WASHINGTON — A trio of senators are calling for an investigation into technical deficiencies that have delayed the operational employment of the KC-46 tanker made by Boeing.

New Hampshire Democrats Maggie Hassan and Jeanne Shaheen, as well as Sen. James Lankford, R-Okla., directed the Government Accountability office on Friday to provide “periodic assessments” on the progress Boeing is making to fix problems impacting the KC-46’s boom and Remote Vision System.

The lawmakers — who represent Pease Air National Guard Base, N.H., and Tinker Air Force Base, Okla., where the KC-46 is based — wrote that they were concerned that Boeing is moving too slowly on correcting ongoing issues.

“While the Air Force has already accepted over 30 aircraft, U.S. Transportation Command has decided not to use the aircraft in operations until the critical deficiencies are fixed, which is not expected to occur until 2023. Instead, it plans to use legacy KC-10 and KC-135 aircraft, some of which are over 60 years old,” they stated in a letter to Gene Dodaro, head of the GAO and comptroller general of the United States.

In addition to reviewing the program’s progress, the senators also ask the GAO to evaluate what steps U.S. Transportation Command could take to alleviate an ongoing shortage of tankers, as well as any sort of penalties Boeing is incurring due to the delays.

In April, Boeing and the Air Force came to an agreement to replace the KC-46’s Remote Vision System — a long fought battled between the two parties that has contributed to delays in accepting and fielding the tanker.

The Air Force has maintained that the existing RVS — a camera system the boom operator relies on for visual cues during the refueling process — does not provide the visual acuity in all lighting conditions needed to use the KC-46 in day-to-day operations. Boeing has agreed to completely redesign the RVS, but it will take until at least 2023 for the new system to be fielded.

Air Force Chief of Staff Gen. Dave Goldfein has said that if absolutely needed, the service could use its KC-46s in a conflict against China or Russia.

However, Army Gen. Stephen Lyons, who leads U.S. Transportation Command, has cautioned against a proposed plan by the Air Force to retire some of its legacy KC-10 and KC-135 tankers in fiscal year 2021, saying those aircraft will be needed to meet daily requirements until the KC-46 is fully operational.

Lawmakers have repeatedly voiced exasperation with the KC-46.

“I don’t think it’s acceptable at this point to say, ‘That’s just the way it goes.’ I think we have to explore what options we might have,” Shaheen told Defense News in March.