What happened
On 30 June 2008, a Piper PA-34-200T Seneca II, registration G-JDBC, was conducting a training flight involving asymmetric power practice. After performing several touch-and-go landings at Tatenhill Airfield, the crew prepared for a full-stop landing at Manchester International Airport to refuel.
During the landing on Runway 23L, the aircraft veered sharply to the right upon touchdown. The instructor took control to prevent the aircraft from leaving the paved surface, maintaining the aircraft off the ground for as long as possible. During the process, the crew observed that the left wheel appeared to be positioned at a 90-degree angle to the airflow, with the landing gear leg deflected rearwards. There were no injuries to the three crew members on board.
The investigation
Investigators examined the aircraft and found that the left main landing gear forward trunnion fitting had fractured into several pieces. A metallurgical analysis of the recovered fragments revealed evidence of fretting—small-scale movement between the fitting, the bolts, and the wing spar. This fretting was accompanied by low-cycle, high-peak stress fatigue cracking around the bolt holes.
While the aircraft had previously implemented a Service Bulletin to strengthen the installation, the investigation focused on why the left gear failed. The maintenance organization had been performing 100-hour torque checks on the trunnion bolts. During the post-accident inspection, the bolts on the right landing gear were found to be within specification, but the bolts on the left gear were removed during the investigation and could not be measured.
Findings
- The left main landing gear forward trunnion fitting failed due to a combination of loose attachment bolts and fretting damage.
- The fretting occurred because the torque on the attachment bolts had slackened over time.
- The failure likely progressed over several landings rather than occurring solely on the day of the accident.
- Although the aircraft had implemented a permanent strengthening modification in 2003, the underlying cause of the bolt loosening was not identified.