Section 1, Chapter 3 - Separation Standards

Question 1

What are the requirements for providing standard separation in different classes of airspace?

Answer 1

Standard Separation Requirements:
Provided Between:

• All flights in Class A airspace.
• IFR flights in Class C, D, and E airspace.
• IFR flights and VFR flights in Class C airspace.
• IFR flights and Special VFR flights.
• Special VFR flights, except where a reduction is authorized by the CAA.

Class G Airspace:

• Separation between aircraft is ultimately the pilot’s responsibility.
• Controllers providing a Deconfliction Service or a Procedural Service will offer information and advice to achieve defined deconfliction minima.

Question 2

When should separation standards be increased?

Answer 2

Separation standards, which are minima, should be increased when:

• Requested by the pilot.
• A controller considers it necessary.
• Directed by the CAA.

Question 3

When can standard separation minima be reduced in the vicinity of aerodromes?

Answer 3

Standard separation minima in the vicinity of aerodromes can be reduced if:

• Adequate separation can be provided by the aerodrome controller when each aircraft is continuously visible to this controller.
• Each aircraft is continuously visible to the pilots of the other aircraft concerned and the pilots report that they can maintain their own separation.
• When one aircraft is following another, the pilot of the succeeding aircraft reports the other aircraft is in sight and can maintain their own separation.

Question 4

When can standard separation be reduced during a Search and Rescue (SAR) escort?

Answer 4

Standard separation may be reduced when a SAR aircraft is escorting an aircraft in an emergency. There is no minimum separation laid down in UK FIRs, and separation may be reduced to what can be maintained visually or with airborne surveillance.

Question 5

What actions should a controller take in a situation where two or more aircraft are separated by less than the prescribed minima?

Answer 5

If two or more aircraft are separated by less than the prescribed minima, the controller should:

• Use every means at their disposal to obtain the required minimum separation with the least possible delay.
• When practicable, pass traffic information if an ATS surveillance service is being provided; otherwise, pass essential traffic information.

Question 6

What is essential traffic information and what should it include?

Answer 6

Essential traffic information is provided when traffic is separated by less than the specified standard separation, usually when ATS surveillance systems are not available.

It should include:

• Direction of flight of conflicting aircraft.
• Type of conflicting aircraft.
• Cruising level of conflicting aircraft and ETA for the reporting point, or for aircraft passing through the level of another with less than normal separation; the ETA for the reporting point nearest to where the aircraft will cross levels.
• Any alternative clearance.

Question 7

What are the vertical separation minima between aircraft?

Answer 7

Vertical Separation Minima:
Between aircraft flying subsonic:
* Up to FL290: 1,000 ft
* Above FL290: 2,000 ft, except between FL290 and FL410 inclusive, 1,000 ft may be applied between RVSM approved aircraft operating in designated airspace.

Between aircraft flying supersonic and between supersonic and subsonic aircraft:
* Up to FL450: 2,000 ft
* Above FL450: 4,000 ft

Additional Considerations:
* If a pilot advises that their aircraft is no longer capable of RVSM operations, the first ATSU aware of the failure must coordinate with subsequent ATSUs.
* The Mode C of some military aircraft is accurate only to the nearest 400 ft during supersonic flight; thus, 4,000 ft separation may be applied at all levels.
* Controllers should assess the vertical distance by observing Mode C responses or obtaining level reports from pilots.

Question 8

How may aircraft be instructed to change levels?

Answer 8

Aircraft may be instructed to change levels at a specified time, place, or rate.

Question 9

Under what conditions can an aircraft be instructed to climb or descend to a level previously occupied by another aircraft?

Answer 9

An aircraft may be instructed to climb or descend to a level previously occupied by another aircraft provided that:

• Vertical separation already exists.
• The vacating aircraft is proceeding to a level that will maintain vertical separation.
• Either:
  1. The controller observes that the vacating aircraft has left the level, or
  2. The pilot has reported vacating the level.

