Boeing is looking ahead to a 2013 critical design review of the U.S. Air Force’s KC-46A refueler after wrapping up a monthlong preliminary design review (PDR) in April.

The PDR, which took place March 21-April 27, validated that Boeing’s design “meets system requirements [and] establishes the basis for proceeding with the detailed design,” according to an Air Force statement.

The KC-46A is based on a yet-to-be-manufactured commercial 767-2C freighter configuration that will include modifications such as a cargo door and structurally enhanced floors, tail, wings and empennage. Boeing conducted its own “PDR-like” activity of the -2C prior to the KC-46A review. But company officials have been mum on details.

Boeing won the KC-46A contract early last year over an EADS A330-based design and is required to deliver 18 combat-ready aircraft by the end of fiscal 2017. Although the target is $4.4 billion, the government estimates the work will cost $5.3 billion to complete, forcing the Air Force to pay $4.9 billion – the agreed contract ceiling amount. The Air Force and Boeing agreed to a 60/40 split for the cost above ceiling. Additionally, government auditors estimate that Boeing will have to invest $400 million of its own money to keep the development program afloat.

The PDR is the first major program milestone. Last year, the government/contractor also conducted an integrated baseline review as a foundation for the program.

Maj. Gen. Christopher Bogdan, program executive officer overseeing the development, says he is “pleased with the path the program is on.”

However, he previously outlined potential pitfalls in the design and manufacturing process resulting from Boeing’s decision to close the Wichita facility that has for decades supported the company’s military tanker work. The decision will prompt a shift of that expertise – including boom and certification work – to the Seattle area.

“I am holding Boeing accountable for everything they promised on that program and I am not going to let them slide one iota just because they closed Wichita down,” Bogdan told Aviation Week in March. “That was a business decision the Boeing company made, and the fact that it introduces some risk into the program is problematic. But from my point of view, it changes nothing. Boeing still has to perform.”

First flight of the KC-45A is set for late 2014, with low-rate initial production slated for 2015.

The Air Force plans to buy 179 KC-46As at an estimated cost of $51.7 billion.