The easiest way do complete this achievement is when joining the Brotherhood. Get yourself some "Vertibird Signal Grenades" from Proctor Teagan inside the Prydwen. The first time he gives you 8 of these, but you can buy more of him over time.
Go to a settlement, place a chair and throw the signal next to it. After a short time a Vertibird will land nearby and you'll get the Misc. objective to board it. It counts as complete once you've done that. When inside, just leave it again. DON'T FLY AWAY! Get on the chair, wait for an hour and the Vertibird will launch off again. Just throw another signal grenade and wait for the next Vertibird. Repeat that until you got your 50 Misc. Objectives.
You can also check your progress on your Pip-Boy: Data -> Stats -> Quests