Schweizer 269C N3947C accident near Fort Lauderdale, Florida

Probable cause

The partial loss of engine power during the initial climb due to a stuck intake valve on the No. 4 cylinder.

NTSB analysis

The helicopter was departing from a rooftop helipad, and the flight instructor noticed that, during the initial climb, as the helicopter crossed over the rooftop edge, the low rotor rpm horn and light activated. The helicopter then began to descend. The flight instructor lowered the collective and attempted twice to increase the throttle, but his actions did not stop the descent. Subsequently, he performed an autorotation to a street below the helipad and landed hard, resulting in substantial damage to the tail rotor and tailboom.

During a postaccident examination and test run of the engine, the engine produced idle power, but the No. 4 cylinder's compression checks were not normal. The No. 4 cylinder intake and exhaust valves were examined, and both displayed a significant amount of carbon deposit buildup on the valve stem. The intake valve was found stuck in its valve guide and was scratched and scarred. The source of the scarring to the intake valve was not determined. Given the signatures observed on the No. 4 cylinder intake valve, it is likely that, during the initial climb, the intake valve became stuck, which resulted in a partial loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA18LA068 for the full record.