Incident
On 9 June 2011 at 15:15 UTC, a Piper PA-36/375, registration CS-AUC, operated by C.C.B. – Serviços Aéreos, Lda, was performing circuit patterns for material verification after an annual inspection to renew the Certificate of Airworthiness. During a touch-and-go on runway 05, the pilot felt an abnormal reaction from the left main landing gear. Suspecting a collapse, he kept the left wing up as long as possible, veered the aircraft to the right side of the runway, and cut the engine. The aircraft came to rest off the runway, supported by the right landing gear leg and the wreckage of the left leg. The pilot exited unharmed.
Aircraft and Operation
The aircraft had accumulated over 3,600 flight hours and approximately 8,400 movements (takeoffs and landings), some on poorly prepared runways with high loads. The weather was good, with few clouds and light north wind about 10 km/h.
Damage and Injuries
The aircraft sustained minor damage ("Ligeiros") to the left landing gear and lower fuselage. There were no injuries; the pilot was the sole occupant.
Probable Cause
The fatigue failure of the left wheel axle was caused by a progressive fracture that initiated due to the aircraft's operational history. The fracture propagated over time, possibly aided by oxidation during a period of immobilization. The annual inspection failed to detect the crack because only visual inspection was used, without special methods such as electromagnetic or ultrasonic testing. The stresses during the test flight's takeoffs and landings caused the final complete fracture, though no exceptional force was applied at the moment of failure.