(Adds detail on KC-46 sales)
March 7 (Reuters) - The U.S. Air Force said the first delivery of KC-46 aerial refueling tankers from Boeing Co , scheduled for the second quarter of 2018, is more likely to occur late in the year.
"This assessment is based on known risks and predicted impacts associated with airworthiness certifications and slower than expected flight test execution," the Air Force said in a statement on Tuesday.
These potential delays will not result in additional program cost to the taxpayer, the statement said.
Boeing could not immediately be reached for comment.
The world's biggest maker of jetliners is expected to deliver 18 tankers.
In the third quarter of 2017 the company took a $329 million charge for its KC-46 aerial refueling tanker program, hurting profit. Charges related to the program have reduced profit by $1.9 billion after tax.
Boeing expects to build a substantial business from the tanker, which is based on its twin-aisle 767 commercial jet. Boeing plans to deliver 179 tankers to the U.S. Air Force and expects to sell about 400 in total worldwide. (Reporting by Ismail Shakil in Bengaluru and Chris Sanders in Washington Editing by Grant McCool and Matthew Lewis)