In every airline there is a calculation for losing crews per year.. Generally it is about 10%; consisting of leaving, retiring, illness, others. RYR = 300pa. Of course that is a mixture of ranks. In a LoCo's case the loss of F/O's is exacerbated. Many leave to better pastures; many are upgraded after a few years with less than traditional hours; a few illness. The exacerbation comes with the rapid expansion. You need commands for all the former reasons, plus the expansion, but the senior F/O guys are leaving. You need to replace them, make new captains and recruit new F/O's to crew the extra a/c arriving. However, without going to the other side of the world the choice at home is becoming wider and T's & C's plus home life are more important in career choices than just getting any job you can. In some companies it will take grounded a/c to change attitude. Share holders will see to that.