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 and 135, the rule would apply to all turbine-powered airplanes type certificated to have six or more passenger seats, excluding any pilot seat. (The FAA stated in the NPRM that the proposed rule applied only to turbine-powered airplanes, but the FAA indicated that it would consider comments on whether the installation of a TAWS on reciprocating enginepowered airplanes should be required. The FAA also stated that it would study data and information submitted by respondents before making a determination whether TAWS should be required for reciprocating engine-powered airplanes.)

The FAA proposed that, beginning 1 year after the effective date of the final rule, U.S.-registered turbine-powered airplanes manufactured after that date be equipped with TAWS and that existing turbine-powered airplanes be equipped with TAWS within 4 years after the effective date of the final rule. The FAA also proposed to amend 14 CFR Sections 121.360 and 135.153 to add an expiration date of 4 years after the effective date of the final rule for the use of current GPWS systems; thereafter, compliance with those sections would not be allowed instead of the provisions proposed within the NPRM. In addition, the FAA's proposal would also require operators to include in their airplane flight manuals the appropriate procedures for operating and responding to the audio and visual warnings of the TAWS.

In a December 24, 1998, letter to the FAA, the Safety Board indicated that the NPRM, if promulgated, would have a positive effect on aviation safety by reducing the possibility for CFIT accidents. However, on May 12, 1999, the Safety Board concluded that the 4-year installation time frame proposed by the FAA should be shortened to 3 years for airplanes that currently lack any GPWS protection (see section 1.18.2.4).

The FAA indicated that it expected to issue the final rule by March 2000, with an effective date 1 year after the date of issuance. According to the FAA, the final rule would mandate the installation and use of TAWS within 1 year after the effective date on new-production airplanes and within 4 years after the effective date for existing airplanes.

1.18.2.3 Department of Transportation Studies on Traditional and Enhanced Ground Proximity Warning Systems

In 1995, the FAA commissioned the DOT's Volpe National Transportation Systems Center to examine the effectiveness of GPWS and enhanced GPWS in preventing CFIT accidents in 14 CFR Part 91 operations. The center studied 44 CFIT accidents that occurred between 1985 and 1994 and involved airplanes operating under 14 CFR Part 91 with 6 to 10 passenger seats. Of the 44 airplanes, 11 were turbojets and 33 were turboprops, and none of the airplanes had GPWS installed. The center used computer modeling techniques to conclude that (1) GPWS could have prevented 33 of the 44 accidents (75 percent) and 96 fatalities and (2) enhanced GPWS could have prevented 42 of the 44 accidents (95 percent) and 126 fatalities.