Boeing has revealed its KC-46A tanker is heavier and slightly longer than any previous version of the 767-200 airframe on which it is based, but still refuses to provide essential details about the airframe configuration and refuelling system more than three months after winning the KC-X contract.
The company's clamp-down on design details is a departure from its practice on the P-8A, which also involved adapting an airliner, a 737, for a military mission, and in the first round of the KC-X bidding process.
Boeing Military Aircraft president Chris Chadwick argues that this approach should not be interpreted as any lack of confidence in the company's commitment to meet all 372 requirements under a fixed-price development contract.
"Rest assured, it is going well," Chadwick said. "We have got a happy customer."
Such essential details as the KC-46A's wing and refuelling boom will be revealed at some point within the next two years, Boeing officials said. More information will be released after the KC-46A clears a system requirements review in August, a preliminary design review next year and a critical design review in 2013.
"That's where we stand," Chadwick said, after repeated questioning. "We're not going to get into any more details."
Boeing officials offered conflicting explanations about the lack of disclosure. Jean Chamberlin, vice-president and general manager of Boeing mobility systems, said details are being held back until Boeing and the USAF fully understand the requirements in the system requirements review.
But Dennis Muilenburg, president of Boeing's Defense, Security and Space division, said that Boeing has a "clear understanding" of the KC-46A's design requirements. "We haven't seen any gaps as we've flowed those down to the supplier level," Muilenburg said.
New information has trickled out into the public domain since the contract award, including the public confirmation that the KC-46A is based on a new commercial freighter internally designated the 767-2C.
Boeing describes the 767-2C as a "minor" variation of the 767-200ER platform, but it is clear that the company has made significant changes from the baseline.
The maximum take-off weight is increased by 9,070kg (20,000lb) to just over 188,000kg, making the freighter version of the -200ER model even heavier than the 767-300ER. The length of the -200ER is also increased by 2m (6.5ft) to 50.5m for the KC-46A.
The 767-2C configuration also includes a cargo floor and door, a 787-based large display system, auxiliary fuel tanks and provisions for tanker systems, such as hose and drogue and boom refuelling systems, Boeing said.
It remains unclear, however, if Boeing has made any other changes from the basic design of the 767-200ER platform.
Company officials declined multiple requests during the 16-month bidding process to disclose the identity of the aircraft configuration contained in its proposal.
It previously had offered the 767-200LRF composite airframe, mating the fuselage of the 767-200ER and the wings of the 767-300ER. That proposal initially lost to a bid from a Northrop Grumman/EADS North America team offering the Airbus A330-200-based KC-45, but the victory was overturned by the US Government Accountability Office after Boeing protested over the air force's evaluation process.
Boeing took a different approach in the follow-up competition by keeping certain details about its offering a closely guarded secret. In contrast, the P-8A was fully briefed before Boeing even submitted its proposal for the US Navy's multi-mission maritime aircraft contract in 2005.
The existence of the 767-2C marks the latest commercial freighter variant in Boeing's product line-up, but it was not immediately clear if the airframe would be offered to the civil cargo market.
Each 767-2C will be assembled in Everett, Washington, then moved to Wichita in Kansas to install military avionics and refuelling systems for the KC-46A.
It was also clear from previously released images that the KC-46A incorporated a 777-style cursor control unit. Contract documents obtained from the USAF also reveal the airframe incorporates a central maintenance computer.
The 767-2C also introduces a new engine option for the 767-200ER variant with the 62,000lb-thrust (275kN) Pratt & Whitney PW4062 turbofan. The model was previously supported by PW4052/4056/4060-series engines and the General Electric CF6-80C2 series.