Air traffic control radars are devices which are used by air traffic controllers to detect, monitor and guide aircraft within a delimited airspace region.
The radar vectoring procedure is one of the management tools which can be used by air traffic controllers (named also ATC) in areas where air traffic control service is provided. The basic methods of radar vectoring are constituted of several rules in order to handle all aircraft to achieve maximum use of airspace.
Several types of radars are used in the framework of civil or military air traffic control. At IVAO, we have only one radar system simulated by IVAO ATC software.
During increased traffic at the airport, radar vectoring becomes the standard procedure in most of the large airports to arrange aircraft in sequence to ensure air traffic flow management for the most efficient use of airspace.
In some airfield procedures, radar vectoring is a mandatory procedure to guide aircraft on the final approach track.
The radar vectoring procedure shall be used by air traffic controllers only for identified aircraft on the radar system whilst maintaining two way radio communications all the time.
In smaller airports or airports in mountainous areas, the approach controller might provide procedural control (published procedures) only or partially.
In the radar vectoring procedure, the controller can assign headings, altitudes and speeds to IFR aircraft in order to guide aircraft in his area of responsibility.
An ATC controller shall not take any risk on aircraft safety when using the radar vectoring procedure. An ATC shall not play with the risk of separation loss. He must ensure that a suitable separation is kept every time after he issues a clearance.
Radar vectoring is mainly used by the ATC as a tool in order to ensure and enhance:
- the air traffic flow management in the arrival and/or approach phase of an instrument approach procedure.
- the IFR aircraft arrangement in sequence in the arrival and/or approach phase of an instrument approach procedure.
- the horizontal and vertical separation between all departing and/or approaching IFR aircraft
Radar vectoring can be used by the ATC as a complementary tool in order to enhance:
Whenever the ATC provides radar vectoring, ATC shall not take any risks regarding:
- The aircraft safety:
- vectoring near mountainous areas or high landmarks where vertical obstacle clearance should be infringed
- descent clearance with ground proximity warning
- vectoring in areas below MRVA or MVA outside a published approach path
- vectoring in areas below MSA outside a published approach path where no MRVA or MVA have been published
- The aircraft separation:
- vectoring with an immediate or future effect of a reduction of separation between traffic under minima.
- ensuring that a suitable separation is kept every time after ATC issues a clearance.
Note that IVAO ATC software radar displays the traffic below MRVA. Traffic do not dissapear below these limits like in real aviation.
Radar vectoring can be used inside controlled airspace where air traffic control service is provided:
Radar vectoring should not be provided to aircraft which do not have to be separated due to airspace class (example VFR traffic in airspace class C or below), except for emergency and pilot assistance.
The use of the radar vectoring procedure can be forbidden at some airfields for the following reasons:
- Regulation of your country/division does not permit it on your airfield or all airfields
- Due to the proximity of mountainous, prohibited, restricted (military) areas, radar vectoring can be restricted or forbidden
- Approach paths are below minimum radar vectoring altitudes (MVA or MRVA) in the considered sector if they are published
- Approach and arrival paths are below minimum sector altitude (MSA) where minimum radar vectoring altitudes are not published on charts. (IVAO)
Whenever a controller provides radar guidance by vectors he is supposed to take responsibility on all navigation parameters: heading, altitude, speed (rate of climb/descent) until the interception of the final approach track.
The ATC must pay attention to:
- The aircraft safety by ensuring that radar separation minima are fulfilled at all times and for all airplanes, whether they are under his responsibility or not.
- Not to issue any altitude clearance below minimum vectoring altitudes (MRVA for Minimum Radar Vectoring Altitude) during radar vectoring (prevent any potential terrain collision) outside any procedure tracks
- Not to issue any altitude clearance below minimum safety altitudes (MSA for Minimum Safety Altitude) during radar vectoring (prevent any potential terrain collision) outside any procedure tracks
- Not to issue any altitude clearance below minimum procedural altitudes published ( Minimum altitude to respect on IAF)
Vector instructions shall be used by ATC when providing radar vectoring.
Here are some examples of standard phraseology:
Radar vectoring is often used to shorten complex or tortuous procedural trajectories using the minimum clearance with respect to the approach gate. Radar vectoring shall be simple and optimized with minimizing the number of radio messages.
Considering these rules above, the most common errors when providing radar vectoring are listed below:
* Except when facing any separation issues where the situation needs further clearances.
Sometimes the situation in the approach area when managing several aircraft, the horizontal separation between two aircraft can be reduced to less than minimum separation distance.
In this case, the air traffic controller can divert aircraft from a previously assigned track using radar vectoring.
In function of the configuration of airspace and traffic, the air traffic controller can give aircraft a minimum 45° turn up to 90°.
When the horizontal separation is increased to more than the wanted separation, the aircraft is vectored back to the primary route or to the approach sequence.
Air traffic controllers may divert aircraft from a previously assigned route for an arbitrary amount of time, which can provide any amount of horizontal separation depending on aircraft altitude and ground speed.
Remember that typical minimum radar separation distance is 5NM and minimum reduced separation distance is 3NM where applicable. Consult IFR radar separation documentation.
Sometimes the traffic situation separation is greater than the requested regulation separation.
In this case, the air traffic controller can give vectors to one or several aircraft in order to reduce the horizontal separation with previous aircraft in the approach sequence or to shorten the distance to the approach gate area.
The advantage of this method is that air traffic controllers will ensure the continuity of air traffic flow management and answer the need of fuel saving requested by airline companies.
If an aircraft is the first aircraft in the approach sequence, his route should be shortened toward the approach gate in order to create separation distance with succeeding traffic.
