The tentative agreement between United Airlines and the Air Line Pilots Association (ALPA) would allow for an increase in the number of large regional aircraft to 255 by 1 January 2016.
The number is based on the Chicago-based mainline carrier meeting a number of contractual conditions, including a "unique" block hour ratio, according to ALPA. It is split between 102 70-seat and 153 76-seat aircraft, and includes both regional jets and turboprops.
United will have 168 large regional aircraft in its United Express fleet at the end of the year, according to a stock exchange filing. This includes 115 Bombardier CRJ700s, 15 Bombardier Q400s and 38 Embraer 170s.
The airline also has an agreement with Republic Airways to increase the number of Q400s to 32 in 2013.
United would be able to add 70 new large regional aircraft to its fleet by 2016 under the proposed contract. The CRJ900, Embraer 175 and Q400 would be likely candidates for an order.
The tentative agreement also calls for the addition of "new small narrowbody aircraft" in United's mainline fleet, according to ALPA. These would have between 90- and 120-seats, and are included the contract's scope section.
Available aircraft with 90- to 120-seats include the CRJ1000 and Embraer 190/195, while the in-development 110-seat Bombardier CS100, which is scheduled for entry-into-service in June 2014, would also be available before 2016.
United could also look to the used market for small narrowbodies, as its competitor Delta Air Lines did when it subleased 88 Boeing 717-200s from Southwest Airlines-subsidiary AirTran Airways. However, there are few comparably sized fleets of similarly sized and relatively new aircraft available on the global market.
The tentative agreement also includes a hard cap of 450 regional aircraft that is again based on United meeting various stipulations in the contract. This would likely involve the reduction in 50-seat regional jets, which have high per passenger operational costs, as Delta did when it agreed to add mainline capacity in exchange for more large regional jets.
United has the largest fleet of 50-seat or smaller regional jets in the USA, with 352 of the aircraft. It also contracts with regional carriers to operate 21 turboprops with between 37 and 50 seats.
Pilots at United will vote on the four-year agreement from 1 December to 15 December. If ratified, it would be the first joint collective bargaining agreement at the airline since its merger with Continental Airlines in 2010.
The ALPA Continental and United master executive councils approved the tentative agreement on 14 November.