Leaders in the pilot union at Northwest Airlines Corp. approved a tentative joint contract with Delta Air Lines Inc. to take effect after the two airlines combine.

The next step is a vote by rank-and-file pilots at both airlines.

The Northwest branch of the Air Line Pilots Association says its Master Executive Council voted unanimously to send the proposed contract to pilots for a vote.

They still need to work out a merged seniority list, and that can be the toughest part of combining two pilot groups. They have agreed on a process for doing the list.