Incident Overview
A pilot reported that while in level cruise flight at 140 knots indicated airspeed and an altitude of 5,500 feet mean sea level (msl), the airplane encountered clear air turbulence. At the time of the turbulence encounter, the autopilot system was engaged and the pilot's hands were not on the cockpit controls.
Sequence of Events
The pilot stated that during the encounter, the airplane was suddenly thrust nose high and vertical. The pilot then pushed the nose over and recovered control of the airplane from the unusual attitude. Following the recovery, the pilot continued the flight to the intended destination and landed without further incident.
Aircraft Examination
Examination of the airplane revealed structural damage to the aft fuselage. Extensive skin wrinkling and tearing were present between the fuselage station (FS) 233.5 and FS 256.9 bulkheads. The left fuselage side exhibited a compression wrinkle extending from the bottom of the FS 256.9 bulkhead diagonally up and forward toward the top of the FS 233.5 bulkhead. The right fuselage side exhibited a compression wrinkle extending from the top of the FS 256.9 bulkhead diagonally down and forward toward the bottom of the FS 233.5 bulkhead. The bottom skin exhibited a compression wrinkle that extended from the middle of the FS 256.9 bulkhead forward and outward toward the FS 233.5 bulkhead.
Additionally, the right ruddervator was measured to have a static underbalance of 20.98 inch-pounds. According to the manufacturer, the acceptable static underbalance weight range for that component is 16.8 to 19.8 inch-pounds.