In 1983, a British Airways Sikorsky on its way from Penzance to the Isles of Scilly fell into 200ft-deep water, killing 20 people. Crash investigators were unable to pinpoint the cause.
Despite the dangers if something goes wrong and repeated attempts by the IRA to down them, helicopters, especially Chinooks, are the favoured form of transport for the Army in Northern Ireland.
A former senior Army commander in Northern Ireland once said: 'If the IRA ever took one of those out and killed everybody on board, then the Government would have internment in by the morning.'
The pilots must fly low and fast across the countryside to avoid coming into the terrorists' sight and range.
Once on a flight to Enniskillen with Margaret Thatcher and her private secretary, Charles Powell, the then Downing Street press secretary, Bernard Ingham, was moved to say: 'It's the first time I've flown underground.'
Mr Powell, who sat beside Mrs Thatcher and close to a soldier in charge of a heavy machine gun, said as their Wessex skimmed the tree- tops above the Clogher Valley: 'Even the cows ducked.'
Britain's worst helicopter crash involved a Boeing Chinook. On 6 November 1986, one operated by the late Robert Maxwell's British International Helicopters, with 44 Shell oil workers on board, plunged 500ft into the North Sea.
As with last night's crash, there was a loud bang before the helicopter, which was coming into land in the Shetlands, dropped like a stone. It broke up on impact and sank, killing all but one of the passengers. The captain survived.
The official report into the tragedy, published in 1989, criticised the aviation industry, Boeing and the Civil Aviation Authority.
Tests on the helicopter's modified gear system were found to be inadequate for detecting wear and tear caused by the change. The tests had been approved by the CAA and the Federal Aviation Administration, its American counterpart.
The Department of Transport report found that the gears had failed totally, causing the twin rotors to clash. The crash prompted the setting up of a pounds 1.5m fund to assist operators in spotting potential faults. However, because of the helicopter's normal vibrations, engineers found that precise measurements proved impossible.
Further research led to the development of a detailed flight recorder, called Health Usage and Monitoring Systems (HUMS). This is gradually being installed in most helicopters.
In May 1984, following engine trouble, a Chinook ditched into the sea near the Cormorant Alpha North Sea oil platform. On that occasion, all 44 workers and three crew were rescued safely.
Designed to carry 50 passengers, the Chinook has proved the most popular civilian and military workhorse since its introduction in 1961. Nearly 2,000 have been built.
The RAF's 30 models were purchased more than 13 years ago and are divided into three Chinook squadrons.
A year ago, half of them were out of service, pending their return from Boeing as part of a four-year 'complete refurbishment' programme.
That was instituted following a scare in 1989, when the squadrons were limited to essential work for about two weeks after two crashes in two days.
Five servicemen were injured when a Chinook crashed during take-off at RAF Odiham in Hampshire. The next day, two more men were injured at Mount Pleasant in the Falkland Islands.
Investigators found that the incidents were caused by identical faults in the Chinooks' rear gearbox.
The RAF said the rear gearboxes on the other 30 Chinooks had been closely checked and found to be in good order.
But following complaints from crews in Iraq that their machines had been damaged by sand, it was announced that all the RAF's machines would go to Boeing for the refurbishment, which is believed to be costing more than pounds 100m.
The Chinook that crashed last night was, according to a spokesman for Boeing, an HC Mk2, believed to be one of those that had been refurbished.
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