"rule of thumb" in procedural control

[ericliu]

In procedural control, the controller must have the ability to calculate the estimated times of passing of two a/c (or more) each on a reciprocal track, so could anybody give me some "rule of thumb" on how to do it rapidly, especially for the aircraft with different speeds?
Many thanks!

[Beside myself]

It's been a LOOONG time since I did any procedural but if I'm not mistaken, it's a quick equation.

Get both aircrafts estimate for a common point, find the average and presto, should be an approximate crossing time.

eg.
ACFT1 est DUMBO at 1630
ACFT2 est DUMBO at 1638 Both ACFT on reciprocal tracks

Their crossing time should be about 1634.
But that's with acft with similar speeds, but a good starting point...

[Take up the Hold]

And using the example of 'Beside myself' aircraft had to have crossed levels, if climbing or descending, 10 minutes before the pass, so vertical had to be achieved by time 24. Of course separation can be closer when using a VOR or NDB for separation.

TUTH

[TheFalcon]

Ask them if they see each other and to report clear. Thats the easiest

[DFC]

To do this you have to do two things, 1 establish the distance between the aircraft and then establish the closing speed.

Beside myself assumes that the flights are travelling at the same speed.

Here is an example that I hope I can explain without a drawing ( and my math is correct);

Airway segment - AAA to BBB. 360nm long

Aircraft 1 passes AAA at 1000 and estimates BBB at 1100

Aircraft 2 passes BBB at 1010 and estimates AAA at 1055

When will they pass?

1. Ask yourself where Aircraft 1 is when aircraft 2 passes BBB

Answer = 10 min after AAA.

2. With the estimates and known segment length you can work out using groundspeed how far Aircraft 1 has travelled in 10 minutes - 60nm in this example.

So when Aircraft 2 passes BBB, Aircraft 1 is 60nm past AAA or more importantly Aircraft 1 is (360-60)= 300nm from BBB

Thus at 1010 the aircraft are 300nm appart.

Based on estimates and segment length, Aircraft 1 has a groundspeed of 360Kt (6nm per minute) and Aircraft 2 has a groundspeed of 480Kt (8nm per minute).

Their closing speed is thus 14nm per minute.

At that closing speed and that distance appart they will cross inbetween 21 and 22 minutes (mental rather than calculator).

That means that the pass happens between 1031 and 1032.

Using 10 minutes before and after the estimated pass, gives you 1021 to 1042.

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You can crosscheck your calculations by asking yourself where each aircraft is at 1031

Aircraft 1 will be 31*6 = 186nm past AAA

Aircraft 2 will be 21*8 = 168nm past BBB.....which is 192 from AAA.

At 1031 the aircraft are 6nm appart closing at 14nm per minute!

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To sumarise, check where the first aircraft to enter the segment is when the second one enters and this gives you the distance appart. Use the estimates and known segment length to calculate the closing speed.

The distance the aircraft are appart when the second one enters the segment divided by the closing speed is the time to cross.

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You can use a similar for overtake.

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The above allows for different ground speeds of the aircraft and uses the info available from the FPS

Regards,

DFC

[Talkdownman]

Not a lot of use, but back in the sixties we used to use a particular formula to determine when the separation had to commence and cease, but I am damned if I can remember it. Something involving T1 plus T2 over the difference in speed etc etc. I wish someone could remind me. I doubt if Bert Spalton and Lew Parton who taught it me are still around....Ho Hum..
anyway, it usually got spoilt by some radar controller or other interjecting on the intercom whilst looking at his AR14 or 232....

[BaldEd]

When faced with opposite direction aircraft of similar speed. Find the time difference between the 2 aircraft at a rep pt and add half that time to the first aircraft to cross that point. They will cross at about that time - this of course depends on them giving you accurate estimates in the first place.

When faced with opposite direction aircraft of different speeds. Find the time difference between the 2 aircraft at a rep pt. If the faster aircraft crosses the rep pt first then the pass will occur prior to 1/2 the time difference. If the slower crosses the rep pt first then the pass will occur after 1/2 the time difference. The amount you need to subtract or add can be roughly estimated (rule of thumb) and will depend on the difference in times of both aircraft crossing the rep pt. e.g. if the time difference at the rep pt is 15 mins and the faster crosses first, then the pass will occur probably 6 mins after the first has crossed the rep pt. Give the pilots warning of the ETP and ask them to look out. At 6 mins if they have not sighted each other then ask each for his DME distance from the rep pt. You can be sure that they will be fairly close to each other. If they have already passed by 10 miles you are sweet to change levels.

There are exact formulae for these cases but I found from experience that using the rule of thumb above and comparing the result with the prayer wheel' s (circular slide rule) answer that they usually agreed.

