WASHINGTON — The U.S. Air Force’s troubled KC-46 tanker program has hit another bump, adding two of the most serious types of deficiencies yet to the list of problems manufacturer Boeing needs to fix.

The service on Thursday evening disclosed two “category one” deficiencies involving the remote vision system and centerline drogue systems, and there is no concrete timeline by which these issues will be fixed, Air Force spokeswoman Ann Stefanek said in an email.

The first deficiency centers on the KC-46’s remote vision system made by Rockwell Collins. The RVS is used by the boom operator to safely steer the boom into the receiver aircraft’s receptacle in all weather conditions.

The RVS performance is not meeting Air Force requirements. That, in turn, is contributing to another, previously disclosed issue: “undetected contact outside the receptacle,” or in layman’s speak, an increased likelihood of scraping the exterior of a receiver aircraft with the boom.

To combat this deficiency, Boeing is developing a software fix to the RVS that will hopefully make it more effective. The Air Force will begin flight testing the amended system this month. If successful, the service may be able to cross out both the RVS and “undetected contact” deficiencies at the same time.

The second deficiency revolves around the centerline drogue system, or CDS. During tests, the Air Force found that sometimes the receiver aircraft unexpectedly disconnects from the CDS.

This doesn’t pose any “immediate” safety risks, and the Air Force and Boeing are conducting systems engineering analysis to determine the cause of the problem and how to mitigate it.

“We are confident that the KC-46 will meet the USAF’s operational need safely and effectively,” Boeing spokesman Chick Ramey said in a statement. “We will continue to refine those capabilities with the Air Force — including the Remote Vision System (RVS) and Centerline Drogue System (CDS). Boeing is flight testing a software enhancement this month that we expect will improve visibility.”

Although new issues have cropped up, the Air Force is making progress in solving other KC-46 problems. It recently downgraded two deficiencies — one of which involved the high-frequency radio and another where the boom would push forward into the receptacle upon disconnect — from category 1 to category 2, Stefanek said.

“Risk from the High Frequency Transmit Inhibit [deficiency report] was found to be acceptable for delivery, but the DR remains open since the system does not meet specification requirements. A long-term fix to the deficiency will still be required to eliminate risk, and Boeing is expected to resolve the issue,” she said.

“A minor software update is expected in the spring, to address the Uncommanded Boom Extension During Flowing Disconnect deficiency,” she said.

Mo’ tankers, mo’ problems

The revelation of the new issues comes just a week after the Air Force disclosed that it now believes the delivery of the first KC-46 will be delayed again, this time likely to the end of the year. Perhaps more importantly, Boeing probably won’t be able to meet its contractual obligation to deliver 18 certified KC-46s in October 2018, with the service now estimating it will happen in spring 2019.

However, Stefanek said the recent deficiencies did not prompt the service to revise its schedule projection, and that the issues are “a normal part of our development process.”

“The timeline for first delivery was modified based on known risks and predicted impacts associated with airworthiness certifications and slower-than-expected flight test execution,” she said. “While these deficiencies weren’t explicitly accounted for, the potential for additional technical findings were accounted for in the schedule risk assessment.”

In a House Armed Services Seapower and Projection Forces Sumbcommittee hearing on Wednesday, lawmakers asked if the Air Force would be able to get the KC-46 back on track. The committee’s top Democrat, Connecticut Rep. Joe Courtney, was especially concerned that the testing issues could cause later problems as new tankers are delivered and the service begins training the first KC-46 pilots.

“How [do] we get this centipede moving along instead of having it bunched up after the planes are coming out of the factory?” he asked.

Air Force acquisition head Will Roper replied that, going forward, the speed that Boeing resolves issues will be a “key metric” that Roper will consider in assessing the program’s heath.

“The fact that there are issues on the program is less concerning to me. What will concern me during this year is if issues don’t get retired quickly,” he said.

The service is planning to begin divesting its smaller KC-10 fleet once the KC-46s are delivered and begin operating. It will retain 300 KC-135s and buy 179 KC-46s for a total fleet of 479 tankers, growing the tanker inventory from the 455 KC-10s and KC-135s currently operated by Air Mobility Command.

However, if the KC-46 is delivered late, the Air Force will not be able to begin retiring KC-10s in fiscal 2019, as is currently planned.

“If we’re late on delivery, I would expect that we would have a similar delay on the retirement of the aircraft,” Roper told the panel.