Ft. Myers, FL, USA
N72LC
Eurocopter AS 350 BA
During the advancement of the fuel control lever, the engine revved and increased power to the point the pilot could not control the bouncing of the helicopter on the pad. The examination of the helicopter's airframe did not reveal any discrepancies that would have prevented normal operation of its flight and engine controls. A test cell run of the engine did not reveal any discrepancies with the operation at various power settings. The manufacturer states that if the fuel control lever is moved beyond the "Flight" detent the emergency valve progressively opens to supply the engine. The pilot's incorrect operation of the fuel lever could have contributed to over revving of the engine.
On November 18, 2006, about 0910 eastern standard time, an Eurocopter AS 350 BA, N72LC, endured a ground resonance occurrence at the Buckingham Field Airport (FL59), Fort Myers, Florida. The airline transport-rated pilot received minor injuries and the helicopter incurred substantial damage. The flight was operated by the Lee County Sheriff's Office as a public use under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and a visual flight rules agency flight plan was filed. The pilot stated that this was his first solo flight after completing his training in the helicopter. He conducted a preflight inspection and a walk around inspection of the helicopter. He started the helicopter and slowly advanced the fuel control lever to the flight gate detent. During this process, he observed a sudden spike in the torque that exceeded the 40% indication and then he heard the engine begin to rev-up rapidly. He stopped the advancement of the throttle and again the torque gauge indicated a spike that exceeded the 40% position. The helicopter started to shake violently and bounce on the ground. He attempted to close the fuel shutoff valve; however, the collective rose when he released it. Witnesses stated they observed the helicopter at flight idle. When it was advanced, it seemed like it advanced very quickly. The helicopter then started with a slight lateral, which progressed into severe, bouncing back and forth from skid to skid. It then rotated 90 degrees to the right and the tailboom fell to the ground before the helicopter was heard shutting down. An examination of the helicopter was conducted by representatives from the American Eurocopter, Turbomeca USA, and the Lee County Sheriff's Office with Federal Aviation Administration (FAA) oversight. Compression damage to the aft landing gear cross tube was observed at the fuselage attaching points. Exterior damage and fluid leakage from the right shock absorber was observed with the helicopter's landing gear shock absorbing system. The tailboom was observed partially separated from the fuselage aft of the attach points and held by the tailboom skin, electric wiring, and flight control cables. The tail rotor drive shaft was separated at the forward flex coupling which exhibited splaying and torsional damage. Flailing damage on the tail rotor pitch change rod near the coupling was also observed. Two of the three star arms were fractured near midpoint, perpendicular to the main rotor blades. Marks were observed on the lower flange of the rotor hub assembly. Once the damaged components were disconnected, full travel and proper resistance of the collective and cyclic controls were confirmed. No abnormalities were noted with the collective locking system. The fuel flow control lever was observed in the off position. The fuel flow control lever was moved throughout its full travel range and resulted in the appropriate movement of the pointer on the fuel control of the engine. The fuel flow control lever spring for the track detent cutouts was properly adjusted. The fuel shutoff lever was not activated; it was observed in the forward position and lock wired. The engine was removed from the helicopter and examined at the Turbromeca USA facility. Eurocopter, FAA, and National Transportation Safety Board representatives were present for the examination and engine run. The engine was examined with a borescope. The oil strainers, oil filter, fuel filter, and magnetic plugs were checked and found free of debris before the test cell run. No discrepancies were observed during the engine test cell run. The constant delta pressure unit of the fuel control was removed and examined. No anomalies were noted with the delta pressure diaphragm. Excerpt from Eurocopter's Operation Principle of Engine Controls (14.4.2) mentions that when the fuel control lever is moved beyond the "Flight" detent, the emergency valve progressively opens to supply the engine. The fuel then flows directly and is adjusted by the function of the collective pitch by the pilot." This is a means of fuel control in the event the governing system fails.
The pilot's failure to maintain aircraft control during engine start. Contributing to the accident was the pilot's improper advancement of the fuel control lever.
Source: NTSB Aviation Accident Database
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