Ground Proximity Warning System (GPWS)

Ground Proximity Warning System (GPWS)

Ground Proximity Warning System (GPWS) - Aviationnepal

Ground Proximity Warning System (GPWS)

In the late 1960’s, hundreds of people loss their life in a series of controlled flight into terrain (CFIT) accidents, in which aircraft having no any physical defect strike the ground while under the direct or indirect control of pilot. Beginning in the early 1970’s a number of studies examined the occurrence of CFIT accidents and conclude that many accident related to CFIT accidents can be reduced if proper warning system is provided to the aircraft and engineer Don Bateman invented a warning system called ground proximity warning system (GPWS). In 1974 the FAA required all large turbine and turbojet airplanes to install GPWS equipment.

Ground Proximity Warning System (GPWS) - Aviationnepal1

 So, What is GPWS?

Ground proximity warning system (GPWS) is a system, carried on many aircraft, specially designed to alert pilots that the aircraft is in immediate danger of flying into a ground or an obstacle. The Federal Aviation Administration (FAA) define GPES as a type of Terrain awareness warning system (TAWS). GPWS help to reduce the occurrence of controlled flight into terrain (CFIT) accidents. Those accident are usually occurred in condition of poor visibility caused due to fog or rain.

Working Principle of GPWS; 

GPWS is a radar based system. The principle of work is based on continuous wave radar. The GPWS automatically and continuously monitor the clearance of aircraft above the surface.  Continuous wave are transmitted toward ground and the reflected wave are collected by receiver. The time taken for wave to return is measured and it indicates the distance between the aircraft and ground.

The main component of GPWS is computer which collects all the data from radio altimeter and predicts the future terrain features. As the radio altimeter only provide the distance between aircraft and the surface which is directly below the aircraft. The computer has to keep track of future terrain and predict terrain that is directly ahead to aircraft. So this can be archived and done correctly if the height of surface does not change significantly, but the place where there is significant change in heights, then the GPWS may fails and it is also referred as “Blind spot”.

However, the blind spot can be eliminated with the introduction of the Enhanced Ground Proximity System (EGPWS).

Limitations of GPWS

There are still certain limitation of GPWS system that pilot have to use their experience and situation awareness to determine if the warning is real. For example, if the GPWS system is giving false alert or if the pilot is intentionally in that situation, the pilot must then ignore the warning that are given to them. And another limitation of this system is that this system can’t locate the blind spot and fail in that situation.


By introduction of Ground proximity warning system (GPWS), the number accident cause by controlled flight into terrain (CFIT) is significantly reduced. Now a days, Modern system such as Enhanced Ground Proximity Warning System (EGPWS) is provided to modern civil and military aircrafts and able to predict terrain ahead of the aircraft without “blind spot” which was present in first ground proximity warning system. Unfortunately despite advancement in technology and modern equipment, the accidents caused by CFIT still happen. The common reason of CFIT accidents are bad weather, navigation system failure or more often pilot error.


Article by: Krishna Ram Sayanju
4th Year Undergraduate Student
Department of Mechanical Engineering
IOE, Pulchowk Campus