Poorly designed wiring bundles for the U.S. Air Force’s KC-135 tanker replacement aircraft have driven program officials to further slip first flight of the Boeing 767-2C aircraft from June to no earlier than the middle of November.

Despite the delay, Air Force Maj. Gen. John Thompson, program executive officer for the KC-46 program, says he is confident the Boeing-led team can deliver the first 18 tankers by August 2017, as required in the contract. "We don’t see anything of great concern there that would really worry us about the ability to get to required assets available [RAA] … in the August of ‘17 timeframe," Thompson tells Aviation Week during a Sept. 11 interview. However, "Schedule performance must improve," he says.

Boeing won the $4.4 billion development contract on Feb. 24, 2011; the fixed-price terms of the deal limit the government’s cost to $4.9 billion. A 2013 cost and risk assessment put total cost of the development at $5.9 billion, Thompson says. Boeing is responsible for paying any overage to meet the 2017 milestone. Ultimately, the Air Force plans to buy 179 of the tankers as the first of three potential tranches of KC-135 replacements.

The company announced a $272 million charge this summer to keep the program on track. At issue was insufficient separation in some of the wiring bundles on the 767-2C baseline platform. Wiring bundles were one of the items that required a new design for the tanker variant because the Air Force requires double- or even triple-redundant wiring for some mission systems. The baseline 767 has about 70 mi. of wiring in the design; the 2C adds about 50 mi. to that, Thompson says. Along with redundancy, some of the wiring for specific systems must be separated by a certain distance for safety reasons. Boeing realized earlier this year while preparing for FAA testing that in 5-10% of the bundles safe separation distance for the wiring systems fell short or the wires were not properly shielded.

The poor design was "due to discrepancies traced to a transition of design tools," Boeing spokeswoman Caroline Hutcheson says. "While it in no way mitigates our disappointment in taking a charge, the issues here are well-defined and understood. There’s no new technology involved, just additional work that has to be accomplished."

Some of the wiring had already been installed in the first of four test aircraft for the program, driving program officials to remove some equipment. The other three test aircraft have been produced and are parked at Boeing’s facility awaiting the newly designed wiring bundles. However, production of these jets was to be fairly concurrent, and the redesign issue has shifted this work into a "serial process," creating a possible choke point for executing flight testing for the program.

The 767-2C was specifically designed for the tanker role. It is a 767-200ER modified with a strengthened main-deck cargo floor, cargo door and freighter features, 787-based cockpit, auxiliary fuel tanks and plumbing and wiring to support the refueling boom and mission systems. Boeing is building these features into the 767-2C as it is being built on the commercial production line in Everett, Washington, to minimize tear down and time to add mission systems at its finishing facility.

First flight for the first KC-46, which will be the second developmental aircraft (the first will be used in the 2C configuration for the amended and supplemental type FAA certification) is slated for April 2015, and Thompson said that schedule is holding, for now. But "if we don’t get the KC-46 variant in the air that first week of April, then we really start pushing almost a day-for-day slip of the Milestone C [Pentagon production decision], which is currently scheduled for September of next year."

He notes that if the Milestone C decision from Pentagon procurement chief Frank Kendall slips "a little bit to the right, that is not a death knell for the August of ’17 RAA." However, the slippage in 2C production is further emphasizing the development and production concurrency built into the KC-46 program. Officials said at the outset of the program this strategy carried little risk, owing to Boeing’s experience overseeing commercial-to-military conversions. However, flight testing will only have just begun on the 2C at the time of the Pentagon decision to produce the first 13 operational aircraft.

Further, the program is embracing a new "Test Once" concept that is designed to maximize the number of test points for different agencies accomplished in each test sortie. The delay could put further pressure on this new system.

Thompson says he is exploring options to mitigate schedule pressure as a result of the wiring bundle issue, though he said it is too early to identify specific measures under review. "There is more than one path through the forest," he said. "Just because we have established a schedule … doesn’t mean we could not better optimize that sequence of events."

Despite the high cost to Boeing of maintaining the schedule, Thompson says he still expects it to be a profitable venture for the company. South Korea and Japan have already expressed interest in a possible buy of KC-46s.

Before disclosure of the wiring bundle problems, Boeing officials maintained their estimate at completion would undercut the government’s estimates. Hutcheson did not refute Thompson’s estimate, but she notes that the company’s charge "is increased spending by Boeing to maintain the overall program schedule with no additional costs to the customer or taxpayer, per the contract design."