History of Flight
On September 19, 2013, at approximately 2127 central daylight time, a Eurocopter AS350B2 emergency medical service (EMS) helicopter, registration N810LE, experienced a total loss of engine power near Canton, Mississippi. The helicopter subsequently made a hard landing in an open field. The pilot sustained serious injuries, while two medical flight crewmembers and a passenger received minor injuries. The flight was operated by Metro Aviation Inc. under 14 CFR Part 135 as an on-demand EMS patient transfer. Night visual meteorological conditions prevailed, and a company visual flight rules flight plan was filed. The flight departed from a private hospital helipad in Ackerman, Mississippi, at 2054, with Jackson, Mississippi, as its intended destination.
According to the pilot, about 10 minutes after departure, a low engine oil pressure warning light illuminated and the oil pressure gauge indicated between 0 and 2 psi. The pilot noted no corresponding rise in oil temperature or engine temperature and continued toward the destination while attempting to verify the loss. Several minutes later, a low torque indication appeared, again without temperature rise. About 25 minutes after departure, the engine temperature gauge began to rise. The pilot lowered the collective, observed the temperature increasing more rapidly, and located an open field for an off-airport landing. The engine lost total power before reaching the field, and the pilot performed an autorotation. After impact, the pilot carried out emergency shutdown procedures. The pilot was using night vision goggles during the flight.
A witness reported seeing “dark black” smoke from the engine exhaust as the helicopter departed the helipad, heaviest when the helicopter tilted westward. The witness also heard a “clanking” noise as the helicopter accelerated and noted it continued flying forward without turning.
Personnel Information
The pilot held an airline transport pilot certificate for airplane multiengine land, a commercial pilot certificate for helicopter and airplane single-engine land, and instrument helicopter rating. He also held flight instructor certificates for airplane multiengine, single-engine land, helicopter, and instrument, as well as advanced ground instructor, instrument ground instructor, and flight engineer certificates. His first-class medical certificate was issued on August 8, 2013. He had accumulated 3,380 total flight hours, including 1,200 hours in helicopters and 77 hours in the same make and model as the accident helicopter.
Aircraft Information
The helicopter was issued an airworthiness certificate in 2010 and registered to Metro Aviation Inc. on May 27, 2010. It was powered by a Turbomeca Arriel 1D1 series engine rated at 732 shaft horsepower. The most recent maintenance inspection under the approved inspection program was completed on September 13, 2013, about 12 flight hours before the accident. This inspection included replacement of the second stage turbine disk (T2). The engine manufacturer required a level III maintenance technician for this task; the technician had the required training and technical manual. During the T2 replacement, the maintenance manual specified cleaning the rear bearing and free turbine nozzle guide vane assembly. The technician judged the bearing as “clean” and did not perform cleaning. However, the manufacturer’s procedures required systematic cleaning of the rear bearing whenever the T2 was replaced every 4,000 cycles, regardless of its condition. The T2 had 3,990.58 cycles at replacement.
The engine oil system consisted of a 5.7-liter tank, pumps, filter, strainers, cooler, breather, and indicating devices. The gas generator rear bearing was lubricated by oil through an external tube, restrictor, and a tube into the bearing housing. Oil coated the bearing, and the housing was sealed by pressurized labyrinth seals. Oil then drained by gravity through a tube, an external tube, a strainer, and the scavenge pump. Air/oil mist from lubrication vented through a tube to the engine exhaust.
Wreckage and Impact Information
The helicopter came to rest upright in an open field surrounded by trees. The landing gear crosstubes were bowed downward. The tailboom separated and came to rest just aft of the fuselage. The main rotor blades remained intact and attached to the rotorhead.
Additional Information
The pilot reported having an intermittent oil pressure gauge issue in a different helicopter “a couple of weeks” prior, so he initially thought this was a similar problem.
Communications
The operator’s communications center provided flight following. Twice during the flight, personnel contacted the pilot to verify normal progress. Approximately 14 minutes before the destination—about halfway through the flight—the pilot reported that “operations were normal.”
Tests and Research
Engine Examination: The engine was removed from the airframe and shipped to the manufacturer in Grand Prairie, Texas. On October 11, 2013, technical representatives from Turbomeca USA, American Eurocopter, and Metro Aviation examined the engine under NTSB supervision. Disassembly revealed heat damage to the gas generator rear bearing, consistent with lack of lubrication. Carbon was found in the scavenge pipe and union from the rear bearing housing. No other anomalies were detected. An additional examination on October 31, 2013, found an obstruction of solidified oil carbon in the rear bearing chip detector housing union of the oil return pipe, just before the strainer.
Vehicle Engine Multifunction Display (VEMD): The VEMD was powered and displayed data for the accident flight, lasting about 32 minutes. An analytical inconsistency between NG (gas generator speed), torque (TRQ), and T4 (gas generator turbine outlet temperature) appeared at 05 minutes 31 seconds, with TRQ information shown in yellow. The last consistent TRQ values were 71.9% two seconds before the fault and 70.0% at fault detection. A similar inconsistency appeared on the right module at 05 minutes 32 seconds. An overlimit T4 temperature of 1215°C occurred during the starting phase, which at that time corresponded to the end of flight when NG decreased from 60% to 10%.
Recorded Flight Data: The North Flight Data Systems Outerlink Voice and Video Recorder (OVVR) provided engine parameters throughout the flight. Data showed the helicopter departed at about 2056:30 CDT. At 2058:30, oil pressure dropped from approximately 4 bar to about 0.2 bar for the remainder of the flight. Gas generator speed began to drop at 2124:25, and oil temperature and T4 began climbing at 2125:10. The last data was recorded at 2125:26. Engine torque dropped to approximately 0 at 2058:30, along with the oil pressure drop. Torque reading on this engine is driven by oil pressure.
Flight Manual Emergency Procedures: The airframe manufacturer’s flight manual stated that if an abnormal engine parameter was observed, the pilot should check the “ENG P” light. If illuminated, check the oil pressure gauge and land immediately if it indicates low or nil pressure. The cockpit checklist found in the helicopter stated: “Land ASAP” if the ENG P light was illuminated.