Ground Proximity Alerts
The GPWS provides alerts for potentially hazardous flight conditions involving
imminent impact with the ground. The GPWS 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.”
The GPWS 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).
