Study Guide:Radar

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This study guide is still work in progress. Stay tuned for further chapters.

Airspace Structure

Austrian Airspace is structured into four different Types of Airspace:

  • Class C: Operations may be conducted under IFR, SVFR, or VFR. All flights are subject to ATC clearance. Aircraft operating under IFR and SVFR are separated from each other and from flights operating under VFR. Flights operating under VFR are given traffic information in respect of other VFR flights.
  • Class D: Operations may be conducted under IFR, SVFR, or VFR. All flights are subject to ATC clearance. Aircraft operating under IFR and SVFR are separated from each other, and are given traffic information in respect of VFR flights. Flights operating under VFR are given traffic information in respect of all other flights.
  • Class E: Operations may be conducted under IFR, SVFR, or VFR. Aircraft operating under IFR and SVFR are separated from each other, and are subject to ATC clearance. Flights under VFR are not subject to ATC clearance. As far as is practical, traffic information is given to all flights in respect of VFR flights.
  • Class G: Operations may be conducted under IFR or VFR. ATC separation is not provided. Traffic Information may be given as far as is practical in respect of other flights.

Classes C-E are referred to as controlled airspace. Class G is uncontrolled airspace. Controlled Airspace is shared between different ATC-Units (TWR, APP, CTR) and within these units they can be split further into different sectors.

Responsibilities

Each Radar Controller has an area of responsibility which may consist of one or more sectors. He has to maintain the required seperation between aircraft within his sector and ensures the expeditious flow of traffic.

Minimum Radar Separation

A Controller has to make sure that two Aircraft which are under his control never get closer than the minimum radar seperation. If two aircraft get closer than that, this incident is called a conflict.

  • The standard Minimum Vertical Seperation is 1000 ft up to FL290 and 2000 ft above that. However Austria is considered RVSM (Reduced Vertical Seperation Minima) airspace so the upper limit of the 1000 ft seperation minimum is raised to FL410. In real life this demands special equipment of the aircraft involved, however on VATSIM all aircraft are considered RVSM capable.
  • The Minimum Horizontal Seperation depends on the radar equipment involved. APP Sectors work with a minimum of 3 nm, CTR Sectors use 5 nm.

There are some cases where these minima may be under-run such as visual seperation or formation flights.

MRVA, MSA, MOCA

MRVA (Minimum Radar Vectoring Altitude): The MRVA is defined as the lowest available altitude above Mean Sea Level (MSL) in controlled airspace under consideration of the MSA (Minimum Safe/Sector Altitude) above ground and the airspace structure within a specified area.

MSA (Minimum Safe/Sector Altitude): Minimum Sector Altitude is the minimum altitude that may be used under emergency conditions which will provide a minimum clearance of 1000ft above obstacles and terrain contained within a sector of 25 NM radius centred on a radio navigational aid. MSA can be given as areas between radials from a VOR at the airport.

MOCA (Minimum Obstacle Clearance Altitude): This is the lowest altitude that an aircraft can fly in IMC (Instrument Meteorological Conditions) and still keep safe clearance from terrain and obstacles. MOCA is often lower then MEA (se below). It is only used in emergencies, especially to get below icing.

Structure of Flightplans and Routings

A route consist of one or more points connected by eithe airways or directs (DCT). SOVIL DCT SITNI DCT BAGSI DCT NANIT In this case SITNI is the first point of the Route, thereafter it direct to BAGSI and so on.

SIDs

SID (Standard Instrument Departure): It is a pre-defined route which aircrafts have to fly to get to their initial airway to follow their desired routing to their destination.

e.g.: Flightplan from LOWW (Wien) to Salzburg (LOWS): SOVIL DCT SITNI DCT BAGSI DCT MATIG - SITNI is our first waypoint of our routing and let us say for instance that in Vienna Runway 29 is in use. We take a look at our charts and we see that we can plan for a socalled SITNI6C departure route.

SIDs are specified by the local Air Traffic Control. A SID can contain the following navigation aids: R-NAV Waypoints, VORs, NDBs, etc.

