A deadline is looming next week for the decade's last undecided combat aircraft competition, which carries high stakes and billions of dollars for the winner.

Lockheed Martin and Boeing, neck and neck, are set to turn over flight performance data to the Air Force on their proposals for the T-X jet, the next combat training aircraft for the Air Force.

With $16.3 billion at stake, a contract award is expected later this year.

The T-X jet won't actually be blasting enemy air defenses or waging dog fights over future battlefields, at least not for the United States. But it will be doing the fighting virtually as a trainer for the service.

The new jet will prepare airmen to pilot advanced aircraft such as the F-35 Joint Strike Fighter and the F-22 Raptor, and it could be doing it so for the next 50 years, meaning a big win for the defense contractor that clinches the deal.

"The opportunity to get an aircraft in service with a large customer like the Air Force, you're going to have multiple decades of work and you're also going to have other foreign sales opportunities, so this is one they'll go after hard," said Roman Schweizer, an aerospace and defense policy analyst with Cowen and Company.

The new trainer will replace the T-38 Talon, an aging supersonic jet first used to train American pilots to fly airplanes deployed during the Vietnam War and the height of the Cold War.

Defense heavy hitters such as Northrop Grumman and Raytheon dropped out of the T-X competition earlier this year, leaving Lockheed and Boeing as the clear frontrunners for the contract, which includes a total of 350 trainers.

Leonardo, an Italian aerospace and defense company, and its U.S. subsidiary DRS Technologies have also entered the competition as underdogs with the T-100, which is based on Leonardo's Aermacchi M-346 trainer jet already flown by Italy, Singapore and Israel.

The T-100's advantage is its "cockpit-embedded tactical training system," which integrates other aircraft and ground-based components as a cost-effective way to add realism to training, according to Leonardo.

But analysts say the Air Force might be moving in another direction. Raytheon had originally planned to partner on the project but split with Leonardo this year when the two companies could not reach an agreement.

Two approaches

The Air Force asked for T-X proposals in December, and the two defense giants have taken different approaches.

Lockheed partnered with Korean Aerospace Industries and opted to go with one its existing airframes, the T-50A, which was developed for the Korean air force and already has 142,000 flight hours. It says the aircraft cockpit has been modified to feel "exactly" like an F-35.

Meanwhile, Boeing partnered with Swedish company Saab to develop a completely new airframe for the T-X competition over the past three years. It now has two "real, no-kidding airplanes as if we were doing it for the Air Force" and are flying them at its facility in St. Louis, Mo., Boeing's program manager Ted Torgerson said.

Now, the Air Force wants defense companies to provide a raft of data on their proposed jet trainers by next week showing how they perform in flight, according to Lockheed and Boeing. Competitors submitted original proposals to the Air Force in March.

The service declined an interview request to discuss its T-X search.

Lockheed spokesman Mike Griswold said his company was confident about its T-50A offering and its performance on a dozen or so flight measures going into the June 28 deadline.

"You have to be able to pull at least six Gs sustained and if your aircraft pulls up to seven and a half Gs sustained you get extra credit, so to speak," Griswold said. "We meet all those extra-credit parameters."

The company did a trade study a couple of years ago exploring the option of developing a new airframe, but ditched the idea after it found the T-50A adequate with some minor changes, he said.

"Frankly, we couldn't make a new aircraft work in the time and budget constraints that the Air Force is operating under," Griswold said.

But Torgerson said Boeing came to a different conclusion and tailored a new aircraft that overcomes all the shortcomings of the Talon trainers — limited cockpit size, lack of maneuverability — and performs like modern fighter jets.

"When you get in it, you are going to have speed, turn capability, be able to pull G's like you would be in an F-22 or an F-16 kind of airplane," Torgerson said. "We tried to very clearly address the gaps to that T-38 and we believe we've done that in spades and we believe that gives us an advantage."

Byron Callan, an analyst with Capital Alpha Partners, said Boeing might be able to take advantage of newer manufacturing processes and technologies to gain the upper hand with the Air Force.

"In my personal view, I think there's some attributes to the Boeing-Saab entrant that would make it more positive, a more likely winner than the Lockheed plane," Callan said. "Sometimes, a newer design might do better than an airplane that is already 10 years old from conception."

Industry outlook

The $16.3 billion would be a major win for both companies, but perhaps more so for Boeing.

The company still has the F/A-18E/F Super Hornet, part of a legacy program that began decades ago, and the Pentagon has proposed buying 14 more of the aircraft in its 2018 defense budget. The Hornets are likely to remain a key part of U.S. air power for years to come.

CEO Dennis Muilenburg said this month he believes domestic demand for the Super Hornets is returning, but numbers may ultimately be limited. He pointed to the T-X contract as a top priority for the company.

Boeing could also shore up its St. Louis production facility, where it makes the Super Hornet and EA-18G Growler, with a T-X contract.

Torgerson said the company picked the location for T-X production because it "just made lots of sense" and would could add 1,800 jobs to the economy.

Lockheed's financial fortunes have meanwhile been buoyed by scoring a top prize among defense contracts, the F-35 fighter, made famous as the most expensive procurement program in Pentagon history. The defense budget proposal calls for 70 of the aircraft next year.

The F-35 accounts for about 23 percent of Lockheed sales, and CEO Marillyn Hewson said this month the company expects it to help drive 3-5 percent growth in the coming years.

Now, with both companies putting forward strong competitors for a new airframe, the contract award may come down to who can offer the Air Force a better price.

"Frankly, both planes are pretty good performers," said Richard Aboulafia, a vice president and analyst with the Teal Group. "It becomes a question of how much of a loss does Boeing want to take in order to win this contract."

Boeing made a significant investment by developing its aircraft from scratch — it would not say how much for this story — and must now figure out how to absorb that non-recurring cost to be competitive with Lockheed's offering, Aboulafia said.

Part of that will depend on future markets for the aircraft beyond the Air Force contract for 350 of the trainers. That could include selling the aircraft as a fighter to other countries or to NASA, which uses the aging T-38 trainer.

Boeing estimates it could sell a total of 2,000 of its aircraft, meaning it could reduce its selling price to the Air Force based on projected profits from those future sales. But the appetite for the aircraft is still uncertain as other countries watch the competition.

"I would argue that the global market has been significantly overstated by just about everybody involved," Aboulafia said.