WASHINGTON (AP) - Lawmakers on Thursday demanded a detailed explanation of what went wrong with the Air Force's management of a $35 billion tanker contract awarded to Northrop Grumman Corp. and its European partner over Boeing Co.

"This isn't the first time the acquisition system has failed," said Rep. Neil Abercrombie, D-Hawaii, chairman of a House Armed Services subcommittee.

Lawmakers sought clarity from Defense Department officials and congressional investigators on whether the recent competition's failure was confined to the Air Force, or indicative of a more systemic problem among the Pentagon's procurement process.

"Is it too complex? Do we have the right people? Do they have the right training?" asked Abercrombie.

Lawmakers also pressed for details on how the Pentagon would proceed with the re-competition of the tanker deal that Defense Secretary Robert Gates announced Wednesday to avoid future mistakes.

The Government Accountability Office last month detailed "significant errors" the Air Force made in the original award to Northrop and Airbus parent European Aeronautic Defence and Space Co. The GAO said Chicago-based Boeing, which protested the deal, might have won had the service not made mistakes in evaluating the bids.

Congress has been highly critical of the Air Force's management of the competition, arguing the latest botched contract continues a recent string of acquisition failures by the service, including a $15 billion deal awarded to Boeing in 2006 for search-and-rescue helicopters, which was later challenged by Bethesda, Md.-based Lockheed Martin Corp. A new contract has yet to be awarded.

Following the hearing, senior Air Force and Pentagon officials including Sue Payton, assistant secretary of the Air Force for acquisition, were scheduled to hold a closed-door session with committee members.

Gates said Wednesday the Air Force would no longer oversee the tanker competition, and appointed Pentagon acquisition chief John Young and a dedicated source selection committee to take the helm. The Pentagon will hold a limited rebid that will look at eight problems the government auditors found in the initial process.

Boeing is concerned the Pentagon's revised request may "significantly alter the selection criteria" beyond what was initially asked for by the Air Force, while Los Angeles-based Northrop hopes the new competition will provide a fair opportunity to present its proposal.

In a speech on the Senate floor Thursday, Boeing supporter Sen. Patty Murray, D-Wash., raised concerns the Pentagon's new selection criteria would likely "bias the contest" in favor of the Airbus plane.

"Changing the rules of the game in overtime will simply result in a repeat of the last contest: an unfair result, more protests and more delays," said Murray.

Northrop supporter Sen. Jeff Sessions, a Republican from Alabama, where Northrop would assemble its planes, will be giving a speech Friday on the tanker program. The Pentagon's decision to quickly re-compete the contract by addressing the GAO's "limited concerns" was a "positive development," he said Wednesday.

The Air Force in February selected the Northrop team to replace 179 Eisenhower-era aerial refueling planes. Boeing filed its protest in March.

The deal - one of the largest in Pentagon history - is the first of three contracts worth up to $100 billion to replace nearly 600 refueling tankers over the next 30 years.