Incident Description
A pilot participating in the CAFE-400 (Comparative Aircraft Flight Efficiency) contest—a 400-mile round-robin course—was descending from 7,000 feet near the end of the flight. The pilot slowed the aircraft to 140 mph to observe traffic. Once clear, he increased speed to 160 mph and began a 500 feet-per-minute descent. At approximately that time, he detected a vibration that increased in intensity. He then noticed that the airspeed had increased to 188 mph. The pilot reduced power, and as the aircraft slowed, the vibration ceased. The aircraft was landed without further incident.
Post-Flight Findings
A subsequent examination revealed that the aft fuselage was wrinkled and buckled over a 3-foot area just forward of the main spar bulkhead for the V-tail. The damage was consistent with flutter, which had resulted in dynamic overload.
Investigation Results
An investigation determined that the ruddervators were out of balance. The aircraft was being operated near its maximum gross weight limit with an aft loading, but it remained within the weight and balance limits.