Air traffic services: definitions and general provisions
Learning objectives
- State the five objectives of air traffic services (ATS), its three services and the three parts of air traffic control (ATC), and identify the unit that provides each.
- Explain how airspace Classes A to G differ for IFR and VFR flights: who is separated, what service you get, and which radio, clearance and speed rules apply.
- Explain what an ATC clearance does and does not do, and state which clearances and instructions you must read back.
- Identify the four parts of a conditional clearance, in order, and the conditions for using one.
The idea
Think of air traffic services as a set of helpers, each with a different job. Some keep aircraft apart, some pass on useful information, and some call for rescue if something goes wrong. How much help you get depends on the letter of the airspace you are in. Once you know the letter, you know what to expect and what is expected of you. A clearance is permission based on known traffic, nothing more, and you repeat the important parts back so that mistakes are caught early.
What ATS is for
ATS has five objectives: prevent collisions between aircraft; prevent collisions between aircraft and obstructions on the manoeuvring area; expedite and maintain an orderly flow of traffic; give advice and information for safe and efficient flight; and notify and assist search and rescue. The same list appears in the ATS requirements for providers.
Three services deliver them. ATC service covers the first three objectives, flight information service (FIS) or air traffic advisory service covers the fourth, and alerting service covers the fifth.
ATC service has three parts.
- Area control looks after controlled flights, except the approach and aerodrome parts.
- Approach control looks after the arrival or departure parts of controlled flights.
- Aerodrome control looks after aerodrome traffic, except the approach part.
Only aerodrome control carries the second objective, obstructions on the manoeuvring area. That makes sense: the tower watches the runways and taxiways, while the area controller never sees them.
ATC, FIS and/or advisory service, and alerting service, mapped to the objectives as above.
Describe this figure
A box at the top lists the five objectives of air traffic services, (a) to (e). Below it, three bands show the three services. ATC service has area control by the area control centre (CONTROL), approach control by the approach control unit (APPROACH, ARRIVAL, DEPARTURE) and aerodrome control by the tower (TOWER, GROUND, DELIVERY); only the tower row carries objective (b). Flight information service, with advisory service, serves objective (d) through the flight information centre and the AFIS unit, both with suffix INFORMATION. Alerting service serves objective (e) and is given by the ATC units, the FIC and the AFIS unit. A note explains ARRIVAL, DEPARTURE, GROUND, DELIVERY and RADAR.
The figure is a family tree. At the top are the five objectives. Below them are the three services, with ATC branching into area, approach and aerodrome control. At the bottom are the units that deliver them and the call-sign suffix each one uses.
"Every ATS objective belongs to ATC." Wrong. ATC covers only the first three. Advice belongs to FIS or advisory service, and rescue notification to alerting service.
Terrain is not on the list. Preventing collision with terrain is not an objective of ATC, so you, as pilot-in-command, must make sure any clearance is safe with respect to terrain.
ATS units and their names
- An area control centre (ACC) gives ATC to controlled flights in the control areas under its jurisdiction.
- An approach control unit gives ATC to controlled flights arriving at or departing from one or more aerodromes.
- An aerodrome control tower gives ATC to aerodrome traffic.
- A flight information centre (FIC) gives FIS and alerting service.
- An AFIS unit gives aerodrome flight information service and alerting service at an AFIS aerodrome. It informs; it does not control.
The suffix on a call sign tells you what kind of service you are talking to.
| Suffix | Unit |
|---|---|
| CONTROL | Area control centre |
| APPROACH | Approach control |
| ARRIVAL / DEPARTURE | Approach radar, arrivals / departures |
| RADAR | Any ATC unit providing ATS surveillance services |
| TOWER | Aerodrome control |
| GROUND | Surface movement control |
| DELIVERY | Clearance delivery |
| INFORMATION | FIC or AFIS unit |
Because an FIC and an AFIS unit both use INFORMATION, neighbouring units must carry different names so they cannot be confused.
"INFORMATION on the call sign means a controller." Wrong. INFORMATION is an FIC or an AFIS unit. It gives information and alerting service, not control.
Designating ATS airspace
The State specifies the portions of airspace and the aerodromes where ATS is provided, in terms of the services given. Airspace is designated as flight information regions, control areas and control zones, or flight information zones. Airspace where ATC is given to IFR flights should be control areas or control zones.
The building blocks are these.
