By Tim Hepher
PARIS (Reuters) - A row has flared up between leading planemakers over the width of tourist-class seats on long-distance flights, setting the tone for a bitter confrontation at this month's Dubai Airshow.
The dispute focuses on the width of seats provided on long-haul flights for economy passengers - not always the ones most courted by airlines, but whose allocated space holds the key to efficiency claims for the latest jets offered by Airbus and Boeing.
The dispute comes as planemakers vie to sell ever-larger versions of their twin-engined long-distance aircraft, with potentially record orders expected at the November 17-21 event.
How the back of the plane is laid out - particularly whether seating is 9 or 10 abreast - is central to the economic performance claims being made for new 'mini-jumbo' jet designs.
Boeing says its revamped "777X" will hold 406 people based on economy seats over 17 inches wide and set out 10 in each row.
Airbus says the competing version of its A350 will carry 350 people in 18-inch-wide economy seat laid out 9 abreast.
Plane giants often trade blows on technical matters through advertising in the trade press. Now, Airbus is appealing directly to the public ahead of the Dubai Airshow, where the 777X is expected to dominate with over 100 orders.
It recently previewed what may be the start of a new ad war by showing financiers a slide illustrating three people squashed together at a restaurant, titled "Would You Accept This?"
"Boeing is proposing long-distance flying in seats narrower than regional turbo-props," said Airbus sales chief John Leahy.
As diets change, people get bigger but plane seating has not radically changed.
Between the early 1970s, when the Boeing 747 jumbo defined modern long-haul travel, and the turn of the century, the weight of the average American 40- to 49-year-old male increased by 10 percent, according to U.S. Health Department Data.
The waist of the average 21st-century American male is 39.7 inches, according to U.S. health statistics, which equates to a diameter of 12.6 inches. This leaves 2 inches either side in many plane seats, which are narrower than at an average cinema.
Airbus says that is not enough for long-haul travel and says its rival is sticking to a seat concept from the 1950s, when the average girth of the newly christened 'jet set' was narrower.
Airbus says it has commissioned research suggesting an extra inch in seat width improves sleep quality by 53 percent.
Boeing disputes Airbus's figures on seat measurements and says it is not up to manufacturers to step into decisions on how airlines balance fares and facilities. It also says research shows cabin experience depends on more than the width of a seat.
"It really comes down to providing flexibility to airlines and allowing them to do the things that they believe they need to do to be successful," said Boeing cabins expert Kent Craver.
"They don't want us to dictate to them what makes them profitable. They know their business better than anyone else."
For flyers it is about more elbow room, but for suppliers it is increasingly an issue that could affect earnings.
Behind the dispute is a race for plane orders with at least $700 billion of estimated business at list prices in coming decades, enough to tip the scales of U.S. and European exports.
As Reuters first reported in July, seat layout is exactly what drives the battle between the latest jets.
Both Airbus and Boeing claim 20 percent better efficiency per seat in their latest twin-engined long-haul designs than the market leader in that segment, the 365-seat Boeing 777-300ER.
Boeing's performance claims depend in part on comparing the 10-abreast 777X with an original 9-abreast 777 design. The gain in unit costs is blunted compared with 10-abreast now in use.
"The reason Boeing are doing this is to cram more seats in to make their plane more competitive with our products," said Kevin Keniston, head of passenger comfort at Europe's Airbus.
On the other hand, analysts say full 10-seat-per-row cabins for existing 777s suggest many passengers are voting for the denser layout, which may go hand in hand with cheaper fares.
"18 inches in seat width would be great for passengers, but the reality is that from a business point of the Airbus proposal is driven by the threat of the 777," said cabin interiors expert Mary Kirby, founder and editor of the Runway Girl Network.
Airbus and Boeing do not supply seats but offer a catalogue of suppliers for airlines to choose from. Globe-trotting jet sellers even carry tape measures to check on competing layouts.
While boasting comfort, all builders also offer jets with high-density layouts for low-cost airlines and regional travel. Airbus offers a 10-abreast A350 but says it has not yet sold it.
Until recently, Airbus was stressing the need for more cabin customization by offering wider aisle seats on some of its jets.
Without the support of the only other maker of large modern jets, experts say its call for a new industry standard is unlikely to fly, but could distract from a wave of 777X sales.
(Additional reporting by Hayley Platt; Editing by Giles Elgood)