I flew with this on Alaskan airlines, and it did not fit under the seat. Luckily I was using it as a carryon for my stuff (because I sort of guessed that it wouldn’t fit) and my cat was actually in a different airline approved carrier (The Sherpa one). I still wanted to check if this one would fit for future reference though so after everyone on the plane deboarded I attempted to squish it under the seat (without the wheels) and I was afraid I was going to snap the support beams so I deemed it unfittable. I actually took 3 separate Alaskan Boeing 737s on an 18 hour trip and the seats are not all the same, one of the flights had even lower seats then the one I tried (ETOPS is what the Alaskan Airlines app says the plane was called vs WINGLETS), and the middle seats on some planes have a sort of box thing that makes the underseat space smaller, so please keep that in mind too.I do however love this carrier for non airline travel. I took my cat to the vet, on a roadtrip, and strolled around downtown Miami in it. Very convenient to wheel your pet around and pick them up when needed. The extenders help them stretch out if you are unable to take them out of the carrier for whatever reason.I do wish there was a zipper pouch though for the owner to put their phone or wallet or whatever. That would be the one thing I would change about this carrier since the only pouch on this carrier is open and things can fall out if not paying close attention to it.My cavapoo had a great time rolling along through the airport like she was in a parade float. (with the top down) :) I like that it maneuvers well. I was able to get on the plane with it, but it is about 1/2 or so too tall to fit under the seat of the American Airlines plane i was on! I though I could squish the top down, but actually it wasn't working. (Of course this is with the wheels removed) But I was in first class and I was able to put it sideways in the space between my seat mate and I partially under the seats in front. I guess it appeared to be "under" the seats, so the flight attendants didn't say anything. I'm glad because I love this carrier, but I'm afraid because I can't always flight first class! Coco did great in it, though.this product is being used for traveling from one gate to another .. at airports .. husband and i have difficulties with carrying baggage and this item will help tremendously us and our pets plenty of comfort and spacious room for them to relax!Igual sirve para viajar, pasear o dormir dentro de la casaOskar loves his carrier. It fits (minus the wheels) under the seat on southwest Boeing planes. He travels everywhere in his personal cart. Like the king he is. The whole carrier and wheels are made extremely well.Buy it. You won’t regret it.This was perfect for our first plane ride!Bella is a 13lb Maltese and she had plenty of room to turn around and was very comfortable. It rolls well and detaches from the wheels if you prefer to carry your pet (which you won't). I would highly recommend for air travel as it fits the guidelines. Specifically for American Airline's.This is great how it easily comes off the frame to store under the plane seat. It wheels around very easily. Will go back on quickly to deplane too. The only thing missing is a pocket for food, toys, etc. since you’re traveling. Will update after first trip in July.Disappointed it did not hold up only used it for two flights back and fourth on vacation only on two flights,one handle tore off first and about four more ready to.My cat weighs 13 lbs.It does NOT fit under the seat and at the second flight I even took the wheels off.