Late last year, American announced that it would be introducing economy class premium seating on its new long-haul Boeing 777-300ER aircraft. Now the airline has revealed that the more spacious seating will be added to all existing and future mainline fleet. The premium economy seats will be called Main Cabin Extra seats and will include an additional four to six inches of legroom compared to standard coach seats. AAdvantage Executive Platinum and Platinum elite members as well as passengers who purchase full-fare economy class tickets will receive complimentary access to Main Cabin Extra seats at the time of booking. Gold elite members will have complimentary access to Main Cabin Extra seats until Dec. 31, 2013. American will continue to offer all elite members complimentary access to Preferred Seats, which are aisle and window seats located toward the front of the main coach cabin.

Non-elite members (and Gold members after Dec. 31, 2013) will be able to purchase a Main Cabin Extra seat for $8 to $108 per flight segment, depending on the flight length. These seats also come with priority boarding and can be purchased when you book your flight. Main Cabin Extra seating will become available as early as this spring for 777-300ER planes and will begin to be offered on additional aircraft later this year.

Bottom line: United’s Economy Plus section and Delta’s Economy Comfort seats, which will be available on Delta’s domestic flights this summer, are especially popular with low-level elites who don’t get upgraded very often. Even if a Silver member doesn’t get a roomy business class seat, the extra-legroom coach seats are a valued consolation prize. United MileagePlus used to offer complimentary access to these seats to all members when they book their flight, but changed this policy so that Silver members can only book an Economy Plus seat 24 hours before the flight. Delta Silver Medallion members receive complimentary access to Economy Comfort seats at check-in and can reserve a seat in Economy Comfort at a 50 percent discount at time of booking. American Airlines lowest-level Gold elite members will be able to book Main Cabin Extra seats at time of booking only until the end of next year for free.