Was'nt that the one in the centre of T2 at the back of the restaurant, which you went through to get to it, then through some glass doors and onto the terrace area, which was a level lower than the Queens Building rooftop garden.
But from fading memory, I believe that it had a limited angle of view to the tarmac stands.
Does anyone remember Stan the commentator on the QB roof gardens and his assistant Elizabeth, gave out details of each movement on the tarmac and runways and, in between times played light classical style music from LP's. Two very nice people. Wonderful times for spotting & photography, in a world that had not turned sour. There goes nostalgia, is'nt it luvverly.