Accident Sequence
Video surveillance captured the approach of the airplane to the airport. As the airplane neared the approach end of the landing runway, it began to climb, rolled left, became inverted, and then impacted terrain.
Thrust Reverser Examination
Postaccident examination revealed that the left thrust reverser (T/R) door was found open and unlatched, while the right T/R door was closed and latched. An asymmetric deployment of the left T/R would have resulted in a left roll/yaw. The airplane was not equipped with a nose landing gear (NLG) ground contact switch intended to preclude inflight operation of the T/R, nor was it required to be so equipped. Electrical testing of the T/R left and right stow microswitches within the cockpit throttle quadrant showed that the left stow microswitch did not operate within design specifications. Disassembly of those microswitches revealed evidence of arc wear due to aging. Additional T/R system components were found to be unairworthy, but operational testing could not be performed due to accident damage.
Cockpit Voice Recorder
The flight was required to have an airworthy and operable cockpit voice recorder (CVR), but the lack of such a device precluded identifying which pilot was performing pilot flying duties, as well as other crew actions and background noises that would have facilitated the investigation.
Toxicology Findings
Toxicology testing of the pilot’s specimens indicated the presence of diazepam at subtherapeutic levels. Given the long half-life of diazepam and its metabolite nordiazepam, it appeared that the medication was taken several days before the accident. The detected amounts were not at impairing levels, and it was determined that the pilot was unlikely to have been impaired at the time of the accident; thus, diazepam use was not a factor.
Probable Cause
The probable cause was the airplane’s unairworthy thrust reverser system due to inadequate maintenance, which resulted in an asymmetric T/R deployment during an approach to the airport and the subsequent loss of airplane control.