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 MSAW alerts while on the approach to the airport. The investigation also determined that the MSAW site variable parameters at the airport required two "current position" radar returns or three "predicted position" radar returns below the 500-foot floor before the aural and visual alerts would activate. A review of the radar data revealed that the airplane generated one radar return below the alert altitude of the runway 1R MSAW capture box.

The Safety Board's investigation of this accident revealed discrepancies with the airport's MSAW equipment. Specifically, the MSAW site variable parameters for runway 1R indicated a discrepancy between the MSAW-defined runway location and the actual threshold location. The FAA said that, when the ARTS III software was programmed for a 10° west variation (the angular difference between true north and magnetic north at Dulles Airport), the computed position for the runway threshold did not correlate to the actual geographic runway location. Further, the "radar-established" runway position was 700 feet northeast of the actual runway threshold. The Safety Board found that the error in the radar position for the runway 1R threshold resulted in a similar displacement of the radar MSAW capture box from its intended position with the actual approach path to runway 1R. The Safety Board concluded that such displacement might compromise the protective intent of the MSAW system.

On November 21, 1994, the Safety Board issued Safety Recommendation A-94-187, which asked the FAA to Conduct a complete national review of all environments using MSAW systems. This review should address all user-defined site variables for the MSAW programs that control general terrain warnings, as well as runway capture boxes, to ensure compliance with prescribed procedures.

In a March 20, 1995, letter, the FAA stated that it planned to review the MSAW site variables to ensure compliance with prescribed procedures. According to the FAA, the