737 Flight Crew Operations Manual
Warning Systems -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
15.20.10 D6-27370-866-EGP
The GPWS provides alerts based on radio altitude and combinations of barometric
altitude, airspeed, glideslope deviation, and airplane configuration. The alerts are
for:
• excessive descent rate
• excessive terrain closure rate
• altitude loss after takeoff or go-around
• unsafe terrain clearance when not in the landing configuration
• excessive deviation below an ILS glideslope
These alerts are “radio altitude based alerts.”
In addition to providing the functions of the basic GPWS, the EGPWS monitors
terrain proximity using an internal world wide terrain data base. Proximate terrain
data shows on the navigation display. If there is a potential terrain conflict, alerts
are provided based on estimated time to impact. These alerts are “look-ahead
terrain alerts.”
Ground proximity alerts are accompanied by voice aural alerts and the PULL UP
annunciation on the attitude indicators or, for deviation below glideslope alert, the
BELOW G/S light.
Note: Terrain ahead of the airplane may exceed available climb performance. A
ground proximity alert does not guarantee terrain clearance.
Look-ahead terrain alerts and radio altitude based alerts are prioritized based on
the level of hazard and the required flight crew reaction time. Look-ahead terrain
alerts and radio altitude based alerts are inhibited by an actual windshear warning
(airplane in windshear).
Look–Ahead Terrain Alerting
The EGPWS terrain data base contains detailed terrain data near major airports,
and data in lesser detail for areas between airports. Terrain within 2,000 feet of
airplane barometric altitude shows on the navigation display. The terrain data is
not designed to be an independent navigation aid.
The terrain display is generated from a data base contained in the EGPWS
computer and correlated to GPS position.
Terrain and weather radar cannot show together on a display. If one pilot selects
terrain and the other pilot selects weather radar, each display updates on
alternating sweeps. All other displays (TCAS, LNAV routing, etc.) can show with
terrain data.
Look-ahead terrain alerts are based on the airplane’s position, barometric altitude,
vertical flight path, and ground speed.
September 25, 2014
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