Air Force identifies new category 1 deficiency on KC-46 refueler

WASHINGTON — The US Air Force and Boeing discovered a new “category 1” deficiency on the already embattled KC-46 tanker, though the service said the plane-maker is working quickly to remedy the issue.

Called the “bleed air duct deficiency,” the issue stemmed from vibrations from a fuel pump that were damaging bleed air ducts, Kevin Stamey, the Air Force’s program executive officer for mobility and training aircraft, told reporters here at the Life Cycle Industry Days conference. Aircraft use “bleed air,” or compressed air extracted from an engine or auxiliary power unit (APU), for a range of functions like pressurization and cooling subsystems.

To Boeing’s credit, Stamey said, the company “has been quick to get those repairs done to the damaged aircraft.” Initial flight tests showed that a mitigation technique to minimize vibrations “look[s] very promising” as an interim solution ahead of a permanent fix, Stamey said, adding that the service is “actually on the path to quickly downgrade that one” if test results bear out. The mitigation technique involves “cycl[ing] the pump on or off to minimize the vibrations.”

A Boeing spokesperson said in a statement that “[a] long-term fix is in work, and we have developed a short-term mitigation plan that is being reviewed by the U.S. Air Force to reduce impact to the fleet.” The new issue “is not an immediate safety concern,” the spokesperson added.

The Air Force describes category 1 deficiencies as any issue that could cause loss of an aircraft, injury or death. The aircraft is now subject to a total of seven category 1 deficiencies, though officials today emphasized many issues are on a path to be resolved, and Boeing has talked reporters through its own plans to get the tanker back on track.

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For example, according to the Air Force’s KC-46 Division Senior Materiel Leader Col. David Hall, new flex coupling links to fix a problem in the aircraft’s fuel manifold are being fielded after a final design was approved, though an exact timeline for downgrading that issue is still being worked out. Regarding another category 1 issue, new designs have also been fielded on half the fleet to address cracking on the aircraft’s APU drain masts, which is on a “near term path to closure.” The service and Boeing have also completed a design “within the last couple of weeks” that should prevent cracks from appearing in the drain line for the aircraft’s refueling receptacle. 

As for the other three deficiencies, two are associated with the aircraft’s long-delayed Remote Vision System redesign, expected to field in spring 2026. Lastly, a redesign of the aircraft’s boom actuator, which will enable it to refuel the A-10 Warthog, is now FAA compliant and entered lab testing in May. The Air Force has previously said the solution should be ready by FY26.      

Boeing has so far lost over $7 billion on the program due to its fixed-price development structure. The problems so far have delayed a full-rate production decision, and Stamey said today there is still no firm date for when the milestone might be reached.

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Officials previously described the KC-46 as a likely answer to the question of how to recapitalize the service’s aging KC-135 refueling fleet ahead of a potential brand new tanker design, but in recent months officials have started to question the effort amid budget constraints. The current KC-46 program of record with Boeing calls for 183 aircraft, with options for five more, according to Stamey.

Echoing comments of Air Force Secretary Frank Kendall, “no decisions have been made” regarding the recapitalization effort, he said. Additionally, an analysis of alternatives for the service’s future refueling fleet, dubbed the Next Generation Air refueling System (NGAS), will be completed in October, he added.