I was talking to a fairly senior ATCO at LHR during an ATC visit at West Drayton (several years ago) and he said PRNAV is a load of crap because ATC will always radar vector traffic.
He explained (and this has also been written by other ATCOs known to be senior on the UK scene) that if radar failed, the capacity of all these airports would instantly collapse to a fraction of the present. So they have very good backups for their radars.
That makes complete sense, but it beggars belief that so much effort has been expended into designing 42 STARs (just counted them) for LHR, which are probably never actually flown, and 32 SIDs which are probably partly flown before radar vectoring takes over.
Interestingly, none of the LHR STARs are RNAV, never mind PRNAV. So what is it that has driven the all-PRNAV airports when Heathrow, which is claimed to be the busiest on the earth / the universe / etc seems to manage with procedures which you could fly in a stock 1970 C150
Could it be that the LHR STARs are never actually flown as published, whereas at say Vienna they have gone for ludicrously convoluted RNAV transitions (but I notice they still retain radar vectoring for "non RNAV" aircraft)?
Do they have a different class of aircraft going into LOWW which can perfectly self-separate by flying at 220kt +/- 1kt (or whatever), all tracking the RNAV tracks with perfectly computed and wind-corrected fly-by and fly-through waypoint performance? I know s0d-all about airline autopilots but I understand that even the new ones do not fly precisely calculated
wind corrected track intercepts. I know the capability exists on fairly modern avionics to do this in zero wind...
Or, just perhaps, has somebody created a lot of work by designing all these procedures which, should they actually have to be operated for real, the said airport's capacity will collapse?
When I last flew into Zurich (another similar place) they assigned me a PRNAV SID which I refused but they just said "fly the overlay". No overlay is published but the message was clear (ATC there couldn't care less).
increased adherence to the precise SID has meant that the same (groups of) houses are always receiving the whole noise benefit of jets at full chat.
But surely this issue will not go away, because most jets fly mostly on autopilot and navigation with modern kit is now so accurate that one jet could fly into the back of another one, if timed procedural separation (as over e.g. Africa) failed.