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 the installation of GPWS in 1974 for all 14 CFR Part 121 carriers.) More recently, the Safety Board has issued recommendations addressing the additional benefits of installing enhanced GPWS.

GPWS Development (A-71-53, A-72-19, and A-72-35)

On February 17, 1971, a Southern Airways Douglas DC-9-15, N92S, struck an electric transmission line static cable during a VOR approach to runway 31 at the Municipal Airport in Gulfport, Mississippi A successful missed approach was accomplished, and the aircraft landed safely. On the basis of the results of its investigation, the Safety Board issued Safety Recommendation A-71-53, asking the FAA to

Develop a ground proximity warning system for use in the approach and landing phases of operation, which will warn flight crews of excessive rates of descent, unwanted/inadvertent descent below minimum descent altitudes, or descent through decision heights. It would be desirable if the equipment now installed could meet this need.

The FAA responded that it believed that "the present instrumentation and procedures are safe and adequate provided cockpit disciplines are maintained." The Safety Board subsequently classified this recommendation "Closed--No Longer Applicable" because it was superceded by Safety Recommendation A-72-19. That recommendation was issued as a result of the June 22, 1971, accident involving a Northeast Airlines McDonnell Douglas DC-9-31, N982NE, which struck the water during a nonprecision instrument approach to runway 24 at the airport at Martha's Vineyard, Massachusetts. The Safety Board issued Safety Recommendation A-72-19, asking that

The Administrator require all air carrier aircraft to be equipped with a functional ground proximity warning device, in addition to barometric altimeters.

On November 14, 1972, Southern Airways charter flight 932, a DC-9, N97S, crashed during a nonprecision instrument landing approach to runway 11 at the Tri-State Airport, Huntington, West Virginia. The airplane impacted trees on a hill approximately 1 mile west of the runway threshold. All 71 passengers and 4 crewmembers were killed, and the airplane was destroyed. As a result of its investigation, the Safety Board issued Safety Recommendation A-72-35 to the FAA, asking that

The Administrator evaluate the need for the installation and use of ground proximity warning devices on air carrier aircraft.