Airbus SAS is set to announce a key order for eight to 10 of its biggest twin-engine model, the A350-1000, from Virgin Atlantic Airways Ltd after beating Boeing Co to a scarce order for big jets as economic and political uncertainties overshadow the Farnborough Airshow.

The order, worth some $3 billion at list prices, could perk up Monday's opening of an event clouded by geopolitical uncertainty, including Britain's decision to leave the European Union and concerns over the state of the global economy.

British Prime Minister David Cameron was scheduled to attend the opening day and finalize multibillion-dollar deals with Boeing to buy nine P-8A Poseidon maritime patrol planes and to upgrade 50 Apache helicopters.