Question about how to make minimum separation

[caucatc]

I heard that in busy airports, controllers wish to make two aircraft approaching on same runway with minimum separation when preceding aircraft touchdown.
But I still could not find the right way to make sure two aircraft will not less than the minimum, because that is too close to minimum, for example, 3miles is minimum, but 2.9 is an incident. I know to tell pilots maintain certain speed to certain position, I always tell pilots to maintain 180Kts to 7 miles touchdown, but after 7 miles some pilots reduce speed slowly, some reduce speed to minimum very very fast, that is unable for me to predict.
Can somebody give me some advice about it?
Appreciate

[HEATHROW DIRECTOR]

Try using speed control to 4nm from touchdown. That may help. A great deal of experience is needed to achieve constant minimum separation.

[LoserGill]

As stated by Heathrow Director, experience is key.

Often times, on a particular runway, there may be a tailwind at 500 feet AGL with a headwind on the runway itself causing speed changes that you were not expecting unless you have seen them before (or someone tells you about it).

[caucatc]

Thank you guys, but if the minimum separation is 3NM, will you trying to make it as 3NM not 3.5NM or 4NM? Because 3NM change to 2.9NM is very soon.

[Glamdring]

As stated above experience is key.

If you use speed control to 4nm and have an appreciation of the Aircraft's final approach speed and the wind then it's just a matter of vectoring a little wide so that the catch up on final approach gets you your separation.

[Spitoon]

And remember that if wake turbulence separation is not an issue you can also use reduced separation in the vicinity of the aerodrome inside 4 NM if your rules and the weather are suitable.

[Blockla]

Try 160Kts to 4 miles, works for most types and operators.

180K to 7 miles may be too hot for many types/operators, which is why you get sudden reductions, they may be very keen to slow down ASAP.

[caucatc]

160 Kts to 4NM? Can pilots do that? I normally do not give speed restriction after 7NM to touchdown.

[Gulfstreamaviator]

160 to 4nm is actually how most of our FMS or hand flyers are "designed" to operate.

I only fly corporate Gulfstream aircraft, and we operate with 160 to final flap selection, and 4 miles is above 1000ft (a typical stable or go missed height).

We also would be very happy with 180 to 7 or 8. Again that is how our systems are designed to work..... next flap setting point.

good luck

glf

[HEATHROW DIRECTOR]

<<160 Kts to 4NM? Can pilots do that?>>

They do it all day at many major airfields.

[Talkdownman]

Seems to me that BeiJing needs to send its ATCOs to nats CTC for an advanced APS course, just as ROMATSA has been doing for several years. They keep coming back for more and Bucharest ATC seems all the better for it.

[caucatc]

What we talk to are the pilots from all over the world with different operating skills, someone
can bu someone cannt I asked some pilots, most of them said it is a little bit difficult.

[HEATHROW DIRECTOR]

ATC at most major airports talk to pilots from all over the world, but it all works OK. Some aircraft types need slightly different speeds on final approach but as long as pilots tell ATC in advance it is very easy to fir them in to the landing stream. What sort of landing rate are you achieving?

[Talkdownman]

Have a look at this link (http://webtrak.bksv.com/lhr) to see what 160 kts to 4D achieves at Heathrow. Allow time to load then replay to your heart's content. At Heathrow it is very unusual for a crew to refuse 160 to 4. Most of them know that their IAS is being watched on enhanced Mode S too, so speed control compliance has improved significantly.

[caucatc]

rate of descent? around 700ft/m, descend via glide slope.
Mode S to monitor speed is a good method.
Where is the link?

[FlightPathOBN]

You should probably look at the CAAC standards. What NATS does is not the only standard. The FAA std is completely different. FAA req's min sep from threshold to 5nm, and with RECAT (Memphis so far) from threshold to 10nm.
Min radar sep is 3nm, and wake sep varies, and with RECAT, there is no visual sep allowed.

With regards to speeds, there is the CAT speed of the aircraft approach. CAT C is 140 kts for the final segment. You wont have aircraft like A380's at 160 kts on final either...

Not sure where you are located, but 160kts at Lhasa or Linzhi would be entertaining for everyone!

[Warped Factor]

You wont have aircraft like A380's at 160 kts on final either...

All the A380 operators at LHR do 160kts to 5dme on final.

[HEATHROW DIRECTOR]

I note that FPOBN is an engineer!!!!!!!

[FlightPathOBN]

Well, I dont find anywhere else in the world where sep or speed ends at 5DME! As noted, the FAA standard is to threshold. Losing min sep to threshold is an incident for a controller in the US.

