Accident Description
On 24 August 2010 at 0615 UTC, a Piper PA-28-181 Cherokee Archer II, registration G-BTAM, departed from a private strip near Douglas on the Isle of Man. Shortly after departure, the pilot noticed a loss of aileron control. The aircraft was heading toward Isle of Man (Ronaldsway) Airport at the time. The pilot contacted air traffic control and requested an emergency diversion. He controlled the aircraft's bank angle and heading using the rudder and made an uneventful landing on Runway 26. The aircraft was on a private flight with one pilot and no passengers. There were no injuries to the pilot.
Aileron Control Rod Examination
Each aileron on the PA-28-181 is operated by control wheels through cables and pulleys connecting to a bellcrank in the outer wing. A control rod connects this bellcrank to the aileron with an eye end at each attachment point. After landing, examination revealed that the right aileron control rod had failed at the threaded shank of the eye end at the connection to the aileron. Metallurgical examination determined that the threaded shank failed in bending due to fatigue. The ball inside the plain bearing of the eye end was seized. There was no evidence of lubricating oil inside the bearing, and corrosion buildup was present between the ball and the bearing race. Corrosion pitting was also found on the external surfaces of the eye end.
Maintenance History
According to the aircraft maintenance manual, the aileron control rod eye end bearing requires lubrication every 100 hours with MIL-L-7870 standard oil. The aircraft's last annual inspection was completed on 18 February 2010 at 3,488 airframe hours, during which the rod end was reportedly lubricated. The pilot subsequently performed a 50-hour maintenance check on 11 June 2010 at 3,536 airframe hours but did not lubricate the aileron control rod eye ends. At the time of the failure, the airframe had accumulated 3,586 hours, two hours short of the next 50-hour check and the required 100-hour lubrication.
Environmental Factors
The aircraft was based at a private strip near Mount Rule Field, Douglas, on the Isle of Man, about three miles from the sea. It was not hangared and was regularly exposed to wind containing salt particles from the sea. The Federal Aviation Administration's Advisory Circular AC 43-4A, 'Corrosion Control for Aircraft,' indicates that corrosion severity in the UK is 'severe' in all locations approximately 50 miles or less from the sea. The circular recommends thorough cleaning, inspection, lubrication, and preservation at prescribed intervals, with a suggested interval of 15 days for aircraft in severe corrosion zones.
Previous Incidents
A search of the AAIB's accident database found no previous occurrences of Piper PA-28 aileron control rod failures. The aircraft manufacturer's safety department was not aware of any prior failures on PA-28s. A search of the FAA's 'Service Difficulty Reports' database revealed 79 reports of aileron-related problems on PA-28s since 1995, but none involved seized or separated control rod end bearings.