Question 10

What should be done if severe turbulence is known to exist when instructing an aircraft to change levels?

Answer 10

If severe turbulence is known to exist, instructions shall be delayed until the vacating aircraft is known to be at, or through, another level separated by the required minimum.

Question 11

What must controllers consider when instructing an aircraft to climb or descend to a previously occupied level?

Answer 11

Controllers must exercise caution and consider that aircraft may climb or descend at markedly different rates. If necessary, additional measures such as specifying a maximum or minimum climb or descent rate for each aircraft should be applied to ensure the required separation is maintained.

This is particularly relevant when the aircraft are established in the same holding pattern.

Question 12

Under what conditions may controllers authorize an aircraft to climb or descend in VMC?

Answer 12

Controllers may authorize an aircraft to climb or descend in VMC provided:

• The manoeuvre is restricted to Class D, E, F, and G airspace at or below FL100.
• It is during the hours of daylight.
• The aircraft is flying in visual meteorological conditions.
• The pilot of the aircraft climbing or descending agrees to maintain their own separation from other aircraft and the manoeuvre is agreed by the pilot of the other aircraft.
• Essential traffic information is given.

Question 13

What must be considered regarding TCAS RA when authorizing VMC climb and descent in Class D airspace?

Answer 13

The application of VMC climb and descent could trigger a TCAS RA. Therefore, in Class D airspace when surveillance services are being provided, VMC climb and descent shall only be used where authorized and in accordance with any conditions specified in MATS Part 2.

Question 14

What are the three types of horizontal separation?

Answer 14

The three types of horizontal separation are:

• Lateral separation
• Longitudinal separation
• Separation based on ATS surveillance system information

Question 15

What does “level change” mean in the context of horizontal separation?

Answer 15

“Level change” refers to the portion of the climb and descent during which the vertical separation in relation to the level of another aircraft is less than the minima.

Question 16

What is an “exact reporting point” in air traffic control?

Answer 16

An “exact reporting point” is a position established by a navigational facility which is:

• Overhead a VOR.
• Overhead an NDB.
• A position notified as a reporting point and established by the intersection of VOR radials, or of a VOR radial and a bearing from an NDB.
• A position established by a VOR radial combined with a range from a co-located or associated DME.

Question 17

What are the departure separation minima and their provisions?

Answer 17

Departure Separation Minima:
1 minute:

• Provided that aircraft fly on tracks diverging by 45° or more immediately after take-off.
• May be reduced when aircraft take-off from independent diverging or parallel runways with CAA-approved procedures.

2 minutes:

• The preceding aircraft has filed a true airspeed 40 knots or more faster than the following.
• Neither aircraft is cleared to execute any manoeuvre decreasing the 2-minute separation between them.

5 minutes:

• The preceding aircraft has filed a true airspeed of 20 knots or more faster than the following.
• The 5-minute separation is maintained up to a reporting point within or adjacent to a control zone or terminal control area, and the aircraft will subsequently be separated either:
• Vertically.
• By tracks diverging by 30° or more.
• By ATS Surveillance.
• Only used at locations approved by the CAA.**

10 minutes:

• No additional provisions specified.

Note: Separation minima based on time require the full sixty seconds of each specified minute to elapse.

Question 18

What term is used in radiotelephony to describe the effect of rotating air masses generated behind aircraft wing tips, and what term does it replace?

Answer 18

The term “wake turbulence” is used in radiotelephony to describe the effect of the rotating air masses generated behind the wing tips of aircraft, replacing the term “wake vortex,” which describes the nature of the air masses.

Question 19

What factors affect the strength and persistence of vortices generated by aircraft, and when are they most hazardous?

Answer 19

Factors Affecting Vortex Strength and Persistence:
* All aircraft, including helicopters and tilt-rotor aircraft, generate vortices as a consequence of producing lift.
* Heavier aircraft and slower speeds result in stronger vortices.
* Vortices are especially persistent in calm conditions.

