American Airlines is upgrading the product on its transcontinental routes, where its yields lag far behind those of United Airlines.

On two transcontinental routes, United’s passenger yields far outstrip the competition’s. On the route between New York John F. Kennedy International Airport (JFK) and San Francisco International Airport, United’s yields are 21.64 cents per mile, compared with American’s 13.72 cents, Delta Air Lines’ 10.90 cents, Virgin America’s 10.27 cents and JetBlue Airways’ 8.89 cents. On the JFK-Los Angeles route, United’s yields are 21.82 cents per mile, compared with American’s 17.08 cents, Delta’s 11.52 cents, Virgin America’s 10.88 cents, and JetBlue’s 8.84 cents, an Aviation Week analysis of data from Oliver Wyman’s PlaneStats.com shows.

But these are two high-load routes. In 2011, JetBlue’s load factors on the JFK-San Francisco route were 90.9%, compared with United’s 90.5%, Virgin America’s 88.2%, American’s 86.7% and Delta’s 85.7%. On JFK-Los Angeles, United’s loads were 89.7%, followed by American’s 88.2%. In this market, Virgin America and JetBlue both had 87.1% load factors, while Delta’s were 85.1%, the data show.

These factors–high-load markets in which American lags behind its competition—could explain why the airline plans to upgrade its product on its transcontinental routes.

The carrier next year will begin taking delivery of Airbus A321s in a three-class configuration, including 10 lie-flat first-class seats and 20 lie-flat business-class seats. The main cabin will be divided between 36 premium economy seats and 36 standard economy seats. In addition, the aircraft will have upgraded inflight entertainment systems in all three classes.

These aircraft will replace Boeing 767-200s operating on these two routes, American says in a statement.