Incident Summary
On 10 August 1999, a Piper PA-38-112, registration G-LFSD, was conducting a training flight at Liverpool Airport. The aircraft was being used for a check of a student pilot prior to his first solo flight. After a satisfactory pre-flight check, the student flew a circuit and performed a touch-and-go landing on Runway 27. The instructor noted that the aircraft touched down a little heavily but no damage was apparent, and the aircraft climbed away normally. On the second circuit, the landing was better, but when the student lowered the nose, the nose landing gear collapsed upon contact with the runway. The nose struck the ground, the aircraft slewed slightly to the right, and came to a stop. Both occupants were uninjured.
Damage
The nose landing gear strut failed, causing damage to the propeller, engine, and underside of the cowling. The oleo piston, wheel, and lower end of the cylinder detached and were found about 50 yards behind the aircraft.
Investigation
The AAIB performed a metallurgical examination of the failed oleo strut cylinder. The failure was determined to be the result of a high load application that exploited a pre-existing fatigue crack. The crack had propagated from the cylinder bore at the change in wall thickness at the lower end of the oleo piston upper guide. The fatigue initiated at several locations around the bore in the same plane. Additionally, inspection revealed fatigue cracking in the upper corner of the external lubrication groove in the lower swivel journal, which had been the subject of a previous safety recommendation (No 93-07).
Previous Similar Accident
The report noted a previous nose leg failure on another PA-38 (G-BNSL) at Edinburgh Airport on 24 June 1999, also caused by a pre-existing fatigue crack from the same area of the oleo strut bore.
Safety Recommendations
The AAIB made two safety recommendations (2000-7 and 2000-8) concerning inspection procedures for fatigue cracks in the nose landing gear oleo strut cylinders of Piper PA-38 Tomahawk aircraft.