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19. Steering arrow and dots. When waypoint/OAP or TACAN course line steering is selected, the
steering arrow and dots appear on the HUD.
20. Required ground speed cue. When steering is engaged to the target in a sequence, the required
ground speed cue appears under the airspeed box.
21. Target designation symbology. When a target is designated, a target designation symbol
(diamond) appears below the heading scale indicating target heading. Another target designation
symbol (diamond) appears indicating the target line of sight (LOS).
2.18.4.6.11 HUD Symbology Degrades. The avionics suite has built in redundancy with two mission
computers for data management and two DDIs for symbol generation. Likewise, if the attitude select
switch is in the AUTO or INS position, back up data sources are automatically selected to provide
HUD symbology when failures are detected. Refer to figure 2-46, for the HUD displays discussed
below.
a. HUD Symbology Degrades with INS Failure. When a failure occurs in the INS, HUD
A1-F18EA-NFM-000
I-2-143 ORIGINAL
Figure 2-46. HUD Symbology Degrades
A1-F18EA-NFM-000
I-2-144 ORIGINAL
bank angle, velocity vector, pitch ladder, and heading indications can be expected to be
impacted. With GPS operating, the mission computer utilizes GPS information for the velocity
vector. If INS attitude is valid but INS velocities are not valid the mission computer
automatically uses the INS attitude and GPS velocities to position a non-flashing velocity
vector. With a degradation of the air data function (probe or pressure transmitter set damage
or failure) calibrated airspeed, barometric altitude, indicated Mach number, and vertical
velocity indications may be impacted.
When the INS experiences a total shutdown (dump) with the attitude select switch in AUTO
or INS, or if the attitude switch is deliberately placed in standby, a stationary waterline symbol
replaces the velocity vector indicating that the standby attitude reference indicator is now
providing attitude data. This failure is normally accompanied by the MASTER CAUTION
light, tone, and INS ATT caution. Place the attitude select switch in the STBY position,
crosscheck the HUD against standby instruments, and attempt an in-flight alignment.
Due to the tendency of the standby attitude reference indicator to precess, it is suggested that
flying in instrument meteorological conditions (IMC) using the ARI as a primary attitude
reference be minimized. A partial IFA (In-Flight Alignment) is always recommended whenever
possible to recover the INS attitude platform.
b. HUD Symbology Degrades with Air Data Function Failure. An air data function
failure in the FCC results in loss of associated data from the HUD display as shown in figure
2-46. Such a failure also inhibits operation of cruise flight Automatic Throttle Control and
disables the altitude signal used for IFF altitude reporting. An air data function failure may
affect cabin air flow and cabin air temperature.
The pressure transmitter set can produce erroneous signals without cautions or advisories if
the pitot tube or AOA probes receive damage. As the air data function degrades, loss of some
or all of the following data from the HUD may occur:
(1) Calibrated airspeed or barometric altitude. The loss of calibrated airspeed and/or barometric
altitude data results in activation of the landing gear handle warning light and tone
with the gear UP. Aircrew action is to reference the applicable standby airspeed or altitude
indicator and then silence the tone.
(2) Angle of Attack. Loss of AOA in three or more FCC CHs causes AOA to be removed from
the HUD.
(3) Vertical velocity indicator. Pilot action on loss of the vertical velocity indication is to check
that the aircraft is in the NAV master mode and to reference the standby vertical velocity
indicator.
(4) Mach number. Pilot action on loss of the Mach number indication is to reference the
standby airspeed indicator.
A1-F18EA-NFM-000
I-2-145 ORIGINAL
If an AOA probe becomes jammed (does not move), the FCC continues to receive valid signals until
the pilot executes a maneuver that causes the reading between the AOA probes to differ more than 15°
in UA or 5.5 to 15° in PA, depending on sideslip. HUD displayed airspeed may be inaccurate without
annunciation if a pitot tube is damaged.
A jammed, blocked, or damaged pitot tube/AOA probe may not be
annunciated if system errors are not large enough to set a caution. Be
alert for unannunciated pitot static and AOA errors during flight in icing
conditions or if damage is suspected after a bird strike or IFR basket
impact during inflight refueling.
Air data inputs from the MC are used by the INS to help smooth or dampen pitch ladder and
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NATOPS Flight Manual 飞行手册 1(105)
