What happened
During a flight involving a Cessna 421, the aircraft suffered a catastrophic structural failure of its tail section. The sequence of events began when the left outboard portion of the elevator assembly, which included the balance weight, became detached from the aircraft. This initial separation triggered intense flutter within the empennage, leading to a total in-flight breakup of the tail assembly.
Findings
Post-accident investigations revealed significant structural damage to the control surfaces and stabilizers. Specifically, the left horizontal stabilizer front spar failed in a downward direction. The investigation also identified that the rivets responsible for securing the left outboard hinge to the rear spar of the stabilizer had sheared, and the center hinge of the left elevator had been torn away from the rear spar. Evidence indicated that the left elevator outboard hinge and its associated support structure had experienced hinge overtravel.
Records indicated that approximately 100 flight hours prior to the accident, maintenance had been conducted to address a loose balance weight on the left elevator and to fix a damaged stiffener within the horizontal stabilizer's center structure. Upon inspection of the wreckage, however, the balance weight was found to be securely fastened and the stiffener repair remained undamaged. The accident resulted in three fatalities.