As explained in the previous chapters, the main goal of approach management is to organize a sequence of aircraft providing a continuous flow towards the final approach path. Radar vectoring is one of the best methods to achieve efficient sequencing.
During approach, the distance between aircraft under radar vectoring depends on the runway capacity, the approach type (precision or non-precision) and category, the meteorological conditions (LVP) and the specific operational constraints of the airport.
Nevertheless, the controller must always respect the radar separation minima fixed by the regulations.
A typical 5NM separation target is one of the most used methods to manage the traffic flow on the final approach area. This creates a possible management rule which implies to create a 2 minutes spacing. sequence of aircraft.
A 2 minutes spacing approach sequence will create 5NM separation when using a typical approach speed of about 150kt.
Some advices to reduce the risk of separation loss:
In the case of simultaneous descent of two close aircraft, the controller shall pay attention to their rate of descent in order to avoid separation loss.
Pay attention that aircraft in higher altitude also have higher true air speed.
In the training phase when air traffic controller is learning the approach regulation using radar, one method is to gradually increase the value of horizontal separation minimum of one nautical mile for each additional aircraft and maintain the vertical separation of 1000ft between each aircraft. This procedure should ensure 5 miles of horizontal separations overhead FAF/FAP between all aircraft.
The diagram below shows some examples of radar vectoring tracks from different situations:
In the example presented above, we create downwind radar tracks in order to put all aircraft in the approach gate area (green zone) by using a 30° interception track to the final approach path.
The dotted arrows are possible tracks but not optimized and sometimes dangerous to use them in function of traffic:
Pay attention that the "Base Distance" is very important. When performing a quarter turn (90°) an aircraft will make an arc using a radius estimated at 0.5% (=Speed/200) of the ground speed in terms of Nautical Miles. It will be 1NM for 200kt
To ensure a convenient interception of the final approach axis (LOC axis, VOR radial or NDB track) the approach controller generally shall use standard phraseology and provide:
The approach gate is a radar point taken as a reference point by the air traffic controller for vectoring aircraft towards the final approach path. The approach gate shall not be less than one mile from the FAF/FAP (descending point on final approach), and shall not be less than five miles from the landing threshold.
The approach gate is subject to following rules:
A higher angle than 45° shall only be possible with pilot approval before issuing the interception clearance. The maximum angle shall be 90°. Using a higher angle than 45° will induce overshoot.
A lower angle than 10° should be avoided due to the fact that the interception distance is not guaranteed due to cross wind effect and pilot reactivity.
The interception can be possible up to the FAF/FAP only with pilot approval and where the situation demands it. This is not a normal radar vectoring operation.
The average interception speed of a Medium aircraft is usually between 180 and 200kt IAS.
ATC should respect the defined approach gate at all times in order to ensure optimal final approach interception by aircraft.
In the example above, the aircraft highlighted by the red square is outside of the approach gate. In normal operation and in this situation, the air traffic controller shall vector this aircraft into the approach gate area. If ATC force this aircraft to integrate on final, he can destroy the approach regulation or let the aircraft integrate the approach path with a risk to perform an non-stabilized final approach.
Red point: Approach gate reference fix is defined by a straight leg of at least 30 seconds (1NM or 2NM distance) ahead the point where the aircraft start the descent (FAF or FAP point)
Black point: Final approach fix or point where the aircraft start the descent
Green zone: approach gate zone of good radar interception with a maximum of 45° angle
Black arrows: interception which respects the approach gate constraints
Red dotted arrows: interception which does not respect the approach gate constraints. These solutions should be used by ATC, only with pilot approval and where the situation demands it
Red arrows: bad interception. This situation forces the ATC to vector again the aircraft inside the approach gate zone
In other configurations, vectors can be provided to guide aircraft towards a different approach gate point:
- A fix or the interception path of the initial or intermediate approach procedure where radar vectoring cannot be provided on final approach procedure
- The Initial Approach Fix (IAF)
Vectors shall avoid mountainous areas.
Vectors shall be not used in areas where MRVA are higher than published procedures.
Note that the maximum range of the localizer in flight simulator is 26NM.
In some medium or small airfields or airfields inside mountainous areas, the final approach track cannot be aligned with the runway axis.
The configuration may be one of these:
In these configurations, the air traffic controller shall not guide aircraft towards the runway axis.
In order to compensate the wind effect and pilot effectiveness for performing a base leg with two turns, the minimum base distance should be 3NM.
In order to ensure separation between aircraft on the final approach path and aircraft on the downwind track, the base leg created by radar vectoring shall be greater than the minimum IFR separation value considered in your approach area ( standard separation is 5NM and reduced separation is 3NM where applicable).
Sometimes aircraft will arrive in a bad configuration which does not allow for immediate interception of the final approach track. One simple method is to use a 45°/180° procedural turn form for vectoring toward the approach gate area.
The procedural turn should be started beyond or at the approach gate reference point. The air traffic controller will:
If during radar vectoring one of the aircraft requests priority landing due to an emergency situation, the air traffic controller has to vector this aircraft through a route as short as possible to the final approach fix/point (FAF/FAP).
An aircraft in an emergency situation has absolute priority over all aircraft in the operation area.
The air traffic controller shall follow these basic recommendations:
- Aircraft which are in sequence behind the aircraft in the emergency situation will continue through an unchanged route,
- Aircraft which are in sequence in front of the aircraft in the emergency situation will continue to the end of the approach sequence.
This manoeuvre ensures minimum delay for all flights.
In the example above, the situation is:
The air traffic controller shall cancel the arrival of the first aircraft (orange square) and put it at the end of the approach sequence. The two other aircraft (green rectangle) shall continue and ATC shall monitor the emergency progress and the separation with other traffic.