I took an 11-hour nonstop flight from Paris to Madagascar. I had the aisle seat. The middle seat was occupied by a woman who walked on the plane with a small dog on a leash. Rover spent the flight on a blanket at her feet. How he held his bladder for all that time, I'll never know.
Every time I reached down to get something from my bag on the floor, Rover growled at me. The real fun was during meal service when he suddenly escaped down the aisle. The flight attendant was blocked by her cart, so I went chasing after him. I didn't have a common language with Rover's owner so couldn't really say anything to her about him. The flight attendants just shrugged as if an uncaged dog on a plane was no big deal.
At the end of the flight, Madame and Rover tripped happily down the aisle and out of the plane, neither looking much the worse for wear.
I just looked at the airline's web site. They still accept dogs on a leash in the cabin, but now required that the dog be muzzled. They charge for dogs in carriers in the cabin, but a dog on a leash is transported for free.