Five big contractors on Tuesday withdrew from an Air Force competition to buy 112 new rescue helicopters, with industry officials saying the terms of the competition favored Sikorsky’s Black Hawk helicopter and would not reward extra capabilities offered by their aircraft.

Northrop Grumman Corp, which was teamed with Italy’s Finmeccanica SpA ; Boeing Co ; Textron’s Bell Helicopter unit; and the U.S. unit of Europe’s EADS all said on Tuesday that they would not compete to build 112 new helicopters for the Air Force, raising questions about whether the contest can proceed as planned.

The official denied that either the tanker or helicopter competitions were structured to preference one bidder.

“That is absolutely not the case, period. Absolutely not,” said the official. “We try to write source selections that reflect our requirements and define our requirements as clearly as we can ... It has nothing whatsoever to do with pre-selection of a specific candidate.”

The official said the Pentagon had guidelines for how to handle a sole-source competition to ensure it still got the best deal possible, although no decision had been made yet to change the Air Force’s approach in this case.

“I’m not sure how it’s going to play out at this point ... It may end up with one bidder,” said the official.