Accident
An aircraft conducting an instrument approach in instrument meteorological conditions (IMC) at Spokane-Intl Airport crashed into a hill approximately 4.5 miles from the runway threshold at an elevation of 2,546 feet. The minimum descent altitude (MDA) for the instrument approach procedure was 2,760 feet. The aircraft came to rest near the location of the final approach fix, about 1,800 feet southeast of the Spokane VORTAC.
Occupants and Injuries
Of the nine persons aboard the flight, seven were killed and two sustained serious injuries.
Procedure and Flight Path
The instrument approach procedure required the flight crew to maintain an altitude of 3,500 feet until the aircraft passed the final approach fix, which was located 4.5 miles from the runway threshold.
Probable Cause
The official investigation determined the probable cause to be a premature descent to the minimum descent altitude (MDA) based on the flight crew's use of an incorrect distance measuring equipment (DME) frequency and the flight crew's subsequent failure to remain at or above the MDA. Contributing to the cause was the design of the DME mode selector, which does not depict the frequency selected, and the failure of the flight crew to identify the localizer DME facility.