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Figure 2: Super Puma door fitted with two escape windows
Figure 3:
Type IV emergency exit and escape window in a Super Puma
4.5 USE OF EXITS IN WATER IMPACT ACCIDENTS
Evidence from helicopter accident reports has shown that in about 60 of all water impact accidents, the helicopter either capsizes or sinks Rice and Greear, 1973; Brooks, 1989;
Clifford, 1996. In some cases, capsize is immediate, requiring passengers and crew to escape underwater. In other cases capsize is delayed and occupants may have time to
carry out a controlled surface evacuation of the helicopter. Likelihood of capsize is increased by rough sea conditions very likely in Sea State 6 or above and by high impact
speeds. Many studies have shown that capsize is associated with a high incidence of drowning,
with victims unable to hold their breath for a period sufficient to make an escape. An investigation of survivable world civil water impact incidents Clifford, 1996 provided
evidence of a 1 fatality rate in occupants involved in controlled ditching incidents, all of
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which were attributed to drowning. Fatality rates of 26, 57 and 80 were recorded in vertical descent with limited control, fly-in and uncontrolled impact incidents respectively,
where cause of death was known see Coleshaw, 2003. Cause of death was attributed to drowning in 34, 42 and 14 of these deaths; the highest proportion due to
drowning was thus seen in fly-in incidents. Without the aid of an emergency breathing system EBS the breath-hold time of
individuals must exceed escape time if passengers are to have a good prospect of survival Miles, 2000, particularly in cold sea areas such as the North Sea. Miles
commented every study of underwater escape times from inverted helicopters gives times which are longer than every study of breath hold times [in cold water]. Whilst use
of EBS, where provided, should help to increase the time available for escape, passengers must still locate their nearest exit, operate the exit mechanism and make an
escape through the exit. Not all seats will be next to an exit making escape more difficult. Those who have to swim or pull themselves to an exit from a remote seat may have
difficulty operating the exit due to a lack of hand-holds and difficulty applying pressure to the exit, floating away from it.
In the best-case ditching scenario, the crew may have automatically jettisoned the main exit. This will depend on whether the crew have had sufficient time to carry out this action
after undertaking a controlled landing on water. In a ditching incident in the North Sea in 1988 AAIB, 1990 the crew did not activate the automatic unlatching control of the rear
emergency exit and passengers had difficulty operating this exit in smoke. It has been demonstrated that the cabin door of a Super Puma is very unlikely to jettison if
the helicopter has inverted or is other than upright Bailey, 1990. The emergency release system relies on gravity to release a portion of the sliding door track. In the RHOSS
report, it was stated it is difficult to envisage circumstances in which it would be practicable to use the main exit when the fuselage is not upright. In the event of a
capsize it is therefore likely that passengers will have to operate either a Type III or IV emergency exit window or a push-out escape window.
In the event of capsize, exit operation becomes much more difficult for a number of reasons. Disorientation means that a passenger is likely to reach in the wrong direction
for an exit mechanism, whilst it can also cause errors in a persons perception of the vertical. In the 1988 accident reported earlier AAIB, 1990 the helicopter capsized shortly
after ditching. Both crew had problems reaching the jettison handle for their emergency exit. One of the passengers reported difficulty gripping the rip-tag attached to the beading
sealing the push-out window and had to remove his glove to complete the action. A second passenger broke a bone in his hand whilst attempting to push out a window. It
can be questioned whether this was due to the force needed to remove the window or because the individual did not know how much pressure would be required and applied
maximum force in the stress of the situation. The location and ease of access to exits has also been of concern to the industry.
Following the Cormorant Alpha accident in 1992 the seating layout of a number of aircraft operating in the North Sea sector, including the Super Puma, was improved to give easy
access for each passenger to one clearly defined exit CAA, 1995. This may not be the case in other types of helicopter. Problems will always be greater for those individuals
seated in an aisle or middle back seat. Someone seated next to the exit may block the escape route. Many studies have shown that cross-cabin escapes take longer than
escape from a seat next to an exit. Both disorientation and locating the exit were found to be very difficult by over 50 of subjects undertaking a cross-cabin escape following
inversion of the HUET Jamieson, Armstrong Coleshaw, 2001. The operation of exits
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by individuals who must cross the cabin from these seats is also likely to be more problematic as they must release their harness before reaching the exit, making location
and operation of the exit more difficult. Whilst smoke has been shown to be a problem for surface evacuation, poor visibility is
also a problem in underwater escape. Darkness is the obvious cause, with measures taken to light emergency exits. Regulations do not currently require escape windows to
be illuminated. Poor visibility was a problem in an incident off the West coast of Scotland, when a curtain of bubbles illuminated by emergency lights obscured the exit mechanism
meaning that a crew member could not locate the exit AAIB, 1989.
4.6 CONCLUSIONS
