Accident Narrative
The airplane collided with the runway during the landing flare after the pilot experienced inhibited pitch control movement on approach for landing. The pilot stated that when the landing gear was extended and the wing flaps were partially extended, his ability to move the control yoke was noticeably restricted. He tried to pull back on the yoke and use manual trim to regain control, but the airplane did not respond. The pilot reported losing complete pitch control when attempting to flare, causing the airplane to abruptly nose down and impact the runway surface.
Examination Findings
An examination of the wreckage revealed that the control yoke's movement was restricted, with only partial up-elevator travel obtainable. The autopilot's elevator servo bridle cable was found frayed and broken on one side, detached from the servo capstan bridle cable locking pin. The other servo bridle cable remained attached but was twisted and deformed. Both servo capstan bridle cable guide pins were bent full forward. One nylon guide pin guard was missing and later found in the fuselage belly.
The pitch servo (actuator) was removed and examined. Investigation determined that the bridle cable had not been wrapped correctly, and continued excessive unwrapping caused it to fray and eventually break. The servomotor initially required approximately 12 volts DC to start, though it is designed for 28 volts. After several on-off cycles, it started with 5–6 volts but operated slowly even at 28 volts. The gear train actuator mechanism was found sticky and required maintenance.
Maintenance History
The airplane had operated about 57 hours since its last annual inspection, which occurred approximately 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 manufacturer nor the airframe manufacturer had specified a maintenance or inspection schedule for the bridle cables.