Accident Overview
The accident flight was conducted under instrument flight rules (IFR) in night instrument meteorological conditions (IMC). The pilot had received clearance for an instrument landing system (ILS) approach but elected to use a non-published procedure to intercept the final approach course.
Approach and Impact
After becoming established on the final approach, the airplane continued and struck the ground approximately seven miles from the destination airport. The impact occurred at an elevation roughly equivalent to the airport's field elevation. Flight inspections of the instrument approach, performed both before and after the accident, determined that the localizer and glideslope functions were operating satisfactorily.
Altimeter Examination
Post-accident examination of the aircraft's altimeters revealed a discrepancy. The number one altimeter displayed a reading that was 360 feet higher than the actual altitude. Additionally, the altimeter setting used for the number one altimeter did not match the current altimeter setting at the time of the accident. It could not be determined whether this discrepancy existed prior to the impact. The pilot did not report any pre-flight discrepancies regarding the aircraft's altimeters. No other anomalies were found in the aircraft's structure or systems.
Probable Cause
The official probable cause was the pilot's failure to follow the published instrument approach procedure, which contributed to his failure to maintain altitude and clearance from terrain during the instrument approach. A factor was the night light condition.