What happened
On 24 August 2010, a Piper PA-28-181 Cherokee Archer II, registration G-BTAM, departed from a private airfield near Douglas on the Isle of Man. Shortly after takeoff, the pilot identified a loss of aileron control. The pilot immediately declared an emergency and diverted to Ronaldsway Airport. To maintain the aircraft's heading and bank angle, the pilot relied on the use of the rudder to navigate the descent and approach. The aircraft subsequently completed an uneventful landing on Runway 26 with no injuries to the pilot.
The investigation
Following the incident, investigators examined the aileron control mechanism. The aircraft's control system uses cables and pulleys to connect the control wheels to a bellcrank, which is then linked to the aileron via a control rod. The investigation determined that the eye end of the right aileron control rod had failed at the connection point to the aileron.
Metallurgical analysis of the fractured component revealed that the threaded shank of the eye end had failed due to fatigue. This fatigue was caused by reverse bending loads. The investigation established that the internal ball bearing within the eye end had seized. Evidence of corrosion and pitting was found on the external surfaces of the eye end, and there was no trace of lubricating oil within the bearing. The aircraft had been stored outside near the coast, exposing it to salt-laden air.
Findings
- The failure of the aileron control rod was caused by reverse bending fatigue resulting from a seized bearing.
- The bearing had seized due to a combination of corrosion and a lack of lubrication.
- The aircraft was operated in a high-salinity environment near the sea, which likely accelerated the corrosion process.
- While the aircraft's last annual inspection included lubrication of the rod end, the 50-hour maintenance check performed in June 2010 had not included the lubrication of the aileron control rod eye ends.
- The pilot acknowledged that more frequent inspections and lubrication should have been performed given the aircraft's proximity to the sea.