Air Control

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Air Space Revision

Aerodrome Traffic Zone (ATZ)

The ATZ is airspace of defined dimensions established around an aerodrome for the protection of aerodrome traffic. ATZ's are only established at all military airfields and civil licensed aerodromes (A small grass strip on somebody's farm does not have an ATZ)

Dimensions

Vertical - Surface to 2000 feet above aerodrome level

Horizontal - Circle of radius 2 or 2.5nm centered on the notified mid point of the longest runway.

Adjacent ATZ's

If two ATZ's are close and overlap, one aerodrome is known as the "Controlling Authority" and one as the "Adjacent". The "Controlling Authority" is responsible for the portion of airspace in the overlap.

Control Zone (CTR)

Controlled airspace extending upwards from the surface of the Earth to a specified upper limit


Departure Separation

Separation between departing aircraft is applied so that after one aircraft takes off, the next aircraft does not take-off with less than the number of minutes needed. There are 3 main departure separation methods:

- Vortex Separation
- Route Separation
- Speed Separation

Vortex Seperation

1st Aircraft Vortex Cat. 2nd Aircraft Vortex Cat. 3rd Aircraft Vortex Cat.
Heavy Heavy 1 Minute
Heavy Medium 2 Minute
Heavy Small 2 Minute
Heavy Light 2 Minute
Medium Heavy -
Medium Medium 1 Minute
Medium Small 2 Minute
Medium Light 2 Minute
Small Heavy -
Small Medium -
Small Small 1 Minute
Small Light 2 Minute
Light Heavy -
Light Medium -
Light Small -
Light Light 1 Minute

The time is counted from the moment the 1st aircraft's main landing gear leaves the ground. (At certain airfields it is counted from the time the aircraft starts its take-off roll.)

If the first aircraft commences a full length take-off and the following aircraft departs from an intersection, the spacing must be increased to 3 minutes.

Route Seperation

1 minute separation - The aircraft fly on tracks diverging by 45° or more immediately after take-off.

2 minute separation - The preceding (first) aircraft has filed a true airspeed 40 knots or more faster than the following (second).

5 minute separation - The preceding (first) aircraft has filed a true airspeed of 20 to 39 knots faster than the following aircraft.

10 minute separation - Any other case

ATC Units may have their own reduced separations. These will be detailed in the airport information on our website.

Speed Seperation

Group 3 Group 2 Group 1 Group 0

All Jet Aircraft excluding:

  • C500/501/550/551
  • BA46 and derivatives
  • CL60
  • CRJ1/2/7/9
  • J328
  • E135/145
  • CARG
  • C500/501/550/551
  • BA46 and derivatives
  • CL60
  • CRJ1/2/7/9
  • J328
  • E135/145
  • CARG
  • L188/P3
  • AN22
  • D328
  • L328
  • SB20
  • A748
  • CN235
  • ATP
  • AT43/44/45/72
  • BE20
  • DHC7
  • DH8A/8B/8C/8D
  • E120
  • F27/50
  • G159
  • JS31/32/41
  • SF34
  • SW3/4
  • BE99
  • DC3
  • DHC6
  • E110
  • SH33/36
  • PA31
  • PA23
  • C404
  • C172
  • C152
  • Only the most common aircraft types are included in this table as it would be impossible to group every single type of aircraft made. If you work an aircraft that is not included in the above list, look for a similar aircraft and group it together with it.

    To work out the required speed separation, you first need to calculate the required separation for vortex/route. Once you have that figure, you then need to add on any required speed separation.

    Group 3 aircraft are the fastest - Group 0 aircraft are slowest. When a faster aircraft follows a slower aircraft, the minimum separation is increased by one minute for each successive group.

    Example 1: If we have a 2 minute route separation but a group 2 aircraft is first to depart followed by a group 3 aircraft, we would need to increase the separation by 1 minute, to 3.

    Example 2: If we have a 5 minute route separation but a group 0 aircraft is first to depart followed by a group 3 aircraft, we would need to increase the separation by 3 minutes, to 8 minutes.

    Examples

    Example 1.

    A Boeing 747 is number 1 for departure. A Boeing 737 is number 2 for departure. Immediately after take-off, there tracks diverge by more than 45 degrees. What is the departure separation?

    Boeing 747 is a Heavy Beoing 737 is a Medium

    Medium following Heavy gives a separation of 2 minutes.

