47 planes, mea a around 500 upgrades. There's no way that a new hire will upgrade in less than 5 years.
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500 upgrades??? That requires 1,000 pilots. I think your math skills are lacking unless RAH staffs at 20 pilots per plane.
Far more likely that they need 470 pilots for the new planes; 1/2 of which will be upgrades. So, 235 is the rough number of upgrades before the music stops again.