STARs

STARs (Standart Terminal Arrival Routes): STARs are pre-defined routes to get an aircraft to the airport.

A STAR falls into three parts namely navigational point, version number and runway (depending on the airport), e.g. GAMLI5W arrival. The point at which the STAR ends is called Initial Approach Fix (IAF). In some cases the STARs continue and end at the Final Approach Fix (FAF), and that means that you as controller don't need to vector the aircraft unless there is other traffic in the way. The only thing you have to do is to instruct the pilot how to descend the aircraft.

There are exceptions of course, where the STARs don't end at the final, but at a navigational point some distance away from the runway. You as a controller must give vectors the last part to the runway. If you for some reason don’t give vectors, the pilot must enter holding at the STAR's ending point (clearance limit).

Types of Instrument Approaches

An instrument approach or instrument approach procedure (IAP) is a type of air navigation that allows pilots to land an aircraft in reduced visibility (Instrument Meteorological Conditions [IMC]) or to reach visual conditions permitting a visual landing.

There are 2 types of approaches:


  • Precision Approaches
  • Non-Precision Approaches


1.) Precision Approaches

- ILS (Instrument Landing System)
- MLS (Microwave Landing System)
- PAR (Precision Approach Radar)
- GPS (Global Positioning System)
- LAAS (Ground Based Augmentation System [GBAS] for Global Satellite Navigation Systems [GNSS])
- JPALS (Joint Precision Approach and Landing System)
- GCA (Ground Controlled Approach)

2.) Non-Precision Approaches

- Localizer
- VOR
- NDB (with ADF)
- Localizer Type Directional Aid (LDA)
- Simplified Directional Facility (SDF)
- GPS (Global Positioning System)
- TACAN
- Surveillance Radar Approach (SRA) [also known in some countries as ASR approach]
- Visual

Basic Instructions

Vectoring

There are 2 types of vectoring:

  • Lateral Vectoring
  • Vertical Vectoring

Lateral Vectoring

ABC123, turn left heading 165°
DEF243, turn right heading 300°

When issuing a heading to an aircraft, make sure that you are using a direction ending on 0 (zero) or on 5 (five).

If you provide Radar Vectors to an aircraft then always tell the pilot the reason why you are doing this:

ABC123 turn right heading 080°, radar vectors for ILS approach RWY 11

After vectoring an aircraft you might have to send the aircraft back on its flight planned route:

ABC123, proceed direct to SITNI

It is important to know, that as soon as you take an aircraft of a publsihed route, either by vectoring or by using a direct, you are also responsible for the necessary terrain clearance. To do this always consider the MRVA on the aircrafts path.

Vertical Vectoring

ABC123, climb FL240
DEF243, descend Altitude 3000 feet, QNH 1016

As you can see there are 2 types of heights namely Altitude and Flightlevel (FL).

Flightlevel is used for aircraft flying above the Transition Altitude, Transition Level or climbing through and above the Transition Layer (Altimeter in the aircraft is set to Standard Pressure [1013 QNE]).

Altitude is used for aircraft flying below the Transition Altitude or for Aircraft descending through and below the Transition Layer (Altimeter in the aircraft is set to local QNH).

Speed Control

A controller may issue speed instructions within an aircrafts operating limits. There are two possible ways to do this, either by using Indicated Airspeed (FL280 or below) or by specifying a Mach number (FL280 or above).

ABC123, maintain speed 280 knots
DEF456, maintain Mach 0.81

Seperation and Sequencing Techniques

Planning

To effectively use the sequencing techniques explained below we first have to assess the current situation.

Determining current seperation

In VRC and ES there are tools available to determine the seperation between aircraft. One of them is the Seperation Predictor. It is a very comfortable way to determine the point where two aircraft, given a constant speed, will be closest to each other. Furthermore it gives you the minimum distance and the time to go to this point. To constantly survey the distance between to aircraft (or between an aircraft and a point) you can use seperation links (or anchors).