    Tracks diverge by more than 45 degrees, which gives a 1 minute separation. The greater of the 2 must be taken, so the departure separation here is 2 minutes

    If the 747 commences a full length take off and the 737 departs from an intersection, this spacing is increased to 3 minutes

    In this example, both aircraft are Group 3 so no speed separation is needed.

    Example 2.

    An Airbus 321 is number one for departure. An Airbus 319 is number 2 for departure. Both aircraft are departing in the same direction but the A321 has filed a true airspeed that is 50kts faster than the A319. What is the departure separation?

    Airbus 321 is a medium Airbus 319 is a medium

    Medium following a medium gives a separation of 1 minute.

    The first aircraft has filed a true airspeed more than 40kts faster than the second. That gives a departure separation of 2 minutes. The greater of the 2 must be taken, so the departure separation here is 2 minutes

    In this example, both aircraft are Group 3 so no speed separation is needed.

    Example 3.

    An ATP is number one for departure. An Airbus 320 is number 2 for departure. Both aircraft are departing in the same direction but the A320 has filed a true airspeed that is 150kts faster than the ATP. What is the departure separation?

    Airbus 320 is a medium ATP is a small

    There is no vortex requirement when a medium follows a small.

    The first aircraft has filed a true airspeed slower than the first, so unless local rules dictate differently, a 10 minute departure separation is required.

    The ATP is a group 1 aircraft and is being followed by a group 3 aircraft, so the departure separation must be increased by a further 2 minutes. The departure separation in this case would be 12 minutes

    Final Approach Spacing

    Responsibility

    It is the tower controllers responsibility to determine what final approach spacing to use. Tower controllers should inform approach controllers of the spacing requirements needed unless there is already a set down procedure.

    If there is no set down procedure or coordination, then approach controllers will aim for 3nm spacing or vortex, whichever is greater.

    Any set down procedures can be found on our ATC Knowledgebase.

    Wake Turbulence Spacing

    High pressure air below a wing spills over to the low pressure air above the wing. This creates disturbances in the air, known as wake turbulence.

    Heavier aircraft require more lift thus creating greater disturbances. Lower speeds on approach require a high angle of attack - This also increases the turbulence intensity.

    The spacing between aircraft, determined either by time or distance, is to be applied so that aircraft of a lower weight category do not fly through the wake of an aircraft of a higher category within the area of maximum vorticies.

    Leading Aircraft Following Aircraft Minimum Distance

    Sequencing VFR with IFR

    When sequencing VFR circuit traffic with IFR, you must ensure that you have an adequate gap in the inbound stream to accomodate the aircraft. As a general rule of thumb, you should have required vortex gap + 4 miles (If the required vortex spacing is 8 miles, this means you need a gap of at least 12 miles between IFR inbounds to safely accomodate the VFR traffic. This gap allows for the vortex and the significant catch up that there is likely to be.) This gap can be reduced or increased, depending on aircraft performance.

    Aerodrome control should coordinate with approach control on where and how big the gaps need to be.

    When a circuit aircraft is ready to turn on base leg, they may not be number 1 to make an approach. If the delay is only going to be a couple of miles, they should be instructed to extend the downwind leg and passed information on the traffic they are following:

    "GBGGD, you are number 2 to a 737 on a 1 mile final, caution wake vortex, recommended spacing is 4 miles, extend downwind leg as necessary and report finals."

    The aircraft should then position itself behind the traffic - They may choose to position behind less or more than the required spacing. Monitor the situation, especially any further IFR traffic that is to arrive afterwards.

    If the delay could be several minutes, then the aircraft should be instructed to orbit at the end of the downwind leg and passed information on the traffic they are following:

    "GBGGD, you are number 2 to a 747 on a 7 mile final, caution wake vortex, recommended spacing is 7 miles, orbit at the end of the downwind leg as necessary and report finals."

    If you are unsure where the aircraft is going to fit into the sequence, they should be instructed to orbit and await further instructions:

    "GBGGD, position in the sequence is not determined, orbit at the end of the downwind leg and standby for further instructions."


    Conditional/Delayed Clearances

    Line-Up

    Conditional Clearances for line up can be used but these should be used with extreme caution, especially in our online environment. Make sure that any conditional clearances states specifically what the aircraft should do and when it should do it. There should be no doubt in the pilots mind about what he should do

    "BAW123, behind the landing Easyjet A319, via A1, line up runway 27, behind"

    "BAW456, behind the departing company Boeing 737, via D3, line up runway 33, behind"

    Take-Off

    For traffic reasons, it may be necessary for an aircraft to take off immediately. For aircraft at the holding point, this means rolling onto the runway and commencing take-off without stopping the aircraft and for aircraft already lined up on the runway, commencing take-off without delay. NOTE - An immediate take-off must not be given to an aircraft of a Super or Heavy wake vortex category

    If you require an aircraft to make an immediate take-off, you must first ask the aircraft if they can accept one:

    "BAW123, are you ready for an immediate departure?"

