Windshear Alerts
The Ground Proximity Warning System (GPWS) provides aural and visual alerts
of windshear conditions. Windshear alerts are either warnings or cautions, based
on the level of hazard and the required flight crew reaction time. The aural
warning consists of a two-tone siren followed by the voice warning
WINDSHEAR, WINDSHEAR, WINDSHEAR. The aural warning is activated
only once during a windshear encounter. The visual warning is provided by a red
“WINDSHEAR” alert (message) on each EADI. The message remains until
windshear conditions cease to exist. The windshear warnings take priority over all
other GPWS alerts. Warnings are available below 1500 feet radio altitude. On
takeoff the warning becomes active at rotation.

Windshear alerts are available during takeoff, approach, and landing:

The GPWS provides a warning when the airplane is in a windshear.

Windshear warnings are accompanied by WINDSHEAR on the attitude indicators
and voice aural alerts.
Windshear cautions are accompanied by a voice aural alert.

Windshear Warning (Airplane in Windshear)
AURAL ALERT  VISUAL ALERT  DESCRIPTION 
Two–tone siren followed by WINDSHEAR WINDSHEAR WINDSHEAR  Red WINDSHEAR on both attitude indicators.  Excessive windshear at the current airplane position detected by GPWS. Enabled below 1,500 feet RA. GPWS Windshear detection begins at rotation. 

Copyright . The Boeing Company. See title page for details.
June 6, 2003  15.20.11
Warning Systems -System Description 737 Operations Manual

Enhanced Ground Proximity Warning System (EGPWS)
The EGPWS provides alerts for potentially hazardous flight conditions involving
imminent impact with the ground. In addition to providing the protection of GPWS, the EGPWS monitors terrain proximity using an internal world wide terrain data base. Proximate terrain data show 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.”
The EGPWS provides alerts based on radio altitude and combinations of barometric altitude, airspeed, glide slope 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 glide slope These alerts are “radio altitude based alerts.”

Ground proximity alerts are accompanied by voice aural alerts and the PULL UP annunciation on the attitude indicators or, for deviation below glide slope 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 display 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.
Copyright . The Boeing Company. See title page for details.
15.20.12   August 1, 2003

Warning Systems -System Description 737 Operations Manual
Look-ahead terrain alerts are based on the airplane’s position, barometric altitude, vertical flight path, and ground speed.
Look Ahead Terrain Alerts
AURAL ALERT  VISUAL ALERT  DESCRIPTION 
TERRAIN  PULL UP on both  20 to 30 seconds from projected impact with 
PULL UP  attitude indicators  terrain shown solid red on the navigation 
Red TERRAIN message on navigation display  display (in expanded MAP, center MAP, expanded VOR, or expanded APP modes only). 
(all modes)  Moving the ground proximity terrain inhibit 
Solid red terrain on navigation display  switch to TERRAIN INHIBIT inhibits the alert. 
　
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