These tools give you an overview over the lateral situation. The vertical situations is a bit more complicated since you have to use a bit of math. If you have two converging aircraft who are not at a constant altitude you need their rate of climb/descend to determine the spacing at their closest point.

APP: AUA265, report rate of climb.
AUA265:rate of climb 2500 feet per minute.

Determining current spacing

Often procedures in a sector include a so called "miles-in-trail" requirement. This means that aircraft flying over the same point and for example have a common destination need to cross the point in a certain distance. Also when working as an approach controller we need to know how close two aircraft will be on approach. How can we determine the current spacing?

First we need to choose a merging point. In a miles in trail requirement this would typically be the handoff point. In the approach area that could be a point somewhere on the approach (e.g. 12 nm final or the point of base turn). Now we can measure the distance of both aircraft to the merging point. If both aircraft have the same speed and are routing direct to the merging point you directly get the spacing at this point. However if differnet speeds are involved things get more complicated. In this case there is no easy and fast way to determine the spacing at the merging point. You will have to use your experience to judge these situations.

Of course you can use this technique to determine the spacing between multiple aircraft.

The concept of positive seperation

Imagine you are the controller in a sector when suddenly the radio communication with your pilots does not work anymore. Take this assumption as the basis of the positive seperation concept. It is policy to always keep aircraft guaranteed safe to each other. This means as soon as you recognize a possible conflict, imeediately resolve it. It's never a good idea to say to yourself "I'll get back to it later" because you might forget it, the voice channel might be blocked and so on.

In the dense approach airspace this is often not easy but it will save you a lot of nerves if you keep converging traffic on different levels!

Resolving conflicts

There are multple ways of resolving a conflict. You can alter the aircrafts flight path, altitude or speed.

Changing an aircrafts altitude to resolve a conflict is relatively easy. Just make sure you achieve the necessary seperation when the two aircraft meet. In the cruise phase you have to keep in mind the aircrafts performance. Often aircraft can't climb higher due to their weight, so don't be surprised if the pilot rejects the altitude change. Also have a look at the aircrafts further intentions. For example it is often not a good idea to put an aircraft that has to descend in a short time anyway on top of another one. Pilots prefer to stay at their cruising altitude however in certain situations (e.g. one aircraft overtaking another one) don't hesitate to change the cruise level in accordance with the pilot.

Speed restrictions for seperation are also possible but mostly you should use them to maintain the present seperation. However in congested airspace where other means of seperation are not possible (e.g. due to terrain) you can also use speeds to achieve a certain seperation. Bear in mind that especially during cruise flight an aircrafts speed margin might not be very large.

Changing an aircrafts flight path to achieve a safe situation is often the best way. Consider the following basic situation:

Two aircraft are flying to the same point at the same altitude. If they keep on flying they will meet each other exactly.

To resolve the conflict you have to change the heading of one of the aircraft. You will soon discover that the best possibility is to turn one aircraft behind the other one. The earlier you start such a maneuver the smaller the heading change has to be.

Spacing techniques

There are two possible ways of achieving a certain seperation: Modifying an aircrafts speed or it's flight path.

The Delay Vector

Your working a sector which has an exit agreement that requires you to put aircraft ten miles in trail. This means the distance between two aircraft exiting your sector with the same destination has to be ten nautical miles. In this sector multiple streams of traffic are merged into one and leave your area via an intersection called TEMTA.

First thing you'll have to do is to determine their current spacing using the techniques discussed above. By doing this we get a spacing of 5 nm, so we have to do something. We don't want to change their speed so what else can we do?

What we will do is lengthen the way of one of the aircrafts and shorten the other ones as far as possible. If possible put the first aircraft on a direct to the merging point. Sometimes this is already enough to gain some miles but in this case we put the second aircraft on a so called delay vector. This means we turn the aircraft away from the direct route to lengthen it's flight path.

