Helicopter Emergency Floatation Systems (EFS)

Definition

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.

Description

Emergency Floatation Systems (EFS)

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)

Discussion

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. 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.

Accidents and Incidents

  • AS50, manoeuvring, East River New York USA, 2018 (On 11 March 2018, an Airbus AS350 engine failed during a commercial sightseeing flight and autorotation was initiated. The pilot then noticed that the floor-mounted fuel cut-off had been operated by part of the tether system of one of the five passengers but there was insufficient time to restore power. On water contact, the automatic floatation system operated asymmetrically and the helicopter submerged before the occupants could evacuate. Only the pilot was able to release his harness and escape because the unapproved adapted passenger harnesses had no quick release mechanism. The Investigation found systemic inadequacy of the operator’s safety management system.)
  • AS3B, vicinity Sumburgh Airport Shetland Islands UK, 2013 (On 23 August 2013, the crew of a Eurocopter AS332 L2 Super Puma helicopter making a non-precision approach to runway 09 at Sumburgh with the AP engaged in 3-axes mode descended below MDA without visual reference and after exposing the helicopter to vortex ring conditions were unable to prevent a sudden onset high rate of descent followed by sea surface impact and rapid inversion of the floating helicopter. Four of the 18 occupants died and three were seriously injured. The Investigation found no evidence of contributory technical failure and attributed the accident to inappropriate flight path control by the crew.)
  • A139, vicinity Sky Shuttle Heliport Hong Kong China, 2010 (On 3 July 2010, an AW139 helicopter was climbing through 350 feet over Victoria Harbour Hong Kong just after takeoff when the tail rotor detached. A transition to autorotation was accomplished and a controlled ditching followed. All occupants were rescued but some sustained minor injuries. The failure was attributed entirely to manufacturing defects but no corrective manufacturer or regulatory action was taken until two similar accidents had occurred in Qatar (non-fatal) and Brazil (fatal) the following year and two interim Safety Recommendations were issued from this Investigation after which a comprehensive review of the manufacturing process led to numerous changes.)
  • S92, en-route, east of St John’s Newfoundland Canada, 2009 (On 12 March 2009, a Sikorsky S-92A crew heading offshore from St. John's, Newfoundland declared an emergency and began a return after total loss of main gear box oil pressure but lost control during an attempted ditching. The Investigation found that all oil had been lost after two main gear box securing bolts had sheared. It was noted that ambiguity had contributed to crew misdiagnosis the cause and that the ditching had been mishandled. Sea States beyond the capability of Emergency Flotation Systems and the limited usefulness of personal Supplemental Breathing Systems in cold water were identified as Safety Issues.)

Related Articles

Further Reading

Category: 

SKYbrary Partners:

Safety knowledge contributed by: