(e) Terrain Clearance Gear Down,
Flaps Up (Mode 4b). Mode 4b provides visual and
aural warnings for terrain clearance with gear down
and flaps less than 40%. When aircraft penetrates the
warning boundary at a speed below approximately
145 KIAS with the flaps not extended, the "Too Low
Terrain" aural warning will be sounded and the PULL
UP glareshield indicator lights will begin to flash.
In the event that the landing gear is extended
and then retracted, at 200 feet AGL the "Too Low
Gear" aural warning will sound and the PULL UP
glareshield indicator lights will begin to flash if the gear
is still retracted at that time.
Mode 4b is inhibited below 50 feet AGL for any
gear or flap position. The computer automatically
switches from mode 4b to mode 3 whenever the
boundary of mode 4b is passed in full landing
configuration (gear and flaps down), or whenever the
aircraft is below 50 feet AGL with the gear down.
(f) Descent Below Glideslope (Mode 5).
Mode 5, Figure 3B-166, provides visual and aural
warnings for descent below glideslope when making
and ILS approach. When the aircraft penetrates the
outer warning boundary while on an ILS approach, a
"Glideslope" aural warning will be given softly and the
BELOW G/S glareshield indicator lights will be
boundary is penetrated, the "Glideslope" aural warning
repeats faster and at a higher audio level. The
glideslope advisory alert may be canceled anywhere
below 1000 feet AGL by pressing the BELOW G/S
glareshield switch-indicator. The deviation below
glideslope mode will automatically be reset by climbing
above 1000 feet AGL.
Altitude (Mode 6). Mode 6 provides aural warning for
descending below the radio altitude decision height
selected on the radio altimeter indicator with the
decision height marker for altitudes between 1000 feet
AGL and 50 feet AGL with the landing gear down.
When the aircraft descends below the selected
radio altitude the "Minimums" aural warning will sound.
The mode will not function again until 1000 feet AGL
or 50 feet AGL have been transitioned or the landing
gear has been cycled up or down. There are no
glareshield warning lights associated with Mode 6.
d. Emergency Operation. If any emergency
procedure makes it necessary to land with the gear up
or some situation makes it necessary to disable the
GCAS, pull the GPWS POWER circuit breaker located
on the copilot's sidewall circuit breaker panel.
Figure 3B-166. Descent Below Glideslope (Mode 5)