    If the pilot accepts, then the take-off clearance must include the word "immediate":

    "BAW123, cleared immediate take-off, surface wind 340 degrees 15 knots"

    Landing

    If there is an aircraft on final approach but the runway is not yet clear, then the aircraft should be instructed to continue it's approach. It should also be passed the current surface wind:

    "BAW123, Continue approach, surface wind is 280 degrees 18 knots"

    Late landing clearance

    If you anticipate that an aircraft is going to get very close to the runway before a landing clearance can be issued, it is useful to tell the pilot that he can expect a late landing clearance and if time permits, the reason why:

    "BAW123, Expect a late landing clearance, one aircraft to depart ahead"

    "BAW456, Expect a late landing clearance, vehicle on the runway"

    "BAW789, Expect a late landing clearance, aircraft crossing the runway"


    Visual Approaches

    A visual approach is an approach by an IFR flight when part or all of an instrument approach procedure is not completed and the approach is executed with visual reference to terrain.

    To expedite traffic at any time, IFR flights may be authorised to execute a visual approach if the pilot reports he can maintain visual reference to the surface and the reported cloud ceiling is not below the initial approach level.

    Practicalities

    When transferred by approach, the aircraft should have visual reference to the ground and have been provided with standard separation.

    As the aircraft are not following an instrument approach, they are unpredictable as to when they will turn onto final. You should take this into account when integrating departures.


    Coordination

    Departing Aircraft

    Aerodrome must coordinate departing flights with approach control or area control (Depending on which control departing aircraft talk to) unless the free flow method of departure is in use.

    Aerodrome should request a release (either when the aircraft is taxiing or holding short of the runway) in the following format:

    "Request Release"<Callsign> <Departure Route>

    e.g.

    "Request Release, BAW123 on a BPK1T"

    Approach will then either release the aircraft or specify a time when the aircraft can be released.

    Departing VFR

    When issuing a departure clearance to VFR aircraft (except those wishing to remain within the circuit), the clearance must be issued by approach control and then relayed to the pilot via aerodrome control:

    "Request clearance, GBGGD a C172 to Bournemouth, leaving the zone to the North-East."

    "GBGGD is cleared to the North-Eastern zone boundary, not above altitude 2500ft, VFR, QNH1018hPa, squawk 7055, release subject radar."

    "GBGGD is cleared to the North-Eastern zone boundary, not above altitude 2500ft, VFR, QNH1018hPa, squawk 7055, release subject radar."

    "Correct"

    Release subject radar means that aerodrome control must request a departure release on the aircraft before it can take off as VFR do not operate on a free flow system.

    As the aircraft approaches the holding point, a release should be requested from approach control:

    "Request release, GBGGD, VFR to the North-Eastern boundary"

    "GBGGD is released"

    "GBGGD, Released, Roger"

    Once the aircraft is airborne, they should be handed to the approach controllers frequency.

    Circuit Traffic

    Specific circuit traffic does not need to be coordinated with approach control. The only requirement is that approach control should be informed whenever the circuit is active.

    Free Flow

    If the free flow method of departure is in use, then aerodrome does not have to request a release on each aircraft - They can release them in turn. This continues until free flow is cancelled (i.e. during a missed approach)

    Non-Airways

    Aerodrome must coordinate with approach/area any aircraft who wish to depart with a non-airways clearance (Also aircraft who are unable to fly a SID). Approach/Area will specify what they require the aircraft to do once airborne.

    Arriving Aircraft

    Under normal circumstances, aerodrome does not have to coordinate anything with approach/area regarding arriving flights, except any final approach spacing requirements.

    Arriving VFR

    Approach control should coordinate any arriving VFR traffic with Aerodrome control. Approach control should pass an inbound estimate to aerodrome control:

    "Inbound estimate, GBGGD, C172 from Bournemouth, estimates the field at 1256Z."

    "GBGGD at time 56, Roger"

    Once the aircraft informs the approach controller that they have the airfield in sight, or they arrive at a specified VRP, the aircraft will be handed to aerodrome control for circuit joining instructions.