Understanding the Ground Proximity Warning System

A Ground Proximity Warning System or GPWS is a type of equipment on airplanes that warns pilots if they are at a dangerously low altitude and at risk of crashing. Consequently, their main job is to prevent what is called a “controlled flight into terrain crash” (CFIT) that is an accident in which an aircraft crashes into the ground, water, or an obstacle despite having the proper crew and conditions to fly. CFITs typically come as a result of navigational errors, pilot disorientation or fatigue, or reduced visibility due to poor weather conditions. Since the widespread implementation of the GPWS in the 1970s, CFIT incidents have become much less frequent, proving the system’s effective use in flight operations. Moreover, the use of GPWS on large aircraft has become required by law in many countries, making it an important system with which all aircraft operators should become familiar.

The GPWS generally works by measuring the aircraft’s altitude in relation to the ground below using a radar altimeter. This instrument works by transmitting radio waves downward from the plane to determine how far away the ground is. Routinely, most radar altimeters that are used on commercial aircraft are short-range devices with ranges of less than a mile. Whatever information is picked up from the radar is monitored and analyzed by a computer that can identify hazardous situations and trends in data. These risk factors include a dangerously rapid rate of descent, an unexpected loss of altitude, and other signifiers. If hazardous conditions are detected, the ground proximity warning system gives visual and auditory warning signals to the pilot.

Despite their enormous usefulness, the GPWS is ultimately limited in some aspects. The primary limitation is that it looks only directly below the aircraft. Thus, it can detect when the airplane is too low or losing altitude, but if the terrain itself rises steeply, the GPWS will not be able to inform the pilot until the aircraft is already over the rising terrain. Such a warning could come too late, especially in low visibility conditions. In civilian aircraft, this weakness has been addressed by the development of the enhanced ground proximity warning system (EGPWS). This enhancement came as a consequence of the creation of the global positioning system (GPS). Using a GPS, the EGPWS contains an electronic terrain database and maintains constant contact with the GPS. This successfully tracks the aircraft’s own location, allowing it to provide pilots with accurate information about the terrain beyond the range of its radar.

In high-speed military operations, the limitations of the conventional GPWS led to an even more serious issue than in civil aviation. Thus, many modern military aircraft are equipped with a more sophisticated collection of equipment that combines the radar altimeter, digital terrain maps, and GPS link used in an EPGWS with additional data from the aircraft’s flight control and inertial navigation systems. This interconnected system allows the aircraft to project its current flight path miles ahead, and then evaluate it against its elevation maps to give a more early warning of potential collision.

The ground proximity warning system has been used in aircraft as protective equipment since the 1970’s as a way to prevent collision with the ground.If you are in need of such systems, AOG Unlimited has you covered. As a leading distributor of GPWS, we invite you to browse our online catalogs of products that are readily available for purchase at any time. Begin procuring the parts you need with AOG Unlimited to learn how simple and convenient the fulfillment process can be.


December 23, 2020

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