Approach Profile
The flight was conducting a coupled instrument landing system (ILS) approach with 1/2 mile visibility in snow showers. Three successive fixes on the localizer are defined by distance measuring equipment (DME) paired with the ILS; prior to the ILS DME commissioning six months before the accident, the DME fixes were defined by a VORTAC 4.7 nautical miles past the ILS DME.
The aircraft was 800 feet high at the first fix and 1,500 feet high at the second, but approximately on altitude 4.7 nautical miles past the first and second fixes, respectively. It passed the outer marker 900 feet high and captured the glide slope from above about 1.8 nautical miles from the threshold, 500 feet above decision height (DH) and 700 feet above touchdown.
The aircraft remained on glide slope for 28 seconds, during which time its speed decayed to stall speed. It then dropped below glide slope and crashed 1.3 nautical miles short of the threshold.
Cockpit Configuration
The pilot's FLT DIR DME-1/DME-2 switch, which controls the DME display on the pilot's horizontal situation indicator (HSI), was found set to DME-2; the NAV-2 radio was set to the VORTAC frequency.
Stall Recovery
Up to 800 feet may be required for stall recovery.