Amateur-built ROTORWAY 162F N78291 accident near Merced, California

Probable cause

The helicopter pilot/owner's decision to install a belt type not recommended by the kit manufacturer in the tail rotor drive system using the incorrect tension values, which led to the belt’s in-flight failure and the subsequent loss of tail rotor drive during a practice autorotation.

NTSB analysis

The pilot, who was also the owner/builder of the experimental, amateur-built helicopter, reported that he was conducting a practice autorotation and that, during the landing flare and power recovery, the helicopter yawed left. The pilot applied the right antitorque pedal to correct; however, the helicopter did not respond. The helicopter then began to spin and subsequently landed hard and rolled onto its side. A postimpact fire ensued, which consumed most of the helicopter.

Examination of the tail rotor drive system revealed that the aft tail rotor drive belt remained intact and connected between the tail rotor gearbox and aft pulley and that the majority of the forward belt had been consumed by fire. The center belt had fractured, and subsequent examination of the belt revealed that it exhibited signatures consistent with tensile overload failure.

The pilot/owner reported that the helicopter's center tail rotor drive belt, which was a noncogged design in accordance with the kit manufacturer's recommendation, had failed previously. He chose to replace the failed belt with a cogged belt that had the same dimensions, and he had installed the cogged belt in the airplane less than 3 flight hours before the accident. The cogged belt had slightly different tensioning requirements; however, the owner installed the belt using the tension values required by the noncogged belt, which likely precipitated the cogged belt's tensile overload failure. The cogged belt was also not recommended for pulsation, shock loads, and high-tension configurations, all of which would have been present during the critical power recovery phase when the failure occurred and likely contributed to the belt's failure.

Text from the NTSB. Open the NTSB docket for WPR14LA225 for the full record.