- A flight information region (FIR) is airspace in which FIS and alerting service are provided. It includes all airspace within its lateral limits, unless an upper flight information region limits it.
- A control area (CTA) is controlled airspace extending upwards from a specified limit above the earth.
- A control zone (CTR) is controlled airspace extending upwards from the surface to a specified upper limit.
- A flight information zone (FIZ) is airspace in which AFIS and alerting service for aerodrome traffic are provided.
Controlled airspace is the generic term for Classes A to E, so it covers control areas and airways as well as control zones.
A CTA must contain the flight paths of the IFR flights given ATC there. Its lower limit must be at least 200 m (700 ft) above ground or water, unless the competent authority prescribes otherwise. The lower limit may vary across the CTA, which is why control areas around busy aerodromes are stepped. Guidance says a CTA upper limit should coincide with a VFR cruising level, and so should a lower limit above 900 m (3 000 ft) MSL, chosen so that normal pressure changes cannot bring it below 200 m (700 ft) above ground or water.
A CTR starts at the surface. Its lateral limits must contain at least the parts of the IFR arrival and departure paths, for aerodromes used in IMC, that are not already inside a CTA. If a CTR lies within a CTA's lateral limits, it must reach from the surface up to at least the CTA's lower limit. As guidance, a CTR should extend at least 9.3 km (5 NM) from the aerodrome centre in the directions from which approaches are made. A CTR upper limit above 900 m (3 000 ft) MSL should likewise coincide with a VFR cruising level. Class E may not be used for control zones, so a CTR is Class A, B, C or D. ICAO makes the 200 m (700 ft) floor and the 9.3 km (5 NM) CTR extent Standards, without the EU's competent-authority exception for the floor.
All airspace above FL 195 is Class C.
Describe this figure
A side view, not to scale, shows one flight information region as a tall bracket on the left. Above FL 195 a band is labelled Class C, and below it the classes are chosen by the State. A control area has a flat top and a stepped lower limit, with its lowest base at least 700 ft above ground. Under the lowest step stands the control zone, Class A to D, from the surface, and it reaches at least 5 NM from the aerodrome centre toward the approaches. Class G lies under the outer steps, and a dashed flight information zone surrounds the AFIS aerodrome on the right. A diamond marks the limits that should coincide with a VFR cruising level.
The figure is a side-on slice, not to scale. A tall column marks the FIR. At the left, a control zone stands on the surface. Above and around it, a stepped control area has a high base far out and a lower base close in. Under the outer steps is Class G. At the right, a flight information zone surrounds an AFIS aerodrome. At the top, everything above FL 195 is Class C.
CTA lower limit at least 200 m (700 ft) above ground or water unless the competent authority prescribes otherwise. A CTR within a CTA reaches from the surface to at least the CTA's lower limit.
An aerodrome traffic zone (ATZ) protects aerodrome traffic. It is not an airspace class. EU law gives no ATZ dimensions: the State sets them, and they are published nationally.
"A control zone can be any class, including E." Wrong. Class E is not allowed for control zones.
The airspace classes
As you go from A to G, ATC does less and you do more.
