terrain-awareness warning system

terrain-awareness warning system (TAWS)

A system using an electronic map that provides a warning of higher terrain in the vicinity of the aircraft. The TAWS is a computer-based system providing the flight crew with visual and acoustic alerts about the unintended approach to the terrain, taking into account the flight stage, flight crew response time, and aircraft speed. There are two types of TAWS—Class A and Class B. Class A equipment is for installations on large aircraft; it displays FLTA (forward-looking terrain alert), premature descent, excessive closure rate to terrain, flight into terrain when not in landing configuration, excessive downward deviation from an ILS (instrument landing system) glide-slope, excessive rate of descent, and negative climb rate or altitude loss after takeoff alerts. It also displays a voice callout about the altitude above the terrain, terrain display, terrain/airport database, and a voice callout about the passing of a set altitude. Class B equipment does not require a display. The Class B system is required to provide FLTA, premature descent, excessive rate of descent, and negative climb rate or altitude loss after takeoff alerts and international voice callouts. The latter version is used in smaller aircraft and helicopters and does not require interfacing with the radio altimeter. To generate alerts to the flight crew about the threat of a collision with the terrain or an obstacle, modern TAWS systems, in addition to information from the air data system and radio altimeter, use data from the satellite systems and databases containing information on the digital elevation model and aeronautical data (artificial obstacles, aerodromes).
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved