West Plains, MO, USA
N2756A
Bell 206L-1
The helicopter was substantially damaged during a hard landing following a loss of engine power. The operator reported that during the training flight, the check airman initiated a simulated engine failure. The report stated that the pilot lowered the collective and entered an autorotation. The operator stated that when the throttle was advanced to recover from the autorotation, the engine out annunciator light illuminated and a full autorotation was performed which terminated in a hard landing. The main rotor subsequently contacted the tail boom severing it. Engine test runs revealed that the engine would not reach 100-percent power, remaining at 95 to 98-percent (cruise) power. The fuel control unit and power turbine governor units were tested according to current production test specifications. Minor anomalies to the test requirements were observed on both units, however, none of the anomalies were consistent with a loss of engine power. The post accident inspection and testing did not reveal any conditions which would have precluded sustained engine operation.
On July 13, 2005, about 1000 central daylight time, a Bell 206L-1 helicopter, N2756A, operated by Air Evac EMS, Inc., was substantially damaged during a hard landing following a loss of engine power at West Plains Municipal Airport (UNO), West Plains, Missouri. The instructional flight was operating under 14 CFR Part 91 without a flight plan. Visual meteorological conditions prevailed. The pilot and check airman reported no injuries. The local training flight departed UNO at 0910. The operator reported that during the training flight, the check airman initiated a simulated engine failure. The pilot lowered the collective and entered an autorotation. The operator stated that when the throttle was advanced to recover from the autorotation, the engine out annunciator light illuminated and a full autorotation was performed which terminated in a hard landing. The main rotor subsequently contacted the tail boom and severed it about 2 feet inboard of the tail rotor gear box. The engine was removed and shipped to the engine manufacturer's facility for testing. Federal Aviation Administration (FAA) inspectors provided oversight during the engine test runs. The engine did not exhibit any external damage. The compressor and turbine sections rotated without binding when turned by hand. The engine was mounted on a test stand. The start-up was normal and the engine speed stabilized at idle. Engine vibrations were within operational limits. Acceleration testing revealed that the engine would not reach 100-percent power, remaining at 95 to 98-percent (cruise) power. The fuel flow setting was changed from low to high and the acceleration testing was repeated with the same results. The fuel control unit and power turbine governor were removed and shipped to the component manufacturer for testing. The testing was conducted under supervision of the NTSB investigator-in-charge. Testing was performed according to the current production test specification. The drive shaft and control lever on both units moved freely when inspected. The units did not exhibit any external damage. The fuel control unit tested within the specification parameters, with a few exceptions. Acceleration flow testing measured fuel flow provided by the unit as engine speed increased. Test readings were taken at 11 points from engine speeds of 600 RPM to 4,000 RPM. During testing, the fuel flow provided by the unit conformed to production requirements at engine speeds from 600 RPM to 3,900 RPM. However, test point 12.120 (4,000 RPM) measured 322 pounds-per-hour (PPH). This was slightly below the required limits of 326 - 350 PPH. Metering valve maximum stop adjustment flow rates exceeded the production requirements. However, the adjustment setting had been changed during the engine test runs. The power turbine governor unit tested within production test parameters with two exceptions. The engine speed commanded by the governor at maximum throttle setting measured 4,470 RPM which was below the test range of 4,500 - 4,570 RPM. At the reduced throttle setting as specified in the test procedure, the engine speed measured 3,518 RPM which was below the test range of 3,591 - 3,681 RPM. None of the conditions noted above were consistent with a loss of engine power. The post accident inspection and testing did not reveal any conditions which would have precluded sustained engine operation. The check airman held a commercial pilot with a helicopter class rating and a instrument-helicopter rating. He also held a flight instructor certificate with a helicopter rating. According to the report, he had accumulated 5,101 hours total flight time, all of which were in rotorcraft. Of that flight time, 1,416 hours were in a Bell 206L helicopter. The pilot held a commercial pilot certificate with helicopter and single-engine land airplane class ratings. The certificate also included instrument ratings for helicopters and airplanes. He held a flight instructor certificate with helicopter, single-engine airplane, and instrument-airplane ratings. He had accumulated 5,920 hours total flight time, of which 4.327 hours were in rotorcraft. Of that flight time, 509 hours were in a Bell 206L helicopter. The FAA, Rolls-Royce Corporation, and Honeywell were parties to the investigation.
A loss of engine power for undetermined reasons during the intentional autorotation. The pilot's misjudgment of the touchdown flare leading to a hard landing was an additional cause. A contributing factor was the intentional autorotation.
Source: NTSB Aviation Accident Database
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