Squabbly.... you deserve a sensible reply. Splatt has provided details of the ANO but not of standard separation provided by Air Traffic Control, and the aeroplanes you saw would be under postive control from ATC. It's extremely unlikely that what you saw was a loss of separation, or "airmiss". If two aircraft got as close together as you suggest there would have to be major problems with a) the ATC system and b) the collision avoidance system on the aircraft.
In the holding pattern they have to be 1000 ft vertically apart and no horizontal separation. So your eyes have to differentiate between two objects 300 yards apart at a distance of well over one mile. You said they were around 5-6K high; I presume you mean thousands of feet? If the aircraft you saw were near the bottom of the stack they would be around 7-8000 ft. Outside the holding pattern they may be at the same altitude but in that case they would have to be at least 3 nautical miles apart horizontally.
It is exceptionally difficult to estimate the vertical distance between two aircraft. During my time in ATC I have taken numerous phone calls from people claiming to see something dangerous - even senior airline pilots have rung Heathrow to say they have seen an "airmiss" - one gent was adamant and said he would file a report! He was simply mistaken and there had been no incident.
Last edited by HEATHROW DIRECTOR; 30th August 2005 at 09:00.