PARIS (Reuters) - Bombardier (>> Bombardier, Inc.) could produce a third, larger version of its CSeries aircraft in the future, an executive at the Canadian train and planemaker said on Wednesday, potentially giving the high-stakes project a lucrative boost.

Critical to the future of Bombardier's planemaking unit, the CSeries made its air show debut in Paris this week.

Bombardier expects the smaller CS100 model to be certified by the end of 2015 after years of delays and cost overruns. The CS300 is due to follow next year, and a potential CS500 model is now also on the cards.

"It's a possibility, yes," Rob Dewar, vice president of the CSeries, told Reuters when asked about a CS500. "The platform has the capability to be a larger aircraft."

Bombardier was focused on ensuring the current models enter service for now, starting next year, however.

The 110-to-160 seat CSeries is Bombardier's first direct competitor to the top-selling 737 and A320 single-aisle jets built by Boeing (>> Boeing Co) and Airbus (>> Airbus Group). A larger version would open up a wider market to Bombardier.

The company is under pressure to drum up new sales for the CSeries. So far it has 243 firm orders, with two-thirds for the CS300, still short of its target of 300 orders by the time the aircraft enters service.

The CSeries' wings performed better in tests than expected, Dewar said, implying a larger CSeries model could be developed without major new expense as a complete wing redesign would not be required.

"That wing, if we ever did the 500, of course would be used and modified to do that," he said.

Customers have already shown an interest in a larger CS500 version, Dewar said.

"We get demand for a larger aircraft, but we give them exactly the same response, we're focused on the CS100 and 300," he said.

(Editing by James Regan)

By Sarah Young

Stocks treated in this article : Airbus Group, Boeing Co, Bombardier, Inc.