Methane discharges from offshore oil platforms are routine, and potentially lethal to helicopter crew and passengers. The NTSB issued safety recommendations Aug. 26 citing two accidents involving turbine helicopters that crashed after a partial or complete power loss in the vicinity of a significant methane discharge.
High concentrations of methane can cause turbine engine failures including flameout, compressor stall, or engine surging that lead to partial or complete power loss during takeoff or landing.
The safety agency noted that methane vent pipes are often located near oil platform helipads, and urged the U.S. Department of Interior Bureau of Safety and Environmental Enforcement and U.S. Coast Guard to take action beyond the warnings already issued to operators following accidents in 2011 and 2013 that resulted in injuries.
In the 2011 incident, the pilot of a Bell 206-L3 executed an autorotation and deployed the float system after a partial power loss on takeoff from an oil platform in the Gulf of Mexico. The helicopter rolled inverted in the water, and the pilot and two passengers suffered minor injuries. In 2013, a complete engine failure in a Bell 407 sent the pilot and two passengers into the Gulf. They also suffered minor injuries, and those involved in both incidents told investigators a loud bang preceded the power loss. The NTSB investigation of the 2013 incident remains incomplete, though the agency has confirmed a flameout occurred. The pilot told investigators that he lifted off into a stationary hover and made a left pedal turn to avoid a boom that was venting methane, unbeknownst to the pilot at a rate much higher than usual.
The NTSB contends that oil platform operators should be required to install visual indicators including windsocks and rotating beacons on or near discharge vents so pilots can see which way the gas is likely to be drifting, and see when large quantities of the invisible, odorless gas are being released from vents.