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 Part 135, and TSO C151 Class B equipment would be the minimum requirement for airplanes operating under 14 CFR Part 91 and for airplanes configured with six to nine passenger seats operating under 14 CFR Part 135. The FAA indicated that both classes of equipment would include the TAWS features of comparing airplane position information with an on-board terrain database and providing appropriate caution and warning alerts, if necessary. Further, the FAA stated that it revised the proposed TSO to include the airworthiness requirements for both classes of equipment.

The FAA indicated that it expected to issue the final TSO by September 1999 and 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 of TAWS within 1 year after the effective date on new-production airplanes and within 4 years after the effective date for existing airplanes. The FAA indicated that these compliance dates, which were established in the current NPRM, were developed based on product availability and the anticipated manufacturing approval process. The FAA further indicated that a change in the compliance dates, as recommended in this safety recommendation, would require publishing a supplemental NPRM. The FAA believed that any change to the current rulemaking effort would delay the implementation of TAWS well beyond the proposed dates of the current final rule, as well as the compliance dates included in the recommendation. On October 1, 1999, the FAA stated that it had issued the TSO C151 on August 16, 1999.

The Safety Board's evaluation and classification of Safety Recommendation A-99-36 are discussed in section 2.8.2.

1.18.3.1 Flight Safety Foundation Study of Controlled Flight Into Terrain Accidents

In the early 1990s, the Flight Safety Foundation (FSF) created a CFIT Awareness Task Force to promote general CFIT awareness. This task force evolved into an international Approach and Landing Accident Reduction Task Force, working under the auspices of the FSF. According to statistics compiled by the task force, CFIT accidents have killed more than 9,000 passengers and crewmembers since the beginning of commercial jet operations in the late 1950s. The statistics also indicate that, between 1988 and 1997, more than 2,800 people were killed in 39 CFIT-related accidents worldwide.

The FSF task force estimated that about 25 CFIT accidents occur worldwide each year involving large commercial jet transports and large commuter and regional turboprop airplanes. Several factors that frequently appeared in CFIT accident reports included night and limited visibility conditions, terrain not observed until just before impact, loss of horizontal or vertical situational awareness, unfamiliarity with terrain and obstructions, flight crew uncertainty about altitudes and distance from the airport, navigational equipment improperly set or misinterpreted by the flight crew, and an unstabilized approach.