What happened
During flight, the pilot and passenger heard a loud noise, which was later identified as the tail rotor drives andhaft failing. This mechanical failure caused the helicopter to begin yawing to the right. In an attempt to investigate the source of the noise, the pilot reduced airspeed to prepare for an approach. However, the loss of tail rotor authority became apparent, and as the pilot reduced throttle to arrest the yaw, the rotor RPM dropped significantly. This left the crew with no choice but to execute an immediate landing.
The investigation
Investigators examined the aircraft and noted scraping within the tail rotor driveshaft cowling. An inspection of the hardware by the manufacturer revealed that the driveshaft tube had suffered a fracture. The investigation focused on the structural integrity of the component and the conditions leading to its failure.
Findings
- The primary cause of the failure was a fracture in the driveshaft tube caused by fatigue cracking.
- This fatigue cracking was linked to an area of corrosion pitting located on the exterior of the tube, near the second hanger bearing.
- The loss of tail rotor authority occurred while the helicopter was at a low altitude and low airspeed, which significantly reduced the pilot's ability to manage the emergency and assess the situation.