ERA15FA173 · Bell Helicopter Textron 206 L-1

The purpose of the flight was to assist in the scheduled burn of an 800-acre wooded area. The helicopter was under contract with the US Department of Agriculture Forest Service. A Forest Service employee reported that, as the helicopter neared the conclusion of a 61-minute controlled burn mission, he observed it complete a turn to a northerly heading at the southwestern end of the burn area. About 7 seconds later, he heard a sound that resembled an air hose being unplugged from a pressurized air tank. A crewmember, who was the sole survivor, reported that the helicopter was about 20 ft above the tree canopy when the pilot announced that the helicopter had lost power. The helicopter then descended into a group of 80-ft-tall trees in a nose-high attitude and impacted terrain. Witnesses participating in the controlled burn at the time of the accident did not observe any other anomalies with the helicopter before the accident.

The fuel system, fuel pump, and fuel control unit were destroyed by fire, which precluded a complete examination. During the engine examination, light rotational scoring was found in the turbine assembly, consistent with light rotation at impact; however, neither the turbine rotation speed nor the amount of engine power at the time of the accident could be determined. The rotor blade damage and drive shaft rotation signatures indicated that the rotor blades were not under power at the time of the accident. An examination of the helicopter's air tubes revealed that they were impact-damaged; however, they appeared to be secure and properly seated at their fore and aft ends.

On the morning of the accident flight, the helicopter departed on a reconnaissance flight with 600 lbs of JP-5 fuel. The helicopter returned with sufficient fuel for about 133 minutes of flight, and the helicopter was subsequently serviced with an unknown quantity of uncontaminated fuel for the subsequent 60-minute accident flight. Based on the density altitude, temperature, and airplane total weight at the time of the accident, the helicopter was operating within the airplane flight manual's performance limitations.

Most of the cockpit control assemblies were consumed by fire except for the throttle, which was found in the "idle" position. Given the crewmember's report that, after the engine failure, the helicopter entered and maintained a nose-high attitude until it impacted trees and then the ground, it is likely that the pilot initiated an autorotation in accordance with the Pilot's Operating Handbook engine failure and autorotation procedures. A review of the pilot's records revealed that he passed the autorotation emergency procedure portion of his most recent Federal Aviation Administration Part 135 examination, which occurred 1 month before the accident, and this may have aided in his recognition of the engine failure and decision to initiate an emergency descent.

Although a weather study indicated that smoke and particulates were present in the area before, during, and after the accident, witnesses reported an absence of smoke near the area where the helicopter lost power and impacted the ground.

Verbatim NTSB analysis and probable cause from the NTSB dataset