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Accepting unit. Air traffic control unit next to take control of an aircraft.
Accident. An occurrence associated with the operation of an aircraft which, in the case of a manned aircraft, takes place between the time any person boards the aircraft with the intention of flight until such time as all such persons have disembarked, or in the case of an unmanned aircraft, takes place between the time the aircraft is ready to move with the purpose of flight until such time it comes to rest at the end of the flight and the primary propulsion system is shut down, in which:
- a) a person is fatally or seriously injured as a result of:
- — being in the aircraft, or
- — direct contact with any part of the aircraft, including parts which have become detached from the aircraft, or
- — direct exposure to jet blast,except when the injuries are from natural causes, self-inflicted or inflicted by other persons, or when the injuries are to stowaways hiding outside the areas normally available to the passengers and crew; or
- b) the aircraft sustains damage or structural failure which:
- — adversely affects the structural strength, performance or flight characteristics of the aircraft, and
- — would normally require major repair or replacement of the affected component,except for engine failure or damage, when the damage is limited to a single engine, (including its cowlings or accessories), to propellers, wing tips, antennas, probes, vanes, tires, brakes, wheels, fairings, panels, landing gear doors, windscreens, the aircraft skin (such as small dents or puncture holes), or for minor damages to main rotor blades, tail rotor blades, landing gear, and those resulting from hail or bird strike (including holes in the radome); or
- c) the aircraft is missing or is completely inaccessible.
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Annex 11 — Air Traffic Services Chapter 1
Note 1.— For statistical uniformity only, an injury resulting in death within thirty days of the date of the accident is classified, by ICAO, as a fatal injury.
Note 2.— An aircraft is considered to be missing when the official search has been terminated and the wreckage has not been located.
Note 3.— The type of unmanned aircraft system to be investigated is addressed in Annex 13, 5.1.
Note 4.— Guidance for the determination of aircraft damage can be found in Annex 13, Attachment E.
ADS-C agreement. A reporting plan which establishes the conditions of ADS-C data reporting (i.e. data required by the air traffic services unit and frequency of ADS-C reports which have to be agreed to prior to using ADS-C in the provision of air traffic services).
Note.— The terms of the agreement will be exchanged between the ground system and the aircraft by means of a contract, or a series of contracts.
Advisory airspace. An airspace of defined dimensions, or designated route, within which air traffic advisory service is available.
Advisory route. A designated route along which air traffic advisory service is available.
Aerodrome. A defined area on land or water (including any buildings, installations and equipment) intended to be used either
wholly or in part for the arrival, departure and surface movement of aircraft.
Aerodrome control service. Air traffic control service for aerodrome traffic.
Aerodrome control tower. A unit established to provide air traffic control service to aerodrome traffic.
Aerodrome traffic. All traffic on the manoeuvring area of an aerodrome and all aircraft flying in the vicinity of an aerodrome.
Note.— An aircraft is in the vicinity of an aerodrome when it is in, entering or leaving an aerodrome traffic circuit.
Aeronautical fixed service (AFS). A telecommunication service between specified fixed points provided primarily for the safety of air navigation and for the regular, efficient and economical operation of air services.
Aeronautical Information Publication (AIP). A publication issued by or with the authority of a State and containing aeronautical information of a lasting character essential to air navigation.
Aeronautical mobile service (RR S1.32). A mobile service between aeronautical stations and aircraft stations, or between aircraft stations, in which survival craft stations may participate; emergency position-indicating radio beacon stations may also participate in this service on designated distress and emergency frequencies.
Aeronautical telecommunication station. A station in the aeronautical telecommunication service.
Airborne collision avoidance system (ACAS). An aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft that are equipped with SSR transponders.
Aircraft. Any machine that can derive support in the atmosphere from the reactions of the air other than the reactions of the air against the earth’s surface.
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Chapter 1 Annex 11 — Air Traffic Services Air-ground communication. Two-way communication between aircraft and stations or locations on the surface of the earth.
AIRMET information. Information issued by a meteorological watch office concerning the occurrence or expected occurrence of specified en-route weather phenomena which may affect the safety of low-level aircraft operations and which was not already included in the forecast issued for low-level flights in the flight information region concerned or sub-area thereof.
Air-taxiing. Movement of a helicopter/VTOL above the surface of an aerodrome, normally in ground effect and at a ground speed normally less than 37 km/h (20 kt).
