The Allied Pilots Association (APA), which represents 15,000 pilots at the Texas-based carrier, said 72.7% of the pilots voted for the deal, which secures more than $9.6 billion in additional value compared with their prior agreement.

Pilots at U.S. legacy carriers American, United Airlines and Delta Air Lines are securing vast gains in wages and working conditions in new agreements reached this year as travel soars after a sharp decline during the pandemic.

"It's unprecedented and historic," the Allied Pilots Association's president, Captain Ed Sicher, told Reuters on Monday.

"For pilots the biggest victory is not just the wages but the work-life stuff."

The 48-month contract brings pay improvements including about $1.1 billion in immediate, one-time payments and ratification bonuses. On average, pilots will see an immediate pay raise of more than 21%, the union said in a release.

Quality-of-life improvements represent nearly 20% of the increased value of the new contract. For example, pilots would get premium pay if the company reassigns them from a trip they bid on, or have asked to fly, Sicher said.