Bell 206B N49746 accident near Woodsboro, Texas

Probable cause

The pilot’s failure to recognize and correct for flight conditions conducive to a loss of tail rotor effectiveness, which resulted in a rapid, uncommanded right yaw and subsequent hard landing.

NTSB analysis

The pilot was conducting an aerial pipeline observation flight when the helicopter suddenly yawed to the right and he received a low rotor rpm warning. The pilot applied left pedal to correct the yaw; however, the helicopter continued its right turn, impacted the ground, and rolled onto its side, resulting in substantial damage. Examination of the wreckage and testing of components did not reveal any preimapct anomalies that would have precluded normal helicopter operation.

Nonvolatile memory obtained from the helicopter indicated that its groundspeed varied during the last 10 seconds of recorded data to a low of about 9 knots, increasing to about 25 knots, then decreasing to about 12 knots. During this time period, the helicopter's altitude decreased to about 50 feet above ground level (agl). The last recorded point showed the helicopter about 30 feet agl at a groundspeed of about 15 knots on a northwesterly heading. Weather observations from a nearby airport indicated variable wind from the south at 10 knots with gusts to 21 knots about the time of the accident.

The helicopter's orientation to the prevailing wind and its slow airspeed made the helicopter susceptible to a loss of tail rotor effectiveness (LTE). Additionally, the helicopter's low altitude at the time of the LTE encounter was inadequate to allow for recovery before its impact with terrain.

Text from the NTSB. Open the NTSB docket for CEN15LA002 for the full record.