Note.— The actual height may vary, and some helicopters may require air-taxiing above 8 m (25 ft) AGL to reduce ground effect turbulence or provide clearance for cargo slingloads.
Air traffic. All aircraft in flight or operating on the manoeuvring area of an aerodrome.
Air traffic advisory service. A service provided within advisory airspace to ensure separation, in so far as practical, between
aircraft which are operating on IFR flight plans.
Air traffic control clearance. Authorization for an aircraft to proceed under conditions specified by an air traffic control unit.
Note 1.— For convenience, the term “air traffic control clearance” is frequently abbreviated to “clearance” when used in appropriate contexts.
Note 2.— The abbreviated term “clearance” may be prefixed by the words “taxi,” “take-off,” “departure,” “en route,” “approach” or “landing” to indicate the particular portion of flight to which the air traffic control clearance relates.
Air traffic control service. A service provided for the purpose of:
- a) preventing collisions:
- 1) between aircraft, and
- 2) on the manoeuvring area between aircraft and obstructions; and
- b) expediting and maintaining an orderly flow of air traffic.
Air traffic control unit. A generic term meaning variously, area control centre, approach control unit or aerodrome control tower.
Air traffic controller schedule.† A plan for allocating air traffic controller duty periods and non-duty periods over a period of time, otherwise referred to as a roster.
Air traffic flow management (ATFM). A service established with the objective of contributing to a safe, orderly and expeditious flow of air traffic by ensuring that ATC capacity is utilized to the maximum extent possible and that the traffic volume is compatible with the capacities declared by the appropriate ATS authority.
Air traffic service. A generic term meaning variously, flight information service, alerting service, air traffic advisory service, air traffic control service (area control service, approach control service or aerodrome control service).
† Applicable 5 November 2020.
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Annex 11 — Air Traffic Services Chapter 1 Air traffic services airspaces. Airspaces of defined dimensions, alphabetically designated, within which specific types of
flights may operate and for which air traffic services and rules of operation are specified.
Note.— ATS airspaces are classified as Class A to G as described in 2.6.
Air traffic services reporting office. A unit established for the purpose of receiving reports concerning air traffic services and flight plans submitted before departure.
Note.— An air traffic services reporting office may be established as a separate unit or combined with an existing unit, such as another air traffic services unit, or a unit of the aeronautical information service.
Air traffic services unit. A generic term meaning variously, air traffic control unit, flight information centre or air traffic services reporting office.
Airway. A control area or portion thereof established in the form of a corridor.
ALERFA. The code word used to designate an alert phase.
Alerting service. A service provided to notify appropriate organizations regarding aircraft in need of search and rescue aid, and assist such organizations as required.
Alert phase. A situation wherein apprehension exists as to the safety of an aircraft and its occupants.
Alternate aerodrome. An aerodrome to which an aircraft may proceed when it becomes either impossible or inadvisable to proceed to or to land at the aerodrome of intended landing where the necessary services and facilities are available, where aircraft performance requirements can be met and which is operational at the expected time of use. Alternate aerodromes include the following:
Take-off alternate. An alternate aerodrome at which an aircraft would be able to land should this become necessary shortly after take-off and it is not possible to use the aerodrome of departure.
En-route alternate. An alternate aerodrome at which an aircraft would be able to land in the event that a diversion becomes necessary while en route.
Destination alternate. An alternate aerodrome at which an aircraft would be able to land should it become either impossible or inadvisable to land at the aerodrome of intended landing.
Note.— The aerodrome from which a flight departs may also be an en-route or a destination alternate aerodrome for that flight.
Altitude. The vertical distance of a level, a point or an object considered as a point, measured from mean sea level.
Approach control service. Air traffic control service for arriving or departing controlled flights.
Approach control unit. A unit established to provide air traffic control service to controlled flights arriving at, or departing from, one or more aerodromes.
Appropriate ATS authority. The relevant authority designated by the State responsible for providing air traffic services in the airspace concerned.
Apron. A defined area, on a land aerodrome, intended to accommodate aircraft for purposes of loading or unloading passengers, mail or cargo, fuelling, parking or maintenance.
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Chapter 1 Annex 11 — Air Traffic Services Apron management service. A service provided to regulate the activities and the movement of aircraft and vehicles on an
apron.
Area control centre. A unit established to provide air traffic control service to controlled flights in control areas under its jurisdiction.
Area control service. Air traffic control service for controlled flights in control areas.
Area navigation (RNAV). A method of navigation which permits aircraft operation on any desired flight path within the coverage of ground- or space-based navigation aids or within the limits of the capability of self-contained aids, or a combination of these.