RDR: AUA91, proceed direct TEMTA, maintain speed 290 knots indicated.
AUA91: Proceeding direct TEMTA, maintaining 290 knots indicated.
RDR: AFR291, for seperation turn right heading 130, maintain speed 290 knots indicated.
AFR291: turning right heading 130, maintaining speed 290 knots indicated.

To be sure we assigned a common speed and we also gave a short hint to the pilot about the cause for the vector.

Now we have to constantly assess the spacing between these two aircraft. As soon as we achieved our required spacing we put the Air France back on it's route.

RDR: AFR291, proceed direct TEMTA.
AFR291: proceeding direct TEMTA.

In this case we used a delay vector of about 40 degrees. You will learn by experience how big this delay vector has to be, however as before, the earlier you start the maneuver the smaller it has to be.

Speed Control

It is often also necessary to use speed restrictions to achieve or maintain a certain spacing. In these cases IAS should be used below FL 240 and Mach in the regions above. Especially in cruise flight most aircraft have a small speed margin, so the effect of speed control is limited. Often speed control is used additionally to putting the aircraft onto a delay vector.

Aircrews are expected to maintain instructed speeds as accurately as possible (+ / - 10knts). In case of unability to maintain instructed speed (weather reasons, operating limitations etc.) the controller has to be informed immediately.

Holding

Useage
The primary use of a holding is delaying aircraft that have arrived over their destination but cannot land yet because of traffic congestion, poor weather, or unavailability of the runway. Several aircraft may fly the same holding pattern at the same time, separated vertically by 1,000 feet or more.

How does it look like A holding is situated around a holding fix. In a standard holding pattern the aircraft flies inbound to the holding fix on a certain course (Inbound leg). After passing the fix it turns right (standard turn: 2° per second) and flies one minute (1,5 min above FL 140) into the other direction (outbound leg). After one minute the pilot turns right again (standard turn) and establishes again on the inbound leg.

If you count all this together you end up with four minutes required to finish one holding pattern. However some holding patterns use left turns, others don't use one minute to measure the outbound leg, but fly to a certain distance.

Also every holding has a minimum altitude.

Flying a Hold
Most aircraft have a specific holding speed published by the manufacturer.Maximum holding speeds are established in order to keep aircraft within the protected holding area during their one-minute inbound and outbound legs.

As a rule of thumb the Speed to be flown depends on the altitude or flight level the aircraft is at within the hold as follows:

   * At 6,000' MSL and below: 200 knots
   * From 6,001' to FL 140: 230 knots
   * At and above FL140: 265 knots
  • Duration

A Complete hold should take:

   * FL140 and below 4 minutes
   * FL140 and above 5 minutes
  • Holding Clearance

A holding clearance issued by ATC includes at least:

- A clearance to the holding fix.
- The direction to hold from the holding fix.
- A specified radial, course, or inbound track.
- If DME is used, the DME distances at which the fix end and outbound end turns are to be
  commenced.
- The altitude or FL to be maintained. 
- The time to expect further clearance or an approach clearance.
- The time to leave the fix in the event of a communications failure.
  • Standart Holding Pattern
   * Standard Hold: A hold where all turns are made to the right
   * Non Standard Hold: A hold where all turns are made to the left
   * Holding Course: The course flown on the inbound leg to the holding fix.
   * Inbound Leg: The standard 1 or 1.5 minute leg to the holding fix as Published
   * Holding Fix: This can be a VOR, a VORDME, an Intersection or an NDB
   * Outbound Turn: A standard rate, 180 degrees turn which is begun at the holding Fix.
   * Abeam: The position opposite the holding fix, where the outbound begins.
   * Outbound Leg: This leg is defined by the inbound leg, pilots should adjust the outbound leg
     so that the inbound turn, the other standard 180° turn is completed just as the holding
     course is intercepted.
   * Holding Side: The side of the course where the hold is accomplished.
   * Non Holding Side: The side of the course where you do not want the pilot to be holding
  • Non Standart Holding Pattern

A non-standard holding pattern is one in which

- The fix end and outbound end turns are to the left; and/or
- The planned time along the inbound track is other than the standard one-minute or
  one-and-a-half minute leg appropriate for the altitude flown.
  • Entry Holding Procedure
    • Direct Entry (aircraft flies directly to the holding fix, and immediately begins the first turn outbound)
    • Parallel Entry (aircraft flies to the holding fix, parallels the inbound course for one minute outbound, and then turns back, flies directly to the fix, and proceeds in the hold from there
    • Teardrop Entry or Offset Entry (aircraft flies to the holding fix, turns into the protected area, flies for one minute, and then turns back inbound, proceeds to the fix and continues from there).

