20- it
could be Manhattan KS, although Frontier is the only airline I can recall serving MHK and they weren’t yet in Chicago ... Ozark might have made the 30-some-mile hop from Kansas City with a Fairchild Hiller FH-227B, but since the turboprops made two or more stops between ORD and St. Louis, I can’t in any way imagine a one-stop FH7 trip to MCI
sooooooooo ... I am left to believe we’re looking at Manhattan BEACH, which strongly suggests a flight into LAX, which opens up a veritable Pandora’s Box of options
I fully expect to go zero for four with this first guess, but nothing ventured nothing gained:
TWA, 707, Kansas City (MCI) and Phoenix (PHX)