NTSB Identification: FTW02LA129.
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Accident occurred Sunday, March 24, 2002 in Amarillo, TX
Probable Cause Approval Date: 05/13/2003
Aircraft: Beech F35, registration: N4257B
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that while in level cruise flight at 140 knots indicated airspeed, at an altitude of 5,500 feet mean sea level (msl), the airplane encountered "clear air turbulence." The pilot stated that at the time of the accident, the airplane autopilot system was engaged, and his hands were not on the cockpit controls. During the accident, the airplane "was suddenly thrust nose high and vertical." The pilot then "pushed the nose [of the airplane] over," and recovered control of the airplane from the unusual attitude. The pilot continued the flight to his intended destination and landed without incident. Examination of the airplane revealed that the aft fuselage exhibited extensive skin wrinkling and tearing 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 FS 233.5 bulkhead. The right ruddervator was 20.98 inch-pounds static underbalanced. According to the manufacturer, the static underbalance weight range is 16.8 to 19.8 inch pounds.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

Flutter due to the improper balance of the ruddervator, which resulted in structural damage to the aft fuselage.

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