Most Hazardous Phases:
* Vortices are most hazardous to aircraft with a small wingspan during the take-off, initial climb, final approach, and landing phases of flight.

Question 20

When do wake vortices begin and end for fixed-wing aircraft?

Answer 20

Wake vortices begin to be generated by fixed-wing aircraft when the nose wheel lifts off the runway on take-off and continue until the nose wheel touches down on landing.

Question 21

How do helicopters and tilt-rotor aircraft generate wake turbulence, and how does it differ from fixed-wing aircraft?

Answer 21

Helicopters:
* When mass is transferred from the landing gear to the rotor, a strong downwash is created in all directions, which can be moved by the wind.
* In forward flight, the downwash from the main rotor(s) transforms into a pair of trailing vortices similar to the wingtip vortices of a fixed-wing aircraft.
* Evidence suggests that, per kilogram of gross mass, the wake turbulence generated by a helicopter is more intense than that of a fixed-wing aircraft.

Tilt-Rotor Aircraft:
* Combine characteristics of aeroplanes and helicopters.
* For vertical flight, rotors are angled horizontally to lift like a helicopter.
* As indicated airspeed increases, rotors progressively tilt forward, eventually becoming vertical to provide thrust while fixed wings provide lift.
* On final approach, rotors tilt backward as speed reduces.
* Operate as helicopters on final approach and departure, and as aeroplanes in en-route and intermediate approach phases.

Question 22

What are the wake turbulence separation minima and their applicability?

Answer 22

Wake Turbulence Separation Minima:
Definition:
* Spacings between aircraft, determined by time or distance, to prevent aircraft from flying through the wake of a preceding aircraft within the area of maximum vortices.

IFR Separation:
* Where IFR separation minima are greater than the recommended separation for wake turbulence, IFR separation minima shall be applied.

Visual Flight:
* When a flight is operating visually (i.e., IFR or SVFR with reduced separation in the vicinity of aerodromes, VFR, or IFR making a visual approach) and is following or crossing behind another aircraft, the pilot must be informed of the recommended wake turbulence separation minima.

Question 23

What are the surveillance-based wake turbulence separation minima for en-route flights?

Answer 23

Surveillance-Based Wake Turbulence Separation Minima for En-Route Flights:

• A minimum of 5 NM between a HEAVY (including a SUPER) and a MEDIUM (UPPER and LOWER), SMALL, or LIGHT aircraft following or crossing behind at the same level or less than 1,000 ft below.

Question 24

What are the wake turbulence separation minima for the intermediate approach segment?

Answer 24

Wake Turbulence Separation Minima for Intermediate Approach Segment (SERA.8012):

5 NM:

• Between a HEAVY (excluding a SUPER) and a MEDIUM (UPPER and LOWER) or SMALL aircraft following or crossing behind at the same level or less than 1,000 ft below.

6 NM:

• Between a HEAVY (excluding a SUPER) and LIGHT aircraft following or crossing behind at the same level or less than 1,000 ft below.

As per Final Approach Minima:

• For aircraft following or crossing behind a SUPER at the same level or less than 1,000 ft below.

Note: The intermediate approach phase is specific to each individual Instrument Approach Procedure. ATC units should define and specify in MATS Part 2 the area or portion of a procedure where the intermediate approach wake turbulence separation minima apply.

Question 25

When are wake turbulence separation minima applied to aircraft on final approach according to SERA.8012?

Answer 25

Wake turbulence separation minima are applied to aircraft on final approach when: * An aircraft is operating directly behind another aircraft at the same altitude or less than 1,000 ft below. * An aircraft is crossing behind another aircraft at the same altitude or less than 1,000 ft below. * Both aircraft are using the same runway or parallel runways separated by less than 760 m.

Question 26

When are wake turbulence separation minima applied to aircraft on departure according to SERA.8012?

