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2A-34-00 PRODUCTION AIRCRAFT SYSTEMS
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October 11/01
Revision 5
unless the TAD is inhibited. The floor is defined as seven hundred feet
(700’) above terrain for all areas except within fifteen (15) miles of airport
with a runway of 3500 feet or longer that is in the EGPWS database. As the
airplane approaches a database airport, the floor drops to four hundred
feet (400’) between twelve (12) miles and four (4) miles of the center of the
runway. On airplanes with EGPWS software version -210 -210 and higher
(SN 1426 and subsequent), the inner alert floor is lowered to two hundred
forty-five feet (245’) and positioned closer to the center of the runway
(typically 1/3 NM to 1 NM) due to the higher resolution of airplane position
relative to the terrain database. For SN 1426 and subsequent, this software
version also provides an identification logic that determines the most likely
destination runway based on airplane position and navigation information.
C. Runway Clearance Floor:
The Runway Clearance Floor (RCF) is very similar to the TCF, and is
available on -210 -210 software (SN 1426 and subsequent) equipped
airplanes. The RCF uses a computed Geometric Altitude (see the
description of Geometric Altitude in the following sections) in lieu of radio
altitude. RCF provides improved terrain alerting in locations where the
runway is located at a much higher altitude than the surrounding terrain, or
where an approach to the runway transits a steep decrease in terrain
clearance. If the airplane enters the RCF alert envelope, an aural “TOO
LOW TERRAIN” alert is sounded and the amber TERRAIN text message is
displayed on the PFD. The aural alert is not repeated unless there is a
further twenty percent (20%) decrease in terrain clearance. The amber
TERRAIN text message remains displayed on the PFD until the RCF alert
envelope is exited.
D. Look Ahead Terrain Alerting:
The EGPWS is able to anticipate potential hazards to the airplane by using
the terrain database and algorithms based on airplane position, flight path
vertical component (climb or descent), and airplane track and speed
relative to the terrain database. See Figure 19. The EGPWS projects a
terrain alert envelope ahead of the airplane, above and below the projected
flight path and laterally within ¼ mile and out to within ± three degrees (3°)
of track (or more if the airplane is turning). If the system algorithms predict
that the airplane will encounter hazardous terrain within sixty (60) seconds,
an aural “TERRAIN, TERRAIN” caution is sounded and the amber
TERRAIN text message is displayed on the PFD. The aural caution is
repeated every seven (7) seconds while the airplane is in the caution alert
envelope, and the text TERRAIN remains displayed until the airplane
clears the terrain caution envelope. If the airplane is projected to encounter
a terrain hazard within thirty (30) seconds, an aural “TERRAIN, TERRAIN”
followed by a “PULL UP, PULL UP” warning is sounded, and a red text
message PULL UP is displayed on the PFD. The aural warnings are
repeated continuously and the red PULL UP is displayed until the airplane
exits the terrain warning alert envelope.
E. Terrain Awareness Display (TAD):
The Terrain Awareness Display (TAD) is graphic representation of the
terrain within two thousand feet (2000’) above or below the airplane,
usually selected to the NAV / RADAR cockpit EFIS display by the EGPWS
options on the Display Controller. (The TAD may be selected for view on
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-34-00
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October 11/01
Revision 5
the PFD, in which case the display is similar to the weather radar display
mode in HSI format.) The terrain display defined altitudes are shown in
Figure 20. The TAD as it appears on cockpit EFIS displays is seen in
Figure 21. This display will automatically appear on the NAV display if a
terrain conflict is detected. The automatic display function is initiated by the
EGPWS computer that switches the Display Controller to the TAD mode. If
desired by the crew, the automatic TAD function may be inhibited with the
TERR INHIB switch on the O-RIDES panel located on the center pedestal.
CAUTION
THE TERRAIN AWARENESS DISPLAY (TAD) IS
INTENDED FOR USE ONLY AS AN ADVISORY OF
POTENTIALLY THREATENING TERRAIN AHEAD. IN
NO WAY SHOULD THE FLIGHT CREW USE THE
DISPLAY FOR NAVIGATION OF THE AIRPLANE OR
FOR GUIDANCE IN STEERING THE AIRPLANE
CLEAR OF TERRAIN.
The TAD offers a plan view image of surrounding terrain in patterns of
green, yellow and red in varying densities. Each specific color and intensity
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