1. CODE OFF Flag
2. MILLIBARS Display
3. IN HG Display
4. Needle Pointer
5. Drum Display
Figure 3A-26. Pilots Encoding Altimeter
(2) MILLIBARS. Indicates local barometric
pressure in millibars. Adjusted by use of set knob.
(3) IN HG.
Indicates local barometric
pressure in inches of mercury. Adjusted by use of set
altitude in hundreds of feet with subdivisions at
(5) Drum Display. Indicates aircraft altitude
in ten thousands, thousands, and hundreds of feet
above sea level.
c. Encoding Altimeter Operation.
If the altimeter does not read within 70 feet
of field elevation when the correct local
barometric setting is used, the altimeter
needs calibration or internal failure has
occurred. An error of greater than 70 feet
also nullifies use of the altimeter for IFR
(1) Turn-On Procedure. Encoding altimeter
will operate when transponder is operating with M-C
switch set to center position.
1. Barometric set knob Set desired
altimeter setting in IN HG window.
2. CODE OFF flag Check not visible.
Needle indicator Check operation.
d. Encoding Altimeter Emergency Operation.
1. Altimeter circuit breaker Pull, if encoder
The ground proximity altitude advisory
system will provide little, if any, warning
approaching a sheer wall if there is little
gradually rising terrain before reaching the
a. Description. The Ground Proximity Altitude
Advisory System (GPAAS) is provided to aid the flight
crew in terrain avoidance. Refer to Figure 3A-27.
The GPAAS is a completely automatic system,
requiring no input from the crew, which continuously
monitors the aircraft's flight path at altitudes of
between 100 and 2000 feet AGL.
The GPAAS computer processes the data and,
when conditions warrant, selects the appropriate
digitized voice advisory/warning message from its
memory. This message is then announced over the
pilots and copilot's audio system. If the condition is
not corrected, the GPAAS will rearm, and will again
announce and repeat the warning if the condition
recurs. The GPAAS computer remains ready to
announce a different message during the intervals
between repetitions. All messages are disabled below
100 feet AGL.