ATLANTA — Delta Air Lines Inc. and Northwest Airlines Corp. pilots are headed to arbitration to resolve their stalemate over how to integrate their seniority lists when the two carriers combine later this year.

Pilots value their seniority because it determines their schedule, the aircraft they fly and layoff protection.

A three-member panel has been selected to resolve the issue. As many as 12 hearing days could be scheduled.

Details on where and when proceedings will be held have not yet been released. A written decision, which would be binding, is due by Nov. 20.

Tuesday was the deadline for the two sides to reach a deal on their own before submitting to arbitration. By late afternoon, there was no announcement of an agreement, and a Delta pilot union spokeswoman indicated none was forthcoming. Nothing prevents Delta and Northwest pilots from continuing to negotiate to try to ink a deal on their own while the arbitration process proceeds.

The members of the panel are Fredric Horowitz, a California labor attorney; Dana Eischen, an attorney who worked as an independent arbitrator for Major League Baseball in the late 1990s and was a member of a Presidential Emergency Board appointed to head off a railroad strike in 1975; and Richard Bloch, who sided in 2005 with the Philadelphia Eagles as arbitrator of their decision to bench star receiver Terrell Owens, who now plays with the Dallas Cowboys.

Horowitz and Bloch also served on an arbitration panel selected in 2006 to determine whether Delta, which was under bankruptcy protection at the time, could void its pilots' contract and impose pay and benefit cuts unilaterally. Delta's pilots union, which had threatened to strike, eventually agreed to concessions, and that panel never issued a ruling.

Pilots at Delta and Northwest have approved a joint collective bargaining agreement. Voting results were announced Monday. Ratification of that agreement has been a key element of Atlanta-based Delta's efforts to achieve a smooth integration of the two companies when it acquires Eagan, Minn.-based Northwest.

The joint contract agreement covers roughly 12,000 pilots of the two airlines. It will become effective when the Delta-Northwest combination closes, which is expected by the end of the year.

Delta's stock-swap deal to acquire Northwest, announced April 14, is subject to shareholder and U.S. regulatory approval. European regulators cleared the deal last week.

The combination, proposed at a time of persistently high fuel prices and airline industry financial woes, would create the world's largest carrier in terms of traffic.