NCAA Instrument Rating Theory key terms

The set of regulations and procedures governing flight in conditions where the pilot cannot reliably see and avoid obstacles or other traffic, requiring instrument qualification, an IFR flight plan and, in controlled airspace, an ATC clearance.

The regulations under which a flight operates when visibility and cloud separation meet prescribed minima, allowing the pilot to navigate and avoid traffic mainly by outside visual reference rather than by instruments alone.

Weather conditions expressed in terms of visibility, distance from cloud and ceiling that are below the minima specified for visual flight, so that flight must be conducted under instrument flight rules.

Weather conditions meeting the prescribed visibility, cloud distance and ceiling minima that permit flight under visual flight rules, either as reported by an observer or as encountered by the pilot.

An ATC authorization letting a pilot operate in a control zone below visual meteorological minima, normally requiring clear of cloud and flight within the zone; it is not an IFR clearance and does not permit flight in instrument conditions.

An authorization from air traffic control for an aircraft to proceed under instrument flight rules within controlled airspace, normally containing the aircraft identification, route or limit, altitude, and any departure or arrival instructions.

A published altitude providing a specified obstacle clearance, usually 1,000 feet, within a defined radius around a navigation aid or waypoint, used for emergency reference rather than for routine navigation.

The lowest published altitude between radio fixes on an airway that assures acceptable navigational signal coverage and meets obstacle clearance requirements along the entire route segment.

The lowest published altitude on an airway segment that meets obstacle clearance requirements, though it may not guarantee reception of navigation signals along the whole segment; it is often lower than the minimum enroute altitude.

A specified altitude in a precision or approach-with-vertical-guidance procedure at which a missed approach must be initiated if the required visual reference has not been established, referenced to mean sea level.

A specified height above the touchdown zone elevation at which a missed approach must be initiated during a precision approach if the required visual reference is not established; it is a radio altimeter or barometric height, not an altitude.

The lowest altitude, expressed in feet above mean sea level, to which descent is authorized on final approach during a non-precision procedure without the required visual reference, below which the aircraft must not descend.

The point on a final approach course at which a missed approach must be initiated if the required visual reference to continue has not been established, often defined by a fix, a navigation aid or a distance.

A published sequence of turns, climbs and altitude limits flown when an approach cannot be completed to a landing, designed to keep the aircraft clear of obstacles and return it to a point from which another approach or a diversion can begin.

An instrument approach procedure that provides course guidance but no electronic vertical guidance, flown down to a minimum descent altitude before the required visual reference must be acquired and the landing continued.

An instrument approach procedure providing both lateral and vertical electronic guidance, such as ILS, allowing descent to a decision altitude or height before the required visual reference must be established.

A ground-based approach aid combining a localizer for lateral guidance, a glide path for vertical guidance and marker beacons or distance information, permitting precise approaches to a runway in low visibility.

The lateral guidance component of an ILS, transmitting on a VHF frequency between 108 and 112 MHz and providing course guidance aligned with the runway centreline, with a typical usable width of a few degrees either side.

The vertical guidance component of an ILS, normally transmitted on a UHF frequency and defining a descent angle, typically about three degrees, toward the runway touchdown zone.

A ground navigation beacon transmitting on 108 to 117.95 MHz that lets an aircraft determine the magnetic bearing from the station, supporting airway navigation and radial-based approach procedures.

A magnetic bearing extending outward from a VOR station, numbered from 000 to 359 degrees; flying a given radial inbound or outbound is the standard method of tracking along a VOR-defined airway.

A transponder-based system in which the aircraft interrogates a ground station and measures slant range distance in nautical miles, commonly paired with VOR or ILS to provide fix information.

A method of navigation permitting flight on any desired path within the coverage of navigation aids or satellite systems, rather than being constrained to fly directly to or from ground stations.

A navigation specification stating the on-board performance monitoring and alerting capability and the lateral accuracy, such as RNP 0.3, that an aircraft must achieve for a given airspace or procedure.

A satellite-based positioning system, such as GPS, providing worldwide position and time signals used for enroute navigation and for approach procedures, subject to integrity monitoring and availability requirements.

The cockpit display showing lateral displacement from a selected course, with a needle or symbol that centres when the aircraft is on course and full-scale deflection representing a defined off-course distance.

A flight instrument combining a heading indicator with a course deviation display and glide path indication, reducing pilot workload by showing aircraft heading and course guidance in a single presentation.

A gyroscopic instrument showing pitch and bank relative to the horizon, forming the primary reference for aircraft control during instrument flight when outside visual cues are unavailable.

A gyroscopic direction instrument displaying the aircraft heading, used with the attitude indicator and turn coordinator to control and cross-check heading during instrument flight; it requires periodic alignment with the magnetic compass.

The disciplined, continuous pattern of eye movements among flight instruments used to detect and correct deviations in attitude, heading, altitude and airspeed without fixating on any single instrument.

A pilot's mistaken perception of position, attitude or motion relative to the earth, typically arising when visual cues are lost and vestibular or other sensory signals give false information, requiring reliance on instruments.

A false sensation of pitch caused by linear acceleration or deceleration, such as the illusion of pitching up during acceleration on takeoff or the reverse during deceleration, which can lead to inappropriate control inputs.

The height above ground or water of the lowest layer of cloud reported as broken or overcast, or of the vertical visibility into an obscuration, used to determine whether conditions permit visual flight.

The pressure value, such as QNH or QFE, set on the altimeter subscale so that the instrument indicates the correct altitude or height for the phase of flight and the applicable transition level or altitude.

The altitude at or below which the aircraft's altitude is controlled by reference to the altimeter set to local pressure, and above which the standard pressure setting is used for flight levels.

A surface of constant atmospheric pressure related to a standard datum of 1013.25 hectopascals, expressed in hundreds of feet and used above the transition altitude for vertical separation between aircraft.

The accumulation of ice on airframe surfaces, such as wings, tailplane and propeller, which increases weight and drag and reduces lift, potentially degrading performance and handling before the pilot notices.

Ice formation in an engine's carburettor venturi or throttle area caused by fuel vaporisation and pressure drop, able to occur at outside temperatures well above freezing and to cause rough running or power loss.

Ice accumulation on air intake filters, ducts or throttle bodies of a fuel-injected or carburetted engine, restricting airflow and reducing power; it may form in visible moisture at temperatures near or below freezing.

The lowest altitude in the atmosphere at which the air temperature is zero degrees Celsius, a key planning figure for assessing icing risk and for choosing altitudes in visible moisture.

The pilot's repetition to air traffic control of clearance elements such as route, altitude, heading, frequency and transponder code, confirming that the instruction has been correctly received and understood.

The service that provides clearances, separation and traffic information to aircraft, using radar, surveillance and flight plan data to maintain safe and orderly flow within controlled airspace.