| Class | Flights | Separation provided | Service | Speed limit | Radio capability | Continuous two-way voice | ATC clearance |
|---|---|---|---|---|---|---|---|
| Class A | IFR | From all flights | ATC | No limit | Required | Required | Required |
| VFR | VFR not permitted: Class A is IFR only | ||||||
| Class B | IFR | From all flights | ATC | No limit | Required | Required | Required |
| VFR | From all flights | ATC | No limit | Required | Required | Required | |
| Class C | IFR | From IFR and VFR | ATC | No limit | Required | Required | Required |
| VFR | From IFR; traffic information on other VFR | ATC | 250 kt IAS * | Required | Required | Required | |
| Class D | IFR | From IFR; traffic information on VFR | ATC | 250 kt IAS * | Required | Required | Required |
| VFR | None; traffic information on all other flights | ATC | 250 kt IAS * | Required | Required | Required | |
| Class E | IFR | From IFR | ATC; traffic information as far as practical | 250 kt IAS * | Required | Required | Required |
| VFR | None | Traffic information as far as practical (no ATC) | 250 kt IAS * | Not required † | Not required † | Not required | |
| Class F | IFR | From IFR as far as practical (advisory) | Air traffic advisory service; FIS on request | 250 kt IAS * | Required | Only if using the advisory service | None (no ATC) |
| VFR | None | FIS on request | 250 kt IAS * | Not required † | Not required † | None (no ATC) | |
| Class G | IFR | None | FIS on request | 250 kt IAS * | Required | Not required | None (no ATC) |
| VFR | None | FIS on request | 250 kt IAS * | Not required † | Not required † | None (no ATC) | |
| * Below 3 050 m (10 000 ft) AMSL. Where the transition altitude is below 3 050 m (10 000 ft), FL 100 is used instead. | |||||||
| † Except in a radio mandatory zone (RMZ): continuous listening watch and two-way communication as necessary. | |||||||
| ATC service is also given to all special VFR flights and to all aerodrome traffic at controlled aerodromes. | |||||||
Describe this figure
A table has one block per class, A to G, each with an IFR row and a VFR row. Class A is IFR only. In Classes A and B every flight is separated from all flights, gets ATC and has no speed limit, and needs radio capability, continuous two-way voice and a clearance. In Class C, IFR is separated from IFR and VFR, while VFR is separated from IFR only and is limited to 250 kt IAS below 10 000 ft. Classes D and E apply the 250 kt limit to everyone, and VFR in D is not separated from anyone. In Class E only IFR gets ATC, so VFR needs no radio or clearance, and Classes F and G give no ATC clearance at all.
The figure is a table with Classes A to G down the side, each split into an IFR row and a VFR row. The VFR rows are set in heavier type and carry a "VFR" label. The columns show separation, service, speed limit, radio, continuous two-way communication and clearance.
Work through it class by class.
- Class A: IFR only. All flights get ATC and are separated from each other. Continuous two-way voice communication and a clearance are required.
- Class B: IFR and VFR. All flights get ATC and are separated from each other. Voice communication and a clearance are required, with no 250 kt limit.
- Class C: IFR and VFR, all with ATC. IFR is separated from IFR and from VFR. VFR is separated from IFR only, and gets traffic information on other VFR plus avoidance advice on request. Voice communication and a clearance are required. A VFR clearance in C gives no separation from other VFR.
- Class D: IFR and VFR, all with ATC. IFR is separated from IFR only and gets traffic information about VFR. VFR is separated from nobody and gets traffic information on all other flights, with traffic avoidance advice on request. Voice communication and a clearance are required.
- Class E: IFR and VFR. Only IFR gets ATC and is separated from IFR. All flights get traffic information as far as practical. Voice communication and a clearance are required for IFR only.
- Class F: IFR and VFR. Participating IFR flights get air traffic advisory service, and all flights get FIS on request. No clearance.
- Class G: IFR and VFR. No separation, FIS on request, no clearance.
The radio rules in short.
- Capability and continuous two-way communication are both required for all flights in A to D, and for IFR in E.
- In F, IFR needs the capability, but continuous communication is mandatory only for flights using the advisory service.
- In G, IFR needs the capability only.
- VFR in E, F and G needs neither, except in a radio mandatory zone.
A clearance is required for all flights in A to D, for IFR only in E, and never in F and G.
The 250 kt limit is indicated airspeed (IAS) and applies below 3 050 m (10 000 ft) above mean sea level. It applies to VFR in Classes C to G and to IFR in Classes D to G, but not in A and B, nor to IFR in C. Where the transition altitude is below 10 000 ft, FL 100 is used instead. The reason is simple: flights that are not separated need time to see each other.
Class F is temporary
Class F is a temporary measure until another class can replace it. Guidance says its intended duration should not exceed 3 years. Air traffic advisory service is not ATC. It keeps IFR flights separated as far as practical, but the unit's picture of the traffic may be incomplete.
Where two classes meet
When two airspaces sit one above the other, a flight at the shared level follows the requirements, and gets the services, of the less restrictive class. Class B is less restrictive than A, C less than B, and so on.
Describe this figure
Two boxes are stacked. The upper one is Class D, labelled less restrictive. The lower one is Class C, labelled more restrictive. A dotted line marks the common level where they meet, and an aeroplane flies along it. A note says that on the common level the flight follows the rules of the less restrictive class, here Class D.
The figure shows two stacked blocks of airspace with a shared line between them. An aircraft symbol sits on the line, with an arrow pointing to the less restrictive block.
