Boeing [BA] said that it has replaced or retorqued 22 Auxiliary Power Unit (APU) duct clamps on 12 of the 38 KC-46A tankers delivered to the U.S. Air Force after a ground maintenance inspection last year revealed small cracks.
“Though we have made recent progress on design deficiencies, we continue to monitor production quality closely and hold Boeing accountable for ensuring the KC-46 meets stringent quality control metrics,” Air Force acquisition chief Will Roper said in an Oct. 27 statement issued to Defense Daily. “Production quality deficiencies tax maintenance time for unnecessary repairs. We look forward to resolving them quickly.”
Of the 38 KC-46s Boeing has delivered to the Air Force thus far, 21 have gone to McConnell AFB, Kan., which is to be a “super tanker base”; six to Altus AFB, Okla., the tanker training base; seven to Pease Air National Guard Base, N.H.; and four to Seymour Johnson AFB, N.C.
The U.S. Air Force said that it first noticed the cracks on the clamps during KC-46A ground maintenance at Altus AFB on June 7th of last year.
“This discovery resulted in a June 11, 2019 product quality deficiency report (PQDR),” per the Air Force. “Boeing is using a more robust APU duct clamp design, utilized on the Boeing 777 [airliner], to resolve this deficiency. The improved clamps are being installed at no additional cost to the government. Retrofits are expected to be complete in early to mid-calendar year 2021.”
Boeing said that the cracking did not pose a safety risk and recommended that the Air Force replace the APU duct clamps on an attrition basis only.
“The problem with the duct clamps is a product quality issue which impacts fleet operational availability,” per the Air Force. “It is not a performance issue. By definition, Product Quality Deficiency Reports (PQDRs) include failures that result after the item was placed in service and are suspected as latent defects or quality escapes resulting from poor workmanship, nonconformance to applicable specifications, drawings, standards, processes, or other technical requirements.”
The KC-46A program is undergoing a high level of scrutiny at the DoD and congressional level.
On Oct. 1, Pentagon acquisition chief Ellen Lord told a hearing of the Senate Armed Services Committee’s readiness and management support panel that the KC-46A is “an extremely problematical program.”
Lord said that senior DoD leadership will continue paying careful attention to the program to address lingering problems, and she criticized the use of a $4.9 billion firm fixed price contract arrangement with Boeing as ill-suited to correct those issues.
“One issue is, frankly, the technical solution that was the original design and it’s now being redesigned. But also, we have had a myriad of manufacturing issues with [foreign object debris]. We have both an engineering, design and execution issue as well as a manufacturing problem,” Lord said. “At this point with KC-46, it will take very careful senior DoD attention. Secretary [Mark] Esper and I have both spoken to the CEO of Boeing, as well as Leanne Caret, but Dave Calhoun as well. And we will do that on a frequent basis.”
In June, the Air Force said it had pushed back KC-46’s timeline for Initial Operational Test & Evaluation, as well as delaying a full-rate production for the program until at least fiscal year 2024 (Defense Daily, June 10).
The Air Force has identified six Category 1–critical–deficiencies with the KC-46A: two Category 1 performance deficiencies with the Remote Vision System (RVS), which is to allow air refueling operator station (AROS) personnel in the front of KC-46A aircraft to steer refueling booms using Collins Aerospace [RTX] cameras on the fuselage ; a performance deficiency with the boom telescope actuator for connecting the refueling boom with slower aircraft, such as the A-10; a PQDR related to fuel manifold leaks; a PQDR related to the APU drain mast; and the PQDR related to APU duct clamp cracks. The Air Force has said that it has worked with Boeing to plan out fixes, including a new RVS 2.0 and a more pliant standard for the boom.
“RVS 2.0 field retrofits are expected to commence in August 2023,” the Air Force said. “The Boom Telescope Actuator Redesign (BTAR) effort will correct boom stiffness deficiencies. The BTAR retrofits are expected to commence in late 2023. Boeing is re-designing KC-46 fuel manifold coupling seals to improve capability and maintainability at no additional cost to the government. The re-design is expected to be complete at the end of calendar year 2020 with fielding available in early calendar year 2022.”
“A Product Quality Deficiency Report was issued for the auxiliary power unit (APU) drain mast, which was found susceptible to early fatigue,” per the Air Force. “At no additional cost to the government, Boeing developed a more robust, machined version of the drain mast and all affected aircraft have received the update.”
Regarding the cracked APU duct clamps, the Air Force said that it “classified this issue as a Category 1 PQDR because the cracked and failed APU duct clamps caused unacceptable levels of maintenance downtime which negatively impacted KC-46 operational availability.”
“It is a product quality issue for which there is not an acceptable field-level workaround,” the service said.
A Government Accountability Office (GAO) annual assessment of DoD acquisition programs in June discussed Category 1 KC-46A deficiencies.
“The most recently identified deficiency relates to auxiliary power unit duct clamps detaching, which could pose personnel safety risks,” the report said.
Like Boeing, the Air Force said that the cracked APU duct clamps did not pose a safety risk.
“This was not a safety issue,” the Air Force said. “This is a product quality issue not repairable by flight line maintainers. The cracked and failed auxiliary power unit (APU) duct clamps caused unacceptable levels of repair downtime and negatively impacted the operational availability of the KC-46. If an APU duct clamp is broken on the ground there could be operational impacts to maintenance, but no safety impacts. In the air, the APU is considered a back-up system to [engine-mounted] Integrated Drive Generators (IDGs), and cracked APU duct clamps do not pose a safety risk. Boeing is contractually obligated to resolve this deficiency at no additional cost to the government.”
Honeywell [HON] in Phoenix supplies the KC-46A APU, located in the tail of the aircraft in front of the exhaust. APUs provide start-up engine power and back-up electrical power for avionics, communications, flight control and other systems on aircraft.
In one celebrated APU incident, Chesley “Sully” Sullenberger, a retired Air Force fighter pilot, was able to ditch U.S. Airways Flight 1549 on the Hudson River on Jan. 15, 2009 after a flock of Canada geese hit the plane and caused engine failure. The Airbus A320-214 had an IDG on each engine. Sullenberger started up the Honeywell 131-9A APU to ensure flight controls, avionics and other systems kept running, as the aircraft skidded onto the Hudson River around midtown Manhattan. All 155 people aboard were rescued.
An APU duct clamp detachment can have safety consequences. On May 14, 2017, the cabin of a Boeing 737 flying from Prague to Djerba Zarzis International Airport in Tunisia depressurized at 32,000 feet, likely due to an APU bleed duct leak created by the detachment of a loose clamp on the APU duct valve seal, according to the Flight Safety Foundation. Passenger oxygen masks deployed automatically, as the flight crew donned their masks, conducted an emergency descent to 10,0000 feet and landed at Munich Airport in Germany without incident.