Expungement will not absolutely keep the airlines or TSA from finding out but it can help you get a job.

Airlines are always have in mind how you are going to look in the media after a major accident. "Captain of fatal crash was ex-con, had multiple DUI's, had extensive criminal record, etc, etc"

In such circumstances the media will take any little tidbit and make it into the biggest mountain they possibly can...scandal sells, in a big way. But there's a good chance that the media won't find out about an expunged criminal record....even though the airline knows they sure as hell aren't going to say anything if you are lying in the bottom of a smoking hole.