Ground Proximity Warnings
Better technology is helping airline pilots keep a safe distance from terrain.
- By Damond Benningfield
- Air & Space magazine, September 2003
(Page 2 of 2)
TAWS uses the same warning modes that were used in the older GPWS:
- Mode 1 warns of an excessive descent rate during landing or whenever the aircraft is close to the ground. The initial warning is the phrase “Sink rate”; if the problem isn’t corrected, a “Pull up” warning is issued.
- If the aircraft is flying into the slope of a mountain or across other steep features and the ground clearance is rapidly decreasing, mode 2 issues an aural “Terrain” warning, followed by “Pull up.”
- Mode 3 helps pilots maintain a positive climb rate after takeoff; once the aircraft reaches 1,000 feet, the system sounds a “Don’t sink” warning if altitude begins to descend.
- Mode 4 warns if landing gear or flaps are not properly configured for landing, and if the terrain clearance is inadequate during final descent.
- When the crew is making an instrument landing system—ILS—approach, mode 5 announces “Glide slope” if the aircraft has deviated below a safe flight path to the runway.
Another operating mode calls out altitudes during descent, and the last warns of significant wind shear.
Today, 18,000 commercial, military, business, and general aviation aircraft have TAWS. Jim Burin, director of technical programs at the Flight Safety Foundation, says the F-28 that crashed in Peru and two other aircraft victimized by CFIT this year—a 737 in Brazil and an RJ100 in Turkey—all had the older GPWS systems, not the newer TAWS.
As TAWS comes to predominate in coming years, aircraft may have an easier time staying in the skies—and away from unexpected mountain peaks.