ALEXANDRIA, Va. -- A bankruptcy judge agreed Saturday to allow U.S. Airways to terminate its pilots' pension plan, but said his ruling will be subject to the pending decision of an arbitrator.

The pension issue is the last hurdle US Airways faces in its plan to emerge from bankruptcy by March 31. U.S. Bankruptcy Judge Stephen Mitchell's ruling means the airline has not yet completely cleared that hurdle and will be under immense pressure to resolve the pension issue quickly.

"We think this is an important ruling because it allows us to stay on track," U.S. Airways spokesman Chris Chiames said.

Roy Freundlich, a spokesman for the Airline Pilots Association, said the union is pleased that an arbitrator will decide if terminating the plan violates the pilots' collective bargaining agreement.

The key issue is whether the pilots' union agreed to allow the airline to terminate the pension plan in a secret agreement reached in December.

In the agreement, management promised to begin a new, smaller pension plan if the old one were terminated. They kept the agreement secret because if it became public, they thought it would torpedo efforts to get Congressional legislation to fix their problem.

But union and management differed on the agreement's meaning. U.S. Airways said the letter constituted acquiescence from the pilots to termination of their plan.

But the union said the agreement was only designed to give them protection in the event that the federal Pension Benefit Guaranty Corp. instituted efforts to terminate the plan.

Judge Mitchell said Saturday that it was a close call but sided with the union's interpretation.

On all other matters, Mitchell sided with the airline. He agreed that the airline faces imminent threat of liquidation if it does not resolve the pension issue and he agreed that the airline does not have the money to fully fund its pension plan.

The union said most pilots would receive annual benefits of $50,000 to $70,000 a year under the old plan. Under the new plan, those benefits could be cut in half.

An arbitrator is scheduled to hear the issue March 13. The final hearing for U.S. Airways to emerge from bankruptcy is scheduled for March 18.