I am not sure of the year, probably 56/7, but the only thing I can remember about a day trip to Heathrow was a line of Constellations. I first saw them, gleaming in the sunshine, when we were about a mile away. When we were taken past them I could see that they were covered in green mould and were obviously awaiting disposal. The visit was part of an ATC camp which was either at Andover or Benson.