Incident Overview
During an en route climb, the aileron controls became progressively stiffer. At cruise altitude, the autopilot disengaged and the ailerons would not move. Aileron control was restored after a descent below the freezing level, and the aircraft was flown below the freezing level for the remainder of the flight.
Post-Flight Inspection
A post-flight maintenance inspection revealed no physical evidence for the temporary loss of aileron control.
Investigation Findings
An investigation revealed that before takeoff, the aircraft was exposed to rain for about 50 minutes while parked at a gate. The temperature in Washington was in the mid 40s Fahrenheit. The operator suspected ice build-up on the aileron cables.
Manufacturer Actions
The manufacturer had issued a service bulletin (SB B-757-0079) to remove the aileron cable grommets and apply a sealant to eliminate the problem. That service bulletin had been complied with. After the incident, a revised service bulletin, dated November 6, 1986, was issued to replace the aileron cable grommets with new grommets with an increased internal diameter.
Operations Guidance
Additionally, an operations manual bulletin (number 87-1) was issued on January 22, 1987, to advise flight crews.