Radio and transponder zones
A radio mandatory zone (RMZ) is airspace where carrying and operating radio is mandatory. VFR flights in parts of Class E, F or G, and IFR flights in parts of Class F or G, designated as an RMZ must keep a continuous listening watch and establish two-way communication as necessary. An RMZ creates no clearance requirement. Before entering, you make an initial call with the station called, call sign, aircraft type, position, level and intentions.
A transponder mandatory zone (TMZ) is airspace where carrying and operating a pressure-altitude-reporting transponder is mandatory. You need Modes A and C, or Mode S.
RMZ: listening watch, two-way contact as necessary, initial call before entry. TMZ: Modes A and C, or Mode S.
Separation and responsibility
ATC clearances provide separation between all flights in A and B, between IFR flights in C, D and E, between IFR and VFR in C, and between IFR and special VFR. Special VFR flights are separated from each other unless the competent authority prescribes otherwise.
In Classes D and E there is one exception. When one pilot asks, the other pilot agrees and the competent authority has so prescribed, a flight may be cleared to maintain its own separation for a portion of a climb or descent below 3 050 m (10 000 ft), by day in VMC. While you are cleared to do so, ATC gives you no separation and you must keep clear of others.
A controlled flight is under the control of only one ATC unit at a time, and control passes to the next unit only with its consent.
The EU rule is the rule in force. ICAO says each State chooses its classes, while the EU adds that everything above FL 195 is Class C. The ICAO read-back list is shorter than the EU list, so learn the EU list.
ATC clearances
A clearance is authorisation for an aircraft to proceed under conditions set by an ATC unit. Clearances are issued solely to expedite and separate traffic, based on known traffic conditions that affect safety. They must be issued early enough to reach the aircraft in time to comply.
A clearance authorises the aircraft to proceed only as far as known air traffic is concerned. It never authorises breaking any regulation and never relieves the pilot-in-command of responsibility for a possible violation.
"If ATC cleared it, it is safe from terrain and legal." Wrong. Terrain is not an ATC objective, a clearance never authorises breaking a rule, and the pilot-in-command stays responsible.
You must obtain a clearance before operating a controlled flight, or a portion of one, and you request it by submitting a flight plan to an ATC unit. If a clearance is not satisfactory, tell the ATC unit, which will issue an amended clearance if practicable. When ATC cannot grant a requested change, it says "UNABLE" and, when circumstances warrant, offers an alternative. At a controlled aerodrome you may not taxi on the manoeuvring area without clearance from the tower.
A clearance states the aircraft identification, the clearance limit, the route, the levels, and other necessary instructions such as approach manoeuvres, communications or the expiry time.
Read-back
Read-back is how the system catches errors. The flight crew must read back the safety-related parts of voice clearances and instructions. Always read back these.
- ATC route clearances.
- Clearances and instructions to enter, land on, take off from, hold short of, cross, taxi on or backtrack on any runway.
- The runway in use, altimeter settings, SSR codes, newly assigned communication channels, and level, heading and speed instructions.
- Transition levels, whether given by the controller or in an ATIS broadcast.
Describe this figure
Four cards are stacked, each with an icon and a READ BACK tag. Card one, with a route icon, is ATC route clearances. Card two, with a runway icon, covers clearances and instructions to enter, land on, take off from, hold short of, cross, taxi on or backtrack on any runway. Card three, with a dial icon, lists the runway in use, altimeter settings, SSR codes, new communication channels, level instructions, and heading and speed instructions. Card four, with a level-line icon, is transition levels, from the controller or an ATIS broadcast. A dashed band at the bottom says that everything else, including conditional clearances and taxi instructions, is read back or acknowledged so that it shows the message is understood and will be complied with.
The figure is a checklist with four groups: routes, runway clearances, the numbers, and the transition level. A band below says that every other clearance or instruction is read back or acknowledged.
Everything else, including conditional clearances and taxi instructions, must be read back or acknowledged in a way that clearly shows it is understood and will be complied with. The controller must listen to the read-back and immediately correct any discrepancy.
Read back the safety-related parts of voice clearances and instructions, including the items above. Other clearances and instructions are read back or acknowledged so it is clear they are understood and will be complied with.
Say the whole phrase back rather than a bare "roger", and ask again if you did not understand. This content is educational and does not replace ATO instruction or the aircraft's POH/AFM. Read-back as radio technique is on the communications pages.