With coded procedures, such as RNP and GBAS, the CAT speed is always for an entire leg, from wherever the FAF is coded in, sets the minima based on FAS +momentary descent as to not cross the MDA and to make the missed approach. So a CAT C approach is max 140 kts from FAF to threshold, that is both ICAO and FAA std.

The A380's are crossing threshold around 120kts.

[Kiwikid]

DXB regularly requires 180kts to 10nm final and 160kts to 4nm. We get plenty of A380's here and they don't often complain about those requirements. Sure they do slow down a lot from 4nm and some other types don't slow down much at all but you just learn to compensate for that.
I believe that LHR has the extra benefit of only having to apply sep til the first aircraft gets to 4nm which would make life easier though.

[UpperATC]

aucatc,

most of Europe uses the 4DME principle. Many times there's a NAV AID (a marker) just there... And as others stated, 160kts is also a widely recognized speed control down to 4DME, when traffic hits your face...
More or less the 4DME speed control comes from the ICAO rule - no speed control after passing 4DME from the threshold.

(let's forget about wake turb. separation and meteo conditions for a while)

Now, if you need 3NM separation all the way to the threshold, you should try with a "buffer" as mentioned. Maybe 4, 4.5NM and locked on 160kts 'till 4DME?

Different type of aircraft can also be funny... A good turboprop with it's 200+ until 4DME can "run away" or "close up" if you really need. But should be done with pilots concurrence and not by default. A320 family with CONF0,1,2,3,4 is also known to be able to reduce significantly on final approach phase. Not very professional to force them anyway...

Spitoon as well wrote about the "reduced visual" after 4DME. Depends on your rules of course.

[FlightPathOBN]

kiwikid...as a quick note, I have looked at Dubai for several entities, mostly for the parallel ops, but in general, isnt overspeed/overrun a significant issue?

upperATC,

What is interesting is that while ICAO doesnt require speed control inside 4DME, it does still require min sep to threshold..something that appears to be missed.

[Warped Factor]

Well, I dont find anywhere else in the world where sep or speed ends at 5DME! As noted, the FAA standard is to threshold. Losing min sep to threshold is an incident for a controller in the US.

As far as the A380 is concerned, at LHR an additional 1nm separation is added to the minimum wake separation required to compensate for the speed reduction at 5dme.

Ultimately any aircraft can do any speed it wants and ATC will compensate, there's a bit more to it than just quoting facts and figures from a text book.

[FlightPathOBN]

or leaving the pilots opinion out of the mix...

from Paul Johnson..

http://operationsbasednavigation.com/wordpress/wp-content/uploads/2013/03/ScreenHunter_27-Mar.-28-13.071-e1364505331720.jpg

[UpperATC]

FlightPathOBN

was there anything like "separation not important" after 4DME in my post?

Quite the opposite, methinks; buffer + speed control = required minimum until touchdown (hopefully)... If not, an SMS to the tower, with a "go around" text, possibly with a pukey smiley face at the end...

But I see, you, again, are running an inquisition against LHR special procedures... Well, Good luck.

[N90-EWR]

NY Tracon - EWR area controller here. We have a waiver that allows us to run 2.5 miles on final inside 10nm for like types that don't involve wake turbulence separation. on a nice VFR day if we run visuals, its not uncommon to allow them to get as close as 2 miles as long as they're able to get off the first high speed taxi exit. On perfect conditions like that, we run 38 to 41 rate depending of course, of the number of inbound heavies and 75's.

[Spitoon]

What is interesting is that while ICAO doesnt require speed control inside 4DME, it does still require min sep to threshold..something that appears to be missed. It's not really correct to say that ICAO doesn't require speed control, PANS-ATM says 'Speed control should not be applied to aircraft after passing a point 7 km (4 NM) from the threshold on final approach'. And each contracting State has to decide if or how it will implement this statement and to incorporate it into its own rule framework. Consequently there are many different national rules covering this topic.

It is correct that separation must be maintained to the threshold, one could go further and include the aircraft when they're on the runway too. Maybe it is better to simply accept that separation between aircraft that are required to be separated has to be maintained at all times. That's one of the main reasons that ATC is there. In practice, when minimum separation and speed control is being used to separate aircraft until 4 NM from the threshold, the only way to maintain separation after the 4NM point is to use 'reduced separation in the vicinity of the aerodrome' - in most cases this will be achieved by the controller watching the aircraft (no doubt the pilot of the following aircraft will be watching closely too, but it is the controller watching that is providing the separation).

