GWH
Thanks. In my 26 years in ATC I don't recall ever seeing traffic that has become satisfactorily established subsequently deviate from the localiser course to the extent that it would infringe the "No Transgression Zone" (2000ft wide, in between the approaches.) I have seen many fail to satisfactorily establish though.
I think autopilot/flight director may be mandated because we are going to need to operate parallel and without vertical separation for at least 5nm outside the current ICAO limitations. These require that 1000' vertical is maintained down to 10nm from touch down, which basically means using 2000' and 3000' as joining altitudes - not an option for Heathrow. Airspace limitations around Heathrow means that vertical will have to be thrown away at 15nm minimum. What is not yet know is the technical implication of that - the localiser beam is obviously wider that far out. The quesiton is can we guarantee sufficient navigational accuracy until traffic reaches the 10nm point, from which curent ICAO standards can be met.
The UK CAA seem very reluctant indeed to move on any of this stuff without unending studies and proof. If they can't be moved on this then mixed-mode is dead in the water, as would be alternation if runway 3 is built. The only realistic operating option in a 3 runway Heathrow would be (from the north) Mixed-mode, Departures, Arrivals.
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