Bell Helicopter Textron 206L-1 N2611 accident near Thibodaux, Louisiana

Probable cause

The pilot’s failure to maintain clearance to powerlines during an agricultural application pass.

NTSB analysis

The accident occurred during the first application flight of the day while the pilot was applying pesticide to a sugar cane field. He departed from a temporary operating area about one-third mile from the field to be sprayed. According to on-board position data, about one minute later, the helicopter was aligned with the spray field, and the spray system was on. At that time, the helicopter was at an altitude of about 59 ft mean sea level (msl) and traveling about 49 miles per hour. The final Ag-Nav data point was recorded at 0653:42 when the helicopter was about 0.50 nm from the power lines and at an altitude of about 43 ft msl. The sugar cane crop was about 6 to 8 ft high and a tree line bordered the west edge of the field.

A set of powerlines was located about 180 ft from the north edge of the field being sprayed. The lines consisted of three transmission and two static lines. The static lines were about 85 ft above ground level (agl) at the supporting H-frames. The south static line was broken during the accident sequence. The operator noted that the transmission line was marked and included in the geospatial mapping data provided for the flight.

The fuselage came to rest about 60 ft north of the severed static line. The right landing skid forward of the attachment strut was separated and located about 70 ft south the static line. The upper surface of the separated skid exhibited repetitive abrasion marks consistent with contact to the static line. The outboard portions of both main rotor blades had separated and were located within the debris field. Both blade leading edges exhibited repetitive abrasion marks consistent with contact to a powerline.

The tailboom was separated at the aft fuselage and fragmented. The tail rotor blades and transmission were intact, and the tail rotor gear box rotated freely by hand. Examination of the flight control system did not reveal any anomalies consistent with a preimpact failure or malfunction.

The engine did not exhibit any anomalies consistent with a preimpact loss of engine power. Engine drive train continuity was confirmed. Rotational witness marks were present on both the main drive (power output) shaft, as well as the tail rotor drive shaft consistent with engine operation at impact.

The investigation revealed no preimpact anomalies with respect to the helicopter. The forward portion of the right landing skid contacted the static line causing it to separate from the airframe. Secondary contact to the main rotor blades and the subsequent separation of both blades resulted in the loss of control of the helicopter.

The pilot reported a history of diabetes. However, the A1c noted in the toxicology report indicated good long-term control, and the vitreous glucose indicated a low probability of major metabolic disturbance from extreme high blood sugar. However, other diabetes effects such as fatigue or blurry vision could not be excluded based on available medical evidence.

The pilot had conducted agricultural application operations for many years and was familiar with the specific field being sprayed. Additionally, the transmission line was marked and included in the mapping data provided for the flight. Helicopter position data did not cover the final portion of the flight due to the data buffering aspects of the system architecture. This prevented a detailed determination of the flight path as the helicopter approached the powerlines.

Based on the available information, the pilot slightly misjudged the helicopter flight path which resulted in contact of the right landing skid to the static line and, ultimately, loss of control of the helicopter. The exact reason for that misjudgment by the seasoned agricultural pilot could not be determined.

Text from the NTSB. Open the NTSB docket for CEN25FA281 for the full record.