The board of directors for the Southwest Airlines Pilots Association (SWAPA) has agreed in principle to a new deal valued at $12 billion with the airline, the union has announced.

Pilots would see an immediate pay bump of about 29% upon ratification of the contract with 4% increases in each of the following three years, according to an executive summary of the deal shared with The Baltimore Banner. Pilots would see a net pay increase of about 50% over a five-year span.

If passed, the new deal would increase the airline’s contributions to pilot retirement accounts and codify disability insurance, a sticking point for the union, which had previously been responsible for providing its members. Additionally, it makes changes to the airline’s pilot scheduling system that a union representative described as “significantly better.”

SWAPA pilots have bemoaned the previous scheduling system as unsophisticated and the root cause of last year’s holiday meltdown that canceled hundreds of flights.

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The deal will go to a union vote starting on Jan. 8 and could be ratified as soon as Jan. 22.

“We know that the last few years have been difficult for our pilots as well as our customers, but we believe that this TA [tentative agreement] rewards our pilots as well as improving reliability for our passengers,” said SWAPA President Capt. Casey Murray in a press release. “Our membership has fought for almost four years to reach an agreement with Southwest Airlines. They now have the opportunity to evaluate this deal and cast their vote accordingly.”

The announcement comes after more than three years of tense negotiations between the bargaining unit for roughly 10,000 pilots and their employer, which operates the largest share of flights coming and going from Baltimore-Washington International Thurgood Marshall Airport, and the same week a steep $140 million fine for its mismanaging of last year’s holiday meltdown was announced.

In November, SWAPA opened its first regional strike center in Columbia as a meeting and serving point for pilots in the event the union be allowed to walk off the job. Federal law makes it difficult for pilots to lawfully strike. SWAPA had previously asked federal contract mediators in July to allow them to cease negotiations with the airline and strike but were denied.

The union was prepared to make the same request at the end of November, but mediators sent both parties back to the negotiating table. The negotiations lagged behind those of the airline industry’s ‘big 3′ — Delta, United, and American airlines — which all reached agreements with their respective pilots’ unions earlier this year.

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Home to 1,188 of its pilots, BWI is the fourth-largest hub in the Southwest network.

This story could be updated.