CPL Flight Performance and Planning key terms

Drag created as a by-product of lift, caused by wingtip vortices and rearward-tilted lift. It decreases with increasing airspeed and increases with higher weight or load factor, especially at high angle of attack.

Drag from skin friction, form drag and interference, unrelated to lift production. It rises with the square of airspeed, so total drag is lowest where induced and parasite drag curves cross.

The ratio of lift to drag at a given condition, indicating aerodynamic efficiency. Maximum L/D occurs at the speed for minimum total drag and gives best glide range and best fuel mileage in still air.

The ratio of total lift to aircraft weight, expressed in g. It increases in turns and pull-ups, raises stall speed, and determines the structural limit used in mass and balance and performance calculations.

The lowest airspeed at which the wing can produce the lift required at the critical angle of attack. It increases with weight, load factor and altitude, and decreases with flaps or other lift augmentation.

Pressure altitude corrected for non-standard temperature, representing the altitude the aircraft 'feels' aerodynamically. High density altitude reduces engine power, propeller thrust and lift, lengthening takeoff and climb.

Indicated altitude when the altimeter subscale is set to standard pressure 1013.25 hPa or 29.92 inHg. It is the reference altitude used in performance charts and in flight levels above the transition altitude.

Certified or published airspeeds such as V1, VR, V2, VNE, VNO, VFE and VY. Each defines an operating limit or target for takeoff, climb, flap or structural operation and must be respected in planning.

The takeoff decision speed at which, following an engine failure, the aircraft can either continue to a screen height or stop within the runway. It is chosen from balanced field considerations and runway conditions.

The runway length at which the accelerate-stop distance equals the distance to continue takeoff and reach screen height after an engine failure. It sets the minimum field length for a given weight, configuration and condition.

The distance needed to accelerate to V1, recognise an engine failure and bring the aircraft to a full stop. It includes a pilot reaction segment and braking action and is compared with available runway.

The specified height above the takeoff surface, typically 35 ft for class B or 50 ft for transport aircraft, that must be reached at the end of the takeoff distance. It standardises takeoff performance comparisons.

The horizontal distance from brake release to the point where the aircraft reaches a defined height, including ground roll and initial climb. It varies with weight, density altitude, wind, slope and surface condition.

The distance from crossing the threshold at a specified height to a complete stop, normally on a dry or specified runway condition. It must fit within the landing distance available with any required margin.

A runway covered by standing water, slush, loose snow or ice in a depth that affects braking or directional control. It increases landing distance and reduces takeoff acceleration and is reported in runway condition codes.

A six-level scale from 6 (dry) to 1 (ice) describing braking action and surface contamination. It is used with the runway condition assessment matrix to adjust takeoff and landing performance data.

The vertical speed achieved in feet per minute at a given weight, altitude and temperature. It falls with density altitude and weight, and must meet the required gradient for obstacle clearance on departure.

The ratio of height gained to horizontal distance flown, expressed as a percentage. It is compared with published procedure gradients for obstacle clearance and is affected by weight, temperature, configuration and speed.

The maximum density altitude at which the aircraft can still climb at a specified low rate, typically 100 ft per minute. It indicates the altitude above which useful climb performance is no longer available.

The distance flown per unit of fuel consumed, often nautical miles per kilogram or pound. It peaks near the maximum L/D condition and is used to select cruise altitude and speed for fuel efficiency.

The rate at which fuel is consumed, usually in kilograms or pounds per hour. It varies with power setting, altitude and temperature and is multiplied by time to obtain trip fuel for planning.

The level selected for the en-route phase, balancing fuel burn, winds, turbulence and airspace. It must satisfy terrain clearance, oxygen requirements and aircraft performance limits for the planned weight.

The point through which the total weight of the aircraft acts. Its position, expressed as a percentage of mean aerodynamic chord or in inches from a datum, must stay within the certified forward and aft limits.

An arbitrary reference point from which all longitudinal arms are measured for mass and balance calculations. Arm signs and units must be consistent so that moments sum correctly about the datum.

