That's the bottom combat line. All power cables must meet certain survivable constructs within the aircraft. A well intended military idea, and a proven methodology for combat aircraft. Boeing must string wires independent from each other and allow enough insulation, space and protection for redundant cables between the other power lines, which also are making its way towards a wiring harness, then becomes a transfer point of power destined to equipment, flight deck and other special systems tasked by the KC-46 capabilities.
Boeing has assured the military it will fix the under(mis)-engineered harnesses, which are coupled together not unlike like a harness found in your automobile, such as a car brake light, and/or headlight, or dash board electronics. They all have harnesses bringing its power to different systems.
On the farm, a tractor didn't have a harness to connect power to a tractors electrical system back in that day. A farmer might buy some black electrical tape, stripe the end of two wires and then twists the ends of the wire together, before wrapping the black tape around the wire the farmer just twisted together( A Farm Wire Harness). A modern car has wires going into a plug looking harness and it snaps together routing power to the headlights. Sometimes those harnesses have in line fuses that break the power when a fault occurs or a power surge is encountered The fuse will protect the device drawing power by breaking and shutting off the power surge before it damages the device for what the power is intended.
Take that simple illustration of a harness function and add five redundant power systems with 120 miles of big power cables, bundled in the KC-46 Tanker. If the harness design or the manufacturer of that key part is wrong in its design; the electrical function is subject to failure and electrical system becomes a high risk in its function when considering stringing 120 miles of electrical cable. Its all about exploding fuel tankers, sparks and combat. Wires and harnesses are a touchy subject with the Air Force Tanker program. Boeing needs to review what it is bringing to the military table.
The Air Force inspects systems before first flight is attempted. It's done doing that thing called inspection, and Boeing has now been sent back to fix its under specification harness and wire engineering problems. It's not a show stopper on the project, but its expensive and time consuming for the Boeing R&D workforce to get the power system corrected for it to meet "Air Force Expectation". Cables must meet certain standards in the layout schemed, as the Air Force requested in the bid process, specifically for this aircraft. It appears that Boeing didn't always meet that standards where a small percentage of the electrical cable does not meet those standards or conditions of installment required, and the harnesses over-all needs a "redesign". It is millions of dollars, and thousands of hours, where it will then cost more millions if Boeing comes in late with the KC-46.
Here is what Boeing is saying (paraphrased), "We will get it fixed on our dime, where we will still make money on this project by the time we deliver the contract of 179 tankers. We will not be late, since these type of things are typical on all projects, and we have made provisions for speeds bumps during any project. This certainly is not a show stopper at this phase of the project."
They also hope to sell more after that 179 number to other military partnered countries, once the project takes off during the military delivery cycle.
The good news, the style of fixed cost has its merits. No experimentation on the aircraft structure is needed or is the engine type used a question. The F-35 is going through a vetting process on everything hung on the air frame. The KC-46 issues, so far, are non commercial problems. The problems are and should be confined to the military side of the program. A wire snag which is awkward, but fixable without more experimentation of the aircraft development. Its a "Just Do It" solution throwing more $millions at the problem, while avoiding any Air Force late fees and angst(anger).
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