NTSB Identification: LAX04LA312.
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Accident occurred Friday, September 03, 2004 in Fresno, CA
Probable Cause Approval Date: 10/27/2005
Aircraft: Beech F33A, registration: N1854N
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 airplane collided with the runway during the landing flare after the pilot experienced inhibited pitch control movement on approach for landing. The pilot said that when the landing gear was extended and the wing flaps were partially extended, his ability to move the control yoke was noticeably restricted. The pilot reported that he tried to pull back on the yoke and use the manual trim to regain control, but the airplane did not respond. The pilot said he lost complete pitch control when he attempted to flare during the landing. The airplane abruptly nosed down and impacted the runway surface. An examination of the wreckage revealed that the control yoke's movement was restricted. Only partial up-elevator travel could be obtained. One side of the autopilot's servo bridle cable for the elevator was found frayed and broken, and was detached from the servo capstan bridle cable locking pin. The other servo bridle cable was found attached to the main elevator control cable and servo, but it was twisted and deformed. Both servo capstan bridle cable guide pins were bent full forward. One nylon guide pin guard was missing and was found in the fuselage belly. The pitch servo (actuator) was removed from the airplane and examined at a repair station. Upon investigation it was determined that the bridle cable had not been wrapped correctly and continued excessive unwrapping of the bridle cable from the capstan had caused it to fray and eventually break. The servomotor initially would not start running until approximately 12 volts of direct current (DC) were applied to the motor. The servo is designed for 28-volt DC operation. After several on-and-off cycles of DC, the motor started running with approximately 5 to 6 volts DC applied. However, even at the full 28 volts, the motor operated slowly. The servo gear train actuator mechanism was found sticky and needed maintenance. The airplane had been operated about 57 hours since last receiving an annual inspection, about 11 months before the accident. No evidence of autopilot system maintenance was found in the 23-year-old airplane's maintenance records. Neither the autopilot or airframe manufacturers had specified a maintenance or inspection schedule for the bridle cables.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the pilot's loss of pitch control authority during landing flare due to an autopilot system failure that inhibited control yoke movement. A factor was inadequate autopilot system maintenance. Full narrative available
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