On December 29, 1972
, an Eastern Air Lines Lockheed
L-1011 crashed into the Florida Everglades
while on approach to Miami International Airport
. Almost two years later, on December 1, 1974, a TWA Boeing 727 crash
ed into a mountain while on approach to Washington Dulles International Airport
in Virginia. One hundred ninety-one persons died in the two tragedies. There was one common factor: no mechanical malfunctions contributed to either accident. The Safety Board concluded that these accident
s - termed "controlled flight into terrain," or "CFIT" for short - could have been prevented by a terrain warning system in the cockpit.
The Board's first recommendation calling for the development of an onboard warning system was issued after a nonfatal accident in 1971 involving a DC-9 that struck antennas as it was landing in Gulfport, Mississippi. In 1975, after further Board recommendations following accidents in the Florida Everglades and Virginia, the Federal Aviation Administration (FAA) began to require large passenger aircraft to be equipped with a ground proximity warning system (GPWS). This device warns flightcrews if their aircraft is approaching terrain, descending too quickly, or improperly configured for landing, usually with an aural warning like "Pull Up, Pull Up," or " Terrain." This requirement has dramatically lowered the frequency of CFIT accidents involving transport-category aircraft in U.S. airspace.
By contrast, CFIT accidents continue to occur overseas in countries where such devices are not required, and a special International Civil Aviation Organization task force is working on preventing such accidents. In 1986, based on a series of accidents involving commuter aircraft, the Safety Board recommended that the requirement for GPWS be extended to smaller passenger airliners. Following subsequent commuter CFIT accidents, the Board added the issue to its "Most Wanted" list.
Since April 1, 1994, commuter aircraft having 10 or more seats must be equipped with GPWS. This requirement should greatly increase the safety of commuter flights, especially during approach to landing in instrument meteorological conditions. Another CFIT accident prompted the Safety Board to recommend that the FAA require aircraft to be equipped with the next generation of "enhanced" GPWS, which gives flightcrews significantly more advance warning. The recommendation grew out of the December 20, 1995, crash of an American Airlines Boeing 757 on approach to Cali, Colombia, killing all but four of the 163 persons on board. During the descent, with the speedbrakes extended, the pilots failed to clear the mountain following a ground proximity warning.
Based upon the Board's investigation and recommendations, action by the FAA includes an automatic speedbrake retraction design review, amendments to the crew resource management training advisory circular, and standardization of navigational aid identifiers on printed charts and electronic charts displayed on aircraft computers. The FAA is working on an advanced terrain avoidance warning system regulation with a proposed rule expected in late 1998, followed by a final rule in 1999. A major aviation association and numerous air carriers announced in early 1998 that they had begun to voluntarily install the new advanced devices.