WASHINGTON — With the July 15 refueling of the A-10 Warthog, the KC-46A has officially completed all flight tests needed ahead of a milestone decision this August.

Now the tanker program can a request approval from Pentagon acquisition head Frank Kendall to move forward with a Milestone C decision for low rate initial production, the Air Force announced Monday evening. That approval would allow the Air Force to award a contract to Boeing for LRIP 1 and 2, which amounts to 19 aircraft.

"Today's flight marks the final step we needed to see on the boom fix in order to request production go-ahead," Brig. Gen. Duke Richardson, the Air Force program executive officer for tankers, said in a statement. "Our joint team's tireless efforts are paying off, preparing us for the next step of this critical need to our warfighter."

During the A-10 refueling, the KC-46A transferred 1,500 pounds of fuel to the Warthog, according to the Air Force. It previously conducting refueling demonstrations with the C-17 Globemaster II and F-16, which use the air refueling boom, with the F/A-18 Hornet and AV-8B Harrier — Navy and Marine Corps aircraft that use a probe and drogue system — and with another KC-46.

The Air Force announced the successful refueling of the C-17 and F-16 last week, a boon to the program after it was found that the KC-46 boom had difficulties refueling heavier aircraft such as the C-17. That problem contributed to a delay that pushed a Milestone C decision from June to August, and the delivery of the first 18 certified tankers to the Air Force from August 2017 to January 2018.

The refueling boom has since been reworked and has conducted flight demonstrations since early July. The new design includes a bypass that helps control the flow of fuel when heavier aircraft are refueled.

"It is great to see the KC-46 boom back in action and the program moving forward to a production decision" said Col. John Newberry, the KC-46 system program manager.

Still unknown is exactly how the program delay will affect Boeing's bottom line. Under the fixed-priced contract negotiated by the Air Force and Boeing, the service is responsible for up to $4.9 billion of the cost of developing the aircraft. Boeing must pay for any cost overruns in excess of that sum, and has already been hit with $1.5 billion in penalties.