ICAA PPL Theory key terms

A set of rules allowing a pilot to operate an aircraft by reference to outside visual cues, provided specified weather minima and cloud-clearance criteria are met. It places responsibility for seeing and avoiding other traffic on the pilot.

An authorisation, requested by the pilot and granted by air traffic control, permitting flight within a control zone in weather below normal VFR minima. The pilot must remain clear of cloud and in sight of the surface.

Airspace of defined dimensions within which air traffic control service is provided to flights in accordance with airspace classification. Classes differ in whether clearance, continuous two-way radio contact, and instrument flight rules are required.

An authorisation issued by air traffic control for an aircraft to proceed under specified conditions. It is not a guarantee of separation from terrain, obstacles, or unknown traffic unless explicitly stated, and the pilot remains responsible for safe conduct.

The mandatory repetition back to air traffic control of safety-related clearance elements such as route, altitude, heading, speed, and runway, confirming the instruction was correctly received and understood. Incorrect or incomplete read-backs must be corrected immediately.

A four-digit octal number set in the aircraft transponder, assigned by air traffic control to identify the flight on radar displays. Specific codes, such as 7700 for emergency, are reserved for particular situations.

An airborne radio device that replies to ground radar interrogations, transmitting a code and, in Mode S or with altitude encoding, pressure altitude. It improves identification and enables traffic alerting and collision avoidance systems to function.

The pressure reference set on a barometric altimeter so that the instrument indicates the intended altitude. QNH gives elevation above mean sea level, QFE gives height above a reference datum, and standard pressure is used above the transition altitude.

The altitude, published for a location, at which a climbing aircraft changes its altimeter reference from local pressure to standard pressure. Descending aircraft change back at the transition level, which lies at or above it.

A surface of constant pressure altitude referenced to standard pressure of 1013.25 hPa, expressed in hundreds of feet. Flight levels are used above the transition altitude so that all aircraft share a common altitude reference.

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

The angle of attack at which airflow over the wing begins to separate significantly and lift reaches its maximum. Any further increase causes a stall, regardless of airspeed, weight, or attitude.

A condition in which airflow separates from the wing because the critical angle of attack is exceeded, producing a loss of lift and often buffet or a nose drop. Recovery requires reducing the angle of attack, typically by lowering the nose.

The ratio of the total aerodynamic and inertial loads on the aircraft to its weight, expressed in g. Higher load factors raise the stall speed, so a level steep turn stalls at a higher airspeed than straight flight.

The direction of the air approaching the aircraft as a result of its motion through the air. It determines the angle of attack and therefore the lift produced, and is opposite to the flight path in still air.

The drag component created as a by-product of producing lift, caused by spanwise airflow around the wingtips. It increases with angle of attack and decreases with higher airspeed, dominating at low-speed flight.

The point through which the total weight of the aircraft acts. Its position affects stability and control, and must remain within the certified forward and aft limits for safe flight and adequate rotation, stall, and recovery characteristics.

The calculation ensuring that the aircraft's total mass and the position of its centre of gravity remain within certified limits for the intended flight. It accounts for empty mass, fuel, occupants, and baggage at their respective arms.

The pressure altitude corrected for non-standard temperature, representing the altitude at which the air density would occur in a standard atmosphere. High density altitude reduces engine power, propeller thrust, and lift, lengthening takeoff and climb.

The altitude indicated when the altimeter is set to standard pressure of 1013.25 hPa. It forms the basis for performance calculations and is used to derive density altitude once temperature is taken into account.

A condition in which insufficient oxygen reaches body tissues, causing symptoms such as euphoria, impaired judgement, headache, and eventual unconsciousness. It develops insidiously, so pilots may not recognise their own deterioration, and it worsens with altitude.

Rapid or deep breathing that lowers carbon dioxide in the blood, producing dizziness, tingling, and confusion that can mimic hypoxia. Deliberate slowing of breathing or controlled breathing usually restores normal carbon dioxide levels.

A pilot's mistaken perception of the aircraft's position or motion relative to the earth, often caused by conflicting or absent visual cues in cloud or darkness. Recovery relies on trusting flight instruments rather than bodily sensations.

A false sensation of pitch caused by linear acceleration or deceleration, such as a feeling of pitching up during takeoff acceleration or pitching down during deceleration. It can lead a pilot to make inappropriate control inputs without instrument reference.

The period after exposure to a given altitude during which a person can still perform useful, purposeful actions before incapacitation. It shortens rapidly with increasing altitude and is reduced by physical exertion or cold.

The altimeter setting that, when set on the subscale, causes the altimeter to indicate elevation above mean sea level at the aircraft's position. It is derived from station pressure corrected to sea level using standard atmosphere assumptions.

The pressure at a specified reference point, usually aerodrome level, which when set causes the altimeter to read height above that point. It is used in some circuit and approach operations and must be changed before climbing above the transition altitude.

The formation of ice on aircraft surfaces from supercooled water droplets in cloud or precipitation. It adds weight, disrupts airflow, and can reduce lift and increase drag, with severe effects on performance and control.

Ice forming in the carburettor venturi or throttle area due to fuel vaporisation and pressure drop cooling, most likely at temperatures between roughly minus ten and plus twenty degrees Celsius with high humidity. It can occur in clear air and is countered with carburettor heat.

The altitude at which the air temperature falls to zero degrees Celsius in the standard atmosphere or in a given sounding. Above it, supercooled water and airframe icing become possible, so it is a key planning figure.

A change in wind speed or direction over a short distance, horizontally or vertically, which can abruptly alter airspeed and lift. Low-level shear near thunderstorms or fronts is a significant hazard during takeoff and approach.

A navigation method calculating the aircraft's present position from a known starting point using heading, airspeed, elapsed time, and wind. It requires an accurate heading and wind estimate and is normally cross-checked with other navigation aids.

The direction the aircraft's longitudinal axis points, measured clockwise from true north. It is converted to magnetic heading by applying magnetic variation and to compass heading by applying deviation.

The angular difference at a location between true north and magnetic north, which changes with position and slowly over time. It is applied to convert between true and magnetic directions, with east variation subtracted from true heading.

The error in a magnetic compass caused by the aircraft's own magnetic fields and electrical currents, varying with heading. It is recorded on a compass correction card and applied to magnetic heading to obtain compass heading.

Disturbed air, chiefly counter-rotating wingtip vortices, left behind by a moving aircraft. It is strongest behind heavy, slow, clean aircraft and can cause severe upsets, so pilots use spacing and fly above the preceding flight path.

A discontinued approach or landing in which the pilot applies power and climbs away to rejoin the circuit or follow instructions. It is a normal, safe manoeuvre and should be initiated early when an approach is unstable or unsafe.

A systematic external and internal check of the aircraft before flight, covering structure, controls, fluids, fuel quantity and contamination, tyres, and documents. It confirms the aircraft is airworthy and correctly configured for the planned flight.

The initial tendency of an aircraft, after a disturbance, to return to its original flight condition. Positive static stability aids handling, and it is influenced by the position of the centre of gravity relative to the aerodynamic centre.