Coordination with adjacent Sectors

The coordination respectively the communication between controllers (and of course pilots) is on of the most important things in aviation.

A clear instruction to the person I want to speak to falls into 4 parts:

- Who am I calling
- What do I want
- How are we going to archieve this (short and clear instructions!) 
- Did the person I called unterstand my instruction properly

The Handoff

At some point you'll have to send the pilot on to the next controller. With a Tower this is relatively easy: Just drop the track and send him onto the Tower frequency.

However between Radar controllers a more sophisticated system is used. A Handoff consists of two stages:

  • Transfer of Control
  • Transfer of Communication.

Transfer of Control

The first part is done by sending a handoff request to the next controller. You may only do this if the plane is safe and will remain safe within your sector at all time. So initiate the handoff if you don't need him anymore, but not before that. The other controller accepts the handoff. Again he only does this if he can really accept the traffic without creating a conflict. If that's not possible the two of you will have to work out a different solution.

If the next controller rejects the handoff, the aircraft is not allowed to enter his sector and it is your responsibility to ensure it doesn't.

You are responsible for everything that happens in your sector. And you are not allowed to do anything in somebody else's if it is not stated in your sectors Letters of Agreement or without his permission.

If the handoff is accepted, transfer of control is complete.

Transfer of Communication

This is easy, just send him on the next frequency.

The Release

Some times it comes in handy to change an aircrafts direction, altitude or speed while he is still in the previous sector. In this case you can coordinate with the controller responsible that you change one of these things early. This is called a release and often the phrase:

"Released for ..."

is used.

VFR Traffic

Flight Information Positions

Flight Information Service (FIS) is an air traffic facility that provides a myriad of services to the pilot, such as pilot briefings, relaying of clearances and broadcasting of weather information. At selected locations, FIS also provides en-route Flight Advisory Services.

Abnormal Situations - Emergencies, Radio Failures

Emergencies

Emergencies are very uncomfortable situations for every controller. Emergencies shall be handeled expeditiously to get them safe down to the ground.

The pilot tells the ATC what his intentions are and what he will do next and not the other way round. ATC keeps all the traffic in the vicinity of the emergency aircraft away to assure that no other aircraft gets injured.

Radio Failures

There are two ways to recognize a radio failure. Either you call the aircraft and don't get an answer or the pilot notices the failure and sets Squawk 7600. In the second case you will get an indication on your screen.

First thing to do, is to find out if the pilot can still hear you:

"RDR: FLT1, if you read Squawk Ident"
or
"RDR: FLT1, if you read turn right by 30° for 30 seconds.

If he does you can give him instructions as usual. It is a good idea to let the pilot acknowledge each of the instructions:

"RDR: FLT1, Acknowledge all further instructions by Squawking Ident"

Inform the other controllers involved of the situation.

If the pilot is not able to hear you, he will continue his flight according to his flightplan until he reaches his clearance limit. There he will enter the associated holding pattern, stay there 5 minutes and then conduct the approach to the active runway. In this case keep the other aircraft out of his way and again inform the other controllers involved.

Information Positions

  • Traffic Information
  • Weather Information
  • Special Requests


LOWW_I_APP (118.520) and LOVV_I_CTR (124.400) are the FIS/FIC Positions within Austrian airspace. They are responsible for the VFR Flights. They allocate Squawks, provide Traffic Information and offer Weather Information (worldwide) and coordinate with other controllers requests from pilots.