GCAA Ghana CPL Theory Exam key terms

The altitude above mean sea level at or below which an aircraft's vertical position is expressed as altitude, and above which it is expressed as flight level. It is published for each aerodrome and marks the lower limit of the transition layer.

The lowest flight level available for use above the transition altitude, ensuring at least 1,000 ft of separation from the transition altitude. It varies with atmospheric pressure and is provided by ATC.

The fixed pressure datum of 1013.25 hPa (29.92 inHg) set on the altimeter subscale when flying at or above the transition level, so that all aircraft share a common vertical reference for flight levels.

The altimeter subscale setting that, when applied at aerodrome elevation, causes the altimeter to indicate elevation above mean sea level. It is the standard setting for approach and landing.

The altimeter subscale setting that makes the altimeter read zero on the aerodrome reference point, giving height above that point rather than altitude. Used in some aerodrome and circuit operations.

A surface of constant atmospheric pressure related to the standard pressure datum of 1013.25 hPa and expressed in hundreds of feet, for example FL 150 means 15,000 ft on the standard setting.

Visual meteorological conditions: the weather minima of visibility and distance from cloud in which flight under visual flight rules is permitted. The exact values depend on airspace class and altitude.

Instrument meteorological conditions: weather conditions below the visual flight rules minima, in which flight must be conducted under instrument flight rules and normally requires an instrument rating.

A clearance allowing a flight to operate under visual flight rules within a control zone when weather is below normal VFR minima, subject to ATC approval, ground visibility limits and clearance from cloud.

Controlled airspace extending upwards from the surface to a specified upper limit around an aerodrome, protecting approach and departure paths. Entry requires an ATC clearance.

The acute angle between the wing chord line and the relative airflow. Increasing it raises lift up to the critical angle, beyond which the airflow separates and the wing stalls.

The angle of attack at which the wing produces maximum lift and beyond which it stalls. It is a fixed value for a given aerofoil regardless of weight, speed or bank angle.

Drag produced as a by-product of lift, caused by the spanwise flow and wingtip vortices that deflect air downward. It increases with angle of attack and decreases as speed rises.

The reduction in induced drag and increase in effective lift experienced when flying within about one wingspan of the surface, caused by interference with the airflow around the wing.

The ratio of total lift to weight, expressed in g. It rises in level turns and manoeuvres, raising the stall speed, since stall speed increases with the square root of load factor.

The lowest indicated airspeed at which an aircraft can maintain level flight before reaching the critical angle of attack. It increases with weight, load factor and forward centre of gravity.

The point through which the total weight of the aircraft acts. Its position affects stability and control; too far forward raises stall speed and stick forces, too far aft reduces longitudinal stability.

The pressure altitude corrected for non-standard temperature. High density altitude reduces engine power, propeller thrust and lift, lengthening take-off and landing runs and reducing climb performance.

The altitude indicated when the altimeter is set to 1013.25 hPa. It is the basis for performance charts and for computing density altitude and true altitude corrections.

The horizontal distance required from the start of the take-off roll to reaching a specified height, typically 50 ft, with the aircraft at a defined weight and configuration under stated conditions.

The runway length at which the accelerate-stop distance equals the take-off distance to 50 ft with one engine failing at the critical point, giving the minimum field required for a given weight.

The take-off decision speed. Above it, a failure before rotation should be followed by continuing the take-off; below it, the take-off can be safely abandoned on the remaining runway.

The rotation speed at which the pilot applies back pressure to raise the nose during take-off, chosen so the aircraft reaches the required climb speed and lift-off attitude safely.

The take-off safety speed to be achieved by 35 ft above the runway with one engine inoperative, giving the minimum climb gradient required by performance rules.

A deficiency of oxygen reaching body tissues. In aviation it commonly results from high altitude without supplemental oxygen and impairs judgement and vision before the pilot notices symptoms.

The period after loss of oxygen supply during which a person can still take deliberate corrective action. It shortens rapidly with increasing altitude, falling to seconds above 40,000 ft.

Abnormally rapid or deep breathing that lowers blood carbon dioxide, causing dizziness, tingling and visual disturbance. Its symptoms resemble hypoxia but respond to slowing the breathing rate.

A pilot's mistaken perception of the aircraft's position or motion relative to the earth, usually when external visual references are lost and vestibular illusions replace reliable instrument information.

The inner ear organs, semicircular canals and otoliths, that sense rotation and acceleration. They can produce convincing false sensations during coordinated flight without visual reference.

A false sensation of pitch caused by linear acceleration or deceleration. Strong acceleration on take-off may feel like a nose-up attitude, prompting an inadvertent push on the controls.

The change in QNH over the past three hours, reported in the METAR remarks. A falling trend signals approaching deterioration, a rising trend generally indicates improving weather.

A routine coded observation of surface weather at an aerodrome, giving wind, visibility, cloud, temperature, dewpoint, pressure and significant weather, issued at fixed intervals, usually hourly or half-hourly.

A terminal aerodrome forecast of expected weather at an aerodrome over a stated period, typically 9 to 30 hours, using the same code forms as a METAR plus change groups.

The temperature to which air must be cooled at constant pressure for it to become saturated. A small spread between temperature and dewpoint indicates high humidity and likely cloud or fog.

The accumulation of ice on airframe surfaces when flying through supercooled water droplets. It adds weight, distorts aerofoil shape and can severely reduce lift and increase drag.

The altitude at which the air temperature falls to 0 degrees Celsius. Above it, supercooled water and airframe icing become likely in cloud, affecting route and altitude selection.

The angular difference between true north and magnetic north at a given place, shown on charts as isogonals. It is 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. It is recorded on a compass correction card and applied to obtain compass heading.

The direction the aircraft's nose points relative to magnetic north, obtained by applying variation to true heading and then deviation to reach compass heading.

A very high frequency omnidirectional radio range ground station that transmits radial information, allowing an aircraft with a receiver to determine its bearing from the station.

A magnetic bearing from a VOR station, measured clockwise from magnetic north. An aircraft flying outbound on a radial has that radial as its magnetic track from the station.

Distance measuring equipment that measures slant range from the aircraft to a ground transponder, usually co-located with a VOR or ILS, giving continuous distance readout.

Instrument landing system providing a localiser for lateral guidance and a glide path for vertical guidance to a runway, permitting precision approaches in low visibility.

The altitude on a precision approach at which a missed approach must be initiated if the required visual reference has not been established. It is referenced to the altimeter with QNH set.

The lowest altitude, referenced to QNH, to which descent is authorised on a non-precision approach before the required visual reference is established, after which a missed approach is flown.

The calculation and control of aircraft weight and centre of gravity position within approved limits, ensuring performance, structural limits and handling qualities remain acceptable throughout the flight.

The mass of the aircraft including traffic load but excluding usable fuel. It is a limiting structural value used in mass and balance calculations and performance planning.

The point along a route beyond which the aircraft can no longer return to the departure aerodrome with the fuel remaining, calculated from fuel, wind and consumption.

The point on a route where the time to fly onward to the destination equals the time to return to the departure point, allowing a diversion decision to be made with equal time cost.

The process of calculating usable fuel for taxi, trip, contingency, alternate and final reserve, ensuring the aircraft lands with at least the required minimum reserve.

The four-digit code entered in the aircraft transponder, assigned by ATC or selected from prescribed codes, enabling identification and altitude reporting on radar displays.

The mandatory repetition of safety-related ATC instructions and clearances by the pilot, allowing the controller to verify that the message was received and understood correctly.

A radar system that interrogates aircraft transponders and displays the returned identity code and, where available, pressure altitude, in addition to primary position information.