An MD11 Captain reported temporary loss of roll control which required 'significant force' to overcome. Maintenance discovered ice on the control cables in the wheel wells.
Synopsis
An MD11 Captain reported temporary loss of roll control which required 'significant force' to overcome. Maintenance discovered ice on the control cables in the wheel wells.
Narrative
During descent I noticed the autopilot had difficulty turning and acquiring a heading during vectoring. As I was selecting the HYD synoptic page to see that everything was operational; the autopilot spontaneously disconnected. I assumed manual control of the aircraft and found the roll axis of the flight controls to be jammed. I applied significant force to the controls and felt them 'break loose' followed by normal operation and freedom of movement. No emergency was declared and problem documented in the logbook after landing with a detailed verbal debrief to Maintenance.The day after the event I checked the aircraft maintenance history and learned they had discovered ice on the flight control cables in the wheel well. I have had several events of this type in both the DC10/MD11 where ice on cables has prevented proper operation of flight controls. Most common seems to be frozen spoiler cables that either prevent the spoilers from actuating or allow the spoilers on one wing to actuate while the other wing panels stay flush causing a severe roll.Other than not flying when it is raining; I'm not sure how to prevent this problem.
NASA callback
The reporter later talked with the Captain who accepted the aircraft after him and; later yet; to Maintenance Management personnel. The Captain was there when the area involved was accessed by Maintenance and he advised there were 'two four foot long icicles' adhering to the control cables passing through that un-pressurized area. Maintenance informed him that where the cables pass from the pressurized cargo areas into and through the involved area they pass through sealing rubber grommets. He also learned there was no 'escape path' for water accumulating in the adjacent pressurized cargo areas. He understood there was speculation that water in the pressurized areas would rise to the level of the grommets and cabin pressure would force the water through the grommets producing a spray that would quickly freeze on the cables. Over time the icicles would form and; in turn; impinge on the pressure bulkheads when the controls were activated; preventing them from actuating the associated systems; including the 'spoiler mixer' which controls the deployment of spoilers in response to roll commands. He felt this was the likely source of the anomaly he experienced.In addition; he was told that the cables had at one time been lubricated with greases that were 'hydrophilic;' thus attracting and holding moisture rather than 'hydrophobic' material that would repel it. He speculated that a change in this lubricant might well have been one ameliorative resolution required by the AD but hadn't researched the matter.Finally; he advised that the MD-11s in his company's fleet are not uniform in their origination and there is some possibility that the AD Notice addressing the issue was not; in all instances; complied with by either their previous operator or during any period of idleness prior to being obtained by his employer.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.