The Man Who May Have Saved Your Life

Air accidents are now quite rare. At least in developed countries. In the U.S., for example, no major U.S. airline has crashed in over twenty years. But when an air accident does take place, an accident investigation team determines its cause and makes recommendations intended to keep what went wrong from happening again. In spite of these efforts, one type of accident used to happen repeatedly, an accident in which the pilots, due to a navigation error, flew into the ground or into a mountain with no awareness at all that they had made a fatal mistake.

Because the pilots in such crashes flew a properly functioning aircraft into the ground, this type of accident was called Controlled Flight Into Terrain (CFIT). In 1969, Don Bateman, Chief Avionics Engineer for Honeywell, developed a device to prevent CFIT. The device used radar to determine the distance between the plane and the ground. If radar information indicated the plane was closing in on the ground, the device checked the position of the landing gear and flaps. If the gear and flaps were not in the proper position for landing, it meant the pilots were not aware they were headed toward the ground. The device triggered a warning, flashing lights and a voice command, “Pull Up, Pull Up." The warning continued until the pilots reversed the plane's closure with the ground. Bateman, who died on May 21st at the age of 91, called his brainchild the Ground Proximity Warning System (GPWS).

Ralph Waldo Emerson said, “Build a better mousetrap and the world will beat a path to your door.” That may be true for a ninety-nine-cent mousetrap, but Bateman’s invention was fairly expensive. Though it could prevent CFIT accidents, the airlines did not beat a path to his door. Nor did the FAA see fit to require airlines to purchase it. But something happened that changed all that.

Normally, when Air Traffic Control issues a descent clearance, the altitude specified is higher than any obstruction on the ground. But late in the night on December 1, 1974, a Trans World Airlines 727 heading into Washington’s Dulles Airport was given a descent clearance with rarely used phraseology that did not ensure terrain clearance. The pilots, believing ATC was still responsible for terrain clearance, descended into the hills twenty-five miles northwest of the airport.

Because of where this crash took place, the GPSW situation changed. The crash took place at an airport many members of Congress use to fly between their home states and Washington. These legislators has the shocking realization, "That could have been me." The device too costly to protect the public was not too costly to protect our nation's lawmakers. But since they could not protect themselves without protecting everyone else, our esteemed members of Congress quickly passed that required every U.S. airliner be equipped with a GPWS. Notice the date the FAA announced the GPWS would be required on all U.S. airliners: December 18! Though years have passed with no legislation to protect the public from weapons designed for soldiers, it took just over two weeks for Congress to protect their own assets.

Bateman’s invention ended CFIT accidents in the United States. Foreign airlines were slow to adopt GPWS technology. But that changed after an Avianca 747 was unintentionally flown into the ground as it approached the Madrid airport in darkness on November 27, 1983.

The original GPWS design has been improved by adding Global Positioning System (GPS) technology. Instead of relying only on a radar signal bounced off the ground to determine the plane's altitude, the Enhanced Ground Proximity Warning System (EGPWS) employs GPS terrain-height information.