Flight Crew Air Transport Pilot (ATP)
Workload; Situational Awareness; Time Pressure
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Diverted; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Landed in Emergency Condition; Flight Crew Took Evasive Action; General Declared Emergency
Incorrect / Not Installed / Unavailable Part; Human Factors; Chart Or Publication; Aircraft; Manuals
At cruise altitude we noticed an Amber followed by a Red Boxed 'A' on both PFDs. After following Cessna procedures we disconnected autopilot. Ailerons were very stiff/difficult to move control column. We briefed passengers in accordance with Flight Operations Manual procedures and declared an emergency. Landing at the divert airport was uneventful.
The reporter stated that the Amber 'A' indicated a minor aileron mistrim. The Red Boxed 'A' indicated a major mistrim requiring a control force in excess of a 25 LBS. When the Boxed Red 'A' appeared the aircraft started an uncommanded turn which took significant force to counter. The Captain was the pilot flying but gave the aircraft to the First Officer for a short time which is when he realized how serious the problem was. The crew decided that an immediate divert was necessary and so completed the QRH then landed at the nearest airport. The reporter has not heard what caused the event.
Myself and coworker were asked to work a Cessna CE-560 so we flew out that night to be onsite the next day. The squawk was at 41;000 feet; the Aileron Trim had frozen and could not be moved. They had a hard time keeping the plane from turning and declared an Emergency Landing. Once back on the ground the Aileron Trim seem to operate normal. We inspected the Aileron and Trim System and everything operated normal. The only thing we found was large amounts of grease around the actuator and history of trim actuators on related aircraft doing the same thing. We were asked to remove the actuator and install a serviceable one; then ship the old one back so they could test it.
A Cessna 560 First Officer reported the PFD displayed an Amber 'A' followed shortly by a Red Boxed 'A'; and then it entered an uncommanded turn. With autopilot OFF as per the QRH; significant forces were required to control the aircraft so an emergency was declared and the flight diverted. Technician reporter suspects the grease used to lubricate the aileron trim actuator retains water and freezes. The same grease is used on elevator trim actuators that have a history of freezing in flight.