Separating by vectoring on crossing traffic

by TURNING ONE AIRCRAFT ONLY

( No wind case )

 

 

In many areas ATCOs prefer to turn 1 aircraft only to produce separation by vectoring . It is considered as easier if the extend of the free and controlled airspace is enough . This is hardly the case with traffic restricted within the airway limits . However , while RVSM favoured non-vectoring solutions in many ACCs by using more the temporary vertical separation , it did block otherwise existing levels for crossing traffic of the 'pre-RVSM' era on the ACCs that are adjacent to the Atlantic control . This is how vectoring became again the main separation tool . 

For those colleagues who do use very often the technique of turning only 1 aircraft at a time we offer the study below . We have to stress however a very strong argument : There are two 'schools' or 'philosophies' about what happens to the heading of the 'other' non-turned aircraft . Many ATCOs will not lock the heading of this 'other' aircraft . We STRONGLY DISAGREE !!! The second aircraft HAS TO BE LOCKED ON HEADING  until the separation is over 

The safety issues are important here :

 

1. Mathematical analysis

The specific situation studied below is  'adapted' initially to these large areas by considering :

The main question is to examine what vectoring angles will be provide the desired separation . The same principles apply of course to any other area and we will also examine later what happens with reduced distances below 60 nm 

 

 

Both aircraft are distant D nm from the crossing point O and they move in same time by a distance X . The Track angle is defined as  q  and the vectoring angle given to the aircraft A is a . The separation is measured from the triangle ABC , where : AB = D*SIN(q)-X*SIN)a+q)  , BC = D - X - X*COS(a+q)  and Separation = AB = SQRT(AB2 +BC2

2. Our 'Rules-of-Thumb'

Despite the apparently complicated mathematical model the RESULTS ARE VERY SIMPLE .  We summarize them on the table below , produced with the MS Excel .

Minimum Separation achieved (nm) for using Vectoring angles at every 5 degrees at Track Angles of 80-6045-30 degrees , vectoring starts 60 nm before crossing point

    Track Angle  
Vect Angle 80 60 45 30
5 4 3 2 1
10 6 5 4 2
15 10 7 6 3
20 15 10 8 4
25 17 13 10 5
30   15 12 7
35     14 8
40       10
45       12

 

We examine crossing tracks at 80,60,45 and 30 degrees . The tracks around 80 are consider as 'wide-angle' tracks and those below 45 as 'tight-angle' tracks . We study the Minimum Separation produced at vectoring angles at every 5 degrees until we achieve a separation well above 10 nm .

For 'wide-angles' 5 degrees lead to 4 nm separation and then every other 5 degrees contribute to another 2 nm of additional separation . To achieve 5 nm separation a vectoring angle of at least 10 degrees is necessary and more than 15 for 10 nm

For 'tight-angles' 5 degrees lead to 1-2 nm separation and then every other 5 degrees contribute to another 1-2 nm of additional separation . To achieve 5 nm separation a vectoring angle of at least 15 degrees is necessary and more than 25 for 10 nm

At times aircraft do have some 'initial' separation meaning the initial relative distance difference from the crossing point , estimated usually below 5 nm . This separation is : 

So overall the initial distance difference from the crossing point may contribute some 1-2 nm to the final minimum separation or simply can be ignored for every practical purpose 

 

Example 1 :  aircraft A and B are found at 61 and 58 nm from a conflicting crossing point making 60 degrees tracks . The A is turned behind B . The minimum separation is 10 nm . What should be the vectoring angle ? 

According to the table for 60 degrees and 10 nm as minimum separation , the bare minimum angle is 20 . We prefer to turn A by 25 degrees 

Example 2 :  aircraft A and B are found at 59 and 58 nm from a conflicting crossing point making 45 degrees tracks . The A is turned behind B . The minimum separation is 5 nm . What should be the vectoring angle ? 

According to the table for 45 degrees the angle of 15 degrees results in 6 nm  . We prefer to turn A by 15-20 degrees

3. If D <> 60 nm

How the above values are adapted to distances from the crossing point that are not 60 ? The answer is based on the rule '1in60' . Any angle good for 60 nm distance is adjusted to any other distance D <> 60 nm by the following simple formula :

Vector Angle from a distance D<>60 = (Vector Angle for D=60) * 60/D

Example : A and B are vectored from 40 nm away from conflict point . Track angle is 60 degrees and we want a minimum separation of 5 nm . What is the vector angle for A ?

At 60 degrees at D=60 nm the angle suggested is 10 degrees . Adjusted for D=40 nm becomes 10*60/40 = 15 degrees

4. Simulator examples :

Simulator Example 1 :

EIN3344 and BAW215 ( on heading 120 ) are on tracks of 60 degrees at about 56 nm from crossing point , separation is 10 nm . What is the vectoring angle for BAW215 ? 

According to our table for 60 deg and 60 nm the vectoring angle is 20 degrees . So we vector BAW on heading 100 and we achieve a minimum of exactly 10 nm !!!

Simulator Example 2 :

DLH101 is crossing EIN3344 at 30 degrees track , about 58 nm from crossing point , our minimum  separation is 10 nm . What is the vectoring angle for DLH101 ?

Our table suggests a vectoring of 40 degrees as the bare minimum . DLH101 is on heading 150 and is turned left 105 ( 45 degrees for more safety ) to achieve a minimum of 11 nm !

Simulator Example 3 :

On the previous case the minimum is 5 nm . What is the vectoring for DLH101 ? 

The table suggests 25 degrees  , we turn DLH101 left heading 125 ...

to achieve a minimum of 6 nm at the end 

 

 

                                         

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