How It Works: Terrain Awareness and Warning System

Learn how TAWS provides pilots life-saving information and warnings.

TAWS How It Works
TAWS pulls aircraft position, speed and direction data from GPS and, along with the aircraft's altitude and configuration information, compares them to a database of Earth's terrain and manmade obstacles.Illustration by Bryan Christie Design

Accidents attributed to controlled flight into terrain (CFIT) have decreased significantly over the years thanks to the introduction of the terrain awareness and warning system (TAWS). The technology provides life-saving information and serves as a vital layer of protection as aircraft navigate changing terrain in various weather conditions.

TAWS pulls aircraft position, speed and direction data from GPS and, along with the aircraft’s altitude and configuration information, compares them to a database of Earth’s terrain and manmade obstacles. This highly accurate database is the result of a combination of radar topography imagery taken by the U.S. space shuttle program, DOD info and other data. When the aircraft’s position and tracking information are superimposed on it, TAWS is able to issue a number of different alerts to ensure pilots take appropriate action to prevent CFIT.

The three categories of TAWS are: advanced TAWS-A, required for large aircraft such as airliners; TAWS-B, required for Part 91 and 135 turbine aircraft with at least six passenger seats; and the terrain map.

Credit for the invention of TAWS belongs to retired Honeywell engineer Don Bateman, who created the ground proximity warning system in the 1970s. 
Adding a terrain and obstacle database laid the foundation for Honeywell’s Enhanced GPWS. Since then, CFIT accidents among U.S. airlines have dropped from a leading cause of deadly crashes to zero.

Key warnings 
provided by TAWS:

  • Warnings when sink rate is too high, regardless of the surrounding terrain.

  • Warnings if separation with terrain diminishes rapidly.

  • Warnings in response to significant altitude loss after takeoff.

  • Warnings if the landing gear or flaps are not appropriately configured.

  • Warnings if the aircraft has deviated too far below glideslope.

  • Callouts for excessive bank angles.