ERA15FA173

A loss of engine power for reasons that could not be determined due to postaccident fire damage.

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.

72-hour History Follow-up interviews with both the pilot's wife and the pilot's roommate were used to construct a 72-hour history. After 7 days of crew rest, the pilot was requested to return to work Sunday, March 29, 2015 as a relief pilot. According to the pilot's wife, he slept normally Thursday and Friday night. On Saturday morning he attended a church conference and then completed a 12 hour drive to Mississippi to prepare for work. The roommate stated that the pilot normally slept "quite a bit." He observed no abnormalities with the pilot's behavior or sleep patterns during the two nights that preceded the accident. Part 137 Operations Specifications According to T&M Aviation's Operations Specifications, the accident helicopter was authorized to conduct Title 14 CFR Part 137. The operations specifications also required the holder to maintain the engine in accordance with the Rolls-Royce 250-C230P operations and maintenance manual and had a Time-in-Service (overhaul) interval of 2000 hours for the turbine assembly. The Time-in-Service intervals for the compressor and gearbox assemblies were noted as "On Condition." USDA Forest Service Contract On January 10, 2012, the USDA Forest Service entered into a contract with T&M Aviation, to provide an aircraft and pilot for the purpose of performing aerial ignition operations. The contract listed numerous requirements and specified the configuration of the aircraft, the installation of required equipment, and the qualifications and duties of the pilot. Aerial Ignition Operation As part of the contract, T&M Aviation provided a pilot and helicopter during plastic sphere dispensed ignition, a common practice in controlled burn operations to ignite ground fuels on large acreage without damaging the tree canopy. According to the PSD manual, the dispenser case is constructed of aluminum and houses a supply of plastic spheres that each contain 3.0 grams of potassium permanganate. The PSD injects a predetermined dosage of ethylene glycol (common automotive coolant) from an inclusive tank and are ejected from the helicopter in batches of 2 or 4. The injection creates a timed combustion to detonate the spheres outside the helicopter. In the event of a malfunction, the unit is equipped with a 1 gallon water reservoir to extinguish burning spheres that remain within the chamber. During aerial ignition operations, the plastic sphere dispenser operator (PLDO) is accompanied by a firing boss who directs the mission. The PLDO is a Forest Service-employed helicopter crewmember responsible for the preparation, installation, operation and maintenance of the PSD. Two sections of the device were recovered from the accident site including the PSD exit chute and a small water tank used in the event of a premature ignition. The unit was bench tested by the plastic sphere dispenser operator (PLDO) prior to the accident flight in accordance with the manufacturer's test procedure and a one-gallon container of water was placed in the helicopter. The Forest Service allows its contract pilots to operate below 500 feet AGL as higher altitudes provide less control of sphere placement, which may result in unintended ignition outside of burn boundaries. The airspeed/altitude combination depends on how the PSD firing boss decides to deploy the spheres, which precludes the use of a prescribed flight profile. Pilot's Operating Handbook (POH) According to the "Engine Failure and Autorotation" section of the pilot's operating handbook, "At low altitude, close throttle and flare to lose excessive airspeed. Apply collective pitch as flare effect decreases to further reduce forward speed and cushion landing. It is recommended that level touchdown be made prior to passing through 70% rotor RPM…" An autopsy was performed on the pilot by the Mississippi State Medical Examiner's Office, Jackson, Mississippi. The cause of death was listed as "thermal injuries and smoke inhalation." The FAA's Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicological testing on the pilot. No carbon monoxide, ethanol, or drugs were detected in the samples submitted. The accident site was located at the southern end of the controlled burn area in a wooded area about one quarter mile north of a road. An initial impact point (IIP) was identified by several 80-foot-tall broken trees, about 70 feet south of the main wreckage. The helicopter tail rotor marked the beginning of the debris path, which was located about 30 feet beyond the IIP on a northerly heading. The main wreckage was oriented northwesterly about 180 feet above msl and comprised of the cockpit, fuselage, engine, main rotor assembly, and main rotor blades. The high landing skid was in the debris path, a few feet aft of the main wreckage. The helicopter upper deck section, which included the main rotor, transmission, and collective/cyclic hydraulic servos, was attached to the fuselage and had sustained fire damage. The cockpit and cabin were destroyed by fire with the exception of the center window frame and portions of the instrument panel, which were co-located with the fuselage. Both main rotor blades sustained significant fire damage, but were attached to the main rotor hub: Blade A (the white blade) was slightly bent opposite the direction of the rotation and Blade B (the red blade) displayed two 45 degree chordwise bends. The tip to Blade B exhibited signs of overload separation that was consistent with impact forces and was located about 20 feet northeast of the main wreckage. Both the tail rotor and tailboom sustained fire damage and were co-located near a tree 20 feet south of the main wreckage. The tail rotor assembly was located next to a tree and was separated from the tail rotor drive shaft. The tail rotor drive system was traced from the tail rotor through the gearbox to the steel tail rotor drive shaft that was mounted to the freewheeling unit on the engine gearbox. There were no indications of spline drive wear on the tail rotor spline shaft coupling at the freewheeling unit and the main drive shaft did not exhibit any resistance when moved forward and aft. The cockpit/cabin section came to rest on its left side and was destroyed by fire. The collective control was found in the cockpit area with the throttle mechanism exposed and in the idle position. Cyclic and collective control continuity from the cockpit to the hydraulic servos could not be attained due to fire damage. The helicopter upper deck section, including the main rotor assembly and transmission, was damaged by fire, but remained attached to the fuselage. Continuity was established from the collective/cyclic hydraulic servos to the swash plate and through overload fractures of the pitch change links. Hand rotation of the main drive shaft confirmed the presence of drive continuity through the main transmission to the main rotor blades. Both main rotor pitch change links exhibited signs of overload separation; the white blade link was separated at the swaged end and the red blade link separated about mid-span. Engine Examination The engine was recovered from the accident site and subsequently disassembled at the manufacturer's facility, under the supervision of the NTSB. Several accessories including the accessory gearbox, power turbine governor fuel control unit, and fuel pump could not be examined as they were consumed by post-crash fire. Both the right and left air discharge tubes displayed some impact damage, but were properly seated at their fore and aft ends. The compressor remained intact in its normal position and did not display any evidence of impact damage. The impeller and impeller shroud did not exhibit any rotational scoring and the no abnormalities were observed on the compressor scroll and diffuser. The combustion section outer case remained in its normal position and was not damaged during the impact. The left side tube was