NTSB Identification: ERA12LA346
14 CFR Part 91: General Aviation
Accident occurred Saturday, May 19, 2012 in Destin, FL
Probable Cause Approval Date: 05/09/2013
Aircraft: ROBINSON HELICOPTER R44, registration: N444WT
Injuries: 3 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The helicopter reached about 200 feet above ground level in the initial climb when the pilot noticed that the engine needle in the dual tachometer (engine/main rotor rpm) had "spiked" and then remained "at the top of the gauge." The pilot turned the helicopter around to return to the airport, and, during the turn, the low rotor rpm warning alarm sounded. The pilot responded by lowering the collective control and increasing throttle but then determined that an airport landing could not be completed because the helicopter had already lost altitude. The pilot selected a forced landing area in a sand pit and responded to another low rotor rpm alarm by again lowering the collective. She attempted to cushion the landing with the available rotor rpm, but the helicopter landed hard, and the main rotor blades severed the tailboom. Examination of the helicopter revealed that the engine had a stuck (open) number 5 exhaust valve caused by buildup of oil carbon deposits. This is an issue with the Robinson Helicopters if the engine is not cooled down properly after flight. Air tour operations seem to be prone to carbon buildup mainly due to quick multiple shutdowns. The operator has established a postflight cool down procedure to prevent further problems. On January 19, 1988, Textron Lycoming published Service Letter No. L197A, Recommendations to Avoid Valve Sticking. The guidance offered included, "Rapid engine cool down from low power altitude changes, low power landing approach and/or engine shutdown too soon after landing or ground runs should be avoided."
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The partial loss of engine power due to a stuck (open) exhaust valve in the No. 5 cylinder. Contributing to the accident was the operator’s failure to follow the engine manufacturer’s directives concerning cooling of the engine after flight. Full narrative available
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