We travel frequently so I started early with Cali. The only uses piddle pads. I would take her to the pad first thing in the morning, or after she had eaten, and put her on the pad and tell her to potty. I keep standing there until she goes then make a big deal about it and give her a treat. Then after she was used to it I would watch closely and give her a treat every time she used the pad.
I would keep training her to go on command, and give good treats and praise. So now she will go anywhere I put a pad down.
When we change planes on long trips, I take her into the restroom and go into the handicap stall, put the paper down and tell her to go potty. The. I throw the pad where ever people are throwing away their diapers And off we go.
Problem: she has not always distinguished between a throw rug and a potty pad
Good luck!