Robinson R44 N44BJ accident near Elgin, Minnesota

Probable cause

The pilot’s decision to operate the helicopter under powerlines, which resulted in a main rotor blade striking a powerline, causing the helicopter to descend from a low altitude and impact terrain.

NTSB analysis

The pilot was conducting an aerial application flight in the helicopter. Just before the accident, a witness saw the helicopter completing east and west spray passes over a cornfield. The helicopter flew two consecutive spray passes over power transmission lines that crossed the field, but, on the third spray pass, the helicopter flew underneath the powerlines while heading west. The witness then entered a nearby barn and, shortly thereafter, heard a loud “boom,” and the barn shook momentarily. The witness exited the barn and saw smoke rising from the cornfield. The witness and another person subsequently found the helicopter engulfed in flames.

According to the wreckage debris path through the cornfield, the helicopter was flying to the east when a main rotor blade impacted a powerline that crossed over the field. The powerline at the point of damage was about 28 ft above the ground. The corn crop under the transmission lines was 8 to 10 ft tall. The operator stated that, during aerial application flights, the helicopter was typically flown 10 ft above the crop to ensure optimal spray disbursement. If the 10.75 ft tall helicopter flew 10 ft above the 8 ft high corn crop, then the main rotor system would be at the same elevation as the transmission line. The position of the sun relative to the helicopter at the time of the accident would likely not have impaired the pilot’s ability to see the powerlines as the helicopter flew to the east.

Postaccident examination revealed no evidence of a pre-existing mechanical malfunction or failure that would have prevented normal operation of the helicopter. Thus, it is likely that the pilot decided to intentionally fly the helicopter under the powerlines.

Text from the NTSB. Open the NTSB docket for CEN21FA330 for the full record.