Dallas, TX, USA
N774SB
Cessna 560
The airline transport pilot and the copilot, who was the pilot flying, were conducting an on-demand air taxi flight with three passengers onboard. The copilot reported that, during the takeoff rotation, he had difficulty maintaining the runway heading and that the airplane experienced a right rolling tendency. He noted that, while continuing to take off and as the airspeed was increased, the pressure required on the control yoke to maintain level attitude also increased. The copilot transferred control of the airplane to the pilot who then attempted to adjust the aileron trim; however, the trim control knob would not move, and the trim indicator appeared centered. The flight crew declared an emergency to air traffic control and requested to return to the airport. When the airspeed was decreased during the approach, the right roll control pressure decreased, and the flight crew was able to free the aileron trim control and land uneventfully. Postincident examination of the aileron trim system revealed that the cannon plug on the back of the autopilot control head was contacting the aileron trim control gear within the cockpit pedestal. Additionally, the wires extending from the cannon plug exhibited chafing. The day before the incident, maintenance personnel had inspected the cockpit pedestal, which required removal of the control heads for the autopilot from the pedestal. The pedestal was then cleaned and reassembled. Therefore, it is likely that, when maintenance personnel reassembled the pedestal, they did not ensure that the cannon head on the back of the autopilot control head and the aileron trim control gear were adequately separated, which resulted in binding of the aileron trim control gear and chafing of the wiring and led to the in-flight loss of aileron trim. A review of the airplane maintenance manual revealed that the Control Pedestal Area General Inspection procedures did not include a step to ensure that sufficient separation existed between the autopilot control head/wiring harness and the aileron trim tab control gear. The lack of guidance in the maintenance manual to verify separation of the autopilot control head and aileron trim tab control gear before completing work on the control pedestal likely contributed to the incident. Following the incident, the airplane manufacturer implemented a change to the maintenance manual to include a step to wrap the wiring harness in a protective sleeve and verify separation between the autopilot control head/wiring harness and the aileron trim tab control. The manufacturer also issued a mandatory service letter that provided instructions to inspect for damage and correct wire harness positioning.
On February 9, 2016, about 0800 central standard time, a Cessna 560 Encore airplane, N774SB, experienced a flight control malfunction during the takeoff from Dallas Love Field Airport (DAL), Dallas, Texas. The two flight crewmembers and three passengers on-board were not injured. The airplane did not sustain damage. The airplane was registered to Bridgeway Enterprises, Inc. and operated by SevenBar Aviation under the provisions of Title 14 Code of Federal Regulations Part 135 as an on-demand air taxi. Visual meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan. The flight was destined for Mc Curtain County Regional Airport (4O4), Idabel, Oklahoma. The copilot stated that during takeoff rotation he had difficulty maintaining runway heading and the airplane experience a tendency to roll to the right. As speed was increased, the pressure required on the control yoke to maintain level attitude increased. The copilot transferred control of the airplane to the Captain who experienced the same flight control difficulty. The Captain attempted to adjust the aileron trim; however, the trim control knob would not move, and the trim indicator appeared centered. The flight crew contacted air traffic control, requested to return to DAL, and declared an emergency. When the airspeed was decreased during the approach, the right roll control pressure decreased, and the flight crew was able to free the aileron trim control. The flight crew landed the airplane at DAL without further incident. The day before the flight, on February 8, 2016, maintenance personnel had completed an inspection of the cockpit pedestal; which required removal of the control heads for the autopilot, the flight management systems, the multi-functional displays, etc. from the pedestal. The pedestal was cleaned and reassembled. After the crew returned from the incident flight stating the aileron trim tab control knob was "jammed" and "wanted to roll right," the mechanic opened the pedestal area and observed the cannon plug on the back of the autopilot control head was contacting the aileron trim gear mechanism. Additionally, the wires extending from the cannon plug exhibited chaffing. Maintenance personnel then inspected the aileron trim system for any other possible anomalies, finding the trim indicator position in the cockpit indicted a neutral position when the trim was elevated above the trailing edge of the aileron. Maintenance personnel adjusted the trim tab and verified its' correct indication in the cockpit. A review of the Cessna Model 560 Maintenance Manual revealed there was no step in the maintenance procedure for "Control Pedestal Area General Inspection" to ensure there was enough separation between the autopilot control head/wiring harness and the aileron trim tab control gearing to prevent interference. Following the incident, in August 2016, Textron Aviation implemented a change to the C560 and C550 airplane's maintenance manuals to include a step to wrap the wiring harness in a protective sleeve and verify separation between the autopilot control head/wiring harness and the aileron trim tab control. Textron Aviation also issued a mandatory Service Letter for the C560 and C550 that provided instructions to inspect for damage and correct wire harness positioning.
The loss of aileron trim due to the lack of separation between the cannon head on the back of autopilot cannon plug and the aileron trim tab control gear. Contributing to the incident was the lack of guidance in the airplane maintenance manual to verify separation of the autopilot control head and aileron trim tab control gear before completing work on the control pedestal.
Source: NTSB Aviation Accident Database
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