In good old days the viewing terrace used to be along the length of T2. There was a raised section reached by two narrow sets of steps. Below it used to be the commentary box. The terrace was accessed between T1 and T2 from the bus station by a raised walkway over the road. There also used to be a restaurant downstairs.
At a later date the terrace shrunk in length with access up a set of steps alongside T2.
The terrace I mentioned on T3 could well have only been open for the occasion of the arrival of the first 747. Airport
PR was better in those days when spectators were welcomed.