Robinson Helicopter Company R44 II N755KT accident near Fort Morgan, Alabama

Probable cause

A partial loss of engine power for reasons that could not be determined because postaccident engine examinations did not reveal any evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation.

NTSB analysis

The commercial pilot was delivering the helicopter to a factory service center for troubleshooting of an engine-idle discrepancy that maintenance personnel could not resolve following a recent engine crankshaft overhaul and reinstallation. The pilot reported that the engine idled smoothly at engine start and that it initially accelerated smoothly and ran continuously without interruption. However, while the helicopter was at 100 knots and in cruise flight at 400 ft above a beach, the pilot felt "violent shaking," which he initially thought was turbulence. He then added aft cyclic, lowered the collective, scanned the instruments, and the shaking stopped. He then noted zero oil pressure, and the oil pressure light illuminated. The rotor rpm began decaying, so he entered an autorotation. Because people were on the beach, he selected an unoccupied area in the water for a forced landing, during which the tailboom separated.

Examination of the engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded the normal operation. Although the electrically operated auxiliary fuel pump was not functional during a postaccident test, the engine-driven mechanical fuel pump operated normally. Given that the mechanical fuel pump can sustain engine operation if the auxiliary fuel pump is inoperative, it is unlikely that a preaccident failure of the auxiliary fuel pump resulted in the partial loss of engine power. The reason for the loss of engine power could not be determined.

Text from the NTSB. Open the NTSB docket for ERA18LA161 for the full record.