Background
The pilot was executing an Instrument Landing System (ILS) approach. During the first attempt, the pilot flew through the localizer course before correcting back to the final approach course. However, at the decision height, the aircraft's altitude was approximately 500 feet higher than expected. The pilot executed a missed approach and received radar vectors for another ILS approach.
Accident Sequence
On the second ILS approach, a witness observed the aircraft about 150 feet above the ground in a nose-low attitude of approximately 60 degrees with a right bank angle of about 80 degrees. The initial ground impact occurred 2,150 feet west of the runway threshold and 720 feet north of the extended centerline. Cloud tops were reported at 3,000 feet with light rime or mixed icing.
Investigation Findings
Examination of the aircraft revealed the flap jack screws and flap indicator were set to the 5-degree flap position. No preimpact anomalies were found in the airframe, engines, or propellers. A radar study indicated that calibrated airspeed on the final approach was about 130 knots but decreased to between 95 and 100 knots during the 20-second period prior to loss of radar contact. According to the aircraft's flight manual, the wings-level power-off stall speed at the accident weight was approximately 91 knots. The ILS approach flight profile specified that 20 degrees of flaps should be used at glide slope intercept while maintaining a minimum airspeed of 120 knots, and at least 20 degrees of flaps should be maintained until touchdown. The "No Flap" or "5 Degrees Flap Landing" profile stipulated a minimum Vref of 115 knots calibrated airspeed.
Probable Cause
The pilot's failure to maintain adequate airspeed during the instrument approach, which resulted in an aerodynamic stall and impact with terrain.