In the early 70's LHR to ABZ and INV were Viscount operated. In about 1976 Aberdeen services were operated by Trident 1E's, formerly from Northeast Airlines. These types, of which there were only 3 in the whole BA Trident fleet were much more suitable for the short runway at Aberdeen than the standard Trident 1C. The Boeing 737-200 then took over in early 80's followed by B737-400 in the 90's. As far as I can recall, LHR-INV continued with Viscounts until the closure of most UK and Ireland routes in about 1982 when Dan Air took on the route. Following their acquisition by BA, B737-400 were introduced until BA stopped the route altogether.