Conditional clearances
A conditional clearance lets you go after something else has moved, as in "behind landing aircraft" or "after departing aircraft". It may not be used for movements affecting an active runway unless both the controller and the pilot can see the aircraft or vehicles concerned. The aircraft or vehicle causing the condition must be the first to pass in front of the other aircraft. It is always given in this order: call sign, condition, clearance, then a brief repeat of the condition. Guidance material says you need to identify the aircraft or vehicle that causes the condition before acting.
Describe this figure
Four numbered bars show the parts of a conditional clearance in the order they are spoken: the call sign CS-ABC, the condition behind the landing Cessna, the clearance line up and wait, and a brief repeat of the condition. Below, a plan view shows a runway with a landing Cessna and a faded copy of it further along. CS-ABC waits on a taxiway at the holding position. An arrow shows that the Cessna passes in front first, and only then does CS-ABC move. Notes say that on an active runway the controller and the pilot must both see the Cessna, and that the pilot identifies it before acting.
The figure uses an original example: "CS-ABC, behind the landing Cessna, line up and wait, behind the landing Cessna." It labels the four parts in order. Beside it, a small picture shows the landing aircraft passing in front of CS-ABC before CS-ABC moves.
Conditional clearances may not be used for movements affecting an active runway unless the controller and pilot both see the aircraft or vehicle concerned. The conditioning traffic passes first. Order: call sign, condition, clearance, brief repeat of the condition.
Your duties as a controlled flight
Once you have a clearance, you have duties too.
- Keep to the current flight plan, which is the filed plan plus changes from later clearances. You may leave it only after asking for and getting a clearance, or when an emergency needs immediate action. After an emergency action, tell the ATS unit as soon as possible what you did and that you acted under emergency authority.
- Fly the route. As far as practicable, fly the centre line of an established ATS route, or directly between the points that define any other route, and notify deviations.
- Report inadvertent deviations. If you drift off track, adjust heading at once to regain it. Tell ATS immediately if you deviate from an ATC-assigned IAS. Tell ATS if your sustained cruising TAS differs from the flight plan by 19 km/h (10 kt) or more. Tell ATS if your estimate for the next reporting point, FIR boundary or destination changes by more than 2 minutes.
- Make position reports. Unless exempted, report the time and level of passing each compulsory reporting point. A report contains identification, position, time, speed if assigned by ATC, and anything else ATC asks for. Where there are no designated points, guidance says to report soon after the first half hour and then every hour.
- Tell ATC when control ends. Do so as soon as you stop being subject to ATC service, except when landing at a controlled aerodrome.
- Keep listening. Keep a continuous voice watch on the ATC unit's channel and establish two-way communication as necessary.
The separation methods behind all this are simple. Vertical separation uses different levels, nominally 300 m (1 000 ft) up to and including FL 410 and 600 m (2 000 ft) above, and geometric height from GPS or a radio altimeter may not be used for it. Horizontal separation is either longitudinal, an interval in time or distance, or lateral, different routes or areas. Minima are chosen by the air navigation service provider and approved by the competent authority.
When you leave one unit's airspace, control passes at the transfer of control point, and only with the accepting unit's consent. A downstream clearance, obtained from the next unit before the transfer point, must be clearly identifiable as such.
A controlled flight keeps to its current flight plan unless it has obtained a clearance for a change, or an emergency needs immediate action.
In the real world
At Zurich on 18 June 2010, in Class D airspace, the crew of an ATR 42 read back a take-off clearance that was meant for an A340 on a crossing runway. The two read-backs overlapped, and the controller never heard the wrong one. A crew waiting at a holding point warned the tower, and the ATR was stopped. Read-back works only if the controller listens to it, and a clearance belongs only to the call sign it is addressed to.
Report: Swiss Transportation Safety Investigation Board, Final Report No. 2113, 8 September 2011. Link: https://www.sust.admin.ch/inhalte/AV-berichte/2113_e.pdf
In April 2018 EASA and national authorities launched an EU-wide campaign for general aviation pilots because airspace infringements had risen steadily over the previous decade. It comes back to this page: know which class you are in, know where a clearance is required, and know what an RMZ and a TMZ demand.
Source: EASA news, "Avoiding airspace infringement - launch of EU-wide campaign for General Aviation pilots", April 2018. Link: https://www.easa.europa.eu/en/node/46245
Exam traps
Class D versus Class C. In C, VFR is separated from IFR. In D, VFR is separated from nobody. Both need a clearance and radio contact.
