I had an interesting experience a few months ago in Stansted. I was stuck for half a day. Weather was beautiful so I sat ouside with a few bevvies. Then I noticed these blokes standing near the terminal with binoculars and notebooks.
Being half jarred I wandered over and started talking to them. They are there every day and the books are all full of reg numbers for planes and they note them all down as they arrive or leave and strike them off their " List "
Could tell you anything..." ah thats Ukrainian " etc etc. Private jets and everything, they had them all. One of them was particularly interesting and we had a long chat about the Aardvark etc.
At the end of it he told me the Russians are 20 years ahead of the Yanks in Stealth technology, which if true would be fascinating indeed. Planes bring people together sometimes eh ?