Narrative:

[We departed early in the morning]. The first ATIS temperature read 7C and the second read 8C. It was raining so much that my socks were wet underneath my nearly waterproof shoes by the time I was done with the preflight inspection. Preflight; startup; taxi; and takeoff were relatively normal. We did have the engine cowl heats on during taxi and takeoff; and the wings on during much of the climb due to the temperatures and amount of precipitation. We did not get the ice det EICAS. We popped out of the tops at roughly FL180; and subsequently turned off the anti-ice equipment per procedure.approximately 1 hour 20 minutes into cruise flight at FL370 we heard the master caution beep and watched the 'autopilot' message come up on the EICAS. I disconnected the autopilot with the switch on the yoke; and held the plane at altitude. We selected center command again; and the plane flew fine for a while - maybe 20 or 30 minutes. Then once again autopilot populated the EICAS screen. We selected the left autopilot which eventually kicked off as well as the right. In between each attempt; I flew for a few minutes basically maintaining altitude and flying straight on course. I didn't turn much; but by the time we had examined all 3 channels; the xtk was 0.1 off. In making this tiny correction; I noticed the roll axis of the yoke was stiff and commented to the captain. The center autopilot had been successfully reengaged; and things progressed normally for quite some time. We looked for guidance in the QRH; discussed what the issue might possibly be; and continued on the flight plan route for a while with no issues. We were over mountainous terrain at night with nasty weather; so we continued toward daylight; lower terrain; slightly better weather; and more options for familiar airports where the company has operations. We were in smooth air at FL370; and lower was supposed to be more turbulent. We briefed that we would begin the descent early; get out of rvsm airspace; and troubleshoot more thoroughly with the company's input. Everything was normal as we approached; but we prepared to possibly hand-fly the aircraft.the captain utilized all available resources by asking a jumpseating pilot to sit up front and add a set of eyes and ears to the situation; informing ATC that we would like to exit rvsm airspace and be given some room from other aircraft to troubleshoot issues; then soon included the company and other resources. The company suggested that if the issue was the autopilot not disengaging; perhaps we should fly an autoland approach and just maintain a high level of vigilance for a possible go-around. [The captain] turned to me and asked based on how the controls felt if I'd be comfortable with that. All of us in the cockpit were highly distrustful of the autopilot's capability; so with the autopilot engaged; so we thought we'd test it with a 10 degree turn to the left and then one to the right in heading mode.as soon as I turned the heading bug; the autopilot kicked off. We both felt a serious binding in the control yoke. The captain assigned me to continue flying; cover radio 1; and went to work continuing to troubleshoot with the company; and communicating with ATC; gathering info; formulating; and reformulating plans as information changed. [The captain] tried using all available methods to disengage the autopilot including using the bar disconnect and the aileron trim knob to hopefully break the autopilot free; but had no effect. We checked hydraulic quantities and pressures. All normal. There were no warnings for any other systems.the captain contacted [ATC] and informed them of the degraded roll capability asking for direct to the airport and to give us more space from other aircraft. [The captain] went back to talking to [operations] to get weather for [possible alternates] - anywhere that had decent winds and ceilings. During that time; [ATC] called and said we'd be an emergency aircraft. I agreed; and communicated that with the captain within a few seconds. [The captain] communicated the fuel; souls on board; and all necessary information with ATC. [The captain] also shared that [a nearby alternate] was OVC1500 with winds 150/17g23.flying the aircraft in a steady descent took a lot of effort and concentration. The most effective roll input was actually coming from the rudders; and the compensation required to maintain controlled flight was tedious; so we wanted to get better weather than that. Gusty crosswinds while maneuvering close to the ground did not sound optimal. [A second alternate] was reporting winds 130/12 with a 10;000 ft ceiling; so we headed there. The captain explicitly asked [operations] to verify the weather; the tower; and the availability of emergency vehicle assistance; and they called back saying the tower and emergency vehicles wouldn't be available for another 45 minutes. We didn't want to waste fuel and dwindle our options; so we headed back toward [original destination].heavy rain and gusty conditions were constant throughout the descent. ATC accommodated us with vectors to the ILS. The captain advocated configuring for landing early; and only using 20 degrees of flaps for a little more speed and better aerodynamic control. I concurred; and we were configured to land by the fix prior to the final approach fix (gear down; 20 flaps; speedbrake armed; max autobrake). Up until that point; the captain had been very busy with everything necessary to arrive there with all checklists and procedures complete; but then we were both able to focus completely on the landing; and [the captain] began to ghost me in the controls (as previously discussed).somewhere around 4;000-6;000 feet; the temperatures began to rise up to +14 C then +18 C. I noticed the yoke was freeing up and allowing more movement in response to the wind. I commented and captain said [he] could see and feel it. We touched down and came to a full stop. The emergency vehicles inspected the aircraft and after they didn't see anything obviously wrong with the aircraft; escorted us to the ramp. We parked; and maintenance came out to ask what happened; and began troubleshooting. They considered it most probable that the flight controls had iced up - possibly in the wheel well. Dropping the gear and configuring early may have aided the higher temperatures in clearing the ice out and providing greater flight control capability. Many thanks to all involved in making the outcome of this flight safe.hopefully maintenance can hunt down what exactly happened or froze up and figure out how to prevent that in the future. Maybe water entered an area it generally doesn't; or possibly an incorrect type of grease may have been used at some point.

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Original NASA ASRS Text

Title: B767 flight crew reported experiencing limited aileron control response that was later diagnosed as probable aileron cable icing.

