The service operates from four bases across Scotland

The SAS Air Wing service has four fixed-wing aircraft based in Kirkwall (Orkney), Lerwick (Shetland), Glasgow and Aberdeen.

It also has two helicopters based in Glasgow and Inverness.

The helicopters were upgraded in 2000 to models which use the most up to date navigation and satellite equipment.

Routine journey

A spokesman for the SAS said: "The majority of our journeys are classed as routine, taking patients for clinical procedures. About 20% of our trips are emergencies."

He said that the trip to Campbeltown which resulted in the aircraft crashing into the sea off the Mull of Kintyre was classed as a "routine journey" despite being made at about midnight.

The service operates "24 hours a day, every day", the spokesman said.

Last year the air ambulance service carried out 3,251 missions using a six-strong fleet of aircraft.

The service has contracts agreements to use:

• Three Loganair fixed wing Islander planes based in Glasgow, Kirkwall and Lerwick

• Two EC135 helicopters operated by Bond Helicopters and based in Inverness and Glasgow

• One Beech King fixed wing aircraft based in Aberdeen.

The service, which has saved many lives, has lost an aircraft before.

In May 1996, a crash on Shetland claimed the life of the pilot and injured a doctor and nurse. The plane involved was a Loganair Britten-Norman Islander, the same model that crashed off the Mull of Kintyre on Tuesday.

The 1996 accident happened when the aircraft, returning to Lerwick after taking an injured oil worker to hospital in Inverness, crashed close to Tingwall airstrip, near Lerwick.

Loganair has operated aircraft for the service for almost 40 years.

But last year it was announced a new six-year, �40m contract had been awarded to English company Gama Aviation.

From April 2006, the number of planes will be cut from four to two.

Air wing staff are on call 24 hours a day every day

The new aircraft are purpose-built as air ambulances and will be on average 15 minutes faster, the ambulance service has said.

But concern has been raised about the changes, particularly in Orkney which will lose its fixed-wing air ambulances and instead be served by a helicopter based in Inverness.

The ambulance service said the new planes are of a much higher specification, but some people in island communities are concerned about the small airstrips being unable to cope.

Gama Aviation will use two new Beech 200C Super King aircraft based in Aberdeen and Glasgow and two upgraded Eurocopter EC135T2 helicopters based in Glasgow and Inverness which have been providing an air ambulance service since 2000.