The horizontal distance from the datum to the centre of gravity of an item or station. Multiplying an item's mass by its arm gives its moment, which is summed to locate the aircraft's total centre of gravity.

The product of a mass and its arm, representing its rotational effect about the datum. Moments are summed and divided by total mass to compute the aircraft centre of gravity position.

The certified range of centre of gravity positions, forward and aft, permitted at each weight. Operating outside it can reduce control authority, increase trim drag or compromise stability and structural loads.

The most forward permitted centre of gravity position, set by elevator authority for rotation, flare and stall recovery. Exceeding it increases stall speed, trim drag and takeoff distance.

The most rearward permitted centre of gravity position, set by static and dynamic stability requirements. Exceeding it reduces pitch stability and can make stall recovery or spin avoidance difficult.

The mass of the aircraft and its contents excluding usable fuel. It is checked against a maximum limit and used with fuel mass to derive takeoff and landing mass for performance calculations.

The greatest mass at which the aircraft may begin the takeoff roll, limited structurally or by performance. It may be further restricted by runway, obstacle, climb or tyre-speed considerations on a given day.

The performance-limited takeoff mass for the actual runway, weather and obstacles, which may be lower than the structural maximum. It is the value used to confirm that required takeoff and climb gradients are met.

The greatest mass at which the aircraft may land, limited by structure and landing performance. If the planned landing mass exceeds it, fuel must be jettisoned or burned off before arrival.

The mass of traffic carried, comprising passengers, baggage and cargo, excluding fuel and operating items. It is the difference between zero fuel mass and basic empty mass and drives revenue and weight limits.

The mass of the aircraft with unusable fuel, full operating fluids and standard equipment, excluding crew, payload and usable fuel. It is the starting figure from which all loading calculations proceed.

The maximum load expected in service, expressed as a load factor, which the structure must withstand without permanent deformation. Ultimate load is typically 1.5 times the limit load.

A certified maximum such as maximum mass, maximum load factor or tyre speed that must not be exceeded regardless of performance. Exceeding it risks permanent damage even if the flight is completed safely.

The fuel needed from takeoff to landing at the destination, including taxi-out, climb, cruise, descent and approach. It is the core of the fuel plan to which reserves and contingencies are added.

Fuel added to cover unforeseen factors such as weather, routing or traffic delays, commonly a percentage of trip fuel or a time allowance. It is part of the minimum fuel required before departure.

The fuel that must remain on landing after diversion, typically 30 minutes holding at 1500 ft above the alternate. It protects against unexpected delays and is never planned for use.

The fuel required to fly from the destination to the chosen alternate, including approach and landing. It is included in the fuel plan only when an alternate is required by weather or regulation.

Fuel consumed while waiting in a holding pattern, calculated from holding fuel flow and expected delay time. It is often part of contingency or final reserve and depends strongly on altitude and mass.

The maximum time an aircraft can remain airborne on its available fuel, as opposed to range in distance. It is computed from usable fuel divided by hourly fuel flow at the planned power setting.

The position along a route beyond which it is no longer possible to return to the departure point with the fuel remaining. It is calculated from fuel available, wind and the fuel burn for the return leg.

The point between two airfields where the time to fly to either is equal, accounting for wind. It helps decide the diversion destination when weather or fuel changes in flight.

The process of revising route, fuel or destination while airborne in response to weather, delays or fuel state. It uses remaining fuel, actual winds and updated performance data to maintain a safe reserve.

A declared state indicating that the aircraft's fuel is such that it can only proceed to the planned destination and land with the final reserve intact. It does not yet constitute an emergency.

The altitude at or below which altimeters are set to local pressure and above which flight levels on standard pressure are used. It differs by country and affects vertical separation and performance planning.

The lowest flight level available for use above the transition altitude, ensuring at least the required separation. It is provided by air traffic control and varies with the local pressure setting.

The vertical and horizontal margin maintained between the aircraft's flight path and terrain, buildings or other obstructions. It is assured through published procedure gradients and performance calculations for departure and approach.

Carrying extra fuel from a cheaper airport to avoid higher prices elsewhere, at the cost of extra weight and burn. The decision compares the price saving against the performance penalty and landing mass limits.