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I don't know how the airline defines "physically assist", but from my point of view as a person who cannot walk, equating it with "walk" is a mistake. If I ever have to evacuate an airplane, you can bet your booties that I will physically assist with my own evacuation by scooting on my butt, combat crawling, or whatever else is necessary.

I have flown solo on most major US airlines and have never been denied boarding on the basis of the fact that I do not have a "safety assistant", and the same is true of many independent wheelchair users.

The usual advice is that if the airline, upon boarding, tells you you must have a safety assistant, you turn to another passenger in line and say, "Will you be my safety assistant? Assuming we don't crash, there's nothing you'll have to do."

Edited to add: here's a previous go-round on the same question: http://www.flyertalk.com/forum/disab...vacuation.html