GCAA CAR-66 Category A Exam key terms

The maximum load expected in service, calculated from the aircraft's design weight and flight envelope. Structures must withstand limit load without permanent deformation. Beyond this value, structural damage may begin.

The limit load multiplied by the factor of safety, typically 1.5. The structure must support ultimate load for at least three seconds without failure, although permanent deformation is acceptable.

A multiplier applied to limit load to give ultimate load, usually 1.5 in aircraft design. It provides margin against unexpected loads, material variation and minor damage.

The ratio of lift produced to the aircraft's weight, expressed in g. It shows how much extra load the structure carries during manoeuvres or gusts.

The 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 airflow separates from the upper wing surface and lift reaches its maximum. A wing stalls at this angle regardless of speed, weight or attitude.

A condition where the wing exceeds its critical angle of attack, causing airflow separation and a sudden loss of lift. It can occur at any speed or attitude.

The point on an aerofoil where the total aerodynamic force acts. Its position moves forward as angle of attack increases, affecting pitch balance.

A point on an aerofoil, usually near 25 percent chord, where the pitching moment stays almost constant as lift changes. It is used for stability calculations.

The point through which the total weight of the aircraft acts. Its position affects stability, control and structural loading, and must stay within approved limits.

The upward angle of the wings relative to the horizontal, viewed from the front. Dihedral improves lateral stability by creating a rolling moment when the aircraft sideslips.

A relationship stating that in a steady flow of fluid, an increase in velocity is accompanied by a decrease in pressure. It explains how an aerofoil generates lift.

The reduction in fluid pressure that occurs when a fluid flows through a constricted section of pipe. Used in carburettors and airspeed measurement.

A system of pressure sensors and lines that supplies total and static pressure to flight instruments. It drives the airspeed indicator, altimeter and vertical speed indicator.

The pressure of still air surrounding the aircraft, unaffected by the aircraft's motion. It decreases with altitude and is used as a reference for airspeed and altitude.

The pressure caused by the motion of air, equal to half the density times velocity squared. It is the difference between total and static pressure.

The relationship stating that current through a conductor equals voltage divided by resistance. It is the basis for calculating values in basic electrical circuits.

A circuit where components are connected end to end so the same current flows through each. Total resistance is the sum of individual resistances.

A circuit where components connect across the same voltage points, so current divides between branches. Total resistance is always less than the smallest branch resistance.

An electric current that reverses direction periodically, usually in a sine wave. Its frequency and peak value describe its behaviour in AC circuits.

An electric current that flows in one direction only, with constant polarity. It is supplied by batteries and by rectified aircraft generators.

A device, often a diode bridge, that converts alternating current into direct current. It is used in aircraft DC power supplies and battery chargers.

A semiconductor device that allows current to flow in one direction only. It is used for rectification, protection and signal detection in electronic circuits.

A three-terminal semiconductor device used to amplify or switch electronic signals. It forms the basis of many aircraft electronic control and amplifier circuits.

A digital circuit element that produces an output determined by logical combinations of its inputs, such as AND, OR and NOT. Gates form the building blocks of digital systems.

A number expressed using only the digits 0 and 1, with each position representing a power of two. Digital aircraft systems use binary for processing and data storage.

A shared set of conductors or a data path that carries signals or digital data between components. Examples include power buses and avionics data buses.

A widely used avionics data bus standard that transmits digital data in one direction from a transmitter to multiple receivers over a twisted pair.

An aircraft component designed to be removed and replaced quickly at the aircraft without extensive testing or calibration. It simplifies maintenance and fault isolation.

Diagnostic hardware and software built into an aircraft system that monitors its operation and reports faults. It helps technicians isolate problems during maintenance.

The deterioration of a metal through chemical or electrochemical reaction with its environment. It is controlled by protective coatings, sealants and regular inspection.

Corrosion caused when two dissimilar metals are in electrical contact in the presence of an electrolyte. The less noble metal becomes the anode and corrodes.

An electrolytic process that builds a protective oxide layer on aluminium surfaces. It improves corrosion resistance and provides a good base for paint.

A calibrated tool used to tighten fasteners to a specified torque value. Correct use prevents under-tightening, over-tightening and damage to components.

A safety method where twisted wire is threaded through fasteners to prevent them loosening in service. It is a common positive locking device in aircraft maintenance.

A mistake arising from human action or inaction that affects safe operation or maintenance. It is managed through procedures, training and error-capturing systems.

A set of twelve common human factors that contribute to maintenance errors, including fatigue, complacency, distraction and lack of resources. Recognising them helps prevent mistakes.

A human factors model describing interactions between Software, Hardware, Environment and Liveware. It highlights where mismatches can create errors in aviation work.

A mandatory instruction issued by an aviation authority requiring action on an aircraft or component to correct an unsafe condition. Compliance is legally required.

A document from a manufacturer recommending or requiring modification or inspection of a product. It becomes mandatory only when an authority adopts it.

A certification confirming that maintenance work has been completed satisfactorily and the aircraft or component is fit for return to service.

A permanent fastener used to join aircraft sheet metal structures. Rivet type, size and spacing are chosen to carry the required shear and bearing loads.

The progressive weakening of a structure caused by repeated cyclic loading, leading to cracks. It is managed through design, inspection programmes and life limits.