We've all been there. That moment when you're booking a flight online, selecting a pair of seats for you and a travel companion, and you realize – curse! – the plane only offers seats in clusters of three. Plenty of aircrafts share this 3-3 configuration, including both the Airbus A319/320 as well as the Boeing 737; in fact, most domestic flights between 1 and six hours have it, so chances are fairly high that you've encountered this scenario before. (You can check your configuration ahead of time using SeatGuru.)
The dilemma, of course, lies in that third mystery seat. No matter how you slice it, you and your companion are going to end up sitting next to a lone stranger. (More tolerable on smaller flights, though on longer flights where you'd rather stretch out and get a bit of rest, a much bigger nuisance.)
Thankfully, there's a solution. Or, at the very least, a trick that could work in your favor: book yourself in the window seat and your companion in the aisle seat. Why? Because solo passengers will do everything they can to avoid that single middle seat. I've been strapped into a 15-hour haul from Hong Kong to Detroit with a passenger that couldn't seem to keep his body erect while sleeping, consequently ending up in my lap one too many times over the duration of the flight.
Of course, there are exceptions, but if the plan works, you'll be left with a full row of three seats between two people – and plenty of room to stretch out.
Worst case scenario? On a completely full flight, the person stuck in the middle will happily swap for a window or aisle seat, which still puts you and your companion side-by-side.
It's a no-lose situation, so next time you're booking on one of the above-mentioned aircraft, give it a whirl!