Note.— Area navigation includes performance-based navigation as well as other operations that do not meet the definition of performance-based navigation.
Area navigation route. An ATS route established for the use of aircraft capable of employing area navigation.
ATS route. A specified route designed for channelling the flow of traffic as necessary for the provision of air traffic services.
Note 1.— The term “ATS route” is used to mean variously, airway, advisory route, controlled or uncontrolled route, arrival or departure route, etc.
Note 2.— An ATS route is defined by route specifications which include an ATS route designator, the track to or from significant points (waypoints), distance between significant points, reporting requirements and, as determined by the appropriate ATS authority, the lowest safe altitude.
Automatic dependent surveillance — broadcast (ADS-B). A means by which aircraft, aerodrome vehicles and other objects can automatically transmit and/or receive data such as identification, position and additional data, as appropriate, in a broadcast mode via a data link.
Automatic dependent surveillance — contract (ADS-C). A means by which the terms of an ADS-C agreement will be exchanged between the ground system and the aircraft, via a data link, specifying under what conditions ADS-C reports would be initiated, and what data would be contained in the reports.
Note.— The abbreviated term “ADS contract” is commonly used to refer to ADS event contract, ADS demand contract, ADS periodic contract or an emergency mode.
Automatic terminal information service (ATIS). The automatic provision of current, routine information to arriving and departing aircraft throughout 24 hours or a specified portion thereof:
Data link-automatic terminal information service (D-ATIS). The provision of ATIS via data link.
Voice-automatic terminal information service (Voice-ATIS). The provision of ATIS by means of continuous and
repetitive voice broadcasts.
Base turn. A turn executed by the aircraft during the initial approach between the end of the outbound track and the beginning of the intermediate or final approach track. The tracks are not reciprocal.
Note.— Base turns may be designated as being made either in level flight or while descending, according to the circumstances of each individual procedure.
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Annex 11 — Air Traffic Services Chapter 1 Calendar. Discrete temporal reference system that provides the basis for defining temporal position to a resolution of one day
(ISO 19108*).
Change-over point. The point at which an aircraft navigating on an ATS route segment defined by reference to very high frequency omnidirectional radio ranges is expected to transfer its primary navigational reference from the facility behind the aircraft to the next facility ahead of the aircraft.
Note.— Change-over points are established to provide the optimum balance in respect of signal strength and quality between facilities at all levels to be used and to ensure a common source of azimuth guidance for all aircraft operating along the same portion of a route segment.
Clearance limit. The point to which an aircraft is granted an air traffic control clearance.
Conference communications. Communication facilities whereby direct speech conversation may be conducted between
three or more locations simultaneously.
Control area. A controlled airspace extending upwards from a specified limit above the earth.
Controlled aerodrome. An aerodrome at which air traffic control service is provided to aerodrome traffic.
Note.— The term “controlled aerodrome” indicates that air traffic control service is provided to aerodrome traffic but does not necessarily imply that a control zone exists.
Controlled airspace. An airspace of defined dimensions within which air traffic control service is provided in accordance with the airspace classification.
Note.— Controlled airspace is a generic term which covers ATS airspace Classes A, B, C, D and E as described in 2.6.
Controlled flight. Any flight which is subject to an air traffic control clearance.
Controller-pilot data link communications (CPDLC). A means of communication between controller and pilot, using data
link for ATC communications.
Control zone. A controlled airspace extending upwards from the surface of the earth to a specified upper limit.
Cruising level. A level maintained during a significant portion of a flight.
Cyclic redundancy check (CRC). A mathematical algorithm applied to the digital expression of data that provides a level of assurance against loss or alteration of data.
Danger area. An airspace of defined dimensions within which activities dangerous to the flight of aircraft may exist at specified times.
Data accuracy. A degree of conformance between the estimated or measured value and the true value.
Data integrity (assurance level). A degree of assurance that an aeronautical data and its value has not been lost or altered
since the origination or authorized amendment.
Data link communications. A form of communication intended for the exchange of messages via a data link.
*
All ISO Standards are listed at the end of this chapter.
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Chapter 1 Annex 11 — Air Traffic Services Data quality. A degree or level of confidence that the data provided meets the requirements of the data user in terms of
accuracy, resolution and integrity (or equivalent assurance level), traceability, timeliness, completeness and format.
