Source: Radar Vectoring Techniques
Vectoring on crossing tracks is a trickier business in radar vectoring because it demands some good evaluation of various parameters from the controller . We will divide our study to 2 parts . This one refers to the case where BOTH aircraft are turning , a case more often encountered in areas of short dimension as in APP.
This is why we would like to analyse mathematically the problem and then get out of it some practical and simple ‘rules-of-thumb’ , properly justified from theory and easily applicable to daily life !
A No wind case
A crossing traffic at 90 degrees with aircraft of equal speeds at equal distances from the crossing point
For practical purposes , we assume that the new headings are established 30 NM before the crossing point - a more appropriate distance practically to start vectors in typical ACC operations
Both aircraft are turned , to achieve more in less airspace
The turns should always be on the same sense for both aircraft so it is either both to the pilots' left or both to the pilots' right
We will measure the evolution of their separation while both move towards the crossing point having as a variable the distance run by aircraft while on vectors . Distance is probably easier for a controller to understand than talking about time , when dealing with radar separation.
§ The minimum separation is achieved when aircraft have run, on their headings, a distance equal to the one they started vectoring from the crossing point ( 30 NM in our case ) .
§ The minimum separation achieved is related proportionally to the vectoring angle .
The results indicate that :
The daily "Rules-of-Thumb"
For safety never start vectoring closer than at 10 NM distance before the conflict point . If forgotten or at an emergency consider at this point very strong turns , up to 40-60 degrees and above all NOTIFY PILOT IMMEDIATELY on instruction . You may also consider to vector by relative turns and not by a heading , to avoid the calculation , like : " Turn immediately 40 degrees to the right ... + traffic information ….) " .
The pilot can do a lot for you :
An informed pilot reacts faster and …
He may be in visual conditions and escape the danger with less than standard separation
He might even have an early TCAS/ACAS advisory to help additionally . Note : In the case of TCAS/ACAS II resolution , however , there is a gray area considering a vectoring situation , as these resolutions suggest only vertical maneuvers and not horizontal ones . The early information to the pilot and his/her understanding will save probably a lot of a very probable confusion.