WACE Aviation key terms

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

The specific angle of attack at which airflow separates from the wing and lift begins to decrease. A wing stalls at this angle regardless of speed, weight or attitude.

The direction of air movement past the aircraft as experienced by the wing, produced by the aircraft's forward motion combined with any wind. It defines the reference for measuring angle of attack.

The aerodynamic force generated perpendicular to the relative airflow, mainly by the wings, that supports the aircraft's weight in flight. It increases with airspeed, air density, wing area and lift coefficient.

A dimensionless number describing how much lift a particular wing shape produces at a given angle of attack. It rises with angle of attack until the stall.

Drag created as a by-product of generating lift, caused by higher pressure below the wing spilling around the wingtips. It is greatest at low speed and high angle of attack.

Drag from sources other than lift production, including form drag from the aircraft's shape and skin friction from air passing over its surfaces. It increases with the square of airspeed.

The sum of induced drag and parasitic drag at a given airspeed. It is lowest at the speed where the two components are equal, which is the speed for maximum glide range.

The curvature of a wing's upper and lower surfaces. Greater camber generally produces more lift at a given angle of attack but also more drag.

The straight line drawn from the leading edge to the trailing edge of an aerofoil. The angle between this line and the relative airflow is the angle of attack.

A condition in which airflow separates from the wing because the critical angle of attack is exceeded, causing a sudden loss of lift and an increase in drag. Recovery requires reducing the angle of attack.

The ratio of the total lift acting on an aircraft to its weight. It rises in turns and manoeuvres, increasing the stall speed and structural stress on the airframe.

The initial tendency of an aircraft, after being disturbed from equilibrium, to return toward that equilibrium, move further away, or stay put. Positive static stability is the foundation of safe handling.

Stability about the aircraft's lateral (pitch) axis, largely provided by the horizontal tail and affected by the position of the centre of gravity relative to the centre of pressure.

The point through which the aircraft's total weight acts. Its position affects stability, control and performance, and must remain within the limits set in the aircraft flight manual.

The process of calculating the aircraft's total weight and centre of gravity position before flight to confirm both lie within approved limits. Out-of-limit loading degrades performance and control.

The greatest total weight at which an aircraft is certified to begin its take-off run. Exceeding it lengthens the take-off distance and reduces climb performance.

The altitude in the standard atmosphere at which the air density equals the actual density at the aircraft's location. High temperature, high elevation and high humidity raise it and reduce performance.

The altitude indicated when the altimeter subscale is set to the standard datum of 1013.25 hectopascals. It is used for flight levels above the transition altitude.

The local pressure value entered into an altimeter so it displays height above a reference datum such as mean sea level. It must be updated as pressure changes or the aircraft climbs.

The altimeter subscale setting that, when entered, makes the altimeter read elevation above mean sea level at the aerodrome. It is used for terminal area and low-level operations.

The speed shown on the airspeed indicator, derived from the difference between pitot (ram) pressure and static pressure. It is the reference for aircraft limitations and stall margins.

The aircraft's actual speed through the surrounding air mass, greater than indicated airspeed at altitude because of lower air density. It is used for navigation and flight planning calculations.

The speed of an aircraft relative to the ground, equal to true airspeed adjusted for wind. A headwind reduces it and a tailwind increases it.

The direction in which the aircraft's nose points, measured in degrees from north. It differs from track when wind pushes the aircraft sideways.

The actual path an aircraft follows over the ground, expressed as a direction in degrees from north. Wind causes it to differ from the heading.

The angular difference between the aircraft's heading and its track, caused by crosswind. It is applied to the required track to calculate the heading to fly.

A vector diagram relating true airspeed, wind velocity and groundspeed to solve for heading and track. It underpins the flight computer calculations used in navigation planning.

A navigation method that calculates the aircraft's position from a known starting point using heading, airspeed, elapsed time and wind estimates, without external position fixes.

A document or filed message stating the intended route, altitude, speed, times and fuel for a flight. It supports search and rescue and air traffic coordination.

The minimum fuel that must remain on board at destination, beyond trip fuel, to cover contingencies, diversion and holding. It is a legal requirement for flight planning.

The airspeed that gives the greatest horizontal distance per unit of height lost with power off. It occurs where total drag is minimum and is used in engine failure drills.

Spiralling airflows trailing from the wingtips where high-pressure air beneath the wing curls up into the lower-pressure region above. They create induced drag and wake turbulence.

Disturbed air left behind an aircraft, chiefly wingtip vortices and jet blast. It is strongest from heavy, slow aircraft and requires spacing on approach and departure.

The radius of the circular path flown in a level turn. It increases with airspeed and decreases with bank angle, which matters for remaining inside a confined area.

A condition in which body tissues receive insufficient oxygen, causing impaired judgement, euphoria and eventually unconsciousness. It can occur at altitude in unpressurised aircraft without supplementary oxygen.

A pilot's mistaken perception of the aircraft's position or motion relative to the ground, often caused by conflicting sensory cues in poor visibility. Trusting instruments rather than sensations is the defence.

The equivalent altitude pressure inside a pressurised cabin, normally maintained well below the aircraft's actual altitude for passenger comfort and oxygen supply.

Flying by reference to cockpit instruments rather than outside visual cues, required in cloud or low visibility. It relies on attitude, heading, altitude and speed indications.

The condition of an aircraft being safe and legally fit to fly, maintained through certification, inspections and approved maintenance. It is a shared responsibility of owner, operator and pilot.

A systematic walk-around check of the aircraft's structure, controls, fuel, oil and documents before flight. It is the pilot's final opportunity to detect defects on the ground.

A ground-based service that provides clearances, separation and information to aircraft to prevent collisions and maintain orderly traffic flow. Pilots must comply with issued instructions unless safety requires otherwise.

An authorisation from air traffic control for an aircraft to proceed under specified conditions. It does not relieve the pilot of responsibility for safety or terrain clearance.

The greatest horizontal distance at which prominent objects can be seen and identified. It is a key criterion for visual flight rules and approach minima.

Rules allowing flight by outside visual reference, subject to minimum visibility and cloud separation requirements. They depend on weather conditions and airspace classification.

A shaped surface, such as a wing or propeller blade, designed to produce lift as air flows over it. Its shape and angle to the airflow determine the lift and drag generated.