AIRSHOW-Airbus set for A350 boost with Virgin Atlantic deal

FARNBOROUGH, England, July 11 (Reuters) - Virgin Atlantic is set to announce an order for at least 10 of Airbus's biggest twin-engined plane, the A350-1000, on the opening day of the Farnborough Airshow on Monday, industry sources said.

An order of that size would be worth more than $3.5 billion at list prices.

A deal would be a shot in the arm for a 366-seat model promising greater efficiency but whose sales have slowed as rival Boeing (NYSE: BA - news) develops a larger version of its 777.

Airbus and Boeing have enjoyed years of strong demand, helped by rising airline travel particularly in Asia and the Middle East and new, more fuel-efficient planes.

But analysts are concerned that economic risks -- from slowing growth in China to Britain's move to leave the European Union -- could see orders dry up and some even cancelled, particularly for costly long-haul jets.

British Prime Minister David Cameron will also attend the show on Monday, when he is expected to finalise multi-billion dollar deals with Boeing to buy nine P-8A Poseidon maritime patrol planes and to upgrade 50 Apache (NYSE: APA - news) helicopters. (Reporting by Tim Hepher; Editing by Mark Potter and Keith Weir)