Boeing's effort to develop the Air Force's new tanker has been stymied by technical delays and cost overruns.

Defense chief Jim Mattis has said the Pentagon will not accept any of the tankers that are flawed or fall short of the requirements in the contract.



Defense Secretary Jim Mattis told Pentagon acquisition officials in November that he is "unwilling (totally)" to accept flawed KC-46 tankers from Boeing, which is leading the effort to replace the aging KC-135 tanker aircraft, according to Bloomberg.

Mattis has had limited involvement in the Pentagon's weapons programs, but he is the latest defense chief to comment on the 16-year-long effort to replace the Air Force's tanker.

Boeing won a contract to develop the new tanker in 2011, and the Air Force expects to buy 179 KC-46s. But the $44.5 billion program has been plagued by technical problems and cost overruns.

Under the contract signed with the government, Boeing is responsible for costs beyond the Air Force's $4.82 billion commitment. So far, the defense contractor has eaten about $2.9 billion in pretax costs.

The KC-46 program has been stymied by delays for years.

In summer 2014, Boeing was hit with nearly a half-billion dollars in overruns related to wiring problems in the first program's first four airplanes. The test version, the 767-2C, which was not outfitted with any refueling systems, was supposed to take its first flight in June 2014, but missed that date, taking the air for the first time during the final days of that year.

In mid-2015, issues with the plane's fueling system added another half-billion-dollar accounting charge for Boeing.

The KC-46A Pegasus deploys the centerline boom for the first time, October 9, 2015. Boeing/John D. Parker

In the middle of 2016, it was announced that Boeing would miss its contractual deadline to deliver 18 of the KC-46 tankers to the Air Force by August 2017 due to numerous technical issues. Though the tanker was able to refuel F-16 fighter aircraft at that point, a major issue was refueling the Air Force's huge C-17 cargo plane, which put "higher than expected" pressure on the aerial boom extended by the tanker to distribute fuel.

A technical solution to the boom issue was developed over the following months, but another major problem — this time a "category one" deficiency — arose during testing in late 2016, when the refueling boom was found to have scraped the surface of the aircraft taking on fuel.

Though the damage was minor, the problem not only posed a threat to the aircrews involved but also risked compromising the low-observable coating on stealth aircraft like the F-22 and F-35 fighters. A KC-46 with a refueling boom contaminated by stealth coating may also have to be grounded. The Pentagon's undersecretary for acquisition, Ellen Lord, said the issue was still under investigation as of November.

A KC-46 Pegasus takes its first flight at Paine Field in Everett, Washington, September 25, 2015. U.S. Air Force photo/Jet Fabara

Two other "category one" deficiencies — considered less serious — were also found at that time, but the Air Force has said progress has been made on both.

Boeing's president and CEO of defense and security said on December 2 that the company will miss a self-imposed deadline to give the Air Force the first KC-46 tanker by the end of 2017.

The firm is contractually required to deliver 18 certified KC-46s and nine refueling pods by October 2018.

Despite issues, the KC-46 has been praised by Department of Defense officials and the Government Accountability Office.

Mattis himself in recent days has complimented Boeing's cooperation with the Pentagon.

"I reinforced that the Air Force was not going to accept tankers that weren't completely compliant with the contract," Mattis said of his note during a press briefing en route to Kuwait on Sunday, according to Bloomberg. Boeing has been "excellent," Mattis said, adding that there hadn't been any "pushback" from the contractor

"The Air Force needs tankers done right. The American taxpayer expects tankers done right, and Boeing is committed to tankers that are done right," Mattis told reporters. "We'll get there. It'll be the best tanker in the world."