What happened
During a training flight intended to prepare for a rotorcraft-helicopter practical flight test, a student pilot was practicing autorotations with an instructor on board. The student had successfully completed two "full down" autorotations. However, during the third autorotation attempt, a loud noise was heard as the helicopter settled toward the left rear. This movement caused the tail rotor to strike the asphalt taxiway.
The investigation
A post-accident inspection of the aircraft revealed that the bolt attaching the left rear oleo strut to the crossbeam was missing. The inspection also identified several mechanical failures: the tail rotor blades sustained damage, the tail rotor driveshaft was twisted, and the splined end had separated from the main transmission. Maintenance records showed that the aircraft had flown 5.1 hours since its last 50-hour inspection, during which time the landing gear struts had been overhauled and the skid shoes replaced.