Bell 407 N53LP accident near Ship Shoal 208H, GM

Probable cause

The ingestion of vented methane gas into the helicopter’s engine during takeoff, which caused an engine compressor surge that led to a total loss of engine power.

NTSB analysis

The helicopter departed from an offshore oil platform with the pilot and two passengers onboard. The pilot reported that he heard a loud "bang" just after the turboshaft-powered helicopter lifted off. The low rotor rpm horn sounded, and the pilot subsequently maneuvered the helicopter for a forced water landing and deployed the float system. The helicopter sustained substantial damage when its main rotor blades impacted the water, which resulted in the engine and transmission separating from the helicopter. The three occupants were subsequently rescued from the helicopter by boat. The platform was venting methane gas on the day of the accident; the pilot was not informed about the vented gas.

Examination of the helicopter's engine revealed no preaccident mechanical malfunctions or failures that would have precluded normal operation. A review of data from the helicopter's engine monitoring system (EMS) revealed that, just after liftoff, the engine accelerated at an excessive rate while the full-authority digital electronic engine control system reduced the metered fuel to the engine. The data also revealed that an engine surge occurred followed by an engine flameout. The pilot's report that he heard a bang during takeoff and the EMS data are consistent with the engine experiencing a compressor surge due to the ingestion of vented methane gas.

Text from the NTSB. Open the NTSB docket for CEN13FA491 for the full record.