Class E for VFR. No clearance and no radio, unless an RMZ applies.
The 250 kt limit. It is IAS, not TAS, and applies below 10 000 ft (FL 100 where the transition altitude is lower). It does not apply in Classes A and B, nor to IFR in Class C.
Boundary level. At the shared level between two classes, the less restrictive class applies, not the stricter one.
Explain it back
The controller says: "CS-ABC, after the departing Piper, cross runway two seven, after the departing Piper." Explain in your own words what you must do before you move, what the four parts are, and what the clearance still does not protect you from.
Self-check
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Which of the following is the only part of air traffic control that carries the objective of preventing collisions between aircraft and obstructions on the manoeuvring area?mcq · easy
Show answer
Aerodrome control covers aerodrome traffic, including the manoeuvring area, and is the only part tied to the obstruction objective. Area and approach control serve the collision and orderly-flow objectives only. Air traffic advisory service is not ATC at all; it serves the advice-and-information objective.
Reference: ATS.TR.105(a)
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You fly VFR in Class D airspace with a clearance. Which statement is correct?mcq · medium
Show answer
In Class D, VFR is separated from no one and receives traffic information on all other flights, with avoidance advice on request. The first option describes Class C. The third describes Classes A and B. The fourth is wrong because continuous two-way communication and a clearance are required in Class D.
Reference: SERA.6001(a)(4); SERA Appendix 4
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Class C airspace lies directly under Class A airspace and they share a boundary level. You fly exactly at that level. Which rules apply?mcq · medium
Show answer
At a common level between vertically adjoining airspaces, the flight follows the requirements and gets the services of the less restrictive class. Class C is less restrictive than Class A. The other options have no basis in the rule.
Reference: AMC1 SERA.6001; GM1 SERA.6001(a)
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Scenario: You hold short of the runway in CS-ABC. The tower says: 'CS-ABC, QNH 1018, taxi to holding point, report ready.' Which items must you read back?mcq · medium
Show answer
Altimeter settings are always read back. Taxi instructions are in the second group and must be read back or acknowledged in a way that shows they are understood and will be complied with. A bare 'roger' does not show that, and neither of the single-item answers covers both.
Reference: SERA.8015(e)(1); SERA.8015(e)(2)
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Scenario: The tower says: 'CS-ABC, behind the landing Cessna, line up and wait, behind the landing Cessna.' You see two aircraft on final and are not sure which is the Cessna. What should you do?mcq · hard
Show answer
A conditional clearance on an active runway may only be used when both controller and pilot can see the aircraft concerned, and you must identify the conditioning aircraft before acting. The conditioning aircraft must pass first, so lining up behind a different aircraft or before the Cessna is unsafe.
Reference: SERA.8015(ec); GM1 SERA.8015(ec)
Key concepts
Written with ASD-STE100 writing principles: short sentences, one topic per sentence, active voice, one word for one meaning.
Class E airspace
Class E gives an air traffic control (ATC) service only to IFR flights. ATC separates each IFR flight from other IFR flights. VFR flights need no ATC clearance and no radio, unless a radio mandatory zone (RMZ) applies. All flights get traffic information as far as practical.
Rule: SERA.6001(a)(5)
Class C and D separation
In Class C, ATC separates IFR flights from all other flights. VFR flights get separation from IFR flights only, and they get traffic information on other VFR flights. In Class D, ATC separates IFR flights from other IFR flights only. A VFR flight in Class D gets traffic information, but no separation from any aircraft.
Rule: SERA.6001(a)(3)–(4)
Read-back of clearances
The flight crew must read back the safety-related parts of voice clearances and instructions. Always read back route clearances, runway clearances and instructions, and the runway in use. Also read back altimeter settings, SSR codes, new frequencies, transition levels, and level, heading and speed instructions. Other clearances, such as conditional clearances and taxi instructions, need a read-back or a clear acknowledgement.
Rule: SERA.8015(e)(1)–(2)
Clearance and known traffic
An ATC clearance covers only known air traffic. It never allows a pilot to break a regulation. The pilot in command (PIC) stays responsible for any possible violation. The pilot is responsible for the terrain safety of any clearance, because terrain protection is not an objective of ATC service.
