GCAA CPL Theory Exam (GCAA) key terms

The altitude above which a pilot sets the standard pressure setting of 1013.25 hPa on the altimeter, and below which the local altimeter setting is used, so that all aircraft share a common reference.

The lowest flight level available for use above the transition altitude, chosen so that the transition layer is at least the minimum thickness required by the state; it changes with the local pressure.

A surface of constant atmospheric pressure shown on the altimeter when set to 1013.25 hPa, expressed in hundreds of feet, used to separate aircraft vertically above the transition altitude.

The altimeter subscale setting that, when applied on the ground at aerodrome elevation, makes the altimeter indicate elevation above mean sea level; it reflects the pressure reduced to sea level.

The altimeter subscale setting that makes the instrument read zero on the ground at a specified reference point, so it indicates height above that point rather than altitude above sea level.

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

An authorisation for an aircraft to proceed under conditions specified by an air traffic control unit, protecting it from other known traffic but not guaranteeing terrain or obstacle separation.

A four-digit octal number entered on the aircraft transponder that identifies the aircraft on secondary surveillance radar and links it to the controller's flight data display.

The automatic transmission of pressure altitude in 100-foot increments alongside the identification code, allowing the controller to see and separate aircraft vertically on radar displays.

A predetermined manoeuvre that keeps an aircraft within a specified airspace while awaiting further clearance, flown as a racetrack with defined inbound leg, turns and leg timing or distance.

The acute angle between the wing chord line and the relative airflow, which primarily determines whether the wing produces lift efficiently or stalls regardless of airspeed or attitude.

The angle of attack at which the wing reaches its maximum lift coefficient and any further increase causes airflow separation and a stall, independent of weight, speed and bank angle.

The direction of the air approaching the aircraft as a result of its motion through the air mass, defining the angles on which lift, drag and angle of attack depend.

Drag that results from the generation of lift, caused by the spanwise flow and wingtip vortices, decreasing as airspeed increases and increasing with weight and load factor.

A dimensionless number describing how effectively a wing converts dynamic pressure into lift for a given shape and angle of attack, increasing with angle of attack up to the stall.

The ratio of the total aerodynamic force on the aircraft to its weight, equal to one in level flight and rising in turns or manoeuvres, thereby raising stall speed and structural loading.

The minimum indicated airspeed at which an aircraft can maintain level flight in a given configuration, increasing with weight, load factor and forward centre of gravity position.

The point through which the total weight of the aircraft acts, whose permitted range ensures controllability and balance; moving it aft reduces stability and stick force.

The pressure altitude corrected for non-standard temperature, indicating the air density the aircraft actually experiences and therefore the performance available for take-off and climb.

The altitude indicated when the altimeter is set to 1013.25 hPa, used as the reference for performance charts and for computing density altitude from temperature.

The speed of the aircraft through the surrounding air mass, greater than indicated airspeed at altitude because density falls, and used for navigation and flight planning.

The speed shown on the airspeed indicator, derived from dynamic pressure and therefore affected by air density; it is the reference for aircraft limitations and stall margins.

The highest altitude at which an aircraft can still climb at a specified minimum rate, beyond which climb performance becomes negligible and operational margins are lost.

A condition in which the body tissues receive insufficient oxygen, causing impaired judgement, euphoria and loss of consciousness; it develops insidiously above about 10,000 feet without supplemental oxygen.

The period after loss of oxygen supply during which a person can still perform useful, deliberate actions, roughly 15 to 30 seconds at 35,000 feet and longer at lower altitudes.

Rapid or deep breathing that removes excessive carbon dioxide from the blood, producing dizziness, tingling and faintness whose symptoms resemble hypoxia but which improves with controlled slow breathing.

A pilot's mistaken perception of the aircraft's position or motion relative to the earth, often caused by conflicting vestibular and visual cues in cloud or darkness, leading to dangerous control inputs.

A false sensation of pitching up during acceleration, or pitching down during deceleration, caused by linear acceleration stimulating the otolith organs, which can prompt an inappropriate control correction.

The inner-ear organs, semicircular canals and otoliths, that sense rotation and linear acceleration; they cannot distinguish sustained turns or accelerations from gravity alone.

A layer in which temperature increases with height, suppressing vertical mixing and trapping moisture, haze and pollutants beneath it, often producing poor visibility and low cloud.

The rate at which temperature decreases with height in the atmosphere, about 2 degrees Celsius per 1,000 feet in the standard atmosphere, and less in moist or stable air.

A suspension of water droplets that reduces horizontal visibility below 1,000 metres at the surface, formed when air near the ground cools to its dewpoint or gains moisture.

The temperature to which air must be cooled at constant pressure for it to become saturated, so that further cooling produces condensation, cloud or fog.

The angular difference at a given place between true north and magnetic north, shown on charts and applied when converting between true and magnetic directions.

The error of a magnetic compass caused by the aircraft's own magnetic fields, varying with heading and corrected using a compass swing card.

The direction in which the aircraft's longitudinal axis points, expressed in degrees from a reference north, differing from the track actually flown when drift is present.

The minimum flight visibility and distance from cloud that must be maintained in visual meteorological conditions, which vary with airspace class and altitude.

A clearance allowing flight within a control zone in conditions below visual meteorological minima, subject to air traffic control approval and remaining clear of cloud.

The mandatory repetition to the controller of safety-related clearance elements such as route, altitude, heading and frequency, allowing errors to be detected before they affect flight safety.

The standard set of spoken word equivalents for letters, such as Alpha, Bravo and Charlie, used in radio communication to remove ambiguity between similar-sounding letters and callsigns.