British air crash investigators are flying to Libya to help discover why a plane carrying oil workers plunged into the sea killing at least 17 men, including five Britons.

Another British passenger was among five still missing after the Belfast-built Shorts SD-360 plane ditched in the sea five miles from its destination, an oil refinery in Marsa el Brega, 450 miles east of the Libyan capital, Tripoli.

A further seven Britons were among 19 survivors plucked from the sea by local fishing boats following the accident on Thursday.

Investigations are likely to centre on whether fuel problems caused an apparent simultaneous engine failure on the twin-propeller engined aircraft, forcing the two Swiss-trained Libyan pilots to ditch the plane.

Both pilots were among the survivors, and salvage workers are preparing to recover the wreckage of plane, which is resting in 165 feet of water.

The plane was carrying 41 people in all, the two pilots and a cabin attendant, and 38 passengers, 13 of whom were British.

It was flying from Tripoli to the huge petrochemical centre at Marsa el Brega, which is owned by the Libyan state-owned Sirte Oil Company, for which all the passengers are understood to work.

The Shorts plane - a model with an excellent safety record - was leased from Swiss air charter company Avisto AG.

The Department of Transport said two members of the Air Accidents Investigation Branch were on their way to Libya, to assist Libyan and Swiss experts.

Wife's relief

None of the Britons involved in the crash has been officially named, but the Foreign Office has said that one is from Coatbridge in Scotland.

One of the British survivors, Stewart Bonar, a 59-year-old from Limavady, Co Londonderry, telephoned his wife to say he was being treated in hospital for broken bones.

Mrs Bonar asked her husband, who works in a gas plant in Libya on alternate months, how he managed to escape.

She told BBC Radio Foyle: "He really didn't want to talk about it.

"It was just 'I'm alive and so glad to be able to ring you'.

"I just have to wait and hear now about whether he'll be home or what his injuries actually are.

"But thank God they don't seem to be serious injuries. He has assured me he hasn't, but of course it's all very worrying. At least I know he's alive. It's hard to take it in."

Close-knit community

The British ambassador in Tripoli, Richard Dalton, confirmed that one of the British survivors had suffered a broken leg and broken toe.

The others received only minor injuries including a twisted ankle, a bruised back and other cuts and bruises.

He said: "Of course they are also all very shocked by what has happened. It is a very close-knit community and many people have worked here for a long time.

"It has hit them very hard."

The search for those missing is continuing and is likely to do so until nightfall, he added