The Boeing logo is seen at their headquarters in Chicago, in this April 24, 2013 file photo. REUTERS/Jim Young/File Photo

(Reuters) - Boeing Co BA.N said on Wednesday its KC-46 mid-air refueling tanker program completed the U.S. Federal Aviation Administration certification, nearly three years after the planemaker commenced testing for the certification.

The KC-46, which is derived from Boeing's commercial 767 airframe, will receive a Supplemental Type Certificate (STC). bit.ly/2MQP2OR

The KC-46 is a multirole tanker which will refuel U.S., allied and coalition military aircraft using its boom and hose and drogue systems.

Earlier in July when Boeing reported quarterly results, the company said it would spend an additional $426 million before taxes on the program as it worked through test delays and production changes to eight aircraft in various stages of production.

Analysts had said they were worried that the additional expenses on the KC-46 program would slow shares, adding that the higher tanker costs came with unchanged earnings and cash flow forecasts.

“This milestone is important in that it is one of the last major hurdles in advance of first delivery to the U.S. Air Force,” said Mike Gibbons, Boeing KC-46A tanker vice president and program manager.

Boeing is currently on contract for the first 34 of an expected 179 tankers for the U.S. Air Force, the Chicago-based company said.