Baxley, GA, USA
N8451E
Piper PA 32R-301
While flying at 2300 feet, the pilot shut off the autopilot and immediately could not maintain pitch control and the airplane went into a series of uncontrollable gyrations. The pilot attempted to regain control of the airplane but was unsuccessful. The airplane collided with trees five miles west of Baxley Municipal Airport. During the post accident functional examination of the autopilot assembly disclosed that when the unit was engaged the pitch servo would only correct the pitch attitude in one direction. Internal examination of the pitch servo revealed that three transistors had been replaced and one transistor appeared original to the unit. Additionally, the functional check of the pitch trim servo solenoid revealed that the unit was not within the design specifications. According to the pilot operating handbook, if the autopilot is disengaged when opposing mistrim forces are encountered, the pilot may be required to exert control forces in excess of 50 pounds to maintain airplane attitude. The pilot will have to maintain this control force while he manually retrim the airplane.
On June 13, 2004, at 2245 eastern daylight time, a Piper PA-32R-301, N8451E registered to and operated by the private pilot collided with trees while on approach to Baxley Municipal Airport, Baxley, Georgia. The personal flight operated under the provisions of Title 14 CFR Part 91. Visual meteorological conditions prevailed and an instrument flight plan was filed. The airplane was substantially damaged. The pilot was seriously injured. The flight originated from Fulton County Airport, Wauseon, Ohio on June 13, 2004 at 1800 central daylight time. While enroute at 2300 feet, the pilot checked the weather at Baxley Municipal Airport, and with the airport in sight, the pilot decided to cancel his instrument flight plan. The pilot shut off the autopilot and immediately afterward, the pilot discovered that he could not maintain pitch control. As the airplane went into a series of uncontrollable gyrations, the pilot attempted to disable the electric pitch trim but was limited because of the physical force needed on the yoke. The pilot's attempts to regain control of the airplane were unsuccessful. The airplane descended and collided with trees five miles west of Baxley Municipal Airport. Examination of the airplane at the accident site revealed the left wing was severed approximately three feet outboard of fuselage, and the right stabilator assembly was deflected aft 90 -degrees severed at the right side of the airframe. The functional examination of the autopilot components revealed the pitch servo was only correcting itself in one direction; as viewed at the capstan, the unit would run clockwise but not counter-clockwise. Internal examination of the unit revealed three transistors had been replaced and one transistor appeared to have been original to the unit. The transistor that appeared original to the unit is for the clockwise motion; the motor in the unit also appeared to have been original. The functional examination also disclosed that trim springs were out of design specifications, but the clockwise speed was within specifications and the tachometer output was out of design specifications. External examination of the tachometer revealed that it had been previously repaired and a lacquer or glue compound had been applied. The servo solenoid specifications are 21.87 lbs; the solenoid was observed to hold in the counter-clockwise direction, but would allow popping off at 15 to 18 lbs in the clockwise direction. Also, the servo mount, from the pitch servo unit, specifications are 50 lbs plus or minus 5 lbs. The unit was observed to be set at 67 lbs for clockwise direction and 65 lbs for counter-clockwise direction. According to a caution note in the emergency procedures of the pilot operating handbook, "when disconnecting the autopilot after a trim malfunction, hold the control wheel firmly (up to 45 pounds of force on the control wheel may be necessary to hold the aircraft level)." Additionally, "if the autopilot is disengaged under these conditions ( opposing mistrim forces) the pilot may be required to exert control forces in excess of 50 pounds to maintain airplane attitude. The pilot will have to maintain this control force while he manually retrim the airplane. "
The mechanical malfunction of the autopilot pitch servo, and the pilot's inability to maintain adequate control pressure to manually retrim the pitch attitude.
Source: NTSB Aviation Accident Database
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