As part of my sport diving kit I have a Bouyancy Compensation Device, which is basically an inflatable waste coat that plugs into my main cylinder. Built into the BCD is a small (pony) cylinder and regulator valve. If my main cylinder runs out, it shouldn't, I can use the air in the pony cyclinder for both bouyancy and life support.
Would it not be possible to develop something like this, but not so bulky, for heli crews flying over water?
H.