That piece of sky is extremely familiar to me. It is in cloud right now. I am looking at it as I type.
But for the 1000 feet, I assume that sometimes almost head-on conflict between LHR base approach and LCY departure is played out very frequently - that must sorely push the odds ?
I wonder whether London ATC's special new Mode S kit got a look in this morning, or whether it all happened too fast. (See
http://www.pprune.org/forums/showthread.php?t=287326 post #15 )
Opposite track climbing and descending .... classic.