What happened
On 25 March 2012, a Piper PA-28-151 Warrior, registration G-BCTF, was conducting takeoff and landing practice at Durham Tees Valley Airport. The flight, a training operation involving an instructor and a student, proceeded normally through the first touch-and-go. However, during the second landing, as the student applied power to initiate a subsequent takeoff, the instructor noted a slight wobble. The instructor immediately took control and closed the throttle. The aircraft subsequently slewed to the right on the runway, resulting in the right main landing gear leg separating from the wing spar attachment. There were no injuries to the two crew members.
The investigation
Following the incident, an engineering organisation examined the aircraft. The investigation established that the right main landing gear leg had detached due to the failure of the four upper screws and four lower bolts securing the leg to the right wing main spar.
Analysis of the recovered components revealed that three of the upper screws had failed due to overload. Two recovered bolt ends, identified as part of the lower attachment, showed evidence of fatigue failure. The investigation also noted that some lower attachment bolts on the left gear leg were found to be loose. While the maintenance engineer had performed a visual inspection 35 hours prior to the accident, it was determined that such an inspection would not have detected the internal cracking or the slight loosening of the fasteners.
Findings
- The right main landing gear leg separated from the wing spar due to the failure of several attachment fasteners.
- Two lower attachment bolts failed due to fatigue, characterized by a combined tensile and bending load failure mode.
- The presence of fatigue was likely exacerbated by bending loads, which could have been introduced if the bolts had become loose.
- While the exact cause of the fatigue could not be established, the investigation considered that the bolts may have loosened due to previous heavy landings or bolt stretch.
- The maintenance engineer noted that the attachment bolts had not been disturbed for over seven years, making them susceptible to undetected fatigue cracking.