[PARIS] After dramatically improving sales of its A320 jet by revamping it with newer and more efficient engines, Europe's Airbus is studying whether to apply the same formula to a bigger jet, the A330, industry sources and analysts said.

Sales of the 20-year-old long-haul plane have enjoyed an unexpected boom in recent years after three years of delays in Boeing's radically new 787 Dreamliner drove many airlines to invest in the cheaper and proven Airbus model.

But momentum is fading and analysts say Airbus faces questions over whether it can maintain current A330 production rates in the second half of the decade without something else of its size to offer airlines tempted by the chic new jets.