Helicopter Emergency Floatation Systems (EFS)
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Emergency Floatation Systems (EFS) are designed to minimise the chances that a helicopter which is involved in either a controlled ditching or a water impact sinks or capsizes as a result.
The fitting of an EFS based on floats is well established but the problem of instability on anything but a calm water surface has always been problematic. This is because of the relatively high centre of gravity of helicopters due to the location of the rotors, the transmission and the engines.
The floats which provide EFS buoyancy are either packed within spaces inside the airframe or fitted as externally mounted packs on the lower structure. Inflation is provided by gas stored in pressurised cylinders which are carried on board. The need for rapid inflation is met by the inclusion of helium in the gas but it is usually blended with other gas(es)
The type-certification of helicopters to withstand the undesirable consequences of a ditching does not necessarily prevent such consequences. The system fitted is often damaged by the impact and rendered wholly or partially ineffective. A significant concern has been raised in that although the EFS is normally the subject of an AFM Supplement, there is not normally any reference to it in the Limitations section, yet part of its operational efficacy involves the prevailing sea conditions which will have a material effect on the likelihood of capsize.
In their 2014 Offshore Helicopter Safety Review, the UK CAA were of the view that:
“Following the standard aviation system safety analysis methodology, in view of the historic ditching rate (3.4 per million flight hours) and the likely consequences of post-ditching capsize (‘hazardous’), in order to minimise the probability of post ditching capsize, operations should be prohibited when the sea conditions at the offshore location that the helicopter is operating to/from exceed its certificated ditching performance.”
The same source was equally concerned that:
“Owing to deficiencies in the way in which compliance with the ditching requirements is presently demonstrated, it is possible that the ditching performance of current helicopters in real sea conditions will be less than that claimed.”
Ways of improving the crash-worthiness of the basic float system have also been considered and, although not necessarily a current policy or regulatory requirement everywhere, it is considered by many that an EFS should be manually armed for all overwater arrivals and departures and where practicable activated automatically in all water impacts even when not armed. Such an Automatic Float Deployment System (ADFS) adds additional functionality to an EFS and was the subject of one of the 27 Safety Recommendations made as a result of the UK AAIB Investigation into the inadvertent descent into the sea by an EC225L2.
Another way of increasing the crash-worthiness of the EFS is the installation of additional floats to ensure that if the helicopter does not remain upright, perhaps because of float damage or sea conditions, it will lie on one side rather than capsize. European Aviation Safety Agency (EASA) commissioned an investigation of this in a Study on Helicopter Ditching and Crashworthiness in 2007. This sought to “determine what type of egress procedure could be performed when the helicopter is side-floating and to compare it to the egress of completely inverted cabin”. It involved the addition to the usual EBS floats at low level of additional ones along the top of cabin walls either alone or together with foam-filled cowling panels. Model testing in a water tank in conditions equivalent to sea state 5 showed that both the usual vertical position and the on-the-side position were viable for egress. The same study also found that the tendency for a floating helicopter to oscillate from side to side if insufficient buoyancy is provided can be resolved not only by increasing the amount of buoyancy but alternatively by having buoyancy in the cowling panels i.e. at the maximum lateral displacement from the centre of gravity.
- Ditching: Rotary Wing Aircraft
- Sea State
- Emergency Breathing Systems (EBS) for Offshore Helicopter Occupants
- EASA Study on Helicopter Ditching and Crashworthiness, 2007
- CAP 1145: Civil Aviation Authority – Safety review of offshore public transport helicopter operations in support of the exploitation of oil and gas, February 2014
- Analysis of Offshore Helicopter Reportable Accidents 1976 - 2012 an internal UK CAA review of all UK offshore public transport helicopter reportable accidents during the period 1976 to 2012
- Human Performance in Immersion Suits, by J Power, A Simões Ré, National Research Council of Canada – Institute for Ocean Technology, May 2010
- TP13822E - Survival in Cold Waters: Staying Alive, C. Brooks, TSB Canada, January 2003
- Life Rafts and Lifeboats: An Overview of Progress to Date, Chapter 9A of NATO RTO-AG-HFM-152 ‘Survival at Sea for Mariners, Aviators and Search and Rescue Personnel’, by C. Brooks, February 2008