Yes, air travel is pretty amazing. But between flight delays and bumped seats, airlines give us a lot to complain about, too. Boarding procedures, for example, often annoy passengers because they're seemingly random and pointless. There is, however, a method to the madness.
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There are a handful of different boarding procedures for major airlines just within the United States. Of course, most US airlines board their elite flyers first, but then they use a rear-to-front method. SeatGuru explains:
Many airlines...board back to front, so try reserving a seat toward the back if early boarding and overhead bin space is a priority. If you have a tight connection, and therefore being one of the first to get off the plane is your priority, aim for an aisle seat close to the front of the plane. (But don't expect to have much space for your bag in the overhead bins.)
The US' Alaska, JetBlue, and Spirit all board passengers using the rear-to-front method. Delta and American use this method, too, but they also break up their boarding groups into as many as nine different zones, depending on elite status, airline credit card customers, and so on. After all of these zones, they use the rear to front method for general boarding.
United Airlines uses a boarding process known as WilMA, according to SeatGuru. It stands for Window, Middle, Aisle, and it's basically an outside-in method. After elite flyers, passengers with window seats board first and passengers with aisle seats board last. (Interestingly, an episode of Mythbusters found this to be one of the most efficient methods for boarding.)
Southwest boards randomly without assigned seating. There are three different zones: A, B, and C, and it's first come, first serve. You can sit wherever you want, so you're at an advantage if you're in Zone A. To score this zone, you can pay for priority boarding or try to check-in early.
We can tell you from personal experience that Australia's Qantas and Virgin airlines are relatively simple by comparison: there's no zones as such, and while elite status and business customers are encouraged to come forward first and generally through a dedicated boarding lane (which remains open for the entire boarding process), economy passengers are generally boarded in a couple of different groups (by row number) at most, especially on domestic flights.
Whether you want to board first or you're just curious about your boarding group, it's useful to know how airlines decide to organise passenger seating. If you want to avoid being forced to check your bag, for example, you might want to choose a rear seat, depending on the airline.