WASHINGTON — Northrop Grumman has decided to produce a new, clean-sheet design for the US Air Force's T-X trainer replacement competition, the company tells Defense News.

The move is an about-face after four years of offering an off-the-shelf design in the form of BAE's Hawk training system.

The decision to switch from a well-known system to a new design began germinating two years ago, as the Air Force started making the requirements for T-X more clear to the ​industry, competitors, ​said Marc Lindsley, Northrop's T-X program director.

During that time, the company was still planning to offer on offering ​the Hawk. In recent months, however, the company decided a new design would best meet the technical and affordability requirements. from the service would be best met with a new design.

Northrop informed the Air Force of itstheir​ plan "a few" months back, Lindsley said, adding that there was not​ specific requirement from the service ​that drove the decision but rather an "aggregate" of inputs from the service

"[After] the open dialogue with industry, the understanding [of what] the requirements and capabilities are, and what the costs are of those requirements, we have an opportunity with this clean-sheet design to give them exactly what they want, and that's what we want to do," Lindsley said.

The new design is in the assembly stage, with a first flight expected sometime this year. Northrop declined to give a more detailed timetable on when that would be, but companies always like to make a splash around either the Paris Air Show in June or the Air Force Association's annual convention in September.

The T-X program is intended to replace the Air Force's fleet of T-38 training aircraft with a more highly advanced jet capable of training pilots for use in fifth-generation fighters like the F-22 and F-35. The service plans on issuing an RFP on the program in the fourth quarter of fiscal year ​2016, with a projected contract award in the fall of 2017.

The service signaled its intention to move ahead with T-X in its fiscal 2016 budget request, which earmarked $11.4 million for research-and-development funding. That number escalates to $12.2 million in fiscal 2017, then jumps up to $107.2 million in 2018, $262.8 million in 2019 and $275.9 million in 2020.

Until Northrop's announcement, the only clean-sheet design expected in the T-X competition was from a team of Boeing and Saab. The new designs will go up against a pair of legacy trainers in the form of Lockheed Martin's offering of Korean Aerospace Industries' T-50, and the T-100, a collaboration between General Dynamics and Italy's Alenia Aermacchi based on the latter's M-346 design. Textron AirLand is also planning to enter a trainer variant of its new Scorpion jet in the competition.

Last summer, when the world still believed Northrop was offering the Hawk, the company was officially named the prime on the team. Lindsley characterized that decision as "part of the process" toward moving to a clean-sheet design, but said the plan is to keep the same team of partners as with the Hawk.

The company is in discussions with BAE about including the British company's core training system, which simulates radar threats and other training requirements, as the center of the new jet's internal systems. BAE would also assist on production and design. L-3, meanwhile, will continue to provide in its role as the provider of ​ground training systems such as simulators and classroom activities.

Lindsley added that "for now," the first prototype will use a General Electric engine, but declined to go into details on how what ​a full fleet of Northrop T-X planes would be powered. by.

One benefit of switching to a clean-sheet design is bringing another partner into the process. Northrop signed an exclusive agreement with Detroit-based KUKA Systems Inc.​ in 2012 to help design a production line for the then-expected Hawk offering. KUKA designed the company's F-35 Palmdale, California, production line, which was named 2013 "Assembly Plant of the Year" by Assembly Magazine.

"We're designing producability into our airplane, right from the ground floor. They're sitting right alongside the aircraft design engineers," Lindsley said. "By having them on the ground floor you don't have to go back and tweak your design for how you would automate or how to make it better for access panels for maintenance."

"You're also designing the aircraft with modern manufacturing capabilities and growth potential, because let's keep in mind that we're proposing an aircraft that's replacing one that's been flying for 50 years," Lindsley added. noting that ​Baking in the ability to easily upgrade and modify the design will be important if this T-X design is to last for several decades.

Perhaps the most important partner in this program will be Scaled Composites. Although Northrop bought Scaled in 2007, Scaled operates semi-autonomously as a rapid prototyping house, working for a number of programs both within and outside Northrop's portfolio. The aircraft is being designed at Scaled's facility in Mojave, California.

"Scaled takes their rapid prototyping design and development capability, combines it with the Northrop capability … and we're getting synergy out of that combined effort between the two organizations," Lindsley said.

A spokesman for the company said no decision has been made on where the T-X could be produced, but the two likely spots would be Northrop's Manufacturing Centers of Excellence, one in St. Augustine, Florida, and the other in Palmdale, home , California. The latter is also home ​to the KUKA-designed F-35 line.

As for international sales, Lindsley said the company would be open to considering looking to ​that in the future, but said ​all the focus right now is on winning the T-X competition. first.

For more on Northrop's new offering, check out Monday's edition of Defense News.

Email: amehta@defensenews.com

Twitter: @AaronMehta

Aaron Mehta was deputy editor and senior Pentagon correspondent for Defense News, covering policy, strategy and acquisition at the highest levels of the Defense Department and its international partners.