While everybody at the show seems to be obsessed with the dogfight between arch rivals Airbus and Boeing over orders and sales, there is a smaller sideshow that is as just as bitter - the fight between Bombardier of Canada and Embraer of Brazil, the third and fourth largest aircraft manufacturers in the world.

The two companies are trying to capture a corner of the airliner market neglected by Airbus and Boeing - planes that carry about 100 passengers.

Airbus and Boeing make jets of this size, but they are scaled-down versions of their bigger planes, and not efficient enough to compete against a new generation of aircraft in an era of ever-rising costs.

Five months ago, Boeing decided to cease production of its short-haul 717, a 110-seat jet.

Embraer already has two new models on the market with capacity of 94 to 118 passengers, and early sales suggest that there is demand for larger planes than the old generation of regional jets.

It was Embraer's success as much as anything else that convinced Bombardier that it could not ignore this market, and last month the company committed itself to rolling out its C-series jets, which will carry up to 135 passengers. The US$2 billion project has already won promises of US$700 million in financing from the governments of Canada, Quebec and Britain.

Despite the boldness of Bombardier's move, critics suggest there has been an element of desperation in the Montreal firm's performance in recent months.

Last December chief executive Paul Tellier was forced out just 23 months after being appointed to prune the aircraft and train manufacturer's operations and return it to a position of financial stability.

Mr Tellier had initiated restructuring that involved slashing the workforce from 75,000 to 53,000. Control of the firm has reverted to the Bombardier family and to company chairman Laurent Beaudoin, the son-in-law of its founder.

An indication of Bombardier's troubles came three weeks after the shake-up, with the cancellation of dividends following losses of US$85 million for the year, the third successive annual loss.

Despite such dismal indicators, critics say the volatility of the industry should serve as a warning to all potential competitors.

Scott Hamilton, an aviation industry consultant, pointed out that a number of firms once shared the market, including McDonnell Douglas and Lockheed, which were swallowed by Boeing.

Boeing was initially dismissive of the challenge posed by Airbus, but found itself suddenly overtaken in the sales stakes.

'Boeing had better not make the same mistake with Bombardier, or it could find itself becoming the new McDonnell Douglas, with an insignificant market share in the next 20 years,' said Mr Hamilton.

But Professor Karl Moore of McGill University thinks that Boeing and Airbus are so busy trying to outperform one another that their competition renders any threat from Bombardier meaningless.

He explained that Boeing could form a partnership with Bombardier, a move that was rumoured, but dismissed, last year.

Professor Moore said it was possible that either Airbus or Boeing 'could waltz in and in a few years wrestle much of the C-series marketplace from Bombardier'.

'They have the resources, brands and expertise,' he added.

But he believes that the industry's two heavyweights will probably leave Bombardier alone.

'They have more important fish to fry,' he said.