CSDC provides barometric altitude, altitude rate, and true airspeed as in the IMU/AM mode.
• To update wind speed and direction and magnetic variation, use the CAP.

The AHRS can be operated in any of three subheading modes selected on the compass controller panel:

• SLAVED - Magnetic north referenced (flux value), directional gyro is slaved to flux value, used where reliable magnetic heading reference is available.

• DG - Free azimuth gyro, compensated for drift because of Earth’s (polar operations), used where magnetic reference is unreliable.

• COMP - Magnetic north reference direct (flux value), no gyro damping. The HUD, VDI, HSD, and multiple display indicator use manual magnetic variation (vM) automatically in this mode.

• The RIO can switch from either INS mode to AHRS/AM mode or from IMU/AM mode to AHRS/AM mode for comparison, without fear of degradation, since the AHRS is a separate system.

• This cannot be done with the INS and IMU/AM modes since the IMU is used in both cases and it would result in permanent degradation to the IMU alignment.

• In the case of an IMU failure, the nav system will automatically operate in the AHRS/AM mode with the navigation and data readout panel in INS, as long as the WCS computer receives heading from the AHRS and airspeed from the CADC.

Note: If takeoff is performed in the AHRS/AM mode, MAG VAR and WIND must be manually inserted via CAP for proper navigation computations.

• When the platform is aligned and the AHRS/AM backup navigation mode is selected, the STBY light is off but the READY light is on, indicating that the inertial navigation mode can be selected if desired. The same functions and outputs for display are computed as in INS, however since different inputs are used for some calculations a degraded navigation performance is to be expected.

Steering

There are two basic types of steering: navigation and attack. Attack steering modes will be covered in the Weapons and Weapons Employment overview.

• Navigation steering is computed on either a great circle course or rhumb line to a fixed point on the Earth’s surface or as a deviation from a selected course or heading.
• The point used for steering can be the RIO’s selected destination (three waypoints, fixed point, identification point, surface target, or home base), a TACAN station, ADF information, ACLS information, or a data link waypoint.

Flight Modes and Steering Submodes

The pilot can choose between five VDIG display formats (HUD modes) on the pilot display control panel. These five flight modes are arranged as five vertical, mutually exclusive buttons:

• Take Off (T.O.)
• Cruise (CRUISE)
• Air to Air (A/A)
• Air to Ground (A/G)
• Landing (LDG)

Note: ACM cover open selection overrides all modes, except the T.O. and LDG modes.

• Apart from the VDIG displays, the flight mode selections also control AFCS, armament, and WCS logic. In addition to the essential data such as altitude, vertical speed indicator etc. the VDIG format also provides steering cues.

In each of the flight modes, the pilot can choose between the following five types of steering commands:

• TACAN (TACAN)

• Destination (DEST)

• AWL/PCD

• Vector (VEC)

• Manual (MAN)

• The five selections are arranged horizontally along the bottom of the PDCP. These steering modes determine the display format on the pilot HSD and the RIO multiple display indicator.

• The HSD and multiple display indicator present, in a horizontal plane, steering to the selected point.

• The HSD follows the five submodes when the pilot places the HSD-MODE switch to NAV.

• The RIO can do the same by setting the MODE switch on his multiple display indicator control panel to NAV.

• Also, when LDG is selected, the pilot has the option of displaying ICLS or ACL information via switches on the PDCP that can be used to individually and independently select the HUD and VDI for display. A typical choice would be to select ICLS (SPN-41 /ARA-63) for the HUD and for D/L the VDI.

A/A (air-to-air) and A/G (air-to-ground) modes are further explained in the Weapons and Weapons Employment overview.

Note: The STEERING indicator drum on the navigation control and data readout panel provides a readout for the RIO to inform him of what steering submode the pilot bas chosen.

Takeoff Steering

• To enter the takeoff steering mode, press the T.O. button on the display control panel. The VDIG will display a vertical speed indicator on the left side and an altitude scale on the right side in the HUD.
• Before takeoff, the pilot should check the magnetic heading on top of the HUD and VDI against a known reference (i.e., runway heading and most importantly BRC on the carrier, due to the large magnetic distortion on the ship). The vertical speed indicator should be used to verify a positive climb after takeoff.
• After takeoff, the navigation system normally computes wind and magnetic variation, which are needed for steering. For backup modes, the WCS uses the last computed or RIO-entered wind speed, direction, and magnetic variation.

