PPL Aircraft General Knowledge key terms

Upward angle of the wings relative to the lateral axis. It produces a stabilizing rolling moment when the aircraft sideslips, improving lateral stability about the roll axis.

The imaginary axis through the aircraft running from wingtip to wingtip, about which the aircraft pitches. It is perpendicular to both the longitudinal and normal axes and passes through the centre of gravity.

The initial tendency of an aircraft, after being disturbed from equilibrium, to return toward its original flight condition. Positive static stability means an initial restoring tendency; negative means a tendency to diverge further.

The point through which the total weight of the aircraft acts. Its position along the chord affects both stability and the load the tailplane must carry, so it must stay within a certified range.

The certified forward and aft limits of centre-of-gravity position, plotted against aircraft mass, within which flight is permitted. Loading outside it may cause unacceptable control forces or stability.

The mass of the aircraft as delivered plus optional equipment, unusable fuel and full operating fluids, excluding crew, passengers, baggage and usable fuel. It is the datum from which all loading calculations begin.

The difference between maximum structural take-off mass and basic empty mass. It represents the total mass available for crew, passengers, baggage, usable fuel and any other disposable load.

The maximum mass, certified by the manufacturer, at which the aircraft may begin the take-off run. It may be further limited by runway, obstacle or climb performance on a given day.

The horizontal distance from the reference datum to an item's centre of gravity, used together with its mass to compute a moment. Dividing total moment by total mass gives the aircraft CG position.

The ratio of total lift to weight, expressed in g. It determines the structural loads on the airframe and rises steeply in turns or when pulling out of a dive.

The lowest indicated airspeed at which the wing can produce enough lift to support the aircraft in unaccelerated flight at a given mass. It increases with the square root of load factor.

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

The maximum speed at which the aircraft may be operated in any condition, marked by the red radial on the airspeed indicator. Exceeding it risks structural damage or control reversal.

The angle between the wing chord line and the relative airflow. Lift increases with angle of attack up to the critical value, beyond which the wing stalls.

Pressure altitude corrected for temperature deviation from the standard atmosphere. High density altitude reduces engine power, propeller thrust and lift, lengthening take-off and landing runs.

The altitude indicated when the altimeter subscale is set to the standard pressure of 1013.25 hPa. It is used for flight levels above the transition altitude and as the basis for performance calculations.

The speed shown on the airspeed indicator, derived from dynamic pressure without correction for position error, density or compressibility. It is the reference for most aircraft limitations and stall margins.

The actual speed of the aircraft through the air mass. It exceeds indicated airspeed at altitude because lower density reduces dynamic pressure for the same speed.

The speed of the aircraft over the ground, equal to true airspeed adjusted for wind component along track. It determines time en route and fuel consumed between points.

The vector relationship between true heading and true airspeed, wind direction and speed, and the resulting true track and groundspeed. It is solved graphically or with a navigation computer.

The fuel that must remain at destination or diversion, specified by regulation for the type of operation. It is not available for normal flight planning and must be carried in addition to trip fuel.

Fuel carried to cover unforeseen factors such as forecast errors, routing changes or weather deviations. It is usually calculated as a percentage of trip fuel or a fixed time allowance.

The fuel required from brake release at departure to touchdown at destination, including taxi-out, climb, cruise, descent and approach allowances. It excludes reserves and contingency.

The actual take-off mass permitted for a specific runway, considering field length, obstacle clearance, climb gradient and tyre-speed limits. It is the lowest of the applicable limiting masses.

The runway length at which the accelerate-stop distance equals the take-off distance to 35 ft with one engine failed at the decision speed. It is the minimum field length for a given mass.

The decision speed at which, following an engine failure, the take-off can be continued safely or the aircraft stopped within the remaining runway. It is chosen before take-off.

The pressure value set on the altimeter subscale so that it indicates height above a chosen reference, such as aerodrome elevation or standard pressure. Correct setting is critical for terrain clearance.

An aneroid barometer calibrated to display altitude from static pressure. It senses pressure from the static source and converts it using the subscale setting and the standard atmosphere law.

The flush port or ports on the fuselage that supply undisturbed ambient pressure to the altimeter, airspeed indicator and vertical speed indicator. Blockage causes erroneous readings on all three.

A forward-facing probe that senses total pressure from the airflow and feeds it to the airspeed indicator. Blockage or icing causes the indicated airspeed to behave like an altimeter.

The property of a spinning rotor to resist changes in the orientation of its spin axis. It is the basis of attitude and heading indicators, keeping their references fixed in inertial space.

A gyroscopic instrument displaying pitch and roll relative to the horizon. Its rotor spins in the horizontal plane, so the gyro maintains a stable vertical reference as the aircraft manoeuvres.

A gyroscopic instrument showing aircraft heading against a rotating compass card. It is more stable than a magnetic compass in turns but must be realigned with magnetic north periodically.

The angular difference between true north and magnetic north at a given location, shown on charts as east or west. It converts true courses and bearings to magnetic values for compass use.

A conductive bar that distributes electrical power from sources to the various circuits of the aircraft. Multiple buses allow essential equipment to remain powered after a generator failure.

A generator producing alternating current, rectified to direct current in most light aircraft. It supplies the electrical load in flight and recharges the battery, which provides starting power.

A resettable protective device that opens a circuit when current exceeds its rating, preventing overheating and fire. Unlike a fuse, it can be reset after the fault is corrected.