Datum. Any quantity or set of quantities that may serve as a reference or basis for the calculation of other quantities (ISO 19104*).
Declared capacity. A measure of the ability of the ATC system or any of its subsystems or operating positions to provide service to aircraft during normal activities. It is expressed as the number of aircraft entering a specified portion of airspace in a given period of time, taking due account of weather, ATC unit configuration, staff and equipment available, and any other factors that may affect the workload of the controller responsible for the airspace.
DETRESFA. The code word used to designate a distress phase.
Distress phase. A situation wherein there is reasonable certainty that an aircraft and its occupants are threatened by grave and
imminent danger or require immediate assistance.
Downstream clearance. A clearance issued to an aircraft by an air traffic control unit that is not the current controlling authority of that aircraft.
Duty. † Any task that an air traffic controller is required by an air traffic services provider to perform. These tasks include those performed during time-in-position, administrative work and training.
Duty period. † A period which starts when an air traffic controller is required by an air traffic services provider to report for or to commence a duty and ends when that person is free from all duties.
Emergency phase. A generic term meaning, as the case may be, uncertainty phase, alert phase or distress phase.
Fatigue. † A physiological state of reduced mental or physical performance capability resulting from sleep loss, extended wakefulness, circadian phase, and/or workload (mental and/or physical activity) that can impair a person’s alertness and ability to perform safety-related operational duties.
Fatigue risk management system (FRMS). † A data-driven means of continuously monitoring and managing fatigue-related safety risks, based upon scientific principles, knowledge and operational experience that aims to ensure relevant personnel are performing at adequate levels of alertness.
Final approach. That part of an instrument approach procedure which commences at the specified final approach fix or point, or where such a fix or point is not specified,
- a) at the end of the last procedure turn, base turn or inbound turn of a racetrack procedure, if specified; or
- b) at the point of interception of the last track specified in the approach procedure; and
ends at a point in the vicinity of an aerodrome from which:
- 1) a landing can be made; or
- 2) a missed approach procedure is initiated.
Flight crew member. A licensed crew member charged with duties essential to the operation of an aircraft during a flight duty period.
† Applicable 5 November 2020.
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Annex 11 — Air Traffic Services Chapter 1 Flight information centre. A unit established to provide flight information service and alerting service.
Flight information region. An airspace of defined dimensions within which flight information service and alerting service are provided.
Flight information service. A service provided for the purpose of giving advice and information useful for the safe and efficient conduct of flights.
Flight level. A surface of constant atmospheric pressure which is related to a specific pressure datum, 1 013.2 hectopascals (hPa), and is separated from other such surfaces by specific pressure intervals.
Note 1.— A pressure type altimeter calibrated in accordance with the Standard Atmosphere:
- a) when set to a QNH altimeter setting, will indicate altitude;
- b) when set to a QFE altimeter setting, will indicate height above the QFE reference datum;
- c) when set to a pressure of 1 013.2 hPa, may be used to indicate flight levels.
Note 2.— The terms “height” and “altitude”, used in Note 1 above, indicate altimetric rather than geometric heights and altitudes.
Flight plan. Specified information provided to air traffic services units, relative to an intended flight or portion of a flight of an aircraft.
Note.— Specifications for flight plans are contained in Annex 2. When the expression “flight plan form” is used it denotes the model flight plan form at Appendix 2 to the PANS-ATM (Doc 4444).
Forecast. A statement of expected meteorological conditions for a specified time or period, and for a specified area or portion of airspace.
Geodetic datum. A minimum set of parameters required to define location and orientation of the local reference system with respect to the global reference system/frame.
Gregorian calendar. Calendar in general use; first introduced in 1582 to define a year that more closely approximates the tropical year than the Julian calendar (ISO 19108*).
Note.— In the Gregorian calendar, common years have 365 days and leap years 366 days divided into twelve sequential months.
Height. The vertical distance of a level, a point or an object considered as a point, measured from a specified datum.
Human Factors principles. Principles which apply to aeronautical design, certification, training, operations and maintenance and which seek safe interface between the human and other system components by proper consideration to human performance.
Human performance. Human capabilities and limitations which have an impact on the safety and efficiency of aeronautical operations.
IFR. The symbol used to designate the instrument flight rules.
IFR flight. A flight conducted in accordance with the instrument flight rules.
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Chapter 1 Annex 11 — Air Traffic Services
IMC. The symbol used to designate instrument meteorological conditions.
INCERFA. The code word used to designate an uncertainty phase.
