Two Forest Service employees were on board to initiate the burn by dispersing small incendiary devices at selected locations in the forest.
The Aircraft The AS350 B3 is equipped with a three-blade, fully artic- ulated, hingeless main-rotor system and a conventional two-blade tail rotor driven by a single Safran Arriel 2B1 turboshaft engine. The engine in the 2009 model helicop- ter tasked with the Forest Service contract was rated for 871 shaft horsepower (shp) and had been operated for approximately 1,750 hours since new; the airframe had been flown for approximately 5,027 hours. Its most recent inspection had been performed 72 hours earlier. To conduct the fire-seeding operations, the helicopter had been fitted with an SEI Industries Premo MK III Plastic Sphere Dispenser (PSD). According to the manu- facturer, this device’s function is “to inject ethylene gly- col into plastic spheres containing potassium permanganate and then immediately eject the activated sphere from the aircraft. The addition of ethylene glycol to potassium permanganate creates a rapid exothermic reaction that has sufficient intensity to ignite the plastic spheres and ignite the designated burn area.” The mechanism was mounted in the opening created
by removing the helicopter’s right-side cabin doors. The first Forest Service crew member straddled the PSD to
operate it, secured by a chest harness. The second Forest Service crew member sat in the left front seat, with that station’s flight controls removed.
The Pilot The 50-year-old commercial pilot also held a helicopter instructor’s certificate and a current second-class medi- cal certificate. His estimated 8,760 total hours of flight experience included 3,886 hours in the AS350 B3.
The Flight The crew completed the PSD application without inci- dent and had turned back toward their staging area. Weather was good, with clear skies and 7-kt. southeast winds. At 2:10 pm central daylight time, the engine abruptly lost power. The Forest Service crew member in the left front seat later told investigators, “The engine just quit, and everything went silent.” The pilot entered autorotation into 70-ft. trees at a descent angle later esti- mated as 40 to 50 degrees. The helicopter came to rest on its right side about
60 ft. from the point of the first tree strike: a pine tree puncturing the right side of the cockpit just below the instrument panel and stretching across the pilot’s lap. The pilot was hospitalized with serious injuries. The left- seat crew member escaped with minor injuries, but the Forest Service employee operating the PSD was
MARCH 2023 ROTOR 69
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