At almost $1m a square metre, big jets are the world's most expensive real estate, surpassing London's "Billionaire's Row." Little wonder then, that a row over elbow space is sharpening the latest contest between Airbus and Boeing.
After years of scrapping over smaller, short-haul aircraft, the world's dominant planemakers are turning their attention to one of the most profitable, but risky, parts of their business, as Boeing moves to defend its popular 777 "mini jumbo" from the largest version of Airbus's brand-new A350.
At stake is Boeing's continued dominance of orders worth hundreds of billions of dollars for the largest twin-engined jetliners, driving growth and connectivity between continents.
"It is the part of the market where the dollars are ... and where airlines are able to differentiate and get a price premium for their services," said Jerrold Lundquist, managing director at the Lundquist Group, an aerospace consultant for 30 years.
Boeing has controlled this piece of the industry chess board for a decade. Until recently its best-selling 365-seat 777-300ER had little direct competition and the successful niche has boosted Boeing margins and helped fund other projects.
After a slow start, Airbus is scoring key wins and building up a serious threat to Boeing's mini-jumbo franchise with a 350-seat version of its new carbon-fibre jet, the A350-1000.
Boeing is now offering a revamped "777X" with new engines and a wingspan as wide as its original 747 jumbo is long.
Both aim to offer airlines the most money-making jet in the 350-400 seat market, a cornerstone of future demand as global growth pushes up demand for long-haul trade and tourism.
Airbus sees 20-year demand for 1,900 such jets, built to fly non-stop from Dubai to Los Angeles or Singapore to London.
Tensions erupted at last month's Paris Airshow, where both sides claimed to be winning on economics and comfort - two features that do not always mix when it comes to crowded economy cabins - and accused the other of pushing up the number of seats in their presentations to offer airlines lower unit costs.
"(Boeing) are flailing around trying to work out what to do," said Airbus sales chief John Leahy, urging reporters to "stop using that function key" that says Boeing is winning.
Boeing conceded Airbus had outsold it in the past five years after delays on its 787 model, but said it still led the long-haul jet market on every other score, including order backlog.
"Don't bet against us," said chief executive Jim McNerney.
Airbus says its A350-1000 will burn 25 percent less fuel per seat than the 777-300ER when it enters service in 2017.
Boeing says its 406-seat 777-9X will burn 20 percent less fuel per seat than the 777-300ER, while giving airlines 41 more seats from around 2020, subject to board approval to build it. A longer-range 777-8X is expected to come with 355 seats.
Such promises have a powerful multiplier effect.
The cost of operating a large jet over its 20-year life is several times its purchase price. For planes like the 777 or A350-1000, designed to fly 16 hours a day, every percentage point in fuel saved tomorrow is worth fighting for today.
Both manufacturers will be chasing customers in coming weeks to validate their claims. Buoyed by an order from major Boeing customer British Airways, Airbus is aiming for a breakthrough at Japan Airlines, which says it is looking at both models.
Boeing, meanwhile, is hoping for a major 777X launch order from Emirates as early as November.
But picking apart the numbers shows the trade-offs that airlines will have to consider when making their decisions.
According to sources familiar with confidential briefings, a new 777X engine should increase fuel efficiency per seat by 10 percent and its outsized carbon-fibre wings - designed to fold upwards at the tip when parked - will contribute 7 percent.
But engineers must pay back 4-5 percent of these savings because the larger jet's basic structure is expected to be at least 12 tonnes heavier. The net gain from the latest technology will be closer to 12-13 percent, according to these sources.
To achieve the 20 percent increase in efficiency needed to complete their case, Boeing's marketers are moving in two steps.
Firstly, a longer fuselage gives space for 2-3 more rows, which automatically lowers unit costs and opens the door to extra revenue if airlines have enough demand on their network.
But to make it a slamdunk, Boeing is assuming airlines will adopt a denser layout by adding an extra seat to each row to make 10 seats across, instead of the standard nine on most 777s.
To fend off any concerns about discomfort, Boeing is proposing to carve out an extra four inches in internal cabin space by "scalloping" the inside of the fuselage. It believes this will corner its opponent and show up the A350's narrower cabin, which will sit nine abreast.
"They (Airbus) are having to chase the 777 with a tube that is almost a foot narrower. Now you are competing with the comfort of the 777," said Ihssane Mounir, head of Boeing Commercial Airplanes sales for Northeast Asia, including China.
Airbus dismisses the plan, saying it found during earlier discarded designs that such ideas don't work. It accuses its rival of packing in seats to flatter the older 777's economics.
"There is some sleight of hand going on here," said Leahy in an interview. "Nobody asked them for these extra seats. They are doing it to print lower seat-mile costs."
Boeing executives say it is Airbus that scores well in the industry's long-established game of toying with configurations.
Airbus's claim of a 25 percent per seat fuel advantage for the A350-1000 assumes a layout of 369 seats, rather than 350, and 360 seats for the 777-300ER, five fewer than advertised.
How all this affects sales depends in part on whether airlines and passengers accept the proposed 10-abreast layout.
Higher-density seating may be less comfortable but gets airlines' vote in economy, Sanford C. Bernstein analysts said.
Indeed, of the 22 current Boeing 777-300ER operators for which data is available, 27 percent are already at 10 abreast.
Ironically, that may make the 777X's improved efficiencies harder not easier to prove. Airlines already operating this way would not get the full boost advertised for the 777X since the efficiency goal depends partly on going from nine to 10 abreast.
They include the largest 777 operator, Emirates, whose support is vital to get the new 777X launched. It anticipates having to replace as many as 175 Boeing 777-300ERs from the end of the decade, some of which have not even been delivered.
Still, its president Tim Clark has forecast significant 777X demand, prompting talk of a launch at November's Dubai Airshow.
Getting the size right is critical. An undersized plane will spill lost demand into the hands of an airline's competitor. Too many seats will force airlines to discount and hurt yields.
By leapfrogging the A350, Boeing is betting the 777 market's "sweet spot" will increase to 400 seats. That potentially eats into a larger class where Boeing's own four-engined 747, as well as Airbus's 525-seat A380 superjumbo, made their mark.
"For the next six months, it will be interesting to see if there is any down-sizing from 747 or A380 to the large twinjets - basically, are they taking away 747 or A380 sales?" said a senior aviation executive.
Despite their hostility, some experts say the plane giants could accidentally find a way of co-existing as their constant attempts to outflank each other allow them to find new niches.
"The wide-body market is very tuned to the specifics of each route," said Lundquist. "It's not going to be winner takes all".
Even so, neither project is immune from wider risks.
After staging a maiden flight for the A350-900, Airbus must handle a complex ramp-up in production of new jet technology.
Boeing has to persuade airlines to buy the 777X at a price that convinces its own board - seemingly more conservative of late - to launch the 777X at an estimated cost of $5-7bn.
All those efficiency numbers count for little if the cost of owning this particular piece of flying real estate is too high.
To justify a new wing, industry sources say Boeing is looking for a price increase of about 20 percent compared with the current 777-300ER, which lists at $315m. Airlines typically get discounts around 40 percent or more at launch.
In trying to recoup its investment, it faces a warning from influential plane lessor Steven Udvar-Hazy, who is credited with having forced Airbus to redesign the A350 in its early days.
"When capital costs are included, the (777-9X) benefit compared to the 777-300ER appears to be less than 10 percent," the chief executive of Air Lease Corp told Reuters.
"So it will be important for Boeing to produce the aircraft as efficiently as possible in order to offer it at an appropriate price and keep the ownership costs down."