Accident Description
The airplane crashed while on approach, approximately three-quarters of a mile southwest of the airport. A witness reported hearing a sound he associated with propellers going into reverse, then observed the airplane emerging from clouds in a nose-low attitude.
Cockpit Voice Recorder
The cockpit voice recorder (CVR) tape revealed a sound of an abrupt change in frequency and amplitude occurring ten seconds prior to impact.
Examination of the Beta System
Examination of the left engine beta indicator lamp showed a heavy oxide deposit and stretched coils, indicating the lamp was illuminated at the time of impact. The right engine beta lamp was destroyed. The power levers and beta mode trigger locks operated normally, and the trigger return springs were intact. The flight idle stops showed no evidence of excessive wear or deformation. The power lever (beta) blocking device lockout solenoid was tested electrically and functioned normally. However, the rigging of the beta lockout device could not be checked due to impact damage.
Operator's Fleet Testing
The operator conducted functional tests of the electrical or backup beta blocking devices on the remaining eight Casa 212 airplanes; three were found to be inoperative. Neither the manufacturer nor the operator had an inspection or functional test requirement for the blocking devices.
Occupants
All five occupants were killed.
Probable Cause
The official probable cause is the failure of the beta blocking device for undetermined reason(s), and the second-pilot's inadvertent activation of the power lever, or levers, aft of the flight idle position and into the beta range, resulting in a loss of airplane control.