An employer can check into anything that is job related. For example, if you will drive their trucks, they can check into your driving record.
Since airlines are well known targets for terrorists, they can check anything and everything about you. That does not mean that they will. But, when you fill out your job application, there will be a question about your criminal background. If the airline feels that it is permitted to see expunged records, they will probably ask if your had any records expunged.
However, you were never convicted of a felony. You can answer NO to the felony question no matter if your record was expunged or not. Minor misdemeanors are like parking tickets. They carry almost no weight regarding your criminal record. You would be proper if you never mentioned it. If they ever found out about it, you should just explain it honestly. It should mean nothing with respect to your job application.
Since you were a minor, that record is probably already sealed. If in doubt, run your own background check, or call the authorities that you dealt with when it happened.
Criminal Background Check:
Criminal records are kept by the Clerk of Courts in each courthouse. Every city, town, county, state, and the federal government have their own courthouses. We know there are 50 states, 3000 counties, and over 30,000 cities, towns, or townships in the USA. That is a lot of courthouses, and most of them do not share their information. However, it is all public information, and you are allowed to review it.
If you know where the subject person has lived and traveled, then you know which courthouse records to check. (If you are check on yourself, you would know where you have been.)
Free Search Resources
Do-it-Yourself Free Background check
a)One problem is finding out your subject-persons lifetime travel history. He could have committed a crime anywhere he has ever been.
b)2nd problem is the amount of work you must do to check every courthouse in those locations.
c)3rd problem is that you could miss important records if you miss any of the locations that your subject-person has been to.
d)4th problem is cost. If the courthouse has digitized their records and published them on a website, then you can often review them for free. But if you must travel to the courthouse, that requires your time and travel costs. Finally, if you get copy of the record, some courthouses charge $1 per page. Wow! That can be expensive.
e)So a do-it-yourself background check may cost you a significant amount of money if you want to perform a complete background check.