Hello,
Rather than scrounge up a dive shop to refill an avi airbag cylinder after a commercial flight, I'm thinking a PCP hand pump (for PCP air rifles) would work pretty well and could be stowed in your checked luggage.
After some research it looks like filling a bottle to 2,700 psi is a fair amount of work (probably 10-15 minutes of pumping, with a 15 minute break every 5 minutes of pumping to let the pump cool), though it's not like you'd have to do it very often. The bigger concern is water vapor, which isn't something you have to worry about if filled from a SCBA / SCUBA bottle or dive shop compressor. Definitely don't want enough water vapor in the cylinder to frost the valve closed just when you need all the air volume you can get, but unless some brainiac tests this, it really might not even be an issue.
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