I've never been a big flyer. My family traveled to the east coast on an annual basis when I was a child, but as my siblings and I grew up trips became less frequent, and I opted out of family vacations when they would come up.
Last May I was presented with the chance to visit an encourager friend in Los Angeles. The seating issue never crossed my mind at all- at the time I was around 280 lbs (albiet, 5'6"), but I didn't think I was anywhere near big enough to have issues fitting into a seat. I did however, find myself at the crossroads of not being able to find pants that fit in store (Old Navy only carries up to 42, but has 'extended' sizes online).
I managed to fit into my seat (Southwest) it was a tight squeeze, but I survived. I really struggled with my seatbelt, but That was around 284 lbs. This past October I was flying Southwest again (around 310 lbs or so) and it was unbearably tight squeeze into my seat. At the start of this year I flew again, only 10-15 lbs heavier, but it was absolute torture. Both flights were completely full, and my love handle was spilling over the arm rest, and i had to have my legs and arms wrapped around each other- leaning away from my fellow passenger.
Shortly after this incident Kevin Smith had his
run in with Southwest. While I don't agree while it was handled, having experienced first hand how uncomfortable it can be for myself and I'm sure the person next to me. I was also now terrified of the aspect of being kicked off a flight for being too fat.
On the other hand, the average airplane seat width is 17 -18 inches so if you have wider than a 36 in waist it's going to be a little tight. Now taking into account that I have a 50+ in waist, and my belly/love handles are around 63" sitting, I'm pretty much screwed. Last week I took a trip to LA (via Southwest), booking two seats for the first time. I called customer services when I made the reservation to double check about check-in procedures, and they were very friendly, guiding me through the procedure. The agent I spoke with messed up the reservation- never linking the two seats, but when I checked in at the gate, this problem was promptly fixed, and I was given a 'seat reservation ticket' to put on my 2nd seat. When I got to my gate I was given a pre boarding pass, so I could ensure my 2nd seat and get situated before the other passengers boarded.

Unfortunately the new boarding pass the agent at check in had given me had the wrong gate number, and I not only missed pre-boarding, but I almost missed my flight. I was able to cut ahead of the 'B' group, and upon boarding the plane I showed the flight attendant my 'seat reservation', she gave me a seatbelt extender, and was very polite- telling me 'I wouldn't have necessarily guessed - but you're thinkin' right!'. Her kindess meant alot, after ast year (50+ lbs prior), when I asked for Dr. Pepper as my in flight beverage, the flight attendant barked back 'you know it's not diet, right?'
The 2nd seat made a huge difference I filled up a decent chunk of the other seat and had room to adjust myself/get cozy/whatever. Southwest also has a refund policy, so that if 'customers of size' purchase a 2nd seat, and there is at least one other open seat on the plane they can be refunded the money for the 2nd seat. I'm planning to fly to Fort Lauderdale for
Expansion, but I'm researching alternatives to Southwest. Spirit Airlines has some 'Big' seats that offer more leg room and seats that are a bit wider, and I'm hoping to be able to coax one of my local chaser/encourager friends into being my 'seat buddy'- but I'll have to see how it pans out.