What is interesting is that the NATS slide that is reproduced clearly states that up to 1/2 mile of the minimum wake turbulence separation can be lost before ATC will tell the pilot. I don't know what the ATC book of rules says the controller might/must also do but it seems to me that this needs more consideration.

PANS-ATM (para 5.8.1.1) says 'The ATC unit concerned shall not be required to apply wake turbulence separation:
a) for arriving VFR flights landing on the same runway as a preceding landing HEAVY or MEDIUM aircraft; and
b) between arriving IFR flights executing visual approach when the aircraft has reported the preceding aircraft in sight and has been instructed to follow and maintain own separation from that aircraft'.

And later (para 8.7.3.2) says 'The radar separation minimum in 8.7.3.1 may, if so prescribed by the appropriate ATS authority, be reduced, but not below:
.
.
v) distance-based wake turbulence separation minima in 8.7.3.4, or as may be prescribed by the appropriate ATS authority (e.g. for specific aircraft types), do not apply.

So, for the procedures shown on the NATS slide to be consistent with PANS-ATM, (all?) aircraft must be making visual approaches and the pilot of the following aircraft the aircraft must have reported the preceding aircraft in sight and been instructed to follow and maintain own separation from that aircraft'. Does this happen.....

In the more likely situation, where ATC is providing separation, the book clearly says that reduction in separation cannot be applied where wake turbulence separation is prescribed. So it seems that NATS/UK are not applying this part of PANS-ATM. I don't have the books to hand to check but I guess there must be a difference filed on this particular topic. Although I don't recall having procedures to do this when I last did aerodrome control in the UK.....

[N90-EWR]

We normally assign speeds to maintain to FAF, or 5DME. I find it interesting to see my European colleagues use 4DME. What is your typical transfer of control point from approach to tower? 4DME?

[caucatc]

I am really appreciate for all your replies, I was just try to get some skills or experiences from seniors controllers about how to handle good separations on final.

I do learn a lot here, and I will try more in the real work, but of course will not lose minimum separation.;)

[ATCO Two]

N90-EWR, yes at Heathrow we have formally stated that transfer of control from Approach to Tower takes place at 4 DME. If separation begins to reduce after 4 DME the Tower is able to apply "reduced separation in the vicinity of an aerodrome". Outside 4 DME Approach is responsible for separation. Transfer of communication takes place when the aircraft reports established on the ILS, MLS or RNAV.

[Warped Factor]

FlightPathOBN, every day I'm at work I position aircraft down the final approach at LHR according to our procedures. I don't have a clue what point you're trying to make?

[Occams Razor]

...reports established on the ILS, MLS or RNAV.
Just out of interest, is the MLS used often?

[Glamdring]

Just out of interest, is the MLS used often?

Only to heat up their lunch :}

On a serious note, I believe it was the case that it was only the BA Airbus fleet that used the MLS. That may have changed however.

[Warped Factor]

Just out of interest, is the MLS used often?

Tediously so.

[FlightPathOBN]

N90-EWR, yes at Heathrow we have formally stated that transfer of control from Approach to Tower takes place at 4 DME. If separation begins to reduce after 4 DME the Tower is able to apply "reduced separation in the vicinity of an aerodrome".

Exactly. As many of you have stated, like aircraft are typically crossing the threshold at 2nm or less apart...

In making the assumption that between like aircraft, there is no sep requirement, you appear to assume that aircraft do not make a wake, therefore there is NO sep required between like aircraft, ie a 737-800 hitting the wake from a 737-400 has no effect at 300 feet above threshold.

That is the point of the illustration....

[Warped Factor]

I make no assumptions, I follow the rules and procedures that I am required to follow.

If you know better FPOBN, get in touch with the UK CAA and NATS direct.

[N90-EWR]

We have a letter of agreement with EWR tower that sets the transfer of control point at 8 DME. This is because it is not unusual to have traffic landing on rwy 04R/22L, while at the same time some traffic (usually regionals) landing on rwy 11/29, and departing rwy 04L/22R simultaneously. Even though we still assign speeds to the FAF, the tower local controller will sometimes adjust the speed if there is any potential conflicts involving a no LAHSO aircraft. They do notify us if they have to slow an aircraft before the FAF, so that we can adjust with the traffic behind as well.

[zoneman]

"Even though we still assign speeds to the FAF, the tower local controller will sometimes adjust the speed"
Could you elaborate on this, please. By what means does TWR manipulate with a/c speed? Isn't it too late for that, as we've read in previous posts? I presume that radar display is required for that.

[N90-EWR]

EWR tower has a BRITE radar display. Since we're switching aircraft around 8 DME they sometimes adjust speeds if needed to maintain spacing, specially if there is wake turbulence involved.