Accident Overview
An instrument-rated commercial pilot was conducting a circling VOR/DME instrument approach in instrument flight rules (IFR) conditions. The pilot reported the runway in sight and was circling to land west of the airport just before the accident. Witnesses observed the airplane descending in a near-vertical attitude from the overcast cloud layer and striking a highway curb lane approximately 0.75 miles from the airport.
Aircraft Examination
Post-accident examination found no evidence of preimpact failures or malfunctions with the primary flight controls or engines. The pitch trim position could not be determined conclusively because the trim control cables were broken and disrupted by impact. However, the evidence was not sufficient to conclude that full nose-down trim was present at the time of the upset.
Autopilot System
Examination of the autopilot annunciator module indicated that the HDG, NAV, AUTOTRIM, and FAIL warning lights may have been illuminated. When the autopilot detects a trim system failure, the trim servo is deactivated and the AUTOTRIM and FAIL warning lights flash. The AUTOTRIM light also flashes if the trim master switch is turned off, making the autopilot system evidence inconclusive.
Role of Autopilot
Because the autopilot system evidence was inconclusive, the role of the autopilot in the accident could not be determined. However, airplane descent information provided by witnesses and impact evidence were consistent with an aerodynamic stall at low altitude and were not consistent with an uncorrected autopilot-induced pitch-down excursion.