The deal announced Thursday would require approval by members of each union.
Dallas-based Southwest plans to fold AirTran and create a single carrier. When airlines combine, seniority determines which pilots get the best assignments and, often, more pay.
Southwest pilots belong to the Southwest Airlines Pilots' Association. AirTran counterparts are members of the Air Line Pilots Association.
Also, Southwest says executive vice president Bob Jordan has been promoted to the additional position of chief commercial officer while remaining president of AirTran Airways.