I flew United when I picked up Angel. I did not have a direct flight - so two legs with a plane change. On the first flight, it was practically empty - so as soon as the plane was in the air, she was out of the bag and cuddled with me. The 2nd flight was packed, but I never put the carrier under the seat as it was freezing down there. It was on my lap the entire time and not one of the flight attendants said a word to me. The other passengers didn't even know there was an animal in there until we were descending and she starting whining.
I don't recommend a window seat, as it gets very cold along the outside of the plane if the carrier has to stay under the seat.
__________________  Sissy & Angel |