[Late Landing]

Difficult to explain - easy to do.

Theory:
Acft A crosses XX at (time), Acft B Est for XX is (time), Calculate the difference in minutes at XX.
Now use the formula {Speed of SLOWER Acft divided by (Speed A + B)} and apply this formula to the differnce in time for XX. This will give the time for the FASTER aircraft to/from XX.

Practical:
Acft A speed 250kt crosses xx at 15, Acft B speed 125kt Est xx at 30.
Diffence in time is 15 minutes
Formula {125 divided by (125 + 250)} equals 1/3.
Apply this to the time difference of 15 minutes, gives 5 minutes.
Apply to the faster aircraft and at time 20 Acft A will cross Acft B.

Obviously to confirm the passing time you can apply the 'reverse' formula using the Speed of the FASTER Acft and apply it to the SLOWER Acft Est for XX.

[scran]

Using DFC's example,

Set a base time (in this case 1000) and add the 4 time intervals:

00 1 over AAA
60 1 over BBB (60 minutes after the base time)
10 2 over BBB
55 2 over AAA

Add them: 125

Divide by 4 = 31.25

so Estimated Time of Passing is (rounded up) 1032........................

Gives a quick approximation - thats ehat I was taught back in 1976......

[zkjaws]

There is a simple formula to work out the Estimated Time of Passing (ETP)

ETP = ETO1 + EET1 (ETO2 - ETO1)
EET1 + EET2
EET = Estimated Elapse Time between two points
ETO = Estimated Time Over one point

It can be found on a pray wheel (nav computer) by:
Set EET1 + EET2 on the outer scale over EET1 on the inner scale;
Opposite ETO2 - ETO1 on the outer scale read X on the inner scale
Add X to ETO1 = ETP

[dsham]

In OZ unfortunately we still very much do procedural control..... luckily though we have the "Time of passing tool". Click on the first aircraft, press the TOP button, click on the second aircraft.... whallah! TOP..... we still have to learn the old way though, in case you spill coffee on the keyboard or something.

[ericliu]

dsham：
Could you say more about the "Time of passing tool" ? Where do you click the aircraft? Do you have radar display under procedural control?

[callum91]

I am intrigued by procedural control and the CAP493 guidelines are too vague for my understanding.

When aircraft are being held in flight, the appropriate vertical separation shall be provided between holding and en-route aircraft while such en-route aircraft are within 5 minutes flying time of the holding aircraft’s flight path.

Does the above apply if you have an IFR departure and an IFR arrival (the arrival holding overhead the airfield)?

If not, what is the required separation and what does it depend on? (i.e. if the arrival is already holding when the departure takes off or what if the arrival is still on the inbound track and also does this depend on what direction they are going).

[dsham]

We have a Eurocat system - so all tracks are displayed (ADSB/ADSC/RADAR/PROCEDURAL), it is an interactive system whereby each aircraft has a label and a track designator. You just click on the label (this designates that aircraft) press the TOP button on the keyboard, then click on the label of the other aircraft - and the Flight Data Processor does the rest....

If you want to know more google - TAATS or THALES Eurocat and im sure you'll find something

[Hyperborean]

Callum91, the simple answer is yes. Inbound holds at suitable level and outbound climbs to 1000' below until the 5 minutes is achieved. In practice one would find an alternative separation to improve expedition. Unless you've got a stack when procedural separation becomes very intriguing, which is why I enjoyed it. With just 2 aircraft track separation against the approach procedure is easiest but the joy of procedural is that if you give a problem to 2 controllers they will provide you with 3 solutions ( all perfectly valid).

[callum91]

Hyperborean - Thanks for clarifying that for me - I always thought it was 5 minutes!

[e195-001]

Hi everyone
I'm really sorry for bringing up such an old thread but just wanted to say Bert Spalton is still about and doing well.

I am David, his grandson, never fully followed the family business but do weight and balance at LHR so almost.

I will pass on regards to Bert

Dave

[2 sheds]

Dave

See PMs.

2 s

[Talkdownman]

Dave,

Very, very pleased to hear that Bert is still around!
That man just cracked me up on the area procedural course (Jan 1970) when he would go outside and collect moss and algae and return to decorate the students' 'dead wood'...He and Paddy Holt made learning a pleasure. But I still can't remember that formula. Maybe Bert will remember...

[ZOOKER]

Dave,
Great to hear that. I worked with Bert from 1979 to his retirement at an airfield not far away. He was D Watch supervisor.
I first heard about him in about 1970, at Loughborough College where his nephew, Gerry Spalton, taught me 'O' level chemistry.
ATC is a small world!