Terrain awareness and warning system

[3] A study by the International Air Transport Association examined 51 accidents and incidents and found that pilots did not adequately respond to a TAWS warning in 47% of cases.

[7] Bateman's earliest devices, developed in the 1960s, used radio waves to measure altitude and triggered an alarm when the aircraft was too low, but it was not aimed forward and could not provide sufficient warning of steeply rising terrain ahead.

As a result of these studies and recommendations from the U.S. National Transportation Safety Board (NTSB), in 1974 the FAA required all 14 CFR 121 (Part 121) certificate holders (that is, those operating large turbine-powered airplanes) and some 14 CFR 135 (Part 135) certificate holders (that is, those operating large turbojet airplanes) to install TSO-approved GPWS equipment.

These operators were required to install TSO-approved GPWS equipment or alternative ground proximity advisory systems that provide routine altitude callouts whether or not there is any imminent danger.

[6] Based on these reports and NTSB recommendations, in 1992 the FAA amended §135.153 to require GPWS equipment on all turbine-powered airplanes with ten or more passenger seats.

[6][10] After these rules were issued, advances in terrain mapping technology permitted the development of a new type of ground proximity warning system that provides greater situational awareness for flight crews.

[7] The TAWS improves on existing GPWS systems by providing the flight crew much earlier aural and visual warning of impending terrain, forward looking capability, and continued operation in the landing configuration.

The CFIT of American Airlines Flight 965 in 1995 convinced that carrier to add EGPWS to all its aircraft; although the Boeing 757 was equipped with the earlier GPWS, the terrain warning was issued only 13 seconds before the crash.

[14] On March 7, 2006, the NTSB called on the FAA to require all U.S.-registered turbine-powered helicopters certified to carry at least 6 passengers to be equipped with a terrain awareness and warning system.

[7][18] A modern TAWS works by using digital elevation data and airplane instrumental values to predict if a likely future position of the aircraft intersects with the ground.

[19] The flight crew is thus provided with "earlier aural and visual warning of impending terrain, forward looking capability, and continued operation in the landing configuration.

A six-frame sequence illustrating the manner in which TAWS operates. The TAWS is illustrated in an upper left window. (A) illustrates the aircraft in relation to the outside terrain while (B) and (C) illustrate the manner in which the TAWS system displays the terrain. (D) is providing a caution of terrain to be traversed, while (E) provides an illustration of a warning with an aural and textural advisory (red) to pull up. (E) also illustrates a pilot taking appropriate action (climb in this case) while (F) illustrates that a hazard is no longer a factor. [ 1 ]
A piece of the wreckage of Air New Zealand Flight 901 , which crashed in Antarctica in 1979, despite being equipped with a GPWS. All 257 people on the plane died.
A Mode 5 warning in EGPWS alerts the pilots if they descend below the glideslope during a landing approach.
The FAA specifications have detailed requirements for when certain warnings should sound in the cockpit. [ 21 ]