G200 flight crew experienced jammed ailerons at FL410. Roll control was possible and the crew elected to descend to warmer air where the controls return to normal.
Synopsis
G200 flight crew experienced jammed ailerons at FL410. Roll control was possible and the crew elected to descend to warmer air where the controls return to normal.
Narrative
After leveling at FL410 for 15 minutes (2 hours into flight) the PFD aileron mistrim indicator started to indicate yellow then red in both directions. The aircraft started to oscillate in roll from the left to the right with 15 degrees of bank each time. We disconnected the autopilot and noted that extreme control inputs to the ailerons were required to control the airplane. With about 20-30 LBS of control force we were able to only affect the bank by about 1-2 degrees. We applied both left and right aileron trim; first small amounts then full trim. Even with full right or left trim the aircraft did not bank. We requested a lower altitude with center. We consulted the emergency checklist for jammed roll. As we were still in control of the aircraft and able to maintain straight and level flight we elected not to pull the roll handle and separate the controls. As we descended we called dispatch and discussed the symptoms. We were advised that this has happened to this tail number before. As we descended to a lower altitude we started to gain control of the ailerons. At FL350 we had full control of the ailerons and were able to re engage the autopilot. We continued to our destination. SAT -62 Fuel 4;000 and balanced. The aircraft sat out in the rain the night before. As this is a repeat write-up on this plane I feel it is important to do extensive test flights with this aircraft to make sure this problem is corrected before it is released to the line again. I also think; even though the problem was corrected at FL350; that we should have left RVSM airspace sooner than we did.
Second reporter narrative
Options included descending to a lower altitude; with the assumption that if the ailerons had frozen with water we could regain normal control. In discussions between me and the Captain when the event first occurred; we discussed that it had rained most of the night and that that water may have begun to freeze in the aileron system. This seems to have been confirmed by the fact that after the descent to FL350; the problem went away and did not recur. I believe this event was a malfunction of the aileron control system related to frozen water.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.