I just had a look at the BA timetables for the winter season of 1978-1979 and there are two flights that fly to Washington (IAD):
- BA191 is a daily service using the 747.
- BA189 is available on Tuesday, Friday or Sunday and uses Concorde.
No VC10 flights to Washington in that schedule... I also had a look at Charles Woodley's BOAC book but he doesn't seem to cover that subject.