A B757's ailerons were very sluggish turning left but suddenly became free simultaneous with an EICAS SPOILER alert. The Captain stated the aircraft had been parked in very windy; rainy conditions prior to flight and water may have collected under some control surfaces.
Synopsis
A B757's ailerons were very sluggish turning left but suddenly became free simultaneous with an EICAS SPOILER alert. The Captain stated the aircraft had been parked in very windy; rainy conditions prior to flight and water may have collected under some control surfaces.
Narrative
Cruising at FL 310; 'Dodging' TRW's in the area. The First Officer turned the heading bug on the MCP to the right while the Center Autopilot (A/P) was engaged. Nothing happened. He tried turning the heading selector knob twice back and forth with no results. He disengaged the A/P and tried a 'manual' turn to the right. The control wheel was very stiff for a moment; then broke free and the aircraft turned to the right. We immediately got a 'SPOILERS' advisory caution notation on the EICAS screen. The A/P was re-engaged and systems seemed to operate normally. I contacted Dispatch and told them our condition. Approaching our destination; we decided to enter holding at 10;000 ft MSL and conduct turn tests to see how the aircraft was handling prior to landing. Turns to the right were normal and easy while left turns felt 'stiff and sluggish'. Dispatch was advised. We requested RWY 27 ILS and that equipment be standing by. Approach initiated an Emergency condition for us. I briefed the flight attendants as to our situation; made a PA telling the passengers to ignore the Emergency vehicles and the First Officer continued in for a normal landing. This is just a possible explanation: Conditions at our departure airport were rainy and gusty. The aircraft was parked facing west. Winds were 080 at 20 to 25 knots. The ailerons and rudder were blown to full deflection as noted when I performed the walk-around. Quite possibly; some water was blown into the control surface operating systems or under the spoilers. If that water had frozen at altitude; it may have partially blocked some mechanical system from working; but broke free due to the hydraulic pressure of a manual control movement. Again; this is just a possibility from a pilot's point of view.
NASA callback
The Reporter stated that the sensation of aileron stiffness was similar to manual reversion on other aircraft and when the controls freed it was like hydraulic power had suddenly been turned on. He was unable to perform a walkaround at the destination to inspect the ailerons and spoilers but flew the aircraft the following day and noted that the maintenance sign off for his flight control discrepancy was a new set of right aileron bearings. The Reporter was still of the mind that frozen precipitation may have been the issue.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.