767-Derivative Tanker Manifestly Troubled

More than six-years have passed since the U.S. Air Force identified a number of serious deficiencies plaguing its Boeing-built KC-46 tankers. Comes now August 2023 and no fewer than six Category-1 deficiencies remain outstanding on the 767-derivative aircraft. A seventh such deficiency was downgraded to Category-2 in April—so stated USAF KC-46 program office chief Colonel Leigh Ottati in the first public announcement pertaining to the conundrum.

Colonel Ottati detailed the deficiencies still plaguing the KC-46 Pegasus and shared updated timelines for the resolutions of such.

The Air Force defines a Category 1 deficiency as one which “may cause death, severe injury, or severe occupational illness; may cause loss or major damage to a weapon system; critically restricts the combat readiness capabilities of the using organization; or result in a production line stoppage.” Category 2 defects, conversely, “impede or constrain successful mission accomplishment.” 

The Government Accountability Office (GAO) noted seven Category 1 deficiencies afflicting the KC-46 in January 2022; 19 months later, not a one has been fully resolved.

Colonel Ottati reported the USAF had worked with subcontractor GE Aerospace to develop a software fix for issues with the KC-46’s Flight Management System (FMS). While the remedy appears to have been successful, FMSs across the Air Force’s KC-46 fleet remain under close observation.

“We’re going to do that for a period of time to make sure that all the software fixes that are out there are working, which they have been, and then we’ll close that deficiency completely,” Ottati conceded. 

The most significant of the KC-46’s current woes is a temperamental Remote Vision System, the camera and video systems of which USAF boom-operators employ to refuel U.S. and allied aircraft. The Air Force has identified two Category 1 deficiencies pertaining to subject RVS, one of which precipitates the other. Under certain lighting conditions, KC-46 boom operators are unable to clearly see the fuel-receptacles of recipient aircraft. Under such conditions, refueling booms are apt to strike or scrape along the fuselages of aircraft being fueled—costly mishaps in the instances of stealth aircraft the likes of the B-2 Spirit and F-22 Raptor, the radar-absorbent coatings of which are particularly susceptible to contact damage.

The brand new RVS 2.0 solution with which the Air Force intends to remedy the KC-46’s myopic booms shan’t be deployment-ready until 2025.

Speaking to the planned fix, Colonel Ottati remarked: “We still have challenges and schedule risks with RVS 2.0, but right now, we’re working closely with Boeing and their main subcontractor, Collins, on continuing to progress well with that, and intending to complete the development in late ’25 as previously reported, and then go straight into retrofits.”

Once the RVS 2.0 technology is deemed deployable, Boeing will retrofit the Air Force’s KC-46 fleet at Jacksonville, Florida’s Cecil Airport (VQQ) over a planned two-month period.

Colonel Ottati set forth the second critical action item arising from the KC-46 RVS “  … had to do with the FAA certification plan for the commercial off-the-shelf cameras that are in the RVS 2.0 solution. We’ve been working very closely with Boeing and the FAA on that and we have a good path forward and expect to close out that last critical action from … this quarter, so by the end of September.”

Another of the deficiencies by which the KC-46’s airborne refueling system is hampered is the boom’s lack of rigidity. The USAF’s fleet includes a number of aircraft incapable of producing the thrust required to hold the boom in place during refueling. The problem has been determined to be the boom’s actuator, which “drives the boom out in the telescope direction, and then, when a receiver connects with it, the receiver drives the boom back into sort of a nominal refueling position,” explained Boeing KC-46 Program Manager James Burgess.

Rather than redesign the boom in its entirety, Boeing and the Air Force have opted to redesign the actuator; however, developing a compliant actuator has thus far proved difficult.

Colonel Ottati stated: “We just recently had a Test Readiness Review meeting with Boeing and [subcontractor] Moog, and there’s still some challenges with [the boom telescope actuator redesign]. Right now, we’re still expecting an early fiscal 2025 completion of the development for BATR [the telescoping boom actuator replacement]. And we have some margin until we can start retrofit, because of the long lead items for the retrofit portion. But we’re still struggling a little bit with the BTAR schedule and working closely with Boeing and Moog to make sure that we don’t eat up that margin that we have between the finishing of development and the start of retrofit, based on again, those long lead items.”

The KC-46’s remaining Category 1 deficiencies are related, all, to the quality of the aircraft’s design and construction—which have been found lacking.

One such issue pertains to the drain masts of the tankers’ Auxiliary Power Units (APU), which have been deemed apt to crack or break loose. The USAF previously downgraded the deficiency to a Category 2, believing an interim fix had been identified. The service backtracked, however, when further cracks in the APU drain masts were observed.

Colonel Ottati reported Boeing is developing a long-term fix—“a newer, more robust drain mast, beefed-up APU doors.”

Boeing’s corrective action notwithstanding, the USAF remains hesitant to declare the APU drainage mast problem solved.

Ottati asserted: “[We want to] make sure we have the right data, the appropriate data to ensure that we’re not seeing the same excessive vibrations and cracking in APU drain masts. And I say appropriate data because it’s primarily at high-speeds with the boom lowered that we were seeing those kind of vortices in the back of the aircraft that were causing that vibration. So I want to make sure we have a significant amount of flight-hours showing that those drain masts are not an issue any longer. Maybe six-months or longer before we will look at potentially downgrading those and downgrading that one as well.”

The KC-46 is afflicted, also, with fuel-system leaks deriving of bad valve seals. Boeing officials contend they’ve redesigned the defective seals after a fashion conducive to greater ease of installation.

Addressing the matter of the shoddy valve seals, Colonel Ottati stated: “We’ll analyze in the next six-months if that’s one we could downgrade and close at some point. I don’t want to close … prematurely. I want to make sure that we have the right fix and plan for the retrofit for the entire fleet that’s affected.”

The KC-46’s final quality shortfall relates to cracks in a drain line of which Ottati remarked: “It’s a drain line that comes from the receptacle of the KC-46, through the flight deck, and then exits out the bottom of the aircraft—primarily for any excess fuel or water or anything like that to make sure that it doesn’t stay within the receptacle and drains. And what we’re seeing is because of the design, in cold temperatures with remaining water or fuel in the line, that drain line was cracking, creating the potential that there could be fuel on the flight deck.”

Progress on the cockpit drain line fix has been slowed by glacially-sluggish FAA certification conventions. Boeing, however, hopes to commence flight-testing a solution in September or October 2023.

FMI: www.af.mil