What happened
The Mitsubishi YS-11 was conducting a landing operation at Yokota Air Base under conditions involving a right crosswind. According to the pilot's account, the aircraft touched down with the right main landing gear contacting the runway surface first. Immediately upon touchdown, the right main landing gear collapsed. Despite this mechanical failure, the aircraft remained on the runway and sustained only minor damage.
The occupants included a cockpit crew of two pilots, two flight attendants, seven revenue passengers, and twelve non-revenue passengers who were part of a graduating class of flight attendants. All individuals evacuated the aircraft safely. No injuries were reported during the subsequent evacuation process.
The investigation
Following the incident, investigators examined the collapsed landing gear assembly. The examination of the landing gear trunion revealed significant findings regarding its structural integrity. Inspectors discovered a stress fracture accompanied by heavy corrosion within the component.
The analysis indicated that the corrosion had produced pitting on the metal surfaces. This pitting served as a source of stress concentration, which likely contributed to the initiation and propagation of the fracture. The investigation also reviewed the maintenance history of the landing gear. Records showed that the landing gear had been overhauled in accordance with recommended procedures, which included specific corrosion preventative measures.
Findings
Despite the adherence to overhaul procedures, the corrosion was not detected during normal inspections prior to the flight. The presence of heavy corrosion and subsequent pitting in the trunion component indicates a failure in the detection process for this type of degradation. The stress fracture was directly linked to these undetected corrosive conditions.
The incident highlights the critical nature of thorough inspection protocols for landing gear components, particularly in areas susceptible to corrosion even after overhaul. The collapse occurred during the high-stress phase of touchdown, exacerbated by the crosswind conditions that placed uneven load on the right main gear.