Incident. An occurrence, other than an accident, associated with the operation of an aircraft which affects or could affect the safety of operation.
Note.— The types of incidents which are of main interest to the International Civil Aviation Organization for accident prevention studies are listed in Annex 13, Attachment C.
Instrument flight procedure design service. A service established for the design, documentation, validation, maintenance and periodic review of instrument flight procedures necessary for the safety, regularity and efficiency of air navigation.
Instrument meteorological conditions (IMC). Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling, less than the minima specified for visual meteorological conditions.
Note.— The specified minima for visual meteorological conditions are contained in Annex 2.
Integrity classification (aeronautical data). Classification based upon the potential risk resulting from the use of corrupted data. Aeronautical data is classified as:
- a) routine data: there is a very low probability when using corrupted routine data that the continued safe flight and landing of an aircraft would be severely at risk with the potential for catastrophe;
- b) essential data: there is a low probability when using corrupted essential data that the continued safe flight and landing of an aircraft would be severely at risk with the potential for catastrophe; and
- c) critical data: there is a high probability when using corrupted critical data that the continued safe flight and landing of an aircraft would be severely at risk with the potential for catastrophe.
International NOTAM office. An office designated by a State for the exchange of NOTAM internationally.
Level. A generic term relating to the vertical position of an aircraft in flight and meaning variously, height, altitude or flight
level.
Manoeuvring area. That part of an aerodrome to be used for the take-off, landing and taxiing of aircraft, excluding aprons.
Meteorological office. An office designated to provide meteorological service for international air navigation.
Movement area. That part of an aerodrome to be used for the take-off, landing and taxiing of aircraft, consisting of the manoeuvring area and the apron(s).
Navigation specification. A set of aircraft and flight crew requirements needed to support performance-based navigation operations within a defined airspace. There are two kinds of navigation specifications:
Required navigation performance (RNP) specification. A navigation specification based on area navigation that includes the requirement for performance monitoring and alerting, designated by the prefix RNP, e.g. RNP 4, RNP APCH.
Area navigation (RNAV) specification. A navigation specification based on area navigation that does not include the requirement for performance monitoring and alerting, designated by the prefix RNAV, e.g. RNAV 5, RNAV 1.
Note 1.— The Performance-based Navigation (PBN) Manual (Doc 9613), Volume II contains detailed guidance on navigation specifications.
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Annex 11 — Air Traffic Services Chapter 1
Note 2.— The term RNP, previously defined as “a statement of the navigation performance necessary for operation within a defined airspace,” has been removed from this Annex as the concept of RNP has been overtaken by the concept of PBN. The term RNP in this Annex is now solely used in the context of navigation specifications that require performance monitoring and alerting, e.g. RNP 4 refers to the aircraft and operating requirements, including a 4 NM lateral performance with on-board performance monitoring and alerting that are detailed in Doc 9613.
Non-duty period.† A continuous and defined period of time, subsequent to and/or prior to duty periods, during which the air traffic controller is free of all duties.
NOTAM. A notice distributed by means of telecommunication containing information concerning the establishment, condition or change in any aeronautical facility, service, procedure or hazard, the timely knowledge of which is essential to personnel concerned with flight operations.
Obstacle. All fixed (whether temporary or permanent) and mobile objects, or parts thereof, that:
- a) are located on an area intended for the surface movement of aircraft; or
- b) extend above a defined surface intended to protect aircraft in flight; or
- c) stand outside those defined surfaces and that have been assessed as being a hazard to air navigation.
Operator. A person, organization or enterprise engaged in or offering to engage in an aircraft operation.
Performance-based communication (PBC). Communication based on performance specifications applied to the provision of
air traffic services.
Note.— An RCP specification includes communication performance requirements that are allocated to system components in terms of the communication to be provided and associated transaction time, continuity, availability, integrity, safety and functionality needed for the proposed operation in the context of a particular airspace concept.
Performance-based navigation (PBN). Area navigation based on performance requirements for aircraft operating along an ATS route, on an instrument approach procedure or in a designated airspace.
Note.— Performance requirements are expressed in navigation specifications (RNAV specification, RNP specification) in terms of accuracy, integrity, continuity, availability and functionality needed for the proposed operation in the context of a particular airspace concept.
Performance-based surveillance (PBS). Surveillance based on performance specifications applied to the provision of air traffic services.
