IDAC Air Traffic Controller (CTA) key terms

A rule allowing aircraft approved for precise altimetry to fly with only 1,000 feet of vertical separation between FL290 and FL410, instead of the 2,000 feet applied above FL290 in non-RVSM airspace.

A surface of constant atmospheric pressure referenced to the standard pressure of 1013.25 hPa, expressed in hundreds of feet, used above the transition altitude so all aircraft share one pressure datum.

The altitude at or below which an aircraft's altimeter is set to the local QNH, and above which it is set to standard pressure 1013.25 hPa, separating altitude and flight level operation.

QNH is the pressure setting that makes the altimeter read elevation above mean sea level on the ground; QFE makes it read height above a specified reference point, usually the aerodrome.

A routine coded observation of surface weather at an aerodrome, issued at fixed intervals, reporting wind, visibility, weather phenomena, cloud, temperature, dew point and pressure.

A coded forecast of expected weather at an aerodrome for a stated validity period, including wind, visibility, significant weather and cloud, with temporary and becoming change groups.

An unscheduled aerodrome weather observation issued when specified significant changes occur, such as a sudden visibility drop, thunderstorm onset or a marked wind shift.

A sudden change of wind speed or direction over a short distance, often near thunderstorms or frontal zones, capable of causing abrupt airspeed loss on approach or departure.

A small, intense downdraft that spreads out horizontally on reaching the ground, producing a sharp headwind then tailwind change that can drive an aircraft below the approach path.

An accident in which a serviceable aircraft is flown unintentionally into terrain, water or an obstacle, usually because the crew lost awareness of position or altitude.

A ground-based safety net in ATC automation that alerts the controller when a tracked aircraft's predicted path descends below a defined minimum safe altitude for the area.

An automated function comparing projected tracks of surveillance targets and warning the controller when two aircraft may breach separation within a set look-ahead time, typically about two minutes.

A separation standard applied between identified surveillance targets, expressed as a minimum horizontal distance, typically 5 nautical miles, and sometimes combined with a vertical minimum.

The process by which a controller establishes that a specific surveillance position corresponds to a specific aircraft, by observing a turn, position report correlation, or a transponder ident feature.

A four-digit octal code selected in the aircraft transponder that identifies the aircraft on secondary surveillance radar and links it to the flight plan data in the ATC system.

A secondary surveillance radar interrogation format in which each aircraft has a unique 24-bit address, allowing selective interrogation and data exchange with reduced radio frequency congestion.

A surveillance method in which the aircraft automatically broadcasts position and other data derived from its own navigation systems, requiring no interrogation from the ground station.

A data link service exchanging text clearances and requests between controller and pilot, reducing voice frequency load and readback errors, with defined message sets and alerting.

The pilot's repetition of a controller instruction or clearance to confirm correct reception, mandatory for safety-related items such as route, level, heading, speed and frequency.

An authorization for an aircraft to proceed under specified conditions, issued by ATC, which the pilot must follow unless an emergency or safety concern requires deviation with prompt notification.

A conditional instruction permitting an aircraft to enter the runway and position for departure while awaiting take-off clearance, without authorizing the actual take-off.

Any unauthorized presence of an aircraft, vehicle or person on a protected runway area, a major collision risk that controllers guard against through clearances, signs and surface surveillance.

A row of red lights across a taxiway at a runway holding position that is illuminated to signal a stop and extinguished only when the controller authorizes entry to the runway.

A discontinued approach followed by a climb, initiated by the pilot or instructed by ATC when the landing cannot be safely completed, for example due to traffic or wind shear.

Spacing applied behind heavier aircraft to avoid the hazard of wingtip vortices, based on the leader's weight category and the follower's category, expressed as time or distance.

A classification by maximum certificated take-off mass, such as light, medium, heavy or super, used to determine wake turbulence separation minima and approach speed groupings.

A grouping of aircraft by reference approach speed, from A to E, that determines the minimum visibility and circling area applicable to an instrument approach procedure.

A published series of predetermined manoeuvres, with defined altitudes and tracks, allowing an aircraft to transition from the en-route phase to a point where landing can be completed visually.

A specified altitude in a precision or vertically guided approach at which a missed approach must be initiated if the required visual reference has not been established.

The lowest altitude at which a controller may vector an aircraft while guaranteeing the required terrain and obstacle clearance within a defined area, published on charts.

A controller's or pilot's continuous perception and understanding of traffic, weather, terrain and system state, and the ability to project how that picture will change.

A condition in which the prescribed minimum distance or altitude between aircraft is not maintained, ranging from a minor infringement to a serious incident requiring investigation.

A safety management principle distinguishing inadvertent human error, which should not be punished, from reckless or intentional violations, which require proportionate disciplinary action.

A formal, systematic set of processes and accountabilities by which an aviation organization identifies hazards, assesses and mitigates risk, and monitors safety performance.

A written record of an incident, accident or hazard submitted to the authority or organization, used for analysis and prevention rather than for assigning blame.

A set of scheduling, rest and monitoring measures designed to keep controller alertness within safe limits, addressing the cumulative effects of long duties and night shifts.

A rule prohibiting non-essential conversation and activity during critical phases of flight or high-workload ATC periods, so attention remains on operational tasks.

An ATC function that notifies search and rescue organizations when an aircraft is overdue, has declared an emergency, or is otherwise believed to be in distress.

The dedicated radio channels, 121.5 MHz for civil aviation, used for distress calls and emergency communications, guarded by ATC and rescue coordination centres.

A special squawk such as 7700 for general emergency, 7600 for radio failure or 7500 for unlawful interference, used to alert ATC without voice communication.

A published set of actions followed when two-way radio contact is lost, involving squawking 7600, continuing per the last clearance or flight plan, and watching for light signals.