I don't know too much, but I heard you had to have a certain number of years working as a paramedic, all of the "alphabet soup", and critical care paramedic certification. If you're researching this field, I would call one of these places and speak to a recruiter. It never hurts to ask questions!!
Around here flight medics are employed by the State and they only draw new flight medics from within their own ranks, so in addition to the certification and the experience, you have to be employed as a medic by NY State (at the big State hospital here) and work your way up the list to get a position. One of my friends has been waiting two years so far.
The big 3 out my way (pardon the ebonics) all require a minimum of 2 years of full time pre-hospital (9-1-1 type) of experience for their medics. They prefer the same from the nurses but do not require it. I don't know where you are from, but I will say they are PENNStar, SkyCare, and University Medivac. the are all based in Metro Philadelphia but with the abundance of trauma facilities, they aren't used in the city that often. Maybe once a year if they are lucky. We have 5 level 1 aduld centers, and 3 level 1 ped centers. but only 1 burn unit. That sucks for the firefighters in Philadelphia, Montgomery, and Bucks county. But we get by.