CPL AGK / Systems key terms

The main spanwise structural member of a wing that carries bending loads from root to tip; often the primary load path to which ribs, skin and attachments are fixed.

A chordwise structural element that shapes the aerofoil section, supports the skin and transfers loads between skin, stringers and spars.

A longitudinal stiffener running spanwise or lengthwise along the skin, carrying axial and shear loads and preventing skin buckling under compression.

A transverse structural member in the fuselage that carries concentrated loads, closes a pressure compartment or provides a hard attachment point for major components.

Controls that directly govern aircraft attitude in flight: ailerons for roll, elevators for pitch and rudder for yaw, together with their actuation systems.

Surfaces that modify the lift or drag characteristics of the wing rather than primary attitude, such as flaps, slats, spoilers and trim tabs.

A control architecture in which pilot inputs are converted to electrical signals and processed by computers that command hydraulic or electric actuators, replacing mechanical linkages.

A tank that stores system fluid, allows for thermal expansion and contraction, and provides a head of pressure to the pump inlet while allowing air and contaminants to separate.

A pressure vessel containing fluid separated from a compressed gas or spring, storing hydraulic energy to smooth pump demand, absorb pulses and supply emergency pressure.

A valve that meters hydraulic flow to an actuator in proportion to an electrical or mechanical command, giving precise, fast and reversible control of actuator speed and direction.

A flow-limiting device that closes when downstream flow exceeds a set value, isolating a failed line or component and protecting the rest of the system from loss of pressure.

Hot, high-pressure air tapped from a compressor stage or auxiliary power unit and used for pressurisation, air conditioning, anti-icing and engine starting.

The controlled maintenance of cabin pressure above ambient by regulating the outflow of conditioned air, so that occupants are kept at a safe equivalent altitude.

The equivalent altitude corresponding to the actual cabin pressure, which must be kept within limits to avoid hypoxia and is normally held below about 8,000 feet.

A motorised valve in the pressure hull that modulates the rate at which cabin air escapes, thereby controlling cabin pressure and the rate of climb or descent of cabin altitude.

A machine driven by the engine or auxiliary power unit that converts mechanical energy into electrical power, typically producing alternating current at constant frequency.

A rotating machine that generates alternating current; in light aircraft a belt-driven unit with a rectifier supplying direct current to the battery and distribution bus.

A common electrical conductor to which multiple circuits or power sources are connected, allowing distribution of power and isolation of sections by contactors or switches.

A resettable protective device that opens a circuit automatically when current exceeds its rating, and can be reset manually once the fault is cleared.

A pilot-operated valve that selects which tank or group of tanks supplies the engine and can usually also shut off fuel flow completely.

A container for storing fuel, either integral within the wing or fuselage structure or a separate bladder or rigid tank, fitted with vents, drains and quantity sensing.

An indicating system, usually float-operated or capacitance-based, that shows the quantity of fuel in each tank to the crew.

A propeller whose blade angle is automatically varied by a governor to maintain a selected rotational speed as power and airspeed change.

A control unit that senses engine speed and adjusts propeller blade angle through oil pressure to hold the speed selected by the pilot.

The absolute pressure in the engine induction system, indicated on a gauge and used with engine speed to set and monitor power output.

A system that prevents ice from forming on protected surfaces by continuously adding heat or fluid, for example bleed-air heated wing leading edges or a weeping-fluid wing.

A system that removes ice after it has formed, typically by inflating pneumatic boots on the leading edges or by cycling electrical heaters.

Electrical heating of the pitot tube to prevent ice blockage that would cause erroneous airspeed indications, usually controlled by a cockpit switch with a warning of failure.

The system of pitot and static pressure sources and lines that supplies total and static pressure to the airspeed indicator, altimeter and vertical speed indicator.

An instrument that displays altitude by measuring static pressure and converting it according to a selected pressure reference set in the subscale window.

An instrument that indicates the rate of climb or descent by sensing the rate of change of static pressure through a calibrated leak.

A braking system that senses wheel deceleration or slip and modulates brake pressure to prevent wheel lock-up, preserving directional control and shortening stopping distance.

The wheel-mounted unit, typically multiple discs with hydraulic pistons, that converts hydraulic pressure into friction to slow or stop the aircraft on the ground.

The powered folding of landing gear into the airframe after take-off, and its extension before landing, controlled by selector, actuation and locking systems.

A continuous sensing element in an engine or compartment that responds to overheat or flame and triggers a cockpit warning, often arranged in duplicate for fault tolerance.

A pressurised bottle and distribution plumbing that discharges extinguishing agent into a designated fire zone when activated by the crew.

A central attention-getting indicator, usually red and accompanied by an aural alert, that draws attention to a serious system fault requiring immediate action.

A central amber indicator, usually with an aural alert, that signals a non-immediate system fault or abnormal condition requiring crew awareness and later action.

An automatic flight control system that holds selected aircraft attitudes or flight parameters by commanding the primary flight controls through servos or computers.

A computing and display system that generates steering commands shown on the attitude indicator for the pilot to follow, and which can couple to the autopilot.

The means by which the crew or a system fault removes autopilot authority, normally accompanied by an aural warning and a visual annunciation to the crew.