Rule: GM1 ATS.TR.235; GM3 SERA.8005(b)(c)
ATS objectives and services
Air traffic services (ATS) have five objectives. The ATC service meets the first three: collision prevention, obstruction avoidance on the manoeuvring area, and orderly traffic flow. The ATC service has three parts: area control, approach control and aerodrome control. The air traffic advisory service or flight information service meets objective d, which gives advice and information. The alerting service meets objective e, which notifies search and rescue.
Rule: ATS.TR.100; ATS.TR.105(a)–(c)
Radio mandatory zone (RMZ)
A radio mandatory zone (RMZ) requires VFR flights in parts of Class E, F or G to keep a continuous air-ground radio watch. They must also establish two-way communication as necessary. IFR flights in parts of Class F or G must keep the same radio watch. An RMZ does not create a clearance requirement. A transponder mandatory zone (TMZ) requires every flight to carry and operate an SSR transponder. The transponder must work in Mode A and C, or in Mode S.
Rule: SERA.6005(a)(1); SERA.6005(b)
Conditional clearance
Always give four elements in this order: call sign, condition, clearance, and a brief repeat of the condition. Do not use a conditional clearance for active runway movements unless the controller and pilot can both see the traffic. The aircraft or vehicle that causes the condition must be the first to pass in front of the other aircraft.
Rule: SERA.8015(ec)
Control area and control zone
A control area (CTA) has a lower limit of at least 200 m (700 ft) above ground or water, unless the competent authority prescribes otherwise. A control zone (CTR) extends from the surface and cannot be Class E. The AMC describes a CTR that reaches at least 9.3 km (5 NM) from the aerodrome centre, in the directions of the approaches.
Rule: Part-FPD Appendix 1 Section I(b)(1)–(3); Part-FPD Appendix 1 Section I(c)(1)–(2)
Flashcards
Print them: A6 landscape cards (PDF, front and back) · 4 cards per A4 landscape sheet (PDF, cut lines) · Key figures deck (PDF, 22 figures)
Print double-sided, flip on the short edge.
010-07-01-01How many ATS airspace classes are there, and which letters name them?
Seven classes, lettered A to G.
010-07-01-02Which class must all airspace above FL 195 be?
Class C. This is an EU rule; ICAO lets a State choose its own classes.
010-07-01-03In Class A, which flights get ATC and need a clearance?
Only IFR flights are allowed. All of them get ATC, separation and an ATC clearance.
010-07-01-04In Class E, which flights get an ATC clearance?
IFR flights only. VFR flights need no clearance and no radio, unless an RMZ applies.
010-07-01-05In Class C, which flights does ATC separate from each IFR flight?
All other flights. IFR flights are separated from both IFR and VFR flights.
010-07-01-06In Class C, does ATC separate two VFR flights?
No. VFR flights get traffic information on other VFR flights, not separation.
010-07-01-07In Class D, which flights does ATC separate?
IFR flights from other IFR flights only. VFR flights get traffic information instead.
010-07-01-08Does a VFR clearance in Class D give separation from IFR flights?
No. A VFR clearance in Class D gives no separation at all, from IFR or VFR flights.
010-07-01-09What is the speed limit below 3 050 m (10 000 ft) altitude?
250 kt IAS. It applies to VFR flights in Classes C to G and to IFR flights in Classes D to G.
010-07-01-10Does the 250 kt speed limit apply in Class B?
No. The limit does not apply in Classes A or B, or to IFR flights in Class C.
010-07-01-11Where the transition altitude is below 3 050 m (10 000 ft), which level replaces 10 000 ft?
FL 100.
010-07-01-12What is the minimum lower limit of a control area (CTA)?
200 m (700 ft) above ground or water, unless the competent authority prescribes otherwise.
010-07-01-13Above which level does AMC link a CTA lower limit to a VFR cruising level?
900 m (3 000 ft) MSL. This is GM guidance, not a rule.
010-07-01-14Above which level does GM link a CTR upper limit to a VFR cruising level?
900 m (3 000 ft) MSL.
010-07-01-15Under GM guidance, below which height should pressure changes not lower a CTA lower limit or CTR upper limit?
200 m (700 ft) above ground or water.
010-07-01-16What is the minimum lateral extent of a CTR from the aerodrome centre?
9.3 km (5 NM), in the directions from which approaches are made. This is AMC guidance.
010-07-01-17Can a control zone (CTR) be Class E?
