NTSB Identification: CHI96LA235.
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Accident occurred Sunday, June 23, 1996 in CHESTERFIELD, MO
Probable Cause Approval Date: 07/28/1997
Aircraft: Beech B35, registration: N5001C
Injuries: 2 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/owner reported that he was flying at 140 mph when he encountered light turbulence, and the airplane started to shake. The shaking lasted for about three seconds before the pilot/owner could reduce power and pull back on the yoke to slow the airplane. He then continued on to his destination where he made a normal landing. After landing, extensive damage was found in the area of the aft fuselage. An investigation revealed the airplane did not have a current annual inspection. There were pinholes in the pitot tube where it had been welded. The airspeed indicator was tested, and it did not meet specifications. The ruddervators were examined for proper balance and rigging. The service balance range for the ruddervators is 16.8 to 19.8 inch-pounds trailing edge heavy (underbalance). Using the counterbalance method, the underbalance of the left and right ruddervators was determined to be 22.53 and 22.68 inch-pounds, respectively. Both the left and right ruddervator trim tab hinge pins had been installed incorrectly. The incorrectly installed trim tabs exhibited significant vertical free play near the inboard end; the tabs also had restricted up and down angular travel. The ruddervator balance and the trim tab installation had been performed by two different aircraft maintenance facilities.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: improperly balanced ruddervators and improperly installed ruddervator (elevator) trim tabs, due to improper maintenance, which resulted in ruddervator flutter and substantial damage in the area of the aft fuselage. Factors relating to the accident were: improper planning/decision by the owner/operator (pilot) by failing to ensure that the annual inspection and required aircraft maintenance were performed; and turbulence that led to vibration of the improperly balanced ruddervator. Full narrative available
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