DALLAS (CBSDFW.COM/AP) — Southwest Airlines and a union representing its mechanics say they’re on the verge of ending a bitter, long-running labor dispute that has triggered hundreds of flight cancellations and raised safety concerns.

The two sides say the breakthrough announced Saturday consists of a preliminary agreement on a new contract after six years of negotiation between Southwest and the Aircraft Mechanics Fraternal Association.

The tentative deal still needs to be voted on by the roughly 2,400 mechanics who will receive a 20 percent raise if the contract is approved.

The agreement came after the Federal Aviation Administration warned that the deteriorating relationship between Southwest and its mechanics threatened to undermine the airline’s safety-management system.

Southwest had filed a lawsuit that claimed the mechanics were flagging minor maintenance issues to force unnecessary flight cancellations.

The Dallas-based airlines released a statement from Russell McCrady, vice president of labor relations, that said:

“Our Mechanics certainly deserve a new contract, and we believe this industry-leading Agreement in Principle addresses our Employees’ interests. The parties were able to agree to a work rule change that allowed the Company to add compensation to the previous Tentative Agreement. I want to thank both negotiating teams for finding a solution that takes care of our People and protects the long-term success of our Company. I would also like to thank the National Mediation Board (NMB) for their expertise in helping us reach this agreement.”

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