Note.— An RSP specification includes surveillance performance requirements that are allocated to system components in terms of the surveillance to be provided and associated data delivery time, continuity, availability, integrity, accuracy of the surveillance data, safety and functionality needed for the proposed operation in the context of a particular airspace concept.
Pilot-in-command. The pilot designated by the operator, or in the case of general aviation, the owner, as being in command and charged with the safe conduct of a flight.
Printed communications. Communications which automatically provide a permanent printed record at each terminal of a circuit of all messages which pass over such circuit.
† Applicable 5 November 2020.
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Chapter 1 Annex 11 — Air Traffic Services Prohibited area. An airspace of defined dimensions, above the land areas or territorial waters of a State, within which the
flight of aircraft is prohibited.
Radio navigation service. A service providing guidance information or position data for the efficient and safe operation of aircraft supported by one or more radio navigation aids.
Radiotelephony. A form of radiocommunication primarily intended for the exchange of information in the form of speech.
Reporting point. A specified geographical location in relation to which the position of an aircraft can be reported.
Required communication performance (RCP) specification. A set of requirements for air traffic service provision and associated ground equipment, aircraft capability, and operations needed to support performance-based communication.
Required surveillance performance (RSP) specification. A set of requirements for air traffic service provision and associated ground equipment, aircraft capability, and operations needed to support performance-based surveillance.
Rescue coordination centre. A unit responsible for promoting efficient organization of search and rescue services and for coordinating the conduct of search and rescue operations within a search and rescue region.
Restricted area. An airspace of defined dimensions, above the land areas or territorial waters of a State, within which the flight of aircraft is restricted in accordance with certain specified conditions.
Runway. A defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft.
Runway visual range (RVR). The range over which the pilot of an aircraft on the centre line of a runway can see the runway
surface markings or the lights delineating the runway or identifying its centre line.
Safety management system (SMS). A systematic approach to managing safety, including the necessary organizational structures, accountabilities, policies and procedures.
SIGMET information. Information issued by a meteorological watch office concerning the occurrence or expected occurrence of specified en-route weather and other phenomena in the atmosphere that may affect the safety of aircraft operations.
Significant point. A specified geographical location used in defining an ATS route or the flight path of an aircraft and for other navigation and ATS purposes.
Note.— There are three categories of significant points: ground-based navigation aid, intersection and waypoint. In the context of this definition, intersection is a significant point expressed as radials, bearings and/or distances from ground- based navigation aids.
Special VFR flight. A VFR flight cleared by air traffic control to operate within a control zone in meteorological conditions below VMC.
Station declination. An alignment variation between the zero degree radial of a VOR and true north, determined at the time the VOR station is calibrated.
Taxiing. Movement of an aircraft on the surface of an aerodrome under its own power, excluding take-off and landing.
Terminal control area. A control area normally established at the confluence of ATS routes in the vicinity of one or more major aerodromes.
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Annex 11 — Air Traffic Services Chapter 1 Time-in-position.† The period of time when an air traffic controller is exercising the privileges of the air traffic controller’s
licence at an operational position.
Track. The projection on the earth’s surface of the path of an aircraft, the direction of which path at any point is usually expressed in degrees from North (true, magnetic or grid).
Traffic avoidance advice. Advice provided by an air traffic services unit specifying manoeuvres to assist a pilot to avoid a collision.
Traffic information. Information issued by an air traffic services unit to alert a pilot to other known or observed air traffic which may be in proximity to the position or intended route of flight and to help the pilot avoid a collision.
Transfer of control point. A defined point located along the flight path of an aircraft, at which the responsibility for providing air traffic control service to the aircraft is transferred from one control unit or control position to the next.
Transferring unit. Air traffic control unit in the process of transferring the responsibility for providing air traffic control service to an aircraft to the next air traffic control unit along the route of flight.
Uncertainty phase. A situation wherein uncertainty exists as to the safety of an aircraft and its occupants.
VFR. The symbol used to designate the visual flight rules.
VFR flight. A flight conducted in accordance with the visual flight rules.
Visual meteorological conditions (VMC). Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling, equal to or better than specified minima.
Note.— The specified minima are contained in Annex 2.
VMC. The symbol used to designate visual meteorological conditions.
Waypoint. A specified geographical location used to define an area navigation route or the flight path of an aircraft
employing area navigation. Waypoints are identified as either:
Fly-by waypoint. A waypoint which requires turn anticipation to allow tangential interception of the next segment of a route or procedure, or
Flyover waypoint. A waypoint at which a turn is initiated in order to join the next segment of a route or procedure.
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