Radar ATCO Sequencing
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Radar ATCO Sequencing
This question is directed mostly towards radar ATCOs, working at busy units, where minimum spacing between aircraft on final approach is required to keep the flow going. What kind of techniques are you using to consistently achieve the exact minimum spacing required? Are you working a lot with "hard" speed control (where aircraft are instructed to fly at an exact IAS) or more with soft speed control (e.g. "speed 210 kt or less) and possibly more margin for compression?
How do you decide on the precise time to base an aircraft, behind number one, on final? Are you using the distance measuring tool between the aircraft and turn base at a specific distance (e.g. from downwind to base when the distance between the two aircraft is the minimum required on final) or are you using prediction lines to judge it?
At very busy units, when you are consistently required to achieve minimum spacing on final, I would assume that the required minimum separation might not always be achieved. What are the consequences of a loss of wake turbulence separation between aircraft on final approach? Immediate go-around or just a simple "caution wake turbulence recommended spacing 4 miles - are you happy to continue"?
Regards!
How do you decide on the precise time to base an aircraft, behind number one, on final? Are you using the distance measuring tool between the aircraft and turn base at a specific distance (e.g. from downwind to base when the distance between the two aircraft is the minimum required on final) or are you using prediction lines to judge it?
At very busy units, when you are consistently required to achieve minimum spacing on final, I would assume that the required minimum separation might not always be achieved. What are the consequences of a loss of wake turbulence separation between aircraft on final approach? Immediate go-around or just a simple "caution wake turbulence recommended spacing 4 miles - are you happy to continue"?
Regards!
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Good vectors and hard speed control. First a/c on final 160kts or more until 4 DME subsequent a/c exactly 160 to 4, last one (if there is a gap) 160Kts or less. 180Kts on base, 210Kts with about 25-20nm to go. Don’t lose vortex or it’s coming back to you.
experience helps with the compression after the first a/c passes 4DME (speed control finishes at 4) as there are too many variables wind a/c type etc
experience helps with the compression after the first a/c passes 4DME (speed control finishes at 4) as there are too many variables wind a/c type etc
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Sometimes I use the vector lines, mode S speeds, ERBM lines, sometimes you don’t at all. Having a FIN controller (director) helps make the gaps more consistent when R/T loading is high.
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It comes with practise. What helped me (and sometimes still does) is to ensure vertical separation exists before turning one onto a tight base behind another on final. That way, if you've misjudged it, at least you have separation, and you can then sort out the spacing by taking it through the loc / slowing it down earlier etc.
As to a spacing which reduces below wake turbulence minima...if radar are still working the following aircraft, it's easy - break it off and re-sequence. The minima are there for a reason, and numerous fatal wake encounters over the years (and around the world) are why I have no time for the expression "are you happy to continue?" when they haven't been provided with the correct, safe spacing by radar...
As to a spacing which reduces below wake turbulence minima...if radar are still working the following aircraft, it's easy - break it off and re-sequence. The minima are there for a reason, and numerous fatal wake encounters over the years (and around the world) are why I have no time for the expression "are you happy to continue?" when they haven't been provided with the correct, safe spacing by radar...
A very respected Fleet Captain of a much missed UK airline once said in a Controller/pilot forum "in a capacity strapped scenario if you don't get the odd go-around, you're not trying hard enough." True comment in the early 2000s. Is this true today?
If someone is landing 40 aircraft per hour and you can sit down and knock a quarter of a mile off the spacing then over the next hour you’ll save 10 miles. That’s three extra movements. Even if you have two go arounds that’s still a net increase of one.
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A very wise mentor of mine once put it like this:
If someone is landing 40 aircraft per hour and you can sit down and knock a quarter of a mile off the spacing then over the next hour you’ll save 10 miles. That’s three extra movements. Even if you have two go arounds that’s still a net increase of one.
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Thanks for all the replies guys!
It's interesting to hear how other people are nailing that spacing and it seems like I'm not the only one who can't explain it more than "eyeballing the relative distances and speeds".
In regards to the loss of wake turbulence separation I've heard of busy units where apparently it has become as standard practice that you, up to a certain point, only warn an aircraft of wake turbulence (let's say when the loss of separation equals to less than 0.5 nm) and ask them if they want to continue. However, if the loss of separation will be greater than this the aircraft has to be taken around for another approach. I would imagine that a procedure like this would have to be approved by the "appropriate authority" and described in the MATS part 2. Has anyone else heard of this?
It's interesting to hear how other people are nailing that spacing and it seems like I'm not the only one who can't explain it more than "eyeballing the relative distances and speeds".
In regards to the loss of wake turbulence separation I've heard of busy units where apparently it has become as standard practice that you, up to a certain point, only warn an aircraft of wake turbulence (let's say when the loss of separation equals to less than 0.5 nm) and ask them if they want to continue. However, if the loss of separation will be greater than this the aircraft has to be taken around for another approach. I would imagine that a procedure like this would have to be approved by the "appropriate authority" and described in the MATS part 2. Has anyone else heard of this?
If there is a loss of wake turbulence separation of up to 0.5 nm and you’ve taken remedial action (such as further speed reduction or there’s a significant ‘pull out’ due wind gradient) then it may be prudent to caution the pilot as to loss and ask if they wish to continue.
I don’t think anyone would condone habitually busting vortex spacing by up to 0.5 nm and just asking if they want to continue.
In either case, a loss of 0.5 or greater should result in the following aircraft being repositioned and as you say, this would be apparent in local orders or practices.
I believe LHR tower advise arrivals if the wake turbulence separation reduces to 1/2nm below minimum; any further loss results in being broken off the approach. I stand to be corrected on that.....memory not wot it used to be! And it wasn't FIN habitually breaking the minima, but various factors can cause it occasionally (pilots slow to fly given speeds, changes in wind, etc).
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I think the final director will notice the erosion so won't need to be told! You are right; there are so many factors that can cause the spacing to erode so achieving max runway utilisation is a hard job,
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It all depends if the lead is inside or outside 4DME.
And yes, for LHR certainly all these procedures were in the MATS Part 2.
The new version of TBS has complicated things slightly.
Before TBS, it was pretty simple. If the lead was outside 4DME and wake turbulence spacing was infringed, Director had to rectify. If the lead was inside 4DME, then tower gave a caution to follower when that infringement reached 0.5nm.
Don't forget though, this was with procedures that only provided wake turbulence separation to 4DME, not to touchdown.
And yes, for LHR certainly all these procedures were in the MATS Part 2.
The new version of TBS has complicated things slightly.
Before TBS, it was pretty simple. If the lead was outside 4DME and wake turbulence spacing was infringed, Director had to rectify. If the lead was inside 4DME, then tower gave a caution to follower when that infringement reached 0.5nm.
Don't forget though, this was with procedures that only provided wake turbulence separation to 4DME, not to touchdown.