Answer 26

Wake turbulence separation minima on departure are applied when aircraft are using: * The same runway. * Parallel runways separated by less than 760 m. * Crossing runways if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 1,000 ft below. * Parallel runways separated by 760 m or more, if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 1,000 ft below. *Take-off clearance may be issued with an allowance for the anticipated take-off run on the runway, but the airborne time interval must reflect at least the required time separation.*

Question 27

What are the wake turbulence separation minima for opposite direction departures and approaches?

Answer 27

**Wake Turbulence Separation Minima for Opposite Direction Departures and Approaches:** **SUPER Aircraft:** **4 minutes between a SUPER aircraft making a low or missed approach and a LIGHT, SMALL, or MEDIUM (UPPER and LOWER) aircraft:** * Utilizing an opposite-direction runway for take-off. * Landing on the same runway in the opposite direction or on a parallel opposite-direction runway separated by less than 760 m. **3 minutes between a SUPER aircraft making a low or missed approach and a HEAVY aircraft:** * Utilizing an opposite-direction runway for take-off. * Landing on the same runway in the opposite direction or on a parallel opposite-direction runway separated by less than 760 m. **Other Aircraft Categories:** **3 minutes between a HEAVY aircraft making a low or missed approach and a MEDIUM (UPPER and LOWER), SMALL, or LIGHT aircraft, and between a LIGHT aircraft and a MEDIUM (UPPER and LOWER) or SMALL aircraft:** * Utilizing an opposite-direction runway for take-off. * Landing on the same runway in the opposite direction or on a parallel opposite-direction runway separated by less than 760 m.

Question 28

What are the wake turbulence separation minima for crossing and parallel runways?

Answer 28

**Crossing and Parallel Runways:** **Parallel Runways Separated by Less than 760 m:** * Considered a single runway for wake turbulence reasons. * Apply wake turbulence separation minima listed for landing and departing aircraft respectively. **Wake Turbulence Separation Minima (Paragraph 9G) Apply to:** * Departures from crossing and/or diverging runways if the projected flight paths will cross. * Departures from parallel runways 760 m or more apart if the projected flight paths will cross.

Question 29

What are the wake turbulence separation minima for aircraft operating on a runway with a displaced landing threshold?

Answer 29

**Wake Turbulence Separation Minima for Displaced Landing Threshold:** **SUPER Aircraft:** **3 minutes:** * Between a LIGHT, SMALL, or MEDIUM (UPPER and LOWER) aircraft and a SUPER aircraft if the projected flight paths are expected to cross: 1. A departing LIGHT, SMALL, or MEDIUM aircraft follows a SUPER aircraft arrival. 2. An arriving LIGHT, SMALL, or MEDIUM aircraft follows a SUPER aircraft departure. **HEAVY Aircraft:** **2 minutes:** * Between a HEAVY aircraft and a SUPER aircraft if the projected flight paths are expected to cross: 1. A departing HEAVY aircraft follows a SUPER aircraft arrival. 2. An arriving HEAVY aircraft follows a SUPER aircraft departure. **Other Aircraft Categories:** **2 minutes:** * Between MEDIUM (UPPER and LOWER), SMALL, or LIGHT aircraft following a HEAVY aircraft, and between a LIGHT aircraft following a MEDIUM or SMALL aircraft if the projected flight paths are expected to cross: 1. A departing MEDIUM, SMALL, or LIGHT aircraft follows a HEAVY arrival, or a departing LIGHT aircraft follows a MEDIUM or SMALL arrival. 2. An arriving MEDIUM, SMALL, or LIGHT aircraft follows a HEAVY aircraft departure, or an arriving LIGHT aircraft follows a departing MEDIUM or SMALL aircraft.

Question 30

How should aircraft making a touch-and-go or a low approach be considered for wake turbulence separation purposes?

Answer 30

For wake turbulence separation purposes, aircraft carrying out a touch-and-go or a low approach shall be considered as making a departure from an intermediate point on the runway.

Question 31

How should helicopters and tilt-rotor aircraft be considered for wake turbulence separation purposes when air taxiing across runways?

