Incident Sequence
During flight, the aircraft experienced a partial engine failure. The pilot executed a forced landing, but upon touchdown, the nose gear dug into the terrain, causing the aircraft to flip over.
Investigation Findings
Post-accident examination revealed that the No. 3 cylinder barrel was cracked approximately 90% around its circumference. The crack was located in the barrel area near the cooling fin radius.
Metallurgical Examination
Metallurgical analysis determined that the crack had initiated in fatigue, originating from improper machining of the barrel to cooling fin radius during manufacture. Additionally, corrosion pitting was present at the fatigue origin, which aggravated the original manufacturing defect.