Cessna 550 Citation II, Edinburgh, Scotland, March 14, 2008–Before takeoff from Palma de Majorca, the Citation II had several system warning messages displayed on its indicators. Warnings included door not locked, which the crew could not clear after ensuring all doors were secure; air duct o’heat, which the crew was able to clear during a telephone consultation with maintenance technicians; and fdr fail, which the aircraft commander chose to disregard as the flight had already been dispatched. During the climb after departure, air duct o’heat illuminated intermittently, but extinguished as the aircraft passed 30,000 feet. The pilot’s in-flight attempt to reset the tripped flt/hr equip cool circuit breaker resulted in its immediate retripping. As the crew engaged the autopilot they also experienced difficulties with the air conditioning system.
After receiving clearance to descend to 4,000 feet near their destination, the captain noticed the autopilot had disengaged without visual or aural warning. He attempted to re-engage the system but the indicator lights remained off. After again attempting to disengage the autopilot, he noted the flight controls felt “unresponsive and very stiff,” and informed Edinburgh of the problem. As the airspeed decreased, the twinjet began pitching up and down, causing the pilot to declare an emergency.
The crew wrestled the aircraft into a shallow high-speed approach to the airport and lowered the gear less than two miles from the runway. The Citation landed at a speed of 193 knots, and came to a stop approximately 150 feet from the end of the runway. Subsequent examination of the aircraft by the UK’s Air Accidents Investigation Branch showed two tripped circuit breakers, including one that protected the autopilot engaged and yaw damper engaged switch lights along with the autopilot-disconnect warning horn and light. Ground testing of the autopilot computer revealed intermittent uncommanded roll inputs when the test each flt button was operated, a fault that was repeated when the unit was installed in another Citation II.