Whenever an airplane is functioning properly but nonetheless slams into terrain, either because it is off course or because the pilot has lost track of his position, the technical term is "controlled flight into terrain"―CFIT, pronounced "SEE-fit." Around the world, about four flights succumb to CFIT each year. Investigators recently found CFIT to be a factor when a Fokker F-28 slammed into a cloud-covered mountaintop in Peru last January 9, Wiling all 47 people aboard. The Federal Aviation Administration attempted to reduce the incidence of CFIT by mandating in 1974 that aircraft operate with Ground Proximity Warning Systems (GPWS). But the systems had limitations. GPWS relied on the airplane's radio altimeter, which determines the aircraft's altitude by bouncing a radar signal off the ground and measuring the duration of the signal's round trip. "The sensor was looking straight down," says Greg Francois of Honeywell Aerospace. "If you were going into very steep terrain, then you got a very short warning"―10 to 15 seconds or less. And GPWS cockpit displays were crude; their sole visual warnings were lights. Even with GPWS, the pilot of that F-28 still flew his airplane into a mountain.
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