Incident Details
On February 9, 2016, at approximately 0800 central standard time, a Cessna 560 Encore airplane, registration N774SB, experienced a flight control malfunction during takeoff from Dallas Love Field Airport (DAL) in Dallas, Texas. The aircraft was operated by SevenBar Aviation under 14 CFR Part 135 as an on-demand air taxi. Visual meteorological conditions prevailed, and the flight operated on an instrument flight rules flight plan. The intended destination was Mc Curtain County Regional Airport (4O4) in Idabel, Oklahoma.
The copilot reported that during the takeoff rotation, maintaining runway heading was difficult, and the airplane exhibited a tendency to roll to the right. As speed increased, the pressure required on the control yoke to maintain a level attitude increased. The copilot transferred control to the captain, who experienced similar flight control difficulty. The captain attempted to adjust the aileron trim, but 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 airspeed was reduced during the approach, the right roll control pressure decreased, and the crew was able to free the aileron trim control. The airplane landed without further incident. The two flight crewmembers and three passengers were not injured, and the airplane did not sustain damage.
Maintenance and Inspection
The day before the incident, on February 8, 2016, maintenance personnel had completed an inspection of the cockpit pedestal. This inspection required removal of control heads for the autopilot, flight management systems, and multi-functional displays from the pedestal. The pedestal was cleaned and reassembled.
After the incident flight, the mechanic opened the pedestal area and observed that 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 other anomalies and found that the trim indicator in the cockpit indicated a neutral position when the trim was elevated above the trailing edge of the aileron. They adjusted the trim tab and verified its correct indication in the cockpit.
Post-Incident Actions
A review of the Cessna Model 560 Maintenance Manual revealed that the maintenance procedure for "Control Pedestal Area General Inspection" did not include a step to ensure sufficient 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 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.