WASHINGTON — Boeing will have to pay to fix two new technical problems afflicting the KC-46 refueling tanker, which the U.S. Air Force has designated as “category 1” deficiencies that rank among the program’s most critical issues.

The Air Force has discovered that drain tubes in the KC-46′s air refueling receptacle — which are used to remove water from the aircraft — can become cracked when the tanker operates in cold temperatures, the service stated in response to questions from Defense News. According to the service, this issue has occurred approximately three times, when water in the tubes froze and expanded, forming cracks.

The second problem involves a software bug in the KC-46′s Flight Management System, which has triggered “navigation anomalies,” according to Boeing.

The Air Force said this issue has been limited to “isolated incidents,” most recently during a March 3 flight over the Pacific Ocean. Then, the crew “deferred to other navigation methods and did not declare an in-flight emergency” before landing safely in Honolulu, the service said.

Boeing added that the problem did not make the aircraft less safe and that each KC-46 has since been cleared for flight.

“Boeing will address both issues at its own expense,” Air Force spokesman Capt. Josh Benedetti said in a statement.

“There are no operational restrictions on fielded KC-46s due to either of these deficiencies,” he said. “The [program office] and Boeing have established operational processes and maintenance procedures to mitigate impacts and ensure the issues do not add extra risk to personnel, aircraft or operations.”

As a short term strategy for dealing with the cracked aerial refueling receptacle tube issue, Boeing has issued inspection guidance to the Air Force to mitigate known risk factors. To permanently fix the problem, however, it will have to redesign the drain line tubes and retrofit existing KC-46s with the modification, the service said.

General Electric — Boeing’s subcontractor for the Flight Management System — is already testing a software fix aimed at resolving stability problems.

To mitigate current risks, Boeing has issued guidance to help KC-46 crews to reset the system if a problem is experienced during flight. It has also delivered updated pre-flight procedures aimed at decreasing the likelihood of a software anomaly, the Air Force said.

The Air Force classified the two new problems as “category 1” deficiencies in May 2021.

Four other CAT-1 problems remain on the books: two issues with the Remote Vision System —the camera and sensor suite that provides imagery of the receiver aircraft to boom operators during a refueling — which requires Boeing to redesign the system; a problem with the stiffness of the boom that prevents some aircraft from being able to receive fuel; and an issue with fuel leaks.

Because the imagery currently provided by the tanker’s RVS is degraded in certain weather conditions — making it more difficult for boom operators to refuel other aircraft — the service has restricted the operational missions the KC-46 can perform. Air Mobility Command plans to make the aircraft available to U.S. Transportation Command for limited operations sometime this summer.

Boeing is locked into paying any cost that exceeds its $4.9 billion firm, fixed-price contract with the Air Force, and has so far paid more than $5 billion out-of-pocket to resolve technical problems that have arisen since the agreement was signed in 2011.

“We’re paying $226 million a copy for a lemon,” said Rep. Rob Wittman, R-Va., during a June 16 House Armed Services Committee hearing on the Air Force budget. “Every month, we hear about another category 1 deficiency … I’m frustrated.”

After Wittman asked whether the Air Force would consider recompeting the contract, acting Air Force Secretary John Roth said the service believes sticking with the KC-46 provides the most economical path for recapitalizing its aging tanker fleet.

“We’ve been working with the contractor. … We’re going to work on the Remote Vision System; we’re going to work on the boom, and hopefully they’ll be ready by 2023, 2024,” Roth said.

The Air Force plans on ordering a total 179 KC-46s throughout the program, and thus far 46 aircraft have been delivered.

Boeing is set to complete a preliminary design review of the new RVS 2.0 system in July, according to Air Mobility Command.

The two new deficiencies will not impact AMC’s plan for an interim upgrade of the tanker’s existing vision system.

“We are pleased with the work of the combined joint technical team and the significant improvement to the image our air refueling operators will see when refueling receivers with RVS 2.0,” AMC said in a statement. “We believe we are on track to provide a great solution to the joint warfighter in 2024.”