What happened
On April 17, 2020, a Cirrus SR22, registration JA017C, operated by the Independent Administrative Institution Civil Aviation College, was performing routine touch-and-go training at Obihiro Airport. During the fourth flight of the day, the aircraft landed normally, but approximately four seconds after the nose landing gear made contact with the runway, the aircraft's nose suddenly pitched downward.
Recognizing an abnormality, the captain immediately shut down the engine and used the brakes to bring the aircraft to a halt on the runway. The incident resulted in significant damage to the aircraft, including bent propeller blade tips, a deformed nose fairing, and damage to the nose landing gear strut fairing. There were no injuries to the four occupants on board.
The investigation
The Japan Transport Safety Board (JTSB) examined the nose landing gear (NLG) oleo shock absorber to determine why the piston rod had separated from the cylinder. The investigation revealed that the piston rod locknut had detached from the piston rod. Crucially, the investigators found that the grub screw, which is intended to secure the locknut in place, was missing from the assembly.
Analysis of the piston rod surface showed no evidence that the grub screw had been properly applied during assembly. The investigation also noted that the aircraft's maintenance records showed the most recent inspection, performed just two days prior, followed the manufacturer's manual, which only required exterior inspections of the oleo. Because the grub screw is located internally, it was impossible for the operator to detect the defect during routine maintenance.
Findings
- The primary cause of the incident was the separation of the piston rod from the NLG oleo cylinder, which caused the aircraft to tilt excessively forward during the landing roll.
- The separation was likely caused by the detachment of the piston rod locknut, which occurred because the grub screw had not been properly installed or tightened during the manufacturing process.
- The failure developed over time as the aircraft performed repeated take-offs and landings, allowing the locknut to loosen until the piston rod eventually slid out of the cylinder.
- The extreme nose-down attitude caused the nose gear strut to strike the aircraft's firewall and the propeller blades to make contact with the nose fairing.