I heard that the space is smaller than the underseat space on some airliners, so now I'm wondering.
I've never had any trouble getting my Aeronaut under the seat of any airliner I've been on since getting it, but it does stick out a little on some. Which is OK since I'm 5'4". (I have a bad back and it's easier for me to put it under the seat than heave it overhead. Actually, my doctor said to never ever reach above my head for anything ever. Never again am I permitted to change smoke detector batteries. )
Does the Aeronaut fit under the seat of Amtrak trains? What about the PC Checkpoint Flyer (which Mr. Hiker has, and really stuffs)? Anyone try other TB bags under the seat on Amtrak trains?