Accident Sequence
A Cessna 421 crashed following an inflight breakup. The investigation determined that the left outboard portion of the elevator assembly, including its balance weight, separated first. This separation induced flutter in the empennage, which then failed in flight.
Examination Findings
Post-accident examination revealed evidence of hinge overtravel on the left elevator outboard hinge and its support structure. The left horizontal stabilizer front spar had failed in a downward direction. Rivets attaching the left outboard hinge to the rear spar of the left stabilizer had sheared, and the left elevator center hinge had been pulled off the rear spar.
Maintenance History
Approximately 100 flight hours before the accident, maintenance was performed to repair a loose left elevator balance weight and a damaged stiffener in the center structure of the horizontal stabilizer. However, post-accident inspection found the balance weight to be tight and the stiffener repair intact.
Probable Cause
According to the official investigation, the probable cause was the failure of the left elevator for undetermined reasons, which resulted in flutter and failure of the empennage, and subsequent uncontrolled collision with the terrain.