GROUND PROXIMITY WARNING SYSTEM (GPWS)

Ground Proximity Warning System (GPWS) is a navigational equipment which automatically and timely alerts the flight crew of an unsafe/hazardous terrain proximity. After the development of the system the Controlled Flight Into Terrain (CFIT) conditions drastically reduced.

GPWS requires inputs from the following for proper operation:

1. Air Data System (Barometric Altitude and static air temperature)

2. Inertial Reference Unit (Inertial Navigation Unit if installed).

3. Instrument Landing System.

4. Radio Altimeters

The main component of GPWS is its dedicated LRU/computer consisting of a preloaded worldwide terrain navigational database, i.e., the database is more like 3D model in which the location of aircraft is the dynamic input into the database.

It’s enhanced version is sometimes known as Enhanced GPWS (EGPWS) or Terrain Awareness and Warning System (TAWS). The Enhanced GPWS or TAWS operates in the same manner as GPWS but has forward looking capability and predictive terrain warning awareness.

TAWS has multiple inputs from a variety of sensors such as radio altimeter, baro-altitude, inertial reference unit, flight management system, GPS, and a geographical terrain mapping database from an onboard computer.

Using data from the sensors, TAWS is capable in real time to compare the known geographic position and altitude of the aircraft against the internal terrain database computer to predict and display in advance any potential conflicts between the aircrafts flight path and ground terrain.

GPWS has 7 modes:

• Mode 1: High descent rate

• Mode 2: High terrain closure

• Mode 3: Altitude loss after takeoff

• Mode 4: Proximity to the ground when not in the landing configuration

  • Gears not locked down

  • Flaps not in locked position

• Mode 5: Descent below the Instrument Landing System (ILS) glideslope

• Mode 6: Radio Altitude callouts (information only)

• Mode 7: Windshear protection