Helicopter's good safety record

The Sikorsky S76 has an airspeed of 269 km/hr, a range of 889 km and a passenger capacity of 12.

The Queen has been using a Sikorsky S76 to attend some royal engagements since 1998.

According to its manufacturers it "flies like nothing else in its class".

Experts say it is far too early to say what was to blame for Tuesday night's crash, although with excellent weather conditions speculation is centred on pilot error or mechanical failure.

Aviation writer Jim Ferguson told BBC News the S76 had an impressive safety record.

There had only been two accidents involving Sikorskys, of which one was down to pilot error, in recent years.

Emergency landing

In a separate incident on Monday in Dorset, another Sikorsky helicopter was written off after its engine caught fire in the middle of a rescue.

The pilot of the coastguard helicopter - a Sikorsky S61N model - had to make an emergency landing.

A spokesman for Bristow helicopters, which leases the specially-equipped helicopters, said then that the helicopter "has an excellent safety record".

"It's a hugely reliable aircraft which is why they are used for search and rescue operations and they are regularly overhauled and maintained," he said.

Sikorsky say the S76, with advanced features including dual digital autopilot, is ideal for "corporate, offshore oil, hospital, airline and government operators around the world".

Control features

The helicopter has the style and feel of a corporate jet and manufacturer Sikorsky Aircraft Corporation, based in Connecticut, claims it can be flown in almost any weather.

It has a light, strong, corrosion-resistant airframe and is designed to minimise maintenance and increase fuel efficiency.

The model involved in the latest crash was owned and operated by Bristow Helicopters.

The firm - which specialises in North Sea transportation but also provides search and rescue and military training facilities - says it would have been fully fitted with safety equipment.

This includes flotation bags which hold the helicopter afloat long enough for people to get out, depending on conditions.

And the passengers would have all been wearing immersion suits provided by their employers.

In its fleet of more than 120 aircraft, Bristow has seven S76 helicopters of which four operate out of Norwich making roughly 10 journeys a day.