Does Class D airspace require an ATC clearance, or is that Class B? How about TRSAs — will you ever see one at a Class C airport? If it’s been a while since you’ve thought about airspace, odds are you’re rusty on a few details, say officials at the AOPA Air Safety Institute. Now available — for free — are the institute’s airspace flash cards. The front of each card highlights a particular type of airspace, while the flip side has a summary of all the important facts. Download the flash cards here.