IAA ATCO Licence Theory key terms

The minimum horizontal or vertical distance that air traffic control must maintain between aircraft under its control, set according to surveillance type, airspace class, wake turbulence category, and phase of flight.

A vertical separation standard of 1,000 feet applied between suitably equipped aircraft above a designated transition altitude, instead of the usual 2,000 feet, within designated airspace where altimetry performance is monitored.

Separation of aircraft provided by identifying their positions on a surveillance display and applying prescribed minimum distances, rather than relying on position reports from the crews themselves.

A classification of aircraft by maximum certificated take-off mass, used to apply wake turbulence separation distances between a leading and a following aircraft during approach, departure, and en-route flight.

Counter-rotating air masses shed from the wingtips of a fixed-wing aircraft, strongest when the aircraft is heavy, clean, and slow, which can cause severe upset or loss of control in a following aircraft.

The point to which an aircraft is granted an air traffic control clearance, usually an aerodrome or a significant waypoint, beyond which further clearance must be obtained before proceeding.

An authorisation for an aircraft to proceed under specified traffic conditions, issued by a controller and communicated to the pilot, which does not by itself relieve the pilot of responsibility for safety.

The mandatory repetition by a pilot or controller of safety-related clearance elements so that the issuing unit can verify the message was received and understood correctly.

The defined set of words and sentence patterns published for radiotelephony, designed to be unambiguous and brief so that messages are understood uniformly across languages and radio conditions.

The use of ordinary, clear spoken words in radiotelephony when no standard phraseology exists for the situation, keeping messages short and free of ambiguity.

A ground radar system that interrogates a transponder in the aircraft and displays the reply, typically including identity code and pressure altitude, enabling identification and altitude readout.

A secondary surveillance radar data-link standard in which each aircraft carries a unique 24-bit address, allowing selective interrogation, data exchange, and improved track identification.

A four-digit octal code set by the pilot in the transponder, assigned by air traffic control or selected from a prescribed contingency set, used to identify the aircraft on secondary radar.

Reserved transponder codes with defined meanings, such as the codes for radio communication failure, unlawful interference, and emergency, which alert controllers without the need for speech.

A surveillance technique in which aircraft automatically transmit position and other data derived from on-board systems, which is received by ground stations or other aircraft to build traffic pictures.

A text-based communication service between controllers and pilots that supplements voice radiotelephony, using defined message sets and requiring operational acknowledgement of each uplinked instruction.

The pressure value set on the subscale of a pressure altimeter so that it indicates height relative to a chosen datum, such as mean sea level or a standard pressure surface.

The altimeter setting that, when set on the subscale of an altimeter at a given elevation, causes it to indicate the elevation above mean sea level at that place.

The altitude, published for a given aerodrome or region, at or below which aircraft altimeters are set to the local pressure setting and above which the standard pressure setting is used.

The lowest flight level available for use above the transition altitude, chosen so that the vertical distance between it and the transition altitude is sufficient at the prevailing pressure.

A surface of constant atmospheric pressure, related to a standard datum of 1,013.25 hectopascals, separated from other such surfaces by specified pressure intervals and expressed in hundreds of feet.

The set of operating and navigation rules under which a flight is conducted mainly by reference to instruments, requiring an air traffic control clearance and compliance with notified procedures and separation.

The rules under which a flight may be conducted when the pilot can see and avoid other traffic, requiring specified flight visibility and distance from cloud, and remaining clear of cloud.

The weather conditions expressed in terms of visibility, distance from cloud, and ceiling, equal to or better than specified minima, in which flight under visual flight rules is permitted.

Weather conditions expressed in terms of visibility, distance from cloud, and ceiling that are worse than the specified minima for visual flight, requiring flight under instrument flight rules.

Airspace of defined dimensions within which air traffic control service is provided to flights in accordance with the airspace classification, ranging from Class A to Class G in the ICAO system.

A lettered system from A to G that defines, for each class of airspace, whether instrument and visual flights are permitted, what separation is provided, and what services are available.

The lowest altitude that provides a defined margin above terrain and obstacles within a specified area, used by controllers to ensure clearances do not place aircraft below a safe height.

An on-board system that compares aircraft position and predicted flight path with a terrain and obstacle database, giving visual and aural alerts before a controlled flight into terrain becomes likely.

A stage of uncertainty, alert, or distress declared by air traffic services when an aircraft is overdue, has not reported, or is known or believed to be in serious or imminent danger.

The designated radio frequencies reserved for emergency transmissions, notably 121.5 megahertz in civil aviation, monitored by air traffic services and many aircraft for distress and urgency calls.

A report made by a pilot to air traffic control giving the aircraft's position, time, altitude, and next position and estimated time, used where surveillance is unavailable or as required.

A predetermined manoeuvre keeping an aircraft within a specified airspace while awaiting further clearance, flown as a racetrack with defined inbound track, leg times or distances, and altitude.

The authorisation for an aircraft to carry out a specified instrument approach procedure, which does not remove the requirement for the pilot to remain responsible for separation from terrain.

A pilot's mistaken perception of position and motion relative to the earth, usually arising when visual cues are lost, which can lead to inappropriate control inputs and loss of control.

A false sensation of pitch caused by linear acceleration or deceleration, which may lead a pilot to raise or lower the nose incorrectly after take-off or during a go-around in poor visual conditions.

A controller's or pilot's accurate understanding of traffic, weather, terrain, and system state, both now and in the near future, on which safe decisions and timely interventions depend.

The mental and perceptual effort a controller expends to manage traffic, which rises with aircraft count, complexity, and communication load and is managed through sector capacity limits and assistance.

The maximum number of aircraft that a control sector can safely accept over a period, declared from measured or assessed workload so that controller demand stays within manageable limits.