Accident Details
A commercial pilot was executing a precision instrument approach at night in instrument meteorological conditions. The airplane collided with terrain approximately four miles short of the runway.
Air Traffic Control Communications
Review of air traffic control communications and radar data revealed that the pilot was vectored onto the final approach course but never became established on the glide slope. Instead, he made a controlled descent below the glide slope as he proceeded toward the airport. When the airplane was five miles from the airport, a tower controller received an aural low altitude alert generated by the Minimum Safe Altitude Warning (MSAW) system. The tower controller immediately notified the pilot of his low altitude, but the airplane collided with terrain within seconds.
System Examination
Examination of the instrument approach system and onboard flight navigation equipment revealed no pre-mishap anomalies. A review of the MSAW adaptation parameters showed that the tower controller would only have received an aural alarm for aircraft operating within 5 nautical miles of the airport. However, the frequency change from the approach controller to the tower controller occurred when the airplane was about 10.7 miles from the airport, leaving a 5.7-mile segment where both controllers could receive visual alerts, but only the approach controller received an aural alarm. A tower controller does not utilize a radar display as a primary resource for managing air traffic.
Procedural Issues
In 2004, the FAA changed a policy that eliminated an approach controller's responsibility to inform a tower controller of a low altitude alert if the tower had MSAW capability. The approach controller thought the MSAW alarm parameter was set at 10 miles from the airport, not the 5 miles that existed at the time of the accident. Subsequent investigation revealed that the FAA had improperly informed controllers to ensure they understood the alarm parameters for control towers in their area of responsibility. This led the approach controller to conclude that the airplane was no longer her responsibility once she handed it over to the tower controller. Additionally, the tone of the approach controller's aural MSAW alarm was not sufficient in properly alerting her of the low altitude alert.