Eighteen people have been rescued after a Eurocopter Super Puma helicopter ditched into the sea about 125 miles east of Aberdeen on its way to a BP oil production platform.
How the crash happened
1. Super Puma EC-225 helicopter en route to Etap oilfield 125 miles north east of Aberdeen carrying 16 passengers and 2 crew. Weather conditions: fog, light winds. 2. Aircraft ditches in the sea approximately 500 metres from oil platform at approx. 1915 GMT. Workers on the platform raise the alarm 3. Flotation bags carried in helicopter's wheel bays deploy automatically. Helicopter's tail boom is later discovered to have broken away from the fuselage 4. Passengers and crew scramble into three life rafts, which they tie together, and fire distress flares. GPS signals from locator beacons worn by all on board picked up by satellite 5. Three survivors picked up by helicopter, others by fast rescue craft. RAF Nimrod aircraft co-ordinates operation to prevent helicopters colliding in poor visibility.
The helicopter ditched in the sea approximately 500 metres from the platform at about 1915 GMT on Wednesday night. Workers on the platform saw the aircraft hit the water and immediately raised the alarm.
Flotation bags carried in helicopter's wheel bays deployed automatically. The helicopter's tail boom was later discovered to have broken away from the fuselage, though investigators say it is too early to know whether this happened before or after it hit the sea.
Passengers and crew scrambled into three life rafts, which were tied together. GPS signals from locator beacons worn by all on board were picked up by satellite
Three survivors were picked up by helicopter, others by fast rescue craft. An RAF Nimrod aircraft co-ordinated the operation to prevent helicopters colliding in poor visibility.
Super Puma helicopters are used by more than 37 military forces around the world and about 1,000 civil operators.
In the North Sea, they commonly transport offshore workers to and from oil platforms and carry out search and rescue missions.
The Super Puma was first commissioned in the late 1970s but the aircraft involved in Wednesday's incident was part of a new generation of the fleet.
The five-bladed EC225 was one of three delivered last year to Aberdeen-based Bond Offshore Helicopters, which provides air transport for energy installations in the North Sea.
They can transport up to 24 passengers and three crew, but are usually limited to a maximum of 19 passengers on North Sea operations.
According to the aircraft's French manufacturer Eurocopter, the new EC225 has a "crashworthy design" with a reinforced central structure, a full de-icing system and low vibration rotor blades.
Its flotation system is certified to stay upright in sea swells of up to 18.4ft (5.5m).
All oil workers must complete a survival course before they are allowed to go offshore that includes underwater escape training from a helicopter simulator.
Helicopter pilots are also trained in similar areas and are well qualified.
Paul Cook, a serving North Sea helicopter pilot, told the BBC flight refresher courses take place every six months.
He said: "They undergo skills tests which involves flying, instruments and dealing with emergencies.
SUPER PUMA EC225
Five-bladed helicopter used by more than 1,000 civil operators and 37 militaries around the world
Virtually all of us go once a year to a simulator where we can practice the more dramatic events as was last night," he added.
"On my last simulator visit I did, in fact, practice ditching in adverse conditions."
Mr Cook said the key to survival is landing upright. This gives the passengers and crew a "much better chance of getting out".
Mr Cook said the crash showed that the safety equipment on board the Super Puma "worked as published".
After the crash, the 18 men climbed onto two life rafts, which are equipped with locator beacons.
Satellites detected the location of the life rafts, which were tethered together, allowing rescuers to pinpoint exactly where they were.
Those on board the Super Puma would also have been wearing immersion suits and lifejackets. GPS signals sent from immersion suits worn by all on board were picked up by satellite.
Mike Buckley, another EC225 pilot, said there have been "dramatic advances" in safety in North Sea operations since the 1960s.
"During the first years of offshore flying, passengers wore their normal street clothes when on board," he said.
"The pilots did the same. No lifejackets were worn and virtually all the helicopters were single engined, and flown single pilot. Many didn't have flotation equipment fitted."
He said the safety advances have been forced on the oil industry by pressure from pilots union BALPA and the offshore unions.
Chris Buckler trains with a helicopter rescue crew
"Last night's incident and subsequent rescue operation vindicates all that union pressure," he added.
The Super Puma has been involved in other crashes.
Eleven men died in 1992 when a Super Puma taking oil workers from a Shell platform to a nearby accommodation rig crashed into the sea after take-off 100 miles north-east of Shetland.
In 1995, a Super Puma taking workers to an oil platform crashed in the North Sea 140 miles north east of Aberdeen. All 18 people on board were rescued but the aircraft was lost.
The following year, a Super Puma carrying four crew and 13 oil platform workers developed engine trouble and ditched in the North Sea about 25km (15 miles) from the port of Den Helder, north of Amsterdam.
All 17 people on board were pulled safely from the water.
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