On March 12, 1993, a Cessna 421C (registration N2656N) was involved in an aviation accident near Eagle Mountain, CA. Investigators recorded the probable cause as: FAILURE OF THE LEFT ELEVATOR FOR UNDETERMINED REASON(S), WHICH RESULTED IN FLUTTER AND FAILURE OF THE EMPENNAGE, AND SUBSEQUENT UNCONTROLLED COLLISION WITH THE TERRAIN. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A Cessna 421 broke up in flight after the left outboard elevator assembly separated, causing empennage flutter and subsequent structural failure. Maintenance had been performed about 100 flight hours prior.
Accident Overview
A Cessna 421 experienced an inflight breakup. Investigation revealed that the left outboard portion of the elevator assembly, including the balance weight, separated from the aircraft first. This separation led to empennage flutter and the subsequent in-flight breakup of the empennage.
Structural Findings
Examination of the wreckage showed that the left elevator outboard hinge and its support structure exhibited evidence of hinge overtravel. The left horizontal stabilizer front spar had failed downward. Rivets attaching the left outboard hinge to the rear spar of the left stabilizer were sheared. Additionally, 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 address a loose left elevator balance weight and to repair a damaged stiffener in the center structure of the horizontal stabilizer. Post-accident examination confirmed that the balance weight was tight and the stiffener repair was intact.