CPL Aircraft General Knowledge key terms

A fuselage or wing construction in which the external skin carries a large share of the loads, stiffened by frames, stringers and bulkheads so that it does not rely on the skin alone.

A longitudinal stiffening member riveted to the skin of a semi-monocoque structure, carrying bending and axial loads and preventing the skin from buckling under compression.

A chordwise structural member inside a wing or tailplane that maintains the aerofoil shape, supports the skin and stringers, and transfers loads to the spar.

The main spanwise beam of a wing or tailplane, usually the strongest member, designed to carry bending moments and shear loads from lift and inertia.

A design philosophy in which a structure can sustain a defined level of damage, such as a failed member or fatigue crack, without catastrophic failure until the damage is found at inspection.

The ability of a structure to continue performing its function in the presence of cracks or flaws until they are detected by scheduled inspection, forming the basis of modern structural inspection programmes.

A flush-mounted opening on the fuselage side that supplies undisturbed ambient static pressure to the pitot-static instruments, so that altitude and airspeed indications remain accurate in normal flight.

A forward-facing probe that measures total pressure of the airflow; combined with static pressure it allows the airspeed indicator to compute dynamic pressure and hence indicated airspeed.

A condition in which ice, insects or debris obstruct the pitot tube or static port, causing airspeed, altitude and vertical speed indications to freeze or read falsely, requiring the pilot to use alternate sources.

The pressure-setting window on an altimeter, set to QNH, QFE or standard pressure, which determines the reference datum against which the indicated altitude is displayed.

A barometric instrument that converts static pressure into an altitude display, calibrated to the International Standard Atmosphere and referenced to the pressure set in its subscale window.

An instrument that displays the difference between pitot total pressure and static pressure, graduated in speed units and marked with colour-coded ranges for flap, normal and never-exceed limits.

A rate instrument that senses the rate of change of static pressure and displays climb or descent in feet per minute, often with a lag of several seconds after a change.

The never-exceed speed, marked by the red radial on the airspeed indicator; flight above this speed risks structural damage or loss of control and is prohibited in normal operation.

The maximum operating limit speed for a turbine-powered aeroplane, a structural and handling limit that must not be deliberately exceeded and is displayed on the airspeed indicator.

A self-excited aeroelastic vibration in which aerodynamic forces and structural deflection reinforce each other, potentially causing rapid structural failure at high speed if damping is insufficient.

A weight installed ahead of a control surface hinge line so that its centre of gravity lies forward of the hinge, preventing flutter by opposing the surface's natural vibration.

A movable aerodynamic surface such as an aileron, elevator or rudder that changes the forces on the aircraft to control its attitude about one or more axes.

A small hinged surface attached to the trailing edge of a primary control surface, deflected to hold that surface in a chosen position and relieve continuous control loads from the pilot.

A tab whose deflection is controlled by the pilot and which aerodynamically drives the main control surface, reducing the effort needed to move large or heavily loaded surfaces.

A flight control system in which pilot inputs are converted into electrical signals processed by computers that command hydraulic or electric actuators, replacing mechanical linkage and enabling envelope protection.

The provision of duplicate or multiple independent components, channels or power sources so that a single failure does not prevent a system from performing its required function.

A common electrical conductor within a distribution system to which several power sources and loads are connected, allowing power to be shared and circuits to be isolated.

A rotating machine driven by an engine that converts mechanical energy into electrical power for the aircraft's systems and for charging the battery in flight.

An electrical machine producing alternating current, typically rectified to direct current in light aircraft, used to supply the electrical system and recharge the battery.

A system that transmits force and motion through pressurised fluid to operate actuators such as landing gear, flaps and brakes, offering high power for low weight.

A pressure vessel containing fluid and a gas charge that stores hydraulic energy, smooths pressure fluctuations and supplies short-term flow for emergency or peak demands.

A pressure-limiting valve that opens to bypass or return fluid when system pressure exceeds a set value, protecting components and lines from overpressure damage.

A system using compressed air, bled from a turbine engine compressor or supplied by a pump, to drive services such as engine starting, pressurisation, de-icing and some actuators.

Compressed air tapped from a turbine engine compressor stage and used for cabin pressurisation, air conditioning, anti-icing and engine starting, with associated performance and fuel penalties.

A system that prevents ice from forming on protected surfaces by adding heat, such as engine bleed air or electrical heating, or by releasing fluid, typically on wings, tail and engine intakes.

A system that removes ice after it has formed, for example by inflating pneumatic boots on the leading edges or by electrical heating cycles on propellers and windshields.

Ice formation in a piston engine carburettor caused by fuel vaporisation and pressure drop cooling, which can strangle the mixture and cause rough running or power loss, countered by carburettor heat.

The cockpit control that adjusts the fuel-to-air ratio delivered to a piston engine, leaned for altitude or rich for cooling and full power, affecting efficiency and cylinder temperature.

A measured temperature of exhaust gases used to monitor engine operation, set mixture strength and, in turbine engines, to protect hot-section components from overtemperature.

A powerplant in which air is compressed, mixed with fuel and burned, and the expanding gases drive a turbine that turns the compressor and produces thrust or shaft power.

A propeller whose blade angle is automatically varied by a governor to maintain a selected engine speed as load and airspeed change, improving efficiency across the flight envelope.

A device that senses engine speed and adjusts propeller blade angle through oil pressure to hold the selected rpm, increasing pitch as speed tends to rise and decreasing it as speed falls.

Setting propeller blades to a high angle that aligns them with the relative airflow, minimising drag and windmilling after an engine failure, mainly on multi-engine aircraft.

A central visual and aural alert, often a red lamp with a tone, that draws attention to a serious condition and is usually accompanied by a specific caption on the warning panel.

An amber central alert indicating an abnormal but non-critical condition requiring attention, normally paired with a caption identifying the affected system.

A display of labelled warning and caution lights that identifies the specific system or condition behind a master warning or caution, guiding the pilot's response.

A device, often a reed horn or stick shaker, that alerts the pilot as the angle of attack approaches the stall, giving time to reduce pitch and restore airflow.

The angle between the wing chord line and the relative airflow; the stall occurs at a critical value of this angle regardless of airspeed, weight or attitude.

An alerting system that uses radio altitude, barometric altitude and gear or flap status to warn of imminent terrain contact, typically with aural 'pull up' commands.

A cockpit-operated valve that directs fuel from a chosen tank or tanks to the engine and can be set to shut off supply, central to fuel management and imbalance control.

An opening that allows air to enter or leave a tank as fuel is used or expands, preventing excessive pressure or vacuum and allowing full fuel flow to the engine.

A container, often integral within the wing or fuselage structure, that stores fuel and includes baffles, drains and vents to manage flow, contamination and quantity measurement.

A sensor that detects weight on the wheels and inhibits or enables systems such as retraction, pressurisation and some warnings according to whether the aircraft is on the ground.