No. A CTR is Class A, B, C or D.
010-07-01-18Where a CTR lies within a CTA's lateral limits, how far down must it extend?
From the surface up to at least the CTA lower limit.
010-07-01-19What is the maximum intended duration of Class F airspace?
3 years. The AIP states the intended duration. This is GM guidance.
010-07-01-20What is the nominal vertical separation up to and including FL 410?
300 m (1 000 ft).
010-07-01-21What is the nominal vertical separation above FL 410?
600 m (2 000 ft).
010-07-01-22Can geometric height from GPS or a radio altimeter be used for vertical separation?
No. Do not use geometric height from GPS or a radio altimeter for vertical separation.
010-07-01-23What is the upper limit for an own-separation portion in Classes D and E?
3 050 m (10 000 ft) altitude, in climb or descent, by day in VMC. It needs a pilot request, the other pilot's agreement and a competent authority prescription.
010-07-01-24What sustained TAS difference from the flight plan must be reported at cruising level?
19 km/h (10 kt) TAS or more.
010-07-01-25Which deviation from an ATC-assigned speed must be reported to ATS immediately?
A deviation from an ATC-assigned indicated airspeed (IAS).
010-07-01-26What change in time estimate must be notified to ATS?
More than 2 minutes, for the next reporting point, FIR boundary or destination. The competent authority can set another period. Not required where ADS-C is active.
010-07-01-27Without designated reporting points, when is the first position report after departure?
As soon as possible after the first half hour of flight.
010-07-01-28Without designated reporting points, how often are later position reports made?
Every hour.
010-07-01-29Which clearances and instructions must always be read back?
Route clearances; runway entry, landing, take-off, hold-short, crossing and taxi clearances; runway in use; altimeter settings; SSR codes; new frequencies; level, heading and speed instructions; transition levels.
010-07-01-30How must a pilot answer other clearances, such as conditional clearances?
Read back, or acknowledge in a way that clearly shows the clearance is understood and will be complied with.
010-07-01-31What does an ATC clearance cover?
Only known air traffic. It never allows a rule to be broken, and the PIC stays responsible.
010-07-01-32Who is responsible for checking that a clearance is safe with respect to terrain?
The pilot. Terrain protection is not an objective of ATC service.
010-07-01-33How many air traffic services (ATS) objectives are there?
Five. They cover collisions, orderly flow, advice and search and rescue.
010-07-01-34How many ATS services are there?
Three: the ATC service; the flight information service or air traffic advisory service; and the alerting service.
010-07-01-35How many parts does the ATC service have, and what are they?
Three: area control, approach control and aerodrome control.
010-07-01-36Which ATC part is the only one that covers obstructions on the manoeuvring area?
Aerodrome control. Area and approach control do not carry that objective.
010-07-01-37In a radio mandatory zone (RMZ), what must VFR flights keep?
A continuous air-ground listening watch, and two-way communication as necessary.
010-07-01-38What must every flight carry and operate in a transponder mandatory zone (TMZ)?
An SSR transponder able to work in Mode A and C, or in Mode S.
010-07-01-39What is the fixed order of a conditional clearance?
Call sign, condition, clearance, then a brief repeat of the condition.
010-07-01-40Can a conditional clearance control movements on an active runway?
Only if the controller and the pilot can both see the aircraft or vehicles concerned.
Sources
- Commission Implementing Regulation (EU) No 923/2012 (SERA) — via EASA Easy Access Rules for Standardised European Rules of the Air (SERA), August 2025, with the related AMC/GM.
- Commission Implementing Regulation (EU) 2017/373 (ATM/ANS), Annex I definitions and Annex IV (Part-ATS) — via EASA Easy Access Rules for ATM/ANS – Provision of Services, March 2025, with the related AMC/GM.
- ICAO Annex 11, Air Traffic Services, 15th edition (2018), and ICAO Doc 4444, PANS-ATM, 16th edition (2016): used for ICAO comparisons only.
- Swiss Transportation Safety Investigation Board, Final Report No. 2113 (Zurich, 18 June 2010), 8 September 2011: sust.admin.ch.
- EASA, 'Avoiding airspace infringement – launch of EU-wide campaign for General Aviation pilots', 12 April 2018: easa.europa.eu.
This page is educational. It does not replace instruction at your ATO or your aircraft's POH/AFM. Rules change: check the regulation in force.