Leaving aside the reason for the crash/ditching (which has been endlessly discussed over the last two years) there are three main elements which have to be considered when a helicopter comes into contact with the water:
- if the helicopter is performing other than a controlled manoeuvre; crashworthiness (seat stroking, maintenance of the integrity of the cabin, retention of the seats to their fixings, etc).
- the ability of the occupant to escape from the cabin.
- the ability to survive in open water after escaping from the cabin.
The objectives of 1. are facilitated by the certification standard that applies at the time of the granting of the type certificate (and applies equally to a crash on land as well as on water).
The objective of 2. is facilitated by a number of elements, most of which are satisfied when "certification with ditching provisions is requested". These provision include structural integrity, behaviour of the helicopter in a water landing and 'under reasonably probably water conditions (that) the flotation time and trim...will allow the occupants to leave the rotorcraft and enter the life rafts...'. Ditching approval is usually only required when specified by the Operational Regulations (as it is in ICAO Annex 6 Chapter 2.2.12 and JAR-OPS 3.843).
Point 3. is covered by other provisions (once again, in the Operational Regulations) which specify the carriage of life-rafts (and provisions to ensure that they are available and can be launched) the wearing of survival suits, constant wear life vests, the provision of pop-out windows and measures to ensure that the life-rafts are not punctured immediately after their launching. Operational rules also contain elements to ensure that the location of the helicopter is known during flight and also after ditching.
Some important issues spring to mind (discussed in the accident report): in AC 29-2C is contained the following clarifying text:
The FAA/AUTHORITY has determined that a sea state 4 is representative of reasonably probable water conditions to be encountered. Therefore, demonstration of compliance with the ditching requirements for at least sea state 4* water conditions is considered to satisfy the reasonably probable requirement.
* From AC 29-2C it is established that Sea State 4 (wind 17kts - 21kts and signification wave height of 4 to 8 ft).
As you will have seen from the statistics in the report, the Sea State in the Canadian East Coast, the North Sea (and most other open bodies of water North of 45N and South of 45S) is above SS4 for a significant proportion of the time in the winter. Almost a decade ago, there was an attempt to have the AC amended to take account of that fact - it was not successful. In the meantime, the oil companies, deciding that they could not rely upon the regulator to make changes to the guidance, through discussions with the manufacturers and by contractual arrangements, decided to press ahead in an attempt to meet Sea State 6.
Helicopters can survive upright in quite high sea states - if the waves are regular. As we all know, it is the breaking of the wave that dictates when capsize occurs. For that reason, nothing modelled/established in regular waves can be guaranteed. Because we know that it is likely that the helicopter - with its high centre of gravity - will capsize, the principle of 'side floating' was investigated. (Side floating is intended to ensure that after a capsize, one side of the cabin will remain above water.) It is not easy to retrofit but it can be done.
As has been seen from this accident (and as was established in the RHOSS Report in 1995), most passengers will survive an initial impact but will subsequently drown in the cabin. The reasons why are complex. 'Brooks' established in his Canadian trials that breath-hold capacity was insufficient to permit evacuation of the passengers through the emergency exits, following a capsize. We know that cold shock can reduce the breath-hold capacity to less than 10 seconds - even for very experienced personnel. It is for that reason that pop-out windows are provided with the proviso that every passenger should be only one removed from the emergency exit.
Even with this it may also be necessary to increase the size of the pop-out windows
and provide a method of increasing the breath-hold time to ensure it exceeds the escape time - by some margin.
Automatic float inflation and externally-launched life-rafts have been systematically fitted in the offshore fleet. It is real progress. However, during a crash, any portions of the emergency kit that is in the impact zone is likely to be damaged and cease to function. We have seen in modelling tests that critical elements of the emergency equipment can be lifted away from the likely impact zone - attention must be paid when considering such reasonably probable events.
Just some points with an impact upon offshore survivability.
Jim