ANAC Glider Pilot key terms

An official document confirming that an individual aircraft meets the airworthiness requirements of its state of registry and is therefore permitted to be flown, subject to the conditions and limitations stated on it.

A mandatory instruction issued by an aviation authority requiring inspection, modification, or replacement on specified aircraft types to correct an unsafe condition; compliance is compulsory and normally time-limited.

A certification signed by an authorised person confirming that specified maintenance has been completed satisfactorily and that the aircraft or component is fit for return to service within any stated limitations.

The set of regulations under which a pilot may operate an aircraft by visual reference to the ground, provided specified minimum visibility and cloud-separation criteria are met in the relevant airspace.

Weather conditions in which flight visibility and distance from cloud equal or exceed the prescribed minima for the airspace concerned, allowing the pilot to navigate and maintain separation by outside visual reference.

Airspace of defined dimensions within which air traffic control service is provided to flights in accordance with the applicable airspace classification, and in which some or all aircraft require a clearance.

An authorisation for an aircraft to proceed under conditions specified by an air traffic control unit, which the pilot must comply with unless an emergency or a safety-related instruction requires deviation.

A four-digit octal number selected on the aircraft's transponder so that air traffic control radar displays the correct identification and altitude information for that flight.

The pressure value set on a pressure altimeter so that on the ground at the reference station the instrument indicates the station's elevation above mean sea level, rather than its height above the airfield.

The fixed pressure datum set on an altimeter so that it displays pressure altitude, used above a specified transition altitude to give all aircraft a common altitude reference.

The altitude, published for a given location, at or below which an aircraft's altimeter is set to the local pressure setting and above which the standard pressure setting is used.

The primary structure of a sailplane, comprising fuselage, wings, and tail surfaces, designed to carry flight loads with minimum weight while providing the aerodynamic shape that generates lift.

The main spanwise structural member of a wing that carries bending loads from lift and transfers them to the fuselage, often forming the core of the wing's torsion box.

A deployable surface on the upper wing that disrupts lift and increases drag, allowing the pilot to control descent angle steeply during approach and landing without excessive airspeed.

A device linking the variometer to a static-pressure reservoir so that changes in airspeed are largely cancelled out, leaving an indication of the glider's total energy change rather than raw climb or sink.

A sensitive instrument that displays the rate of climb or descent of the glider, usually in knots or metres per second, helping the pilot locate and centre thermals and set an efficient cruise speed.

The arrangement of a forward-facing pressure probe and static ports that supplies total and static pressure to the airspeed indicator, altimeter, and variometer; blockage or leakage causes erroneous readings.

An instrument that compares total pressure from the pitot tube with static pressure to display speed through the air, marked with colour-coded ranges for normal, caution, and never-exceed limits.

The distance a glider travels forward for each unit of height lost in still air, expressed as a number such as 40:1 and varying with airspeed, wing loading, and contamination of the wing surface.

The technique of adjusting airspeed according to the expected strength of the next climb or sink, so that the total height lost over a cross-country leg is minimised rather than the instantaneous sink rate.

Water or solid weight carried in the wings or fuselage to increase wing loading, improving penetration and cruise speed in strong conditions, and jettisonable so it can be dumped before landing.

The mass of the glider divided by its wing area; higher values give faster cruise and better penetration but raise stall speed and reduce climb rate in weak lift.

The point through which the total weight of the glider acts; its fore-and-aft location must stay within the certified range to preserve stability and control effectiveness in all flight conditions.

The lowest airspeed at which the wing can produce the lift required in a given configuration and loading; it increases with weight, load factor, and forward centre-of-gravity position.

The acute angle between the wing chord line and the relative airflow; lift rises with this angle until the critical value is exceeded, after which the airflow separates and the wing stalls.

The component of drag created as a by-product of lift, caused by the spanwise flow and tip vortices; it is greatest at low speed and high angle of attack and is reduced by higher aspect ratio.

The ratio of a wing's span squared to its area; high values, typical of sailplanes, reduce induced drag and give a flatter glide, while low values favour roll rate and structural simplicity.

The maximum speed at which full deflection of a single control surface may be applied without exceeding the design load factor; above it, gusts or abrupt inputs can overstress the structure.

The ratio of the lift produced to the weight of the aircraft, expressed in g; it rises steeply in turns and pull-ups and determines the structural stress the airframe must withstand.

The rate at which a rising parcel of air cools through expansion without exchanging heat with its surroundings, roughly 3 degrees Celsius per 1000 feet when unsaturated.

A rising column of air warmed by contact with a surface hotter than its surroundings, used by glider pilots to gain altitude; strength depends on surface heating and the environmental lapse rate.

A detached, cauliflower-shaped cloud formed where rising thermals reach condensation level; its base marks the top of the dry updraught and its growth signals increasing instability and convection.

The temperature to which air must be cooled at constant pressure for it to become saturated; a small spread between temperature and dew point favours cloud, haze, and a low thermal cloud base.

An oscillating airflow set up downwind of a mountain barrier in stable, windward-perpendicular flow, producing smooth strong lift and severe turbulence and rotor cloud beneath the wave crests.

A change of wind speed or direction over a short distance, vertically or horizontally, which can abruptly alter a glider's airspeed and glide path during approach and landing.

A condition in which body tissues receive insufficient oxygen, causing impaired judgement, euphoria, and loss of consciousness; it develops insidiously at altitude and is aggravated by cold and fatigue.

Rapid or deep breathing that lowers blood carbon dioxide, producing dizziness, tingling, and muscle cramps; symptoms resemble hypoxia, and treatment is to slow the breathing rate deliberately.

A mistaken perception of the aircraft's attitude or motion, arising when the inner ear misinterprets sustained accelerations without reliable visual reference, and best countered by trusting instruments and keeping the horizon in view.

The last leg of a cross-country flight, planned so that height remaining above the finish point exceeds that needed at the expected glide ratio, allowing for sink, wind, and a safety margin.

A written sequence of actions used before take-off, before landing, and in emergencies to ensure critical items are not omitted, particularly when workload or stress reduces recall.

A pre-flight test in which one person holds each control surface while the pilot moves the corresponding cockpit control, confirming correct connection and freedom of movement before launch.

A method of launching in which a powered aircraft pulls the glider on a rope; the pilot follows the tug's wake, maintains position, and releases at the agreed altitude or in an emergency.

A navigation technique that calculates the expected position from the planned track, true airspeed, elapsed time, and forecast wind, then compares it with observed landmarks or GPS indications.

A vector diagram combining the aircraft's heading and true airspeed with the wind velocity to determine the resulting track and groundspeed, used to plan headings and estimate arrival times.

The actual path over the ground followed by the aircraft, which differs from the planned track when drift caused by wind has not been fully corrected by the chosen heading.