Had a look again at that 1970 Iraqi timetable, they scheduled two Tridents, one with first class and one which was all-economy. Pretty lax utilisation, for half the week only one Trident was required and there were significant periods where all aircraft would be back at Baghdad. The London flights (four a week) were two day leisurely affairs, hopping across the Near East and Europe one day, overnighting at Heathrow and returning the next. The Viscounts were the same, just one needed for much of the week, a second one needed only for a few hours on three days.