NTSB Recommendations on Offshore Methane Gas Venting
The US National Transportation Safety Board (NTSB) have issued a series of recommendations following two accidents were single engined offshore helicopters ditched after the suspected ingestion of vented methane gas caused a full or partial engine power loss near an offshore platform.
Vented combustible gas can cause surging, a compressor stall, or flameout of a helicopter engine. The NTSB quote the UK Civil Aviation Authority (CAA), who state in Chapter 2.3.5 of CAP437 that concentrations above 10% lower flammable limit (LFL) pose a risk. LFL is the lower end of the concentration range over which a flammable mixture of gas or vapour in air can ignite at a given temperature and pressure.
While some safety alerts had been issued in 2011, the NTSB is acting because the second accident occurred after these measures. The NTSB:
…believes this occurrence highlights the need for the identification and development of comprehensive systems and procedures for oil platform operators to mitigate the risk of vented gas ingestion.
The majority of offshore installations in the Gulf of Mexico tend to be small and serviced by small single engined helicopters that are particularly vulnerable to a power loss on take off.
Accidents
24 March 2011 Bell 206-L3 N32041, operated by PHI (ASN Database Entry / NTSB Database Entry)
13 August 2013 Bell 407 helicopter N53LP, operated by Panther Helicopters (ASN Database Entry / NTSB Database Entry)
Wreckage of Panther Bell 407 N53LP (Credit: FAA via NTSB)
Both types are powered by a Rolls-Royce 250 turboshaft engine.
The six people on the two helicopters all received minor injuries.
Recommendations
To the US Department of the Interior, Bureau of Safety and Environmental Enforcement (BSEE):
In collaboration with the US Coast Guard, identify and develop comprehensive systems and procedures to mitigate the risk of ingestion of raw gas discharges, such as methane, by helicopters operating in the vicinity of offshore oil platforms. (A-14-67)
After appropriate mitigations are developed as recommended in Safety Recommendation A-14-67, require fixed offshore oil platform operators to implement these systems and procedures. (A-14-68)
To the US Coast Guard (USCG):
Work with the US Department of the Interior, Bureau of Safety and Environmental Enforcement to identify and develop comprehensive systems and procedures to mitigate the risk of ingestion of raw gas discharges, such as methane, by helicopters operating in the vicinity of offshore oil platforms. (A-14-69)
After appropriate mitigations are developed as recommended in Safety Recommendation A-14-69, require mobile offshore oil platform operators to implement these systems and procedures. (A-14-70)
To the American Petroleum Institute (API):
Finalize revisions to API Recommended Practice 2L, Recommended Practice for Planning, Designing, and Constructing Heliports for Fixed Offshore Platforms, to address the venting of raw gases, such as methane, as a risk to turbine-powered helicopters operating in the vicinity of fixed offshore oil platforms. (A-14-71)
Interestingly, no recommendations are directed at the Federal Aviation Administration (FAA).
The Bureau of Safety and Environmental Enforcement (BSEE) issued Safety Alert No. 311 in 1 April 2014.
UPDATE 24 September 2014: The BSEE issued an Advance Notice Of Proposed Rulemaking on Helideck and Aviation Fuel Safety for Fixed Offshore Facilities. BSEE cite studies by both the Helicopter Safety Advisory Conference (HSAC) who publish Gulf of Mexico (GOM) focused helicopter safety data annually on their website, and a Centers for Disease Control and Prevention (CDC) study in 2013. Aerossurance expand on this and another helideck accident here.
UPDATE 8 September 2015: The NTSB have issued the probable cause of the Panther N53LP B407 accident.
UPDATE 23 October 2015: BSEE gave a presentation to the HSAC on methane venting risks to helicopters. The supporting report (prepared under their Aviation Safety Support Services contract) is here.
UPDATE 17 May 2020: Disappointingly all five NTSB recommendations remain Open with no new progress reported on any since 2015.
UPDATE 13 August 2021: All five NTSB recommendations are still Open.
Other Helideck Safety Resources
- Helideck Safety Alerts: Refuelling Hoses and Obstructions
- Mind the Handrail! – Walk-to-Work Helideck Hazard
- Passive Fire-Retarding Helideck Designs
- US BSEE Helideck A-NPR / Bell 430 Tail Strike
- Troublesome Tiedowns
- Helideck and Helicopter Egress Training Facilities
- Wrong Deck Landings
- FOD and an AS350B3 Accident Landing on a Yacht in Bergen
- UPDATE 16 April 2022: Helideck Heave Ho!
Aerossurance regularly assists oil and gas companies and vessel operators review and update their helideck procedures and adverse weather policies, examine helideck structural integrity issues and provide independent assurance of helideck readiness.
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