Take-Off-TACAN Steering

• The TACAN steering submode works the same, whether used for takeoff, cruise, or landing, by providing the pilot with a TACAN deviation.
• The pilot can set the course or TACAN radial with the CRS control on the HSD. The TACAN displays are available on the HUD, VDI, HSD, and multiple display indicator. The HSD and the CMD display TACAN range and the relative bearing to a selected TACAN station.
• To enter the submode, press the TACAN button on the PDCP. After selection of TACAN course, the HUD and VDI display the TACAN deviation symbol and a TO and FROM symbology.
• On the HSD and multiple display indicator, an arrow on the deviation bar pointing in the same direction as the TACAN course indicates a course toward the station, an arrow pointing in the opposite direction indicates a course away from the station. On the HUD, a dashed line indicates FROM, a solid line indicates TO. On the VDI, a dark bar indicates FROM, a bright bar indicates TO.
• On the HUD, the deviation symbol moves 3° (linear) in the field of view for a 6° deviation from the selected TACAN radial. These limits prevent the symbol from leaving the field of view or interfering with the scales on the left and right side. On the VDI, the deviation symbol is scaled to move 1.5 inches (linear) for a 6° deviation.

Takeoff Manual Steering

• The manual steering mode is similar to the basic takeoff mode.
• The mode is entered by pressing the MAN button and selecting a desired course with the CRS control on the HSD.
• The navigation system will then display a command heading on the VDI as a small diamond under the magnetic heading scale.

Cruise Steering

• To enter the cruise flight mode, press the CRUISE button on the PDCP.
• There are four steering submodes available during cruise operations: TACAN, destination, manual, and vector.
• While it is physically possible to press the AWL/PCD steering button on the display control panel, the action is without function in cruise mode.

Note: Should the AWL/PCD submode be selected while in CRUISE, it will inhibit the display of other steering cues.

Cruise TACAN Steering

• This submode works in the same way as take off TACAN steering and provides the same readouts and displays to the flight crew as described under take off TACAN steering.

Cruise Destination Steering

• To enter the cruise destination steering mode, press the DEST button on the PDCP.
• This will provide steering as a command heading symbol on the VDI and HSD to a waypoint selected by the RIO on the navigation control and data readout panel.
• The RIO can change latitude/longitude of the destination by hooking the point on the TID and inserting new data.

Note: Destination steering to the defended point is provided by the RIO selecting MAN with the TID DEST switch. This option is not available in TARPS.

• In the destination steering submode, the destination selected by the RIO and the NAV MODE in use will be alternately displayed on the bottom center of the HSD.

Landing Steering Modes

• To enter the landing steering mode, press the LDG button on the PDCP.
• Usually, the LDG mode is engaged at any point from marshal point on. In the case of a go-around, waveoff, or bolter, the pilot can press the T.O. button on the PDCP to engage the take-off steering mode.
• The landing mode symbology is in general the same as the takeoff mode symbology. Exceptions are the addition of angle-of-attack error symbol on the HUD (the E-bracket, referenced towards the displayed aircraft wings and not the velocity vector) and the velocity vector symbol, as well as 5° pitch increments on the VDI.

Note: In all landing submodes, a VDIG breakaway symbol can be displayed upon receipt of a D/L waveoff message.

• There are three steering submodes available during landing: TACAN, VEC, and AWL/PCD.
• For the TACAN or VEC submodes of LDG, the HUD, VDI, and HSD displays are similar to the same submodes in CRUISE except that in LDG the HUD display includes the velocity vector symbol, the radar altitude symbol, and the vertical speed indicator symbol.

AWL Steering

• If ICLS information from the ARA-63 is available at the marshalling area, the pilot can select the AWL/PCD sub mode.
• To observe glideslope displays, the HUD and VDI AWL switches on the pilot display and control panel should be placed in the ILS position.
• The HUD and VDIG will then provide vertical and lateral precision course vector symbols, forming crossed pointers that are driven by the ICLS.
• On the HUD, full-scale vector deflection is limited to 2°. Full-scale vector deflection on the VDI is 1.5°.
• In the AWL/PCD submode of LDG, the HSD will additionally display TACAN information if the HSD is set to NAV mode on the PDCP.
• At the acquisition window, the pilot can either continue with the ILS display, or, if ACL information from the SPN-42 data link is available, he can select ACL of the AWL switches for either the VDI or HUD displays or both.
• The ACL display uses the same vertical and lateral precision course vector symbols as the ICLS, but these are now driven by the SPN-42 data link.
• A typical display combination during the final stages of landing is ILS on the HUD and ACL on the VDI. With valid ACL data available, the AFCS may be engaged by selecting ACL on the VEC/PCD, OFF, and ACL switch located on the AFCS control panel.