Answer 31

For wake turbulence separation purposes, helicopters and tilt-rotor aircraft air taxiing across runways shall be considered as making a departure from that intermediate point of the runway

Question 32

What should controllers do to minimize the effects of downwash and associated turbulence from helicopters and tilt-rotor aircraft when hovering or air taxiing?

Answer 32

**To minimize the effects of downwash and associated turbulence from helicopters and tilt-rotor aircraft, controllers should:** * Instruct helicopters and tilt-rotor aircraft to ground taxi rather than air taxi when operating in areas where aircraft are parked or holding. * Avoid air taxiing helicopters and tilt-rotor aircraft close to taxiways or runways where light aircraft operations (including light helicopter operations) are in progress. If air taxiing is imperative, helicopters must be routed to: 1. Avoid overflying parked aircraft, vehicles, or loose ground equipment. 2. Follow standard taxi routes where helicopters and fixed-wing aircraft share common areas on a movement area.

Question 33

What precautions should controllers take when a helicopter or tilt-rotor aircraft is hover taxiing or in a stationary hover?

Answer 33

When a helicopter or tilt-rotor aircraft is hover taxiing or in a stationary hover, controllers should: * Avoid taxiing light aircraft, helicopters, or tilt-rotor aircraft within a minimum area comprising three times the rotor diameter of that helicopter or tilt-rotor aircraft. * Consider increasing this minimum distance for larger helicopters.

Question 34

What caution should be exercised when a lower weight turbulence category aircraft is cleared to land after a higher weight turbulence category helicopter or tilt-rotor aircraft has taken off?

Answer 34

Caution should be exercised when a helicopter, tilt-rotor aircraft, or fixed-wing aircraft of a lower weight turbulence category is cleared to land on a runway immediately after a helicopter or tilt-rotor aircraft of a higher weight turbulence category has taken off from that runway’s threshold.

Question 35

What are the requirements for horizontal separation based on ATS surveillance system information?

Answer 35

**Requirements for Horizontal Separation Based on ATS Surveillance System Information:** **Justification and Approval:** * Must be justified by the ANSP. * Approved by the CAA. * Detailed in MATS Part 2. **Holding Points:** * Shall not be used between aircraft holding over the same holding point. **Increase in Separation Prior to Transfer:** * Any requirement for an increase in separation prior to transfer must be documented and applied in accordance with MATS Part 2.

Question 36

What are the requirements for separation based on PSR and SSR information?

Answer 36

**Requirements for Separation Based on PSR and SSR Information:** **PSR Returns:** * Separation must be applied using PSR returns where PSR information is displayed. * Horizontal separation exists when the distance between the centers of the returns does not represent less than the prescribed minimum, provided that returns do not touch or overlap. **CAA Approval:** * When approved by the CAA, separation based on ATS surveillance-derived information may be applied between an aircraft taking off and a preceding departing aircraft or other aircraft in receipt of an ATS surveillance service. * There must be a reasonable assurance that the departing aircraft will be identified within one mile from the end of the runway and that the required separation will exist at that time.

Question 37

When can SSR alone be used to provide horizontal separation, and what are the limitations?

Answer 37

**Conditions for Using SSR Alone to Provide Horizontal Separation:** **Circumstances:** * In accordance with MATS Part 2. * To overcome temporary deficiencies within PSR cover (e.g., fading or clutter), where the SSR return of one aircraft may be used to provide separation from the PSR or SSR return of another aircraft, provided the PSR and SSR situation displays are correctly aligned. Note: "Unavailable for use due to maintenance" does not constitute a "temporary deficiency." * Immediately after PSR failure, for the minimum time necessary to establish procedural separation. Services normally provided using radar may be resumed when the PSR is serviceable. **Limitations:** * Pilots must be made aware of the limitations of the service. * SSR shall not be used to provide horizontal separation if a controller has any doubt about the accuracy of the position symbol due to equipment malfunction, reflections, or any other reason.