Airlines are choosing to cram more seats into Boeing's hot-selling new 787 Dreamliner than the company expected, giving the plane a potentially decisive advantage over its Airbus rival.

Senior Boeing sales executive Randy Baseler said typical seating in the 787-9 version of the aircraft would rise to about 280 from 259 if airlines switched to having nine seats per row in economy class rather than eight as Boeing had expected.

Both Boeing and Airbus are major sources of work for aerospace component manufacturers in the West Midlands.

Two-thirds of 787 buyers have decided to fit nine seats in each row in economy, executives from the Chicago-based manufacturer said at the Singapore air show.

In doing so, they have improved the ratio that is the Holy Grail of aircraft economics: the cost per seat on each flight. Boeing's sales manager for the project, Marty Bentrott, said: "When we initially started to bring the 787 to the market we felt the market would be for eight abreast and more comfort.

"But 65 per cent of our customers are going for nine abreast, and we think that (ratio) will probably go up."

The 787 is due to enter service in 2008 and is competing against the A350, which Airbus launched in response.

While the narrower seats will disappoint travellers who had hoped the 787 would take another step towards giving economy travellers a little more room - at eight abreast, the seats will be 48 cm (19 inches) wide, compared with 44 cm (17.2 inches) in the 1960s-designed 747 - the greater seating gives Boeing a big lift in its battle against the A350.

The A350 is constrained by its narrower fuselage, which is based on a 1960s design, although a little extra width has been found by thinning the walls. Its predecessor, the A330, is rarely fitted with nine-abreast seats.

"The surprising popularity of nine-abreast seating in the 787 could turn out to be decisive," said Gerard Frawley, editor of industry monthly Australian Aviation. Aircraft and aero-engine makers struggle for every tenth of a per cent of aircraft efficiency, but Boeing's figures suggest costs per seat could fall by a whopping 7.5 per cent if airlines opt for the tighter seating format.

Baseler said that while Boeing had originally expected the roomier seating arrangement to be popular, the 787 cabin had been sized precisely to fit nine 747-size economy seats.

"Some airlines found passengers were not willing to pay for more space," he told Reuters.