Vortex wake separation: crossing traffic

[NorthSouth]

MATS Part 1 says that for operations on crossing runways, a departure whose flight path will cross the flight path of an arrival on the other runway has to wait 2, 3 or 4 mins depending on aircraft category. But what if the climbout from the departure runway crosses the arrival runway at the normal touchdown point, and this point is some way beyond the upwind end of the departure runway? In that case, the departing aircraft cannot possibly fly through the wake of the arriving aircraft since it will be several hundred feet above its flight path by the time the flight paths cross. Surely in these circumstances there is no need to apply any vortex wake separation since it is already assured?
NS

[BigBoeing]

well in the case you describe the flight paths don't actually cross do they. So no, no need for vortex seperation, though some may argue that by the book, you do.

[120.4]

And if the arrival goes around?

.4

[NorthSouth]

If the arrival goes around clearly it's a different scenario. But if the arrival's touched down and the departure will be airborne well before the paths cross there seems to me to be no reason to impose separation on the departure.
NS

[120.4]

Agreed.

If it is evident that the paths cannot cross, wake vortex is not applicable.

However, every approach is an approach to go-around, only if at decision height all things are as the need to be, does one continue to land. It follows that one must always assume the approach will go-around.

.4

[NorthSouth]

Yep, agree with that, but in the case I'm looking at, the guy who is waiting for takeoff clearance won't get it until the landing aircraft touches down anyway, because as he looks down his takeoff runway the touchdown point of the landing runway is straight ahead of him. Oh for a diagram....
NS

[120.4]

In the good ol' days, I understand Heathrow used to operate 05 arrivals and 09R departures, which intersect about 2/3rds of the way down. The 09R departure would be given "traffic one mile for 05, cleared take off 09R" on the basis that there was absolutely no way it could get anywhere near it.

.4

[aerodyne47]

If I understand the runway geometry you describe, I think only a very brave person would not consider wake turbulence separation.

If the arriving aircraft is No 1 and lands - then departure goes, no WT sep required

If the arriving aircraft is No 1 goes round - departure stays on ground until WT sep exists

If departure is No 1 - then normal visual separation except that if the arrival goes round you better have an ace up the sleeve and issue instructions that does not compromise WT separation. Once you are dealing with two airborne aircraft a distance standard is likely to be easier to apply than a time standard.

Why dont you build an airport with runways that cross in about the middle so you could expect one or both aircraft to be on the ground through the intersection. Oh for life to be that simple.

[yellowplane]

http://www.chirp.co.uk/new/Downloads/pdfs/AIC17_99.pdf

[NorthSouth]

Yep, good post, it's *almost* all in there. Key quote is "When departing from a crossing runway, note the large aircraft's rotation point. If it is before the intersection, give sufficient time for the disturbance to dissipate before commencing take-off." But there's no advice about departing after a landing airliner which touches down pretty much at the intersection. Logic says it's no problem.
NS