Bell 206 accident near Clark, Missouri, March 5, 2020

The NTSB's narrative final · quoted from the NTSB record

The pilot of the helicopter air ambulance flight reported that, while en route on the night patient transfer flight, he received low rotor rpm warnings and engine power dropped below 90%. He reduced collective and turned toward a field to perform a precautionary landing, during which the helicopter touched down hard, resulting in substantial damage to the tail boom. A postaccident examination of the helicopter revealed that a pneumatic line, which had been leak-checked about 115 hours before the accident flight, had separated near its filter connection. A leak in the pneumatic line can cause the engine control system to enter a sub-idle fuel flow condition, resulting in a loss of engine power. An examination of the pneumatic line and filter revealed that the tube had fractured completely through at the toe of the weld between the tube and its filter fitting. Surface smearing was present on sections of the separation; however, the separation exhibited surfaces consistent with fatigue that initiated near the top of the tube. The tube's outer diameter surface near the elbow separation exhibited rub damage. A red ribbed hose was present in the engine bay near the tube separation and the ribbed hose exhibited discoloration on its outer surface consistent with rubbing against the pneumatic tube. One weld exceeded its component specification; the remaining tube and weld measurements met their component specifications. The tube, fitting, and weld materials met specifications. According to the engine manufacturer, the accident was the first occurrence of a separation involving this revision of the pneumatic line over 17 million fleetwide flight hours. The cause of the fatigue could not be attributed to the hose and pneumatic tube rubbing or any other issue, and the reason for the failure could not be determined based on the available information.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.

Photographs from the investigation 12 pictures from the NTSB's docket, as the NTSB released them

Photo 1 – Supplied photo with a view of the right side of the helicopter.Photo 2 - Supplied photo with a view of the right side of the tailboom.Photo 3 - Supplied photo with a view of the front of the helicopter.Photo 4 - Supplied photo with a view of the left side of the helicopter.Photo 5 - Supplied photo with a view of the tail rotor.Photo 6 - Supplied photo with a view of the cockpit.Photo 7 - Supplied photo with a view of deformed skin near the junction of the fuselage and tail boom.Photo 8 - Supplied photo with a view of deformed skin near the junction of the fuselage and tail boom.Photo 10 - Supplied photo with a view the Pc Line and its filter. There is a separation in the pneumatic line.Photo 11 - Supplied photo with a view the Pc Line and its filter. There is a separation in the pneumatic line.Photo 12 - Supplied photo with a view the Pc Line part number.Photo 13 - Supplied photo with a close-up view the separation in th Pc Line.

The NTSB's photographs with the NTSB's captions, at screen size. Open a picture to see it full size or to report one that should not be shown.