I think this is a sneaky one, pointing to the long-established BEA/Olympic/Cyprus Airways joint services on Comets that used to change their flight numbers along the way. However, I believe by 1971, when the Comets had been replaced by Tridents, including Cyprus Airways getting their own aircraft, this had come to an end. But Olympic I seem to recall carried on a "through" flight (which as often as not entailed an undocumented aircraft change at Athens) to compete with the others. So, lets go for an Olympic 727-200, stopping at Athens.

Just incidentally, this prompts me that we have a new interesting turboprop service passing directly overhead Chateau WHBM most days, sometimes twice a day at close intervals. The Korean car company Kia have their main European assembly plant in Ostrava, Slovakia. They get a lot of components from the (it's still very much there) car parts industry around Birmingham in the UK, which are taken over there. Because of some considerable disorganisation at UK ports in recent months, in no small part due to a new computer system, they have had to resort to an airfreight shuttle, where they have engaged no less than not one but several Ukrainian-registered Antonov 24/26s, which drone along at typically 20,000 feet, with quite a distinctive noise well audible from the ground and even right inside the house, if you have an ear for them - you can guess whether I do or not ... .

Sometimes there's even been a different tone, about an octave lower, and that's a bigger 4-prop Antonov 12. For whatever reason they always route directly overhead London on the way.

[Edit]And here, an hour after posting, she comes :