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The pilot of a Duke Life Flight helicopter that crashed in 2017, killing all four people on board, likely received confusing cockpit indications that led to him shutting down the wrong engine during an in-flight emergency, the National Transportation Safety Board (NTSB) has determined.
In a final report issued nearly three-and-a-half years after the accident, the NTSB concluded that a failure of the rear bearing in the No. 2 engine of the Airbus EC145 “created multiple and likely unexpected and confusing cockpit indications, resulting in the pilot’s improper diagnosis and subsequent erroneous shutdown of the No. 1 engine.”
Subsequently, the performance of the No. 2 engine continued to degrade until it lost power, and “the complete loss of engine power likely occurred at an altitude and/or airspeed that was too low for the pilot to execute a successful emergency autorotative landing.”
Pilot Jeff Burke, flight nurses Kristopher Harrison and Crystal Sollinger, and patient Mary Bartlett died when their aircraft crashed near Hertford, North Carolina, on Sept. 8, 2017. Several witnesses reported dark smoke trailing behind the helicopter shortly before it impacted the ground in what investigators concluded was a near-vertical descent.
Although the wreckage was heavily damaged by the impact and a post-crash fire, the remains of the two Safran Arriel 1 E2 turboshaft engines yielded important clues. Investigators found that the gas generator shaft rear bearing on the No. 2 engine was seized and damaged, while the same bearing on the No. 1 engine was undamaged. Additionally, the oil return strainer/chip detector for the No. 2 engine was partially obstructed with crystalline carbon-like and metallic debris.
Investigators also discovered that the No. 1 engine twist-grip throttle control in the cockpit was in the OFF position, which would have required the pilot to press a release button on the grip to rotate it below the IDLE position. The No. 2 engine twist-grip throttle was found in the FLIGHT position. “This evidence indicated that the pilot likely shut down the No. 1 engine and that the helicopter continued to fly for some time with power being provided only by the No. 2 engine,” the NTSB report states.
Investigators can’t be sure exactly what Burke saw or what actions he took during the accident flight, because the North Flight Data Systems OuterLink voice and video recorder installed in the aircraft yielded no usable data (possibly due to a failure of its internal replaceable battery). The aircraft was not equipped, and was not required to be equipped, with a crashworthy flight data recorder or cockpit voice recorder.
However, a simulation conducted by Airbus Helicopters led the NTSB to believe that Burke might have been confused by the unfamiliar presentation of his first limit indicator (FLI). A common feature of Airbus helicopters, the FLI presents engine parameters — torque (TRQ), turbine outlet temperature (TOT) and gas generator rotational speed (N1) — on a needle dial gauge, with the parameter that is closest to reaching a limit driving the position of the needle. In the FLI display for the EC145, the numerical values for the No. 1 engine parameters are to the left of the needle gauge, and those for the No. 2 engine to the right.
Prior to the No. 2 engine failure, the simulation found, the needle indicators for both engines would have been closely matched and both based on torque, as indicated by the white boxes to the side of the numerical TRQ values. However, deterioration of the rear bearing in the No. 2 engine would have led to an elevated TOT as excessive play in the gas generator shaft decreased engine efficiency, causing the fuel controller to add more fuel to compensate. As TOT rose for the No. 2 engine, the relevant first limit for that engine would have changed from torque to TOT.
“As a result, a large split in the needles would occur because they would no longer indicate the same parameter for each engine, even though both engines would still be initially producing the same torque,” the NTSB report explains.