Occasionally, aircraft with a seating structure of 2+2 may letter the seats as ACDF to keep with the standard of A/F being window and C/D being aisle on short-haul aircraft (which generally have 3+3 seats).

In the standard 2026 airline seating configurations, the letters C, D, G, and H are the most common aisle seats. On a typical narrow-body aircraft (like a Boeing 737 or Airbus A320) with a 3-3 layout, the seats are labeled A-B-C [Aisle] D-E-F, making C and D the aisle seats. On wide-body "twin-aisle" aircraft (like a 787 or A350) with a 3-3-3 layout, the labeling is usually A-B-C [Aisle] D-E-F [Aisle] G-H-J, meaning C, D, G, and H are all on an aisle. Note that airlines often skip the letter "I" to avoid confusion with the number "1." A 2026 pro-tip: some carriers, like Delta, use a sequential A-B-C-D-E-F-G-H-J system regardless of the aisles, so it is always vital to check the specific seat map in the app during check-in to ensure you haven't accidentally booked a "middle" seat in a center section.