In addition to what Chase said which is very accurate....several states also require the nurse to possess an EMT or Paramedic license as well. While this may be done through a challenge for some, it is still a requirement for some programs.
In short, there is high demand for these positions and a LOT of candidates with years of experience and education. The programs can afford to be very selective so as a candidate with only an ASN...your prospects are slim to none.
Go to Flightweb.com for more detailed information about the employment and education path for flight programs. That is one of your better resources for what you seek.