Hughes 369 N8618F accident near Naples, Florida

Probable cause

The pilot's inadequate flare during the termination of a practice 180-degree autorotation and the flight instructor's delayed remedial action, which resulted in the tail rotor contacting the ground.

NTSB analysis

The flight instructor and airline transport pilot were conducting a recurrent local public helicopter training flight and had performed several straight-in autorotations and two 180-degree autorotations. During the third 180-degree autorotation, when the helicopter was about 50 ft above ground level (agl), the pilot, who was manipulating the controls, initiated a recovery flare. During the flare, the helicopter's tail rotor contacted the turf runway. The instructor took over the controls and landed the helicopter. The helicopter sustained damage to the tail rotor blades, horizontal stabilizer, and tail rotor drive train. Postaccident examination revealed no preimpact mechanical malfunctions or anomalies that would have precluded normal operation.

The pilot reported that he had initiated the flare to arrest the forward motion as he had done during the previous autorotations, but at some point during the flare, he felt a "bump," which he realized later was the tail rotor striking the ground. The flight instructor reported that, during the flare, the helicopter "suddenly lost altitude," and he "grabbed the controls." He then felt a "bump," followed by a "buzz." A witness who was watching the helicopter during the autorotations reported observing the helicopter descend more rapidly and aggressively during the accident approach than during the previous autorotations. When the helicopter was about 100 ft agl, it nosed up "aggressively," followed by the tail striking the ground.

Two areas at the airport at which the accident occurred could be used for practice autorotations: a paved runway and the turf runway. At the time of the accident, only the turf runway was in use due to traffic; however, a suitable hard-surface runway was also available at a nearby airport and could have been used for the practice autorotations. The flight instructor reported that, after the accident, he could see where the tail stinger had touched the grass and dug into the dirt. He noted that, at the helicopter manufacturer's training facility, pilots always conducted autorotations to a hard surface not onto grass. He believed that if they had been operating on a hard surface, the tail stinger would have touched and slid along the pavement, instead of it digging into the dirt, and this may have prevented the tail rotor blades from striking the ground.

Text from the NTSB. Open the NTSB docket for ERA14TA113 for the full record.