20150819013969A

While performing a wildland firefighting mission under 14 CFR part 133, this aircraft experience a partial rotor system power loss (PIC and SIC assumed this was from an engine failure). The event began as the aircraft finished filling its water bucket (attached externally and suspended approximately 150? Below the aircraft) and began transitioning to forward flight. Briefly into transition from the ?dip site? The PIC audibly noticed rotor speed decay. The PIC asked the SIC if there was a problem and received confirmation from SIC, that they had ?lost an engine? (SIC reported feeling a yaw kick and noting an immediate torque split with #2 engine dropping off). The PIC opened the water bucket gate, dumping approx. 4000LBS of water, while continuing with the transition to forward flight. At around 25KIAS SIC reported that he ?wasn?t sure the engine had fully quit (speaking of #2 engine which was presumed to be the bad engine?) And that they needed to lose some more weight. The PIC, using the cyclic emergency hook release button, attempted to jettison the bucket and rigging, but they did not drop clear from the aircraft. The PIC ordered SIC to ?use the emergency throttle? And SIC did this and reported that ?the engine is not responding? (SIC reports that he activated both emergency throttles or manual throttles, however at the accident site only the #2 engine manual throttle lever was activated (copilots story has some inconsistencies in this regard)). At this point, with rotor speed continuing to decay (copilot reported #1 engine was indicating 722 T5 and was presumed to be the good engine), the PIC found a place to make an emergency landing. In close proximity to the ground while maneuvering to land, the bucked became entangled in a barbed wire fence and around a tree. The long line pulled tight and the aircraft impacted ground on its tail wheel followed momentarily by the left main gear then right main gear. The tail wheel strut failed and separated from the aircraft. With the tail wheel missing (ground scars show) the tail rotor briefly contacted the ground and appears to have separated the tail rotor drive shaft at the tail rotor gear box input coupling. In close proximity to the time of aircraft ground impact, the long line physically separated from the aircraft. The combination to high main rotor pitch setting (for landing in rotor droop condition), loss of tail rotor anti-torque function (form ground impact), and the aircraft becoming unrestricted by long line separation, caused the aircraft to tip forward and the main rotor blades to contact the ground. Once main rotors contacted the ground, the right main gear collapsed and separated, the tail pivoted to the right and the aircraft rolled on its side causing substantial damage. Accident site debris and ground scars demonstrate that the entangled bucket and line contributed significantly to the aircraft landing in an unintended position and attitude, and appears to have caused the aircraft to roll on its side after landing.