Pilot in Duke Life Flight crash shut down the wrong engine, NTSB says

Avatar for Elan HeadBy Elan Head | February 1, 2021

Estimated reading time 9 minutes, 50 seconds.

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.

Duke Life Flight helicopter crash scene
The scene of the Duke Life Flight helicopter crash in September 2017. The helicopter impacted a shallow turf drainage pathway between two fields of tall grass near a wind turbine farm. NTSB Photo

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.

Duke Life Flight helicopter crash engine bearings
The undamaged gas generator shaft rear bearing from the No. 1 engine is shown alongside the seized and damaged bearing from the No. 2 engine. NTSB Image

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.

Airbus first limit indicator simulation
A simulated FLI display before and during seizure of the rear bearing on the No. 2 engine. In the display at right, the white box on the right moves to indicate that TOT is now the limit driving the No. 2 needle indicator (while the No. 1 needle remains driven by torque), but this is an unusual scenario that was not incorporated into Airbus or Air Methods training material. NTSB Image

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.

Typically, both needles are always driven by the same parameter. The scenario in which one of the FLI needles changes to indicate TOT while the other continues to indicate torque was not addressed in training material from Airbus or Air Methods, Duke Life Flight’s aviation operator at the time of the crash. The NTSB speculates that Burke “may have erroneously thought that the split was showing that the No. 1 engine was producing much less [torque] than the No. 2 engine, which might have contributed to his decision to shut down the No. 1 engine.”

Burke was an experienced and well regarded pilot with over 4,500 total flight hours and more than 1,000 on the EC145. However, as the aviation consultancy Aerossurance notes in its own summary of the accident, such “propulsion system malfunction + inappropriate crew response” events are not uncommon.

Although the Duke Life Flight helicopter was transmitting GPS tracking data, the frequency was not sufficient for investigators to establish the aircraft’s track, speed, and descent profile before impact, or to determine whether Burke maneuvered for an immediate landing or a diversion to an alternate location.

“However, witness reports indicated that the helicopter appeared to be in control with the main and tail rotors turning at an estimated altitude of about 300 feet above the ground with little or no forward speed just before the helicopter’s rapid final descent. Thus, it is possible that the pilot was attempting an emergency OEI [one engine inoperative] landing when the loss of power in the No. 2 engine occurred,” the NTSB report states.

“The helicopter might have been at an altitude that was too low and/or an airspeed that was too slow to allow for a successful autorotative landing when the loss of power in the No. 2 engine occurred.”

Because of the damage sustained by the No. 2 engine, investigators could not determine the root cause of the rear bearing failure, although they ruled out coking. Safran suggested that the failure could potentially be related to contamination of the oil system, degraded oil quality, or possible mishandling of the engine when it was removed for deep aircraft maintenance just over 300 flight hours before the accident.

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