Delta Air Lines Inc. may soon purchase more narrow-body jets, once a tentative contract with its pilots' union is ratified by a majority of members.

The accord, which includes pay raises of almost 20 percent, would allow many first officers to upgrade to captain while also creating additional openings for new first officers, Tim O'Malley, chairman of the executive council for the Delta chapter of the Air Line Pilots Association, wrote Monday in a letter to members.

The contract would also allow the Atlanta-based airline to add more 76-seat regional jets, although "this access can only occur if Delta first acquires small narrow-body jets flown by Delta mainline pilots," while also getting rid of more 50-seat aircraft flown by regional partners, O'Malley said. Pilots prize jobs on main jet fleets because it means better pay and benefits.

Analysts have speculated that Delta is among the interested buyers of the 88 Boeing 717s that Southwest Airlines acquired when it purchased AirTran Holdings Inc. last year. Southwest has said repeatedly that it would like to get rid of the planes as soon as it can.

The jets have 117 seats and if acquired by Delta would be flown by the carrier's pilots rather than by regional partners.

"We're looking at all arrangements and we have taken note that Southwest has indicated a desire to exit the [717] fleet," Delta President Ed Bastian said at a March 13 conference hosted by JPMorgan Chase & Co.

O'Malley's letter didn't specify what types of planes Delta would buy, although he said it would increase the ratio of domestic flying on Delta's main fleet relative to flying by regional partners by 57 percent over the life of the contract.

The tentative contract will soon be sent to the 10,850 pilots for a ratification vote, and will be finalized if a majority of them approve it. Pilots will get a 4 percent pay raise upon ratification, with an additional 8.5 percent next Jan. 1, then another 3 percent in years 2014 and 2015, O'Malley said in the letter.

The contract would give Delta "productivity gains and additional aircraft flexibility, including an opportunity to accelerate Delta's domestic fleet restructuring strategy, which will result in a better customer travel experience," said Gina Laughlin, a company spokeswoman. She declined to elaborate on what types of planes the company might purchase.

Delta shares rose 4.3 percent to $10.58 Monday. The stock has advanced 31 percent this year.