Speed and wake spacing on final approach

[Eggs Petition]

From my previous unit, I recall part of a debate about responsibility for spacing on final. I seem to remember that this originated from another unit so I presume there were inter-unit discussions about it.

The bones of it was that as speed control can only be applied up until 4DME from touchdown, how responsible should ATCOs be for any erosion of wake turbulence separation within these last four miles?

I am making the assumption here that the spacing and or speed used before the 4nm point was good and correct.

Imagine a scenario of two aircraft of same or similar type both slowed during vectoring similarly then both given 160knots to 4DME and they are both transferred to the tower frequency. The spacing between them is just over the minimum required. The lead aircraft slows to final approach speed shortly after 4DME, whilst the second slows somewhat later.The spacing between these two aircraft erodes to just under the required minimum.

Should the tower controller break off the approach of the second aircraft?

How accountable should the radar controller be for the erosion of separation?

What responsibilities lie with the pilots? As ATCOs we assume they knew that they were in sequence, however I'll concede that the situational awareness of pilots and ATCOs is not always the same. They obviously have different perspectives on any given traffic situation.

Interested to hear your thoughts...

[ozineurope]

Eggs

In OZ the radar standard must exist until the first aircraft crosses the landing threshold. So if you need 5 then number 2 must be at least 5 from the threshold when 1 crosses it. I would expect the tower to send the second guy around if the standard was not going to exist.

We have had APP controllers on the bench for getting 4.9nm nstead of 5.

;-)

[Eggs Petition]

Oz: personally, I agree that TWR should send the 2nd aircraft around. However, real world without automated alarm functions? I've seen many occasions when it has not been done.

Approach/Director ATCOs should be criticized for loose spacing, especially at a unit that is busy, however that .9 is the issue isn't it?! Hit the minimum spacing, be it 3, 4, 5 or 6miles and you get a pat on the head. Lose .1 of a mile and you're in the smelly stuff... for something which is in part out of your control.

[HEATHROW DIRECTOR]

The question of reducing separation within 4DME came up at Heathrow 20+ years ago. Initially we were told that separation for wake turbulence (used to be "vortex") must be provided until touchdown. This caused vast delays because the final approach spacing had to be increased significantly - something like adding a mile to all the wake turbulence spacings. Very, very quickly agreement was reached with the operators that separation would be maintained until 4DME and the erosion in separation thereafter was accepted. That's the way it worked for many years although I do not know what the current procedures are.... maybe somebody in current practice will respond.

[Canoehead]

Which is something that has always puzzled me. Because what the operators are saying is that the wake turbulence minimums are not all that critical! :ugh: And this in a 'dirty' configuration, slow speeds, and close to terra firma.

[babotika]

Yup. Clean(ish) slow and heavy when the greatest lift is being produced, like just after take-off.

It still isn't very fun to fly through the turbulence of the heavy landing ahead...

S.