A Plastic Cap In A KC-46's Fuel Valve Generates More Turbulence For The Troubled Tanker

The revelation is the latest in a line of trash-related problems for Boeing aircraft — and not even the first debris issue for the KC-46.

KC-46A Pegasus takes off
USAF 127th Wing Public Affairs

The U.S. Air Force’s beleaguered Boeing KC-46 Pegasus tanker program hit yet another snag earlier this year. Deliveries were halted for around a month after plastic debris was found inside an internal fuel line in one of the aircraft as it flew to its future home in North Carolina. The small red cap jammed a valve open, causing an uncontrolled fuel transfer between tanks. 

Bloomberg News was first to report this new development with Boeing's long-troubled KC-46A. Aviation Week's Brian Everstein subsequently Tweeted out that the aircraft in question was a Pegasus that touched down at Seymour Johnson Air Force Base in North Carolina on April 30, 2021. A Tweet at the time from that base's 916th Air Refueling Wing, an Air Force Reserve unit, said that the plane had arrived safe and sound without mention of any problems.

This foreign object debris, or FOD, and the problems stemming from it, appear to have been discovered during the KC-46A's flight to Seymour Johnson, but it is unclear what, if any, risk this presented to the crew or whether there was any lasting damage to the aircraft. The Pegasus' crew “was not able to stop the transfer of fuel as desired" and the issue "was found to be caused by foreign object debris — a red plastic cap — that had become lodged in the right main tank shut-off valve,” Captain Samantha Morrison, an Air Force spokesperson, told Bloomberg.

“A shortfall was identified in the previous inspection process, and additional layers of inspections have been added," she continued. The Air Force officer indicated the service had received Boeing’s assurances that the Air Force would not receive any more aircraft with debris in them.

This last promise is significant, given how much trouble the company has had with FOD in their planes in recent years. This is not even the first time debris has been found in a KC-46A fuel tank. In June 2020, the Air Force Times reported inspectors had found foreign objects in a KC-46 fuel tank, delaying delivery of another Pegasus to Seymour Johnson. However, the Air Force told that outlet at the time that it determined this discovery had stemmed from “non-standard factory rework,” rather than “production line quality escapes” of the kind that had led to another pause in deliveries of these tankers in March 2019.

Aviation Week's Everstein had noted on Twitter that Boeing had failed to deliver two KC-46s before sending the one to Seymour Johnson in April. The Air Force had said "the company could not present ready aircraft," he wrote. "AFLCMC [The Air Force Life Cycle Management Center] said there was 'moderate risk' for this April 30 delivery."

The KC-46A production line is not the only part of Boeing to experience similar issues in recent years, either. Earlier this month, The Wall Street Journal reported that inspectors found empty tequila bottles one of two future Air Force One aircraft — more properly known as a VC-25B — at the company’s San Antonio, Texas, plant. Last year, it was separately reported that inspections found debris in the fuel tanks of almost two-thirds of undelivered 737 Max aircraft, after the aircraft was grounded because of software problems implicated in several fatal crashes. And Boeing's 787 Dreamliner has also had its own production debris issues.

For years now, the KC-46A has been beset by problems well beyond quality control, as well, as The War Zone has written about at length. The Air Force itself has described the program as a lemon out of which the service is trying “to make lemonade.” Most notable among the many issues, some of which have been resolved, are problems that impact the ability of the tanker to perform its primary mission, mid-air refueling. The aircraft still has significant issues both in the design of its refueling boom and with the Remote Vision System (RVS) that operators use to steer it into receiving aircraft, as you can learn more about here. Unlike with previous Air Force tankers, boom operators on KC-46As sit in the main cabin rather than in a position at the rear of the plane and use a complex hybrid 2D/3D system to "see" what's going on behind the aircraft and perform their tasks. Fixes are in the works for both of these issues, but are years away from being implemented across the fleet.

The KC-46A Pegasus is derived from Boeing’s commercial 767 airliner, which has been in service since 1982. A tanker version of the 767, the KC-767, was developed in the 2000s for foreign air arms and has been in service with Italy and Japan for years, but the USAF wanted to build a significantly different configuration for its own program to begin replacing the Air Force's elderly KC-135 aircraft. The selection of what is now known as the KC-46 was a major saga in itself that lasted more than a decade.

The Air Force plans to purchase as many as 179 of the Boeing tankers and has taken delivery of at least 47 of them so far. But even as the KC-46 program scrambles to reach full functionality, with updated booms and enhanced remote vision systems still years away, the service is already looking beyond the challenging program to add new tankers, which The War Zone wrote about in June and just last week. This program could involve into everything from an Airbus A330-based tanker to more KC-46s delivered in a more mature configuration.

In the meantime, the venerable KC-135 fleet soldiers on, as well as a decreasing cadre of KC-10s.