Interesting view WaGA
As you will have gathered, I am not so confident of the routine nature of this one. Do remember that the LCY aircraft will have been airborne no more than about 30 seconds when this occurred. Also the LCY aircraft would have been in a right turn to the north and the Air Canada would almost be just completing a right turn south onto base.
Both we are told were changing level.
That's a hell of a lot of conflict resolution to expect from an automatic system which is trying to resolve closure rates which at first seem manageable and then both aircraft almost simultaneously actually turn towards each other!
Ever see the movie "Red October" ? What did Sean Connery remember about the closure rate resolution on the torpedo warhead after he turned at the last possible moment and faced it down head-on? Might be a bit cheesy, but you get my meaning.
Not sure how the accuracy of the original report is verified but if they really got "within 500 feet" per the report, then I am sure this one is being investigated.
LHR and LCY were using the same set up again this morning. It is probably the most common in daily use. Without the plates in front of me just now I am guessing, but that bit of sky just north of Canary Wharf where conflicts could occur in the overlapping STAR and SID might be as small as a cube with 2000 foot sides but usually when there's a LCY SID and LHR arrival converging, you see the Heathrow traffic either turned early nearer Tower Bridge or extended a bit downwind almost to overhead LCY 10 Threshold whilst the LCY traffic is obviously directed to keep its head down in the climb.
When the sky is free of LHR traffic, many of those RJs skyrocket out of City and in one sweeping turn exit to the north and/or then round to the east quite literally like bats out of hell. They often remind me of the Lightnings and Canberras skimming the horizons of my childhood!
Snapshots of the cubic mile centred on that overlap cube when both types of traffic are in view (as they frequently are at peak periods) would yield shots of a myriad of different dances indeed !
My point is that this tiny corner of London's airspace is becoming ever more concentrated, it is where the converging aircraft' crews have their hands full during take-off and approach, and it is the classic opposite track climb and descent scenario. Added to that is the wildcard for the LHR traffic is that LCY aircraft likely to launch off 28 out of LCY mightn't even be on the menu when you are about to turn towards Canary Wharf, but they very soon are up and at you by the time you are coming out of the turn unless the controllers and LCY pilots are right on the ball. The odds of a potential rapid onset conflict during normal operations are then surely as great as can be found anywhere ?
A possibly useful TCAS overview is at
http://techaidproducts.com/PDFs/TCASUncovered.pdf