Hughes 369 N8648F accident near Majuro

Probable cause

The pilot's failure to maintain clearance above the surface of the ocean.

NTSB analysis

The pilot was employed by a US company that leased the helicopter and the pilot's services to a Taiwanese fishing ship. The pilot and the turbine-powered, float-equipped helicopter were stationed on the ship, and a Taiwanese observer provided fish-spotting services. No helicopter maintenance personnel were stationed on the ship.

Most of the brief flight was captured by a shipboard surveillance camera. The camera faced forward, with a field of view that included the helicopter on the landing platform, as well as the ocean surface forward of and on both sides of the ship. The ocean surface appeared glassy, with only slight swells and no waves. According to the Federal Aviation Administration, the visual aspects of glassy water make it difficult to judge an aircraft's height above the water, and the smooth, reflecting surface can lead to confusion.

The helicopter lifted off and immediately entered a right descending turn, flying out of view on the right side of the image. Several seconds later, the helicopter re-entered the field of view via the upper right image frame. The helicopter was traveling nearly horizontal from right to left at an altitude that was sufficiently low for visible ripples to form on the water surface behind the helicopter. The helicopter struck the water, overturned, and remained afloat inverted. Skiff boats responded to the accident location within minutes, and both helicopter occupants, who were still strapped into their seats, were recovered but unable to be resuscitated

Most of the helicopter, absent the tail boom and several main rotor blades, was recovered from the water, transported to shore, and examined two months later.

Subsequent recovery and examination of the helicopter revealed no evidence of any mechanical anomalies that would have prevented continued flight above the water surface. Main rotor blade damage signatures indicated that the engine was providing significant power at the time of water impact.

Two days before the accident, the helicopter, which had been parked outside on the ship's landing platform, was exposed to a significant storm. Afterward, the pilot initially had some difficulty starting the engine because it had too much water in it. These difficulties, which included the expulsion of oil and smoke from the engine during the start attempts were resolved, and the pilot conducted a subsequent flight (before the accident flight) that lasted 1.5 hours. The oil and smoke were likely the result of a stuck check valve in the engine oil system, which would not have affected engine operation.

The pilot's toxicology results indicated the presence of a sedating antihistamine that can reduce reaction time. The pilot's impairment, if any, from this medication could not be determined given the detected level of medication. However, it is possible that the medication affected the pilot's reaction time, which was especially critical given that the glassy, nearly featureless ocean surface could have hampered the pilot's ability to visually determine the helicopter's height above the water surface. This ocean surface condition, either alone or along with a decreased reaction time, could have compromised the pilot's ability to recognize and correct the helicopter's descent toward the water.

Text from the NTSB. Open the NTSB docket for WPR18FA188 for the full record.