Hughes 369A N805LA accident near Unknown, PO

Probable cause

The pilot's failure to detect the presence of water in the helicopter fuel system before the flight, which resulted in a total loss of engine power during cruise. Contributing to the accident was the pilot's delayed recognition of the power loss and late initiation of an autorotation, which resulted in a hard landing on the ocean.

NTSB analysis

The commercial pilot and the nonpilot-rated passenger/spotter were conducting an aerial fish-spotting mission in the turbine-powered helicopter, which was operating from a fishing boat in the south Pacific Ocean. According to the accident report filed by a representative of the parent company of the operator, about 30 minutes into the flight, at an altitude of about 1,000 ft above the ocean, the pilot noticed the GEN OUT annunciator light, indicating a generator problem. The pilot began the procedures to address the generator problem, which in part entails placing the generator switch in the OFF position, but then noticed that the helicopter was in an uncommanded descent, and that the main rotor rpm was below its normal cruise value. The pilot initiated an autorotation, but the float-equipped helicopter subsequently struck the water hard, and the main rotor blades severed the tail boom. The pilot was seriously injured, and the passenger/spotter was reported to have received minor injuries.

The helicopter was recovered, and then examined by investigators about 3 weeks after the accident. No preimpact mechanical deficiencies of the airframe or engine that would have precluded continued flight were observed. The fuel system exhibited multiple signs of fuel contamination, primarily by water. The fuel in the engine fuel pump and in the line to the fuel spray nozzle was contaminated by water to a level that would not support engine operation.

The fuel system design was such that the water in the pump and the fuel line could not have been introduced during or after the impact sequence, indicating that it was likely present in the fuel system before departure. The fishing boat's helicopter fuel storage and dispensing system was not available for examination, and therefore the investigation was unable to determine the source of the water contamination of the fuel.

Because the pilot was not able to be interviewed for the investigation, his procedures regarding fuel contamination prevention and detection could not be determined. Regardless, the pilot's failure to detect the presence of water in the fuel system prior to flight was the proximate cause for the engine power loss.

Although engine power loss in this model helicopter is typically signaled by multiple instrument, visual, tactile, and audio cues, the pilot did not detect the power loss until the helicopter was in an uncommanded descent. There was some evidence that the helicopter was equipped with an engine failure alerting system. The investigation was unable to determine whether the engine failure alerting system was installed and functioned properly, and if so, why the pilot failed to notice and respond to the alert in a timely manner. Because the engine failure alerting system is inoperative when the generator switch is in the OFF position, it is possible that, if the helicopter was equipped with a functional engine failure alerting system, the engine power loss occurred when the pilot was conducting the 'GENERATOR MALFUNCTION' procedures, and the engine power loss alerting system was thereby disabled. The investigation was unable to determine whether the generator problem occurred prior to the engine power loss, or the engine power loss precipitated the GEN OUT annunciation. The pilot's late detection of the engine power loss, and his consequent loss of altitude and delayed initiation of the autorotation, reduced the likelihood of a successful touchdown.

Text from the NTSB. Open the NTSB docket for WPR17LA075 for the full record.