What happened
On 10 August 1999, a Piper PA-38-112, registration G-LFSD, was conducting a training flight at Liverpool Airport to evaluate a student pilot prior to their first solo flight. During the initial circuit, the student performed a touch-and-go landing on Runway 27. While the instructor noted the landing was somewhat heavy, no immediate damage was apparent, and the aircraft continued its flight.
During the second circuit, the student executed a landing on the main wheels. However, as the nose of the aircraft was lowered to the runway, the nose landing gear collapsed upon contact. The impact caused the nose to strike the runway, resulting in the aircraft slewing to the right before coming to a halt. The aircraft sustained damage to the propeller, engine, and the underside of the cowling. There were no injuries to the two crew members on board.
The investigation
Investigators examined the wreckage and found that the nose landing gear oleo strut had fractured just above the lower swivel journal. The force of the failure was significant enough that the oleo piston, the wheel, and the lower portion of the oleable cylinder detached and were found approximately 50 yards behind the aircraft's final position.
Metallurgical analysis of the broken cylinder revealed that the failure was caused by a high load application acting upon a pre-existing fatigue crack. This crack had originated from the cylinder bore at a point where the wall thickness changed near the upper guide of the oleo piston. The examination also identified fatigue cracking in the external lubrication groove, a known issue previously highlighted in a separate safety recommendation.
Findings
- The primary cause of the gear collapse was the failure of the oleo strut cylinder due to a high-load event exploiting an existing fatigue crack.
- The fatigue crack originated within the cylinder bore at a change in wall thickness.
- The aircraft's use in flight training likely contributed to the failure, as training environments involve more frequent heavy loading of the landing gear compared to other operations.
- A similar failure had occurred recently on another Piper PA-38-112, registration G-BNSL, involving a similar fatigue crack in the same area.
Safety action
Following the investigation, the AAIB issued recommendations to address the detection of internal bore cracking. Specifically, it was recommended that the FAA and the manufacturer, New Piper Aircraft Inc., develop an inspection procedure capable of identifying cracks emanating from the internal bore, or alternatively, establish a mandatory service life for these strut cylinders.