Good point NA and a further indication of how we have been backed into a numbers corner.
It used to be a 15kt crosswind limit on the then 28s before Heathrow went onto 23. Then unwillingness to address the Terminal capacity issue led to the requirement to build the Whiskey stands next to T4. Enforced removal of the ILS made 23 a high workload runway for ATC. The limits were increased to 20kts to reduce the amount of usage and then finally to 25kts to all but stop it. The reason of course is that the headwind reduces the landing rates and thereby upsets the fine balance mentioned before, pushing the traffic back into the night. (One night earlier this year we were still landing 23 at 01:00). So, 20kt crosswind gusting 30, wet runway, foul night... you'll be landing 27L.
Wake vortex is another issue. On calm days it is commonplace to get complaints about w/v, very often between B737s as well as the bigger stuff. It would be prudent to add a mile to the gaps to ensure we don't get a major incident. (Remember the AAL A300 in New York). Why don't we?...
In the ATC Forum there is a post from Scott with a map of Dallas. Five North/South parallels and a pair of cross parallels. That is serious runway redundancy at an airport that is comparable to Heathrow.
My point is not that we have to demolish Hounslow and build Heathrow into a 7 runway moster but that we have to make proper provision for what ever level of traffic that Heathrow is asked to handle. At this time that means a third runway.
Point 4