Narrative: [We departed early in the morning]. The first ATIS temperature read 7C and the second read 8C. It was raining so much that my socks were wet underneath my nearly waterproof shoes by the time I was done with the preflight inspection. Preflight; startup; taxi; and takeoff were relatively normal. We did have the engine cowl heats on during taxi and takeoff; and the wings on during much of the climb due to the temperatures and amount of precipitation. We did not get the ICE DET EICAS. We popped out of the tops at roughly FL180; and subsequently turned off the anti-ice equipment per procedure.Approximately 1 hour 20 minutes into cruise flight at FL370 we heard the master caution beep and watched the 'AUTOPILOT' message come up on the EICAS. I disconnected the autopilot with the switch on the yoke; and held the plane at altitude. We selected center command again; and the plane flew fine for a while - maybe 20 or 30 minutes. Then once again AUTOPILOT populated the EICAS screen. We selected the Left autopilot which eventually kicked off as well as the Right. In between each attempt; I flew for a few minutes basically maintaining altitude and flying straight on course. I didn't turn much; but by the time we had examined all 3 channels; the XTK was 0.1 off. In making this tiny correction; I noticed the roll axis of the yoke was stiff and commented to the Captain. The center autopilot had been successfully reengaged; and things progressed normally for quite some time. We looked for guidance in the QRH; discussed what the issue might possibly be; and continued on the flight plan route for a while with no issues. We were over mountainous terrain at night with nasty weather; so we continued toward daylight; lower terrain; slightly better weather; and more options for familiar airports where the company has operations. We were in smooth air at FL370; and lower was supposed to be more turbulent. We briefed that we would begin the descent early; get out of RVSM airspace; and troubleshoot more thoroughly with the company's input. Everything was normal as we approached; but we prepared to possibly hand-fly the aircraft.The Captain utilized all available resources by asking a jumpseating pilot to sit up front and add a set of eyes and ears to the situation; informing ATC that we would like to exit RVSM airspace and be given some room from other aircraft to troubleshoot issues; then soon included the company and other resources. The company suggested that if the issue was the autopilot not disengaging; perhaps we should fly an autoland approach and just maintain a high level of vigilance for a possible go-around. [The Captain] turned to me and asked based on how the controls felt if I'd be comfortable with that. All of us in the cockpit were highly distrustful of the autopilot's capability; so with the autopilot engaged; so we thought we'd test it with a 10 degree turn to the left and then one to the right in heading mode.As soon as I turned the heading bug; the autopilot kicked off. We both felt a serious binding in the control yoke. The Captain assigned me to continue flying; cover radio 1; and went to work continuing to troubleshoot with the company; and communicating with ATC; gathering info; formulating; and reformulating plans as information changed. [The Captain] tried using all available methods to disengage the autopilot including using the bar disconnect and the aileron trim knob to hopefully break the autopilot free; but had no effect. We checked hydraulic quantities and pressures. All normal. There were no warnings for any other systems.The Captain contacted [ATC] and informed them of the degraded roll capability asking for direct to the airport and to give us more space from other aircraft. [The Captain] went back to talking to [Operations] to get weather for [possible alternates] - anywhere that had decent winds and ceilings. During that time; [ATC] called and said we'd be an emergency aircraft. I agreed; and communicated that with the Captain within a few seconds. [The Captain] communicated the fuel; souls on board; and all necessary information with ATC. [The Captain] also shared that [a nearby alternate] was OVC1500 with winds 150/17G23.Flying the aircraft in a steady descent took a lot of effort and concentration. The most effective roll input was actually coming from the rudders; and the compensation required to maintain controlled flight was tedious; so we wanted to get better weather than that. Gusty crosswinds while maneuvering close to the ground did not sound optimal. [A second alternate] was reporting winds 130/12 with a 10;000 ft ceiling; so we headed there. The Captain explicitly asked [Operations] to verify the weather; the Tower; and the availability of emergency vehicle assistance; and they called back saying the Tower and emergency vehicles wouldn't be available for another 45 minutes. We didn't want to waste fuel and dwindle our options; so we headed back toward [original destination].Heavy rain and gusty conditions were constant throughout the descent. ATC accommodated us with vectors to the ILS. The Captain advocated configuring for landing early; and only using 20 degrees of flaps for a little more speed and better aerodynamic control. I concurred; and we were configured to land by the fix prior to the final approach fix (Gear down; 20 Flaps; speedbrake armed; Max Autobrake). Up until that point; the Captain had been very busy with everything necessary to arrive there with all checklists and procedures complete; but then we were both able to focus completely on the landing; and [the Captain] began to ghost me in the controls (as previously discussed).Somewhere around 4;000-6;000 feet; the temperatures began to rise up to +14 C then +18 C. I noticed the yoke was freeing up and allowing more movement in response to the wind. I commented and Captain said [he] could see and feel it. We touched down and came to a full stop. The emergency vehicles inspected the aircraft and after they didn't see anything obviously wrong with the aircraft; escorted us to the ramp. We parked; and maintenance came out to ask what happened; and began troubleshooting. They considered it most probable that the flight controls had iced up - possibly in the wheel well. Dropping the gear and configuring early may have aided the higher temperatures in clearing the ice out and providing greater flight control capability. Many thanks to all involved in making the outcome of this flight safe.Hopefully maintenance can hunt down what exactly happened or froze up and figure out how to prevent that in the future. Maybe water entered an area it generally doesn't; or possibly an incorrect type of grease may have been used at some point.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.