GPWS

The GPWS (Ground Proximity Warning System) is a safety device factory standard in aircraft and aerospace vehicles to alert the flight crew when one of the following thresholds are exceeded.

Mode 1 - Excessive Decent Rate

Mode 1 Envelope

Has two (2) boundaries and is independent of vehicle configuration.

Penetration of the first boundary generates the repeated aural alert of "sink rate".

Penetrating the second boundary causes the repeated aural warning of "WOOP WOOP, pull up", until the rate of decent has been corrected.

Mode 2 - Excessive Terrain Closure Rate

Mode 2 Envelope

Monitors airspeed, AGL altitude and AGL rate-of-change, MSL altitude and vehicle configuration.

It has two (2) boundaries, the first causes an aural alert of "terrain, terrain", followed by the repeated aural warning of "WOOP WOOP, pull up". After leaving the "pull up" area the repeating "terrain" message will be herd while in that portion of the envelope. If both boundaries are penetrated while in the landing configuration, only the repeating "terrain" aural alert will occur. If the landing gear and wing flaps (where applicable) are not in the landing position when leaving the "pull up" area, 91.5 meters MSL altitude must be gained before the aural "terrain" alert is silenced. As the IAS increases with the gear up, the highest altitude at which a mode two alert warning will occur is increased to 746.5 meters. This higher portion is inhibited with the flap inhibit switch on.