Quote: “Look at any 4-parallel-runway airport. You will find that, for a number of good operational reasons, almost all use the two outers for landings and the inners for takeoffs, and the same arguments would apply at LHR, such as minimising the need for aircraft to cross the landing runway."
Looking at the largest and busiest airports, there aren’t that many with four parallel rwys: CDG, LAX come to mind and ATL (with 5 parallel rwys). Many others have pairs of intersecting parallel rwys which in some cases cannot be used simultaneously.
If one looks at LHR’s competitor airports, only one has four parallel rwys (CDG). The others, like LHR have been enlarged incrementally. AMS’s six rwys cannot all be used simultaneously, and of FRA’s four rwys, one is for takeoffs only and one is for landings only. Both airports’ configurations require aircraft to taxi accross “live” rwys and LHR is no different. Rwy crossing is a fact of life and LHR-4 would not have been built where it is if this was not the case.
Your ideal of the two outers for landings and the inners for takeoffs could be applied if starting from scratch with a blank sheet of paper as in the case of CDG (in 1974), and Fantasy Silver Island (never).
Quote: “That, of course, means no alternation.”
Even with 4 parallel rwys, no alternation is a non-starter at LHR!
Quote: “Two northern runways would, presumably, also serve a proportion of T1/T2/T3/T5 traffic (otherwise why bother with two?) and would greatly increase the number of crossings of 09L/27R compared to the single-runway proposal.”
Indeed that is the case, one has to work with what is available, and what is available is mostly open land north and north west of the airport, and that will mean rwy crossing and, in some cases, an element of long AMS-style taxiing between terminal and rwy.
A southern rwy at LHR would certainly minimise rwy crossing by taking LHR-4 and some LHR-5 movements, but the requirement to demolish Stanwellmoor and most of Stanwell north of the “Happy Landing” pub makes it untenable, and land north of the airport would still be required (to relocate the cargo area for example).
Quote: “Or are you now proposing T7 as well as T6? Where will that go?”
LHR-1 will be demolished soon and LHR-3 may also be demolished later on. Maybe one or both of those could end up north of the present airport, so that makes five terminals. Heathrow Airport Ltd. envisage a sixth terminal, so don’t where your “T7” comes from!
You appear to be suggesting that 2 parallel rwys north of the airport should not be built simply because taxiing aircraft would have to cross live rwys. Is this correct?
Last edited by Fairdealfrank; 14th Jul 2013 at 23:17.