Wednesday, January 18, 2012
Helicopter Industry Struggles to Improve Ditching Survivability
Rotor & Wing coverage from the EASA helicopter ditching workshop in Cologne, Germany.
Most ditching events and water impacts would be survived if on the ground. Civil aviation authorities, helicopter makers and equipment manufacturers are struggling to improve the survivability of these accidents, as the number of fatalities due to drowning of conscious occupants is still unacceptable. Improving floatability is a major focus. Just as important, avoiding helicopter capsizing would save many lives.
Emergency breathers can help, but can be challenging to use. Underwater evacuation training helps, too, but only happens once every four years. At December’s European Aviation Safety Agency (EASA) helicopter ditching workshop in Cologne, Germany, about 65 attendees—a lot of them representing North Sea oil-and-gas offshore operators—heard how difficult it will be to make this safety picture somewhat rosier.
Let’s first define what they are dealing with. A ditching event is an emergency landing on water. It is performed so that it enables a “safe and orderly egress” of the occupants. A water impact is uncontrolled or partially controlled. An example is a Sikorsky S-76C+ accident in 2005 near Tallin, Estonia. All 14 passengers and crewmembers drowned (they inhaled water), although there was enough survivable volume after the impact. Statistics show that what is probably the most strictly run helicopter activity, offshore transportation, lags behind in terms of safety. Commercial airlines have 0.9 fatal accidents per million flight hours. Offshore helicopter transportation has 5.7 (2010 numbers).
Why focus on ditching and water impacts? According to a review of world civil water impacts, 98 survivable water impacts happened between 1971 and 1992. They caused 338 fatalities, including 192 caused by drowning. An underwater escape (from a flooded helicopter cabin) too often mismatches breath-hold time.
Shell Aircraft senior aviation advisor Alan Ward insisted his company has “a strong belief in using more modern aircraft.” Oil companies wanting to buy safer aircraft is one more incentive for the manufacturers to carry on with their efforts in this direction. First, they may want to have manufacturers better understand ditching dynamics. Russia-based Kazan Helicopter is thus endeavoring to properly model these forces. “This will help determine proper piloting,” said Dmitry Nedelko, chief of Kazan's calculation bureau.
Operators may want to have their helicopters floating longer. As John Franklin, an EASA safety analysis coordinator, noted, in 26 of 184 accidents (since 1970) that involved ditches, the helicopter sank much too early. This was immediately or during the evacuation.
Sometimes floats did not inflate. Sometimes they inflated, then deflated. So what about emergency floatation system (EFS) crashworthiness? “Statistics indicate improving floatation is the most important factor for better survivability,” noted Dave Howson, UK civil aviation authority (CAA) flight operations research manager. Indeed, the major drowning cause is the inability to escape an inverted helicopter.
Surprisingly, computation has shown that a 100-percent increase of EFS design strength translates into a modest crashworthiness improvement. A designer should think of a greater number of floats rather than stronger floats. In simulations, the helicopter stayed afloat in all impacts, providing it had two high-mounted floats—in addition to the usual four floats at the bottom of the airframe. The two upper floats bring redundancy and a side-floatation capability.
Other ways to save lives by improving floatation include, for example, automatic activation. This can be done with immersion switches. However, to automatically activate the EFS, it has to be armed at all times.
This has a cost. “You either have to demonstrate inadvertent deployment does not jeopardize the flight or certify a system, using speed or altitude switches for example, to prevent such inadvertent deployment,” Howson explained. As a result, the estimated cost per life saved would be about $380,000. This is considered highly cost effective. “Oil & Gas UK uses a figure around $7 million per life saved,” Howson reminded.
For the full story, see the February 2012 issue of Rotor & Wing. More: Helicopter Training News