Incident Overview
During cruise at Flight Level 370, the flight crew encountered a loss of aileron control, describing the controls as feeling frozen. They managed to make heading changes using the rudder and elected to divert to Kansas City International Airport (MCI).
Control Recovery
As the aircraft descended toward MCI, it entered above-freezing air temperatures. The crew noted that control of the ailerons gradually returned until full control was regained. An uneventful landing was subsequently made at MCI.
Investigation Findings
Post-flight investigation revealed that the aileron control bearings in the lateral control actuator system were worn. These bearings were subjected to testing involving soaking in water and freezing. The tests demonstrated that water penetrated a bearing housing and froze inside the bearing race, disabling the bearing. Further disassembly disclosed that the ball bearings were corroded and worn.
Service Actions
To address the inspection and replacement criteria for these bearings, Boeing issued Service Letter 767-S-27-094 and Service Bulletin 767-27-0128.
Prior Exposure
The aircraft had been exposed to rain and standing water before the flight, which likely contributed to the water ingress into the bearing housing. The crew had suspected that the loss of aileron control might have been due to frozen water in the control system.