American Airlines pilots have approved a new contract with an immediate 21% raise and 46% in cumulative pay raises over the four years of the deal, the Allied Pilots Associated said in a statement Monday.

The pay increases were supplemented by higher retirement contributions, improved scheduling, sick leave, insurance benefits, and a bonus, the union said in a statement.

“It’s unprecedented and historic,” the Allied Pilots Association president, Captain Ed Sicher, told Reuters on Monday.

More than 95% of eligible pilots at American participated in the contract vote, with 72.7% in favor. Fort Worth-based American Airlines has 15,000 pilots.

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“The pilots of American Airlines have spoken: It’s time to move forward with a new working agreement that provides substantial monetary gains and quality-of-life improvements,” Sicher said in the statement. “This contract is a big first step toward restoring the wages, benefits, and work rules that were lost during the past two decades while our profession was under continuous assault.”

The $9.6 billion deal was the biggest ever negotiated by a U.S. carrier, topping the $7.2 billion value of an accord Delta Air Lines pilots secured in March, Reuters reported.

“Today is a really great day for our pilots and airline,” AA CEO Robert Isom said in a statement. “This agreement will help American immediately expand our pilot training capacity to support under-utilized aircraft and future flying and provide our pilots with more opportunities to progress in their careers.”

“We’re grateful for the company and APA negotiating teams who worked diligently and collaboratively to reach an agreement we’re proud of, and one our pilots deserve,” Isom said.

The 21% pay increase will take effect immediately. The union said that pilots would also receive a retroactive 21% bonus on earnings between January and July of this year, per The Dallas Morning News.

American’s deal leaves Dallas-based Southwest Airlines as the last of the four major U.S. carriers — American, Delta, United, and Southwest — without at least a preliminary agreement with pilots, The Wall Street Journal reported.