The Air Force has upgraded an existing deficiency on its KC-46A Pegasus tanker program to Category 1, the service said March 30.

The newest CAT-1 deficiency relates to the aerial refueler’s fuel system, where the KC-46 program office first identified excessive fuel leaks after an air refueling test in July 2019, the Air Force said in the Monday release. Boeing [BA] is the prime contractor for the Pegasus program.

“The Air Force and Boeing are working together to determine the root cause and implement corrective actions,” Air Force spokeswoman Capt. Cara Bousie said in the release. “The KC-46 Program Office continues to monitor the entire KC-46 fleet and is enhancing acceptance testing of the fuel system to identify potential leaks at the factory where they can be repaired prior to delivery.”

Boeing, under a $4.9 billion fixed-price contract, is obligated to remedy this deficiency at no additional cost to the government, Bousie noted.

The aerospace company said in a Monday evening statement that it was disappointed to learn of this development and is already implementing assembly and installation improvements to correct the issue.

The KC-46 fuel system is equipped with redundant protection for fuel containment, and there have been instances where fuel is discovered between the primary and secondary fuel protection barriers within the system, Boeing said.

“We have repaired several of the airplanes, and will continue to implement repairs as needed,” the company said. “Boeing is working with the utmost urgency to address this issue.”

The new upgraded deficiency brings the program’s number of Category-1 deficiencies up to four. Two others relate to the tankers remote vision system (RVS), which will require extensive hardware and software fixes to allow operators to observe refueling through a camera without a warped lens.

Will Roper, the Air Force’s civilian acquisition chief, told reporters in a March 27 roundtable that he is very confident that the service and Boeing will reach an agreement on an RVS solution in the near future, despite travel and work restrictions caused by the ongoing COVID-19 coronavirus pandemic.

“I am very confident that the momentum that we started prior to COVID-19 is going to wrap up soon,” he said. “That has not come off the table and we are hopeful that we will reach an equitable agreement soon.”

The service has recorded instances where the KC-46’s boom has scraped against the receiving aircraft, but believe that to be related to the RVS issues.

The fourth CAT-1 deficiency relates to issues with the tanker connecting properly with the A-10 attack aircraft. The Air Force will pay Boeing for the redesign via a requirements change.

As of March 6, Boeing has delivered 33 KC-46 aircraft to the Air Force since the first aircraft flew to McConnell AFB, Kansas, in January 2019. The program of record includes 179 aircraft.