Bell 206 N59600 accident near Perry, Oklahoma

Probable cause

A loss of lateral control during a hover that resulted in an impact with terrain. Based on the available evidence, the reason for the loss of lateral control could not be determined.

NTSB analysis

Prior to the flight, the pilot, who is not a mechanic, installed the flight controls at the helicopter’s left seat position. The pilot and passenger, who was in the right seat and held a student pilot certificate, departed from the pilot’s property for a local area flight. The pilot was demonstrating how he performed low-level aerial application maneuvers to the passenger. During a pass to the east, the two occupants both observed a coyote in a large field. The pilot performed a right pedal turn to get a better look at the coyote. The pilot maneuvered the helicopter to an out-of-ground effect hover over the tall grass, facing to the south, about 40 ft agl, and the two occupants were looking at the coyote. The helicopter then immediately began an uncommanded left roll.

The passenger couldn’t tell what the cyclic positions were (such as if they both went to the left or if just one went to the left) during the uncommanded left roll. The passenger reported the accident sequence happened “very fast” and that the pilot was on the flight controls for the entire flight. The helicopter did not spin, there were no vibrations emitted from the helicopter, and no alarms or warning lights came on during this period. The helicopter impacted a grass field just prior to a barbed wire fence and a postimpact fire ensued.

Postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation; however, the helicopter was destroyed by the postimpact fire. Detailed examination of the flight control system, including determining flight control continuity, could not be established due to the impact and thermal damage. Postaccident scanning and examination of the three hydraulic servo actuators did not reveal any mechanical malfunctions or failures that would result in a cyclic hard over sequence.

Based on autopsy findings, the pilot had severe stenosis of two coronary arteries. However, there was no evidence of sudden incapacitation, and the passenger reported that the pilot was acting fine the entire flight. Thus, the pilot’s cardiovascular medical condition was not a factor in this accident. The drug identified on the pilot’s toxicology results was the non-impairing pain reliever acetaminophen, thus the pilot’s medication use was not a factor in this accident.

The passenger had reported no medical conditions that would be a factor in this accident. Toxicology testing detected no psychoactive compounds from cannabis in his blood but detected tetrahydrocannabinol (THC) and its psychoactive metabolite 11hydroxy-delta-9-THC (11-OH-THC) in his urine. THC’s inactive metabolite, carboxy-delta-9- tetrahydrocannabinol (THC-COOH), was detected in his blood and urine, but this compound can be found long after using cannabis. Thus, it is unlikely that the passenger’s use of cannabis contributed to the accident.

At the time of the loss of lateral control, the pilot and passenger were visually focused outside of the helicopter. With the unexpected and rapid onset of the uncommanded left roll as described by the passenger, there would have been minimal time for the flying pilot to assess and initiate corrective actions.

Based on the available evidence, the reason for the loss of lateral control during a hover could not be determined.

Text from the NTSB. Open the NTSB docket for CEN22FA053 for the full record.