We did this for family entertainment back in the early/mid 50's, at Midway Airport, before jets and before O'Hare opened up to full commercial flights in (I think) 1958. We'd all go to the Midway observation deck (yes, that is what is was called and what it was for) and we'd watch people boarding and getting off the planes. No jetways at the time so everybody walked up or down the stairs rolled up to the planes. Our favorites were, what we thought at time were gigantic, about 70 passengers) TWA triple tail Constellations. Flying was not cheap then and it was mostly wealthier people flying. We'd always discuss where we thought they were flying to or coming from.
Amazing what we did for an afternoon of entertainment then.