Wake Turbulence

[paulhn]

Hello
I was at Heathrow earlier listening in on my scanner. I heard an EL Al 747 cleared for take off after a Virgin A340. The El Al pilot requested another minute for wake turbulence separation, the controller agreed but also asked that he be asked beforehand in future. The controller didn't sound too impressed (who can blame him) but my question is how much trouble does this kind of request cause? Could the controller have squeezed in a smaller aircraft that maybe could climb faster and get above the turbulence, and assuming the aircraft were on different departures, would the wake turbulence cause much trouble to a folowing heavy anyway?
Thanks for any answers
Paul

[747FOCAL]

A 747 probably is not bothered to much by an A340.

The pilot was probably more worried that he might have to slow down once in the air for the slower A340 as a 747 only climbs well above 250 kts and because the earth is round. :E

[Little One]

Both the A340 an B747 are the same wake catagories (heavy) The controller had probably planned to get both off without a delay as with the same wake cats you don't need to wait. With regard to a smaller acft you then need to wait 2 Minutes before launcing or 3 min if from an intersection so a smaller acft would probably not have helped the equation unless you can offer an early turn before the heavy's rotation point.

747FOCAL answer is more probable as the A340 is much slower than the B74 and climbs slowly as well. [Although it does beat an IL76 climb rate (I think a C172 beats an IL76 though) till FL100.] The B747 would probably been given a step climb which they would also try to avoid so they do not have to continuiosly level off so they prefer to wait a bit on the RWY

[Barnaby the Bear]

As I understand it EGLL and most of the larger airports use Speedtables to decide the order of departure. Not withstanding slots, restrictions and as you mentioned the most important Vortex wake.
So if the controller is busy, and has a plan. Although always flexible, it doe's help to be given notice if possible. :8