History of Flight
On September 8, 2017, about 1120 eastern daylight time, an Airbus (formerly Eurocopter) Deutschland GmbH MBB BK117 C-2 helicopter, registration N146DU, was destroyed in an accident near Hertford, North Carolina. The helicopter was powered by two Safran Helicopter Arriel 1 E2 turboshaft engines. The commercial pilot, two flight nurses, and one patient were fatally injured. The flight was operated as a Title 14 Code of Federal Regulations Part 135 air ambulance flight by Air Methods Corporation (AMC).
The helicopter departed from its base at Johnston Regional Airport (JNX), Smithfield, North Carolina, at 0827. It arrived at Elizabeth City Regional Airport (ECG) at about 0924 for refueling. After departing ECG at 1011, it arrived at Sentara Albemarle Medical Center Heliport (NC98) at 1022, where a patient was boarded. At about 1108, the pilot radioed the Duke Life Flight operations center, advising departure for Duke University North Heliport (NC92), 130 nautical miles away, with 2 hours of fuel and four people aboard. No further communications were received.
GPS tracking data transmitted every 60 seconds showed the helicopter departed NC98 to the northwest, climbed to about 1,000 ft mean sea level, turned west, then climbed to 2,500 ft and continued west at 120 knots. About 8 minutes after takeoff, it turned south. The last data, about 1 minute later, showed a southeasterly track at 1,200 ft and 75 knots. The wreckage was located about 15 nautical miles west of ECG.
Several witnesses reported seeing smoke trailing behind the helicopter. Descriptions included heavy, dark, black, dark blue, and blue smoke. One witness reported smoke coming from under the rotor; another described a single wide streak of blue smoke like a truck burning oil. One witness observed the helicopter appearing to hover at about 300 ft before descending straight down. Another heard a popping noise and saw the helicopter turning left and right before descending quickly, with rotors still turning.
Personnel Information
The pilot had been employed with AMC since August 2009, serving as lead pilot, safety officer at the JNX base, and a maintenance test pilot for the BK117 C2. He was also current and qualified on the twin-engine Airbus EC135, with 1,100 hours in that type. Prior to AMC, he flew twin-engine Sikorsky UH-60 helicopters for the US Army, accruing about 2,300 hours, and the EC135 for another air ambulance provider.
Training records showed all required training completed with no deficiencies. The pilot’s most recent recurrent training and checkride for the BK117 C2 included one-engine-inoperative (OEI) flight procedures and a simulated OEI landing. Recurrent training typically included autorotations practiced to a power recovery at a 3-ft hover, but no autorotations were specifically documented. At the time, AMC did not have a BK117 C2 simulator training program for practice autorotations to touchdown; such a program was under development and later implemented. Engine fire light procedures were discussed during training and were oral question topics during the checkride. The pilot’s EC135 simulator training included OEI recoveries, OEI landings, and engine fire light procedures.
The pilot worked 12-hour days (0800-2000) on a 6-days-on/6-days-off schedule. The accident occurred on the third flight leg of the second day. According to his wife, he had no sleep issues in the preceding three days, was in good health, not taking medications, happy with his life, and had no major stressors. Coworkers and managers described him as professional, well prepared, thorough, team-oriented, and with good pilot skills.
Aircraft Information
The helicopter was maintained under an FAA Approved Aircraft Inspection Program. The most recent 30-hour engine inspection was completed on August 15, 2017, at 2,673 total hours. Several routine maintenance tasks were performed on both engines during the ten days prior to the accident, including power assurance checks, compressor wash, and zonal inspections, with no unusual findings. The most recent daily inspection occurred on the accident morning, at about 2,714 hours. A review of engine-related maintenance records for the preceding six months revealed no discrepancies.
Time between overhaul (TBO) for the gas generator section was 3,600 hours; the accident engines’ gas generators were not due for overhaul for another 886 hours. Maintenance records for the last nine months showed multiple routine oil system tasks with no anomalies reported. Engine oil was replaced at least every 300 hours, well within the manufacturer’s 800-hour specification. The fuel control units (FCU) of both engines were last checked in mid-August with no anomalies. From February 22 to March 31, 2017, at 2,406 hours, both engines were removed from the airframe during major maintenance. On May 22, 2017, at 2,521 hours, a flight crew reported an electrical burning smell in the cabin; maintenance troubleshooting found no discrepancy.
Each engine had four chip detectors (two electric) that alert the pilot with a master caution light, an audible gong, and an amber caution message when metal particles are detected. The helicopter was optionally equipped with a pulse chip detector (fuzz burn) system. According to the BK117 C-2 Flight Manual (FLM), upon an ENG CHIP indication, the first action is to depress the FUZZ BURN switch for 1 second and monitor parameters. If the indication extinguishes, no further action is required. If it recurs, fuzz burn may be activated a second time. If not extinguished, the pilot has two options: perform a single-engine emergency shutdown, or reduce the affected engine slowly to idle and monitor indications (allowing use for landing if parameters remain within limits).
The FLM states that emergency procedures in bold with a gray background are memory items to be performed immediately. The helicopter should be operated such that even with one engine inoperative (OEI), the flight can continue safely. The FLM requires that if one engine becomes inoperative, the pilot must determine if OEI flight is possible; if not, land as soon as possible. Conditions affecting OEI flight include weight, outside air temperature, and pressure altitude.
Weight and balance records indicated a takeoff weight between 7,524 and 7,590 pounds. Performance calculations showed an OEI climb rate of about 300 ft per minute at 65 knots with maximum continuous power at 1,000 ft. The helicopter did not have enough power to hover out of ground effect with one engine operating. The FLM indicated that landing in such conditions would require a running landing with approach speed reduced from 65 to 40 knots at 50 ft. A height-velocity diagram for OEI landings showed that a successful landing could be performed from 180 ft above ground level with no initial forward speed. The FLM did not provide a height-velocity diagram for autorotation with both engines inoperative.
For engine fire indications, the FLM procedure includes establishing OEI flight, reducing airspeed below 100 knots, and pressing the fire indication button, which closes the airframe fuel shutoff valve and shuts down the engine via fuel starvation. According to Safran, this can produce a plume of smoke from the engine exhaust. The fire detection system could sense heat but not smoke.
Vehicle and Engine Multifunction Display (VEMD)
The helicopter was equipped with a VEMD, an electronic display serving as the primary reference for engine power management. The central element is the First Limit Indicator (FLI), an analog display showing the limiting parameter (torque, turbine outlet temperature, or gas generator speed) closest to its operating limit for each engine. The FLI has two needles (one per engine) and digital numeric values for torque, TOT, and N1. In normal cruise, both needles indicate torque and are positioned closely. A large deviation (split) between needles could indicate an issue such as a torque matching system problem or an engine failure. The triple tachometer above the FLI shows main rotor RPM and power turbine speeds for each engine. An aural pulsed tone and ROTOR RPM light activate when rotor RPM is below 95%.