Buddy of mine said this is normal. Think of it as a courtesy call ATM to ATM basically warning them that they're taking you, so be prepared. You should expect HR to get in touch relatively soon with your TOL. Keyword though is relatively...this is the FAA after all. The TOL is the official offer that starts the clock though. At that point, HR gets your actual release date from your ATM and then you get the FOL (they said usually it's a week or so from TOL to FOL depending on security clearance review).