Ground Proximity Warning System

A ground proximity warning system, or GPWS, is an onboard alert system that warns a flight crew when their aircraft is at risk of flying into the ground, water or an obstacle, a category of accident the Federal Aviation Administration classifies under terrain awareness and warning systems. It uses a radar altimeter to track the aircraft's height above the terrain, and a computer monitors the trend of those readings against the aircraft's configuration, such as its flap and landing gear settings, to decide when to sound a visual and audio warning; an enhanced version introduced in 1996 added GPS positioning and a digital terrain database so that it can warn earlier, before the radar altimeter alone would detect rising ground. The system was developed by the Canadian born engineer C. Donald Bateman after a run of controlled flight into terrain accidents in the late 1960s, and the Federal Aviation Administration required approved GPWS equipment on all large turbine and turbojet airplanes from 1974, with the International Civil Aviation Organization recommending it worldwide in 1979. Before the 1974 mandate, large aircraft suffered an average of three and a half fatal controlled flight into terrain accidents a year in the affected fleet; no such fatal crash occurred in United States airspace for large jets in the following decades through 2006.