Date: 201206
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Citation II S2/Bravo (C550)
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Climb
Airspace: Class C ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Aileron Trim System
Component problem: Malfunctioning; Improperly Operated
Reporter organization: Corporate
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Multiengine
Human factors: Troubleshooting; Human-Machine Interface; Confusion
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Aircraft; Manuals; Procedure; Chart Or Publication
Primary problem: Aircraft

Narrative: First Officer and I arrived at the FBO and a short time later we spoke with the Maintenance Representative who stated that they had serviced the aircraft air conditioning and that it had been released for flight. After completing a preflight of the aircraft and verifying the maintenance paperwork was signed off and placed in the aircraft; we taxied to obtain fuel and pick up our passengers. After completing the fueling; I walked out to the aircraft and verified the fuel load was correct. The First Officer had also done the same and had performed a second walk around of the aircraft noting no abnormalities. After the passengers had boarded the aircraft and the First Officer had completed the safety briefing; we started the aircraft and completed our before taxi checklist. After receiving clearance to taxi to the runway the First Officer began the taxi checklist. All items were completed on the checklist and verified. It was during this time that we had completed the autopilot function test and also verified that all three trim indications were appropriately centered and set for takeoff. The flight control check was also completed with both the First Officer and I visually verifying that the controls deflected in the proper direction with no faults. We received clearance to depart the runway from the line-up and wait position. The takeoff roll began as normal and no adverse indications were noted. As First Officer called V-1 I placed both hands on the controls. At the V-R 'rotate' call I began a smooth rotation and immediately upon liftoff the aircraft began a severe and uncommanded roll to the right. First Officer completed the 400 FT checklist items placing the yaw damper on and placing the flaps to the up position. At this time I was still having great difficulty holding the aircraft level requiring two hands and extra left rudder to keep it level. I commented to the First Officer that I was having a very difficult time controlling the roll of the aircraft. The First Officer checked on with Departure climbing and we were given a 120 heading. During this time I immediately scanned all aircraft instruments and engine indications and verified that no obvious in cockpit indications were indicating an abnormality. I attempted to move the aileron trim to the left approximately 1-2 turns but did not notice any control change other than it was still attempting to roll to the right even with both hands on the control yoke. I asked the First Officer to verify that he saw nothing outside that could be causing the un-commanded roll and he stated that he saw none. The First Officer also then verified for me that the trim indications were all still indicating centered and appropriate. I then asked the First Officer to assume controls to verify that he was getting the same roll indications and control problems. The First Officer stated that he was and was surprised at the amount of force required to maintain control. The First Officer then asked me if I thought we should return to the airport and I informed him that I did in fact want to return to the departure airport. The First Officer advised ATC that we were having a control issue and wanted to return to the airport. ATC then gave us a heading of 210 and a climb to 5;000 FT. At this time I felt the situation warranted priority handling to return. ATC then cleared us directly to the airport. The First Officer advised ATC of our information and I asked him to assist me on the controls as the amount of force required to maintain control was very significant. It was at this time that I again verified all in cockpit indications; and again (having done so previously several times) verified that the autopilot and yaw damper were off and not causing the un-commanded roll. I noticed at this time that with the autopilot on; controllability was improved but the aircraft was still trying to roll to the right. At this time we were on a wide right downwind for the runway and had been cleared to land.I informed the passengers that we were having an issue with the aircraft which we were returning to the airport and verified that they had their seatbelts fastened and also asked them to place their shoulder harnesses on for landing. All passengers complied with my instructions. I commented to the First Officer that this was going to be an overweight landing and that we should be aware of this in an attempt to land as smoothly as possible. I began slowing the aircraft to its final approach speed and called for the landing gear and flaps on schedule according to the appropriate speed limitations. During this time; unsure if it was possibly a gear door or split flap condition I was aware to make note of any changes in controllability. Noting no changes during gear and flap extension; the First Officer and I continued to maintain dual control of the aircraft and turned final. The First Officer was calling out my glide path as well as speed. Once over the runway; I reduced power to idle on schedule with a normal landing and the touchdown occurred smoothly and without incident. Wanting to ensure I maintained aircraft control; I kept both hands on the yoke and had the First Officer deploy the thrust reversers to aid in slowing the aircraft. We exited the runway and noted no control issues on the ground. We taxied the aircraft to the FBO and after shutting down the aircraft; deplaned and spoke with Airport Operations. It was at this time that the First Officer noted the left aileron trim tab showed a full up deflection. After pointing this out to me I looked back into the cockpit and verified that with the ailerons in the centered (neutral) position and the trim indicator showing centered; the left aileron trim tab was still in full up deflection. The First Officer took the passengers to the terminal and removed their luggage for them. I immediately notified Operations Director of the incident. I also spoke with Maintenance Director; after informing him of the incident and the overweight landing [we were] cleared to taxi the aircraft to the Maintenance Service Center.

Callback: The Reporter stated that he and the First Officer had arrived in this aircraft about eight hours earlier and had not experienced any flight control difficulty. Overnight the air conditioning system was serviced and; unknown to the crew; other inspections and servicing also occurred. One of the items inspected was the flight control trim system. The Reporter assumes; but does not know for certain; that a Maintenance Technician saw the aileron trim knob on the center flight station pedestal not centered and turned it to center but did not verify the aileron trim tab position. The trim indicator itself malfunctioned and because of age; dust or other unknown malfunctions; did not move to the centered position in the same ratio as the trim knob moved so that when the trim indicator was centered the aileron trim tab was in reality fully deflected. The Reporter believes that this malfunction could have been caught by either the Maintenance Technician or the flight crew if the checklists for both Maintenance and flight crews were to include an inspection item verifying trim tab position and trim indicator positions concurring. The current practice is that Maintenance technicians and pilots verify condition of the flight control but in isolation from the trim settings. In this case; neither pilot recalled the position of the trim tab; but both remember that the flight control conditions were normal. The Reporter suggests adding an inspection checklist item for Maintenance and flight crews to set the flight station trim indicators to zero and during the walk around verify that indications and positions are correct.



Synopsis: A CE550 Captain noted extreme aileron trim tab deflection after takeoff which could not be trimmed out so the flight returned to land where it was found the cockpit trim indicator was misaligned with the trim tab. Reportedly; Maintenance had completed overnight serving of air conditioning system and other inspections including the flight control system.