I have some OAG's from 1978 to 1993, here is some information about what was happening in those years:
In 1978, Pan Am was still flying its "round the world" flight, only now its routing for flights 1 & 2were:
Los Angeles-Honolulu-Tokyo-Hong Kong-Bangkok-Tehran-Frankfurt-London-JFK. (Flight 2 was in reverse order). A couple days a week, their was a stop in Delhi between Bangkok and Tehran, At that point, they had made Bombay a second stop on the JFK-Bahrain run which happened frequently so they took it off the Round the World itinerary.
The round-the-worlder did not operate everyday. On some alternate days, they flew Bangkok to Hong Kong to San Francisco.
747-100s were used in all of these operations.
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Photo © Bimbo
By 1985, Pan Am no longer flew from Hong Kong direct to the US, in fact you couldn't really get a direct flight back to the US on any airline. However, Pan Am offered change of plane service at Tokyo, they were flying an Airbus 300 three days a week from Toyko to Taipei to Bangkok. That was the extent of their Bangkok service just prior to selling off their Pacific routes.
In the 1990 OAG, I can find no listed flights for Pan Am into Bangkok. However, in my experience watching planes, it seems like I have seen a great number of "unscheduled" birds under all flags flying into big international airports. I am not sure what they are, sometimes charters perhaps, or maintenance runs, or possibly the plane was on loan to another airline? Who knows?
But here is an interesting point: In the late 50's and early 60's, Pan Am flew from Bangkok to Saigon, and its government fell. In the 70's, Pan Am flew from BKK to Tehran and its government fell. Then Pan Am flew the route via India, and although I can't say the Indian government "fell" in those days, there was a lot of civil unrest there, which somebody from India would have to explain.
Offhand, if I had been an Asian government official back in those days, I would have made quite sure Pan Am didn't launch a route to Bangkok through my backyard!
Of course, sadly, Pan Am can't fly any of these routes anymore
But thanks for the trip down memory lane.