CARC ATPL Theory key terms

The maximum speed by which a rejected take-off must be initiated; above it the aircraft must continue to fly after an engine failure. It is chosen so that the accelerate-stop and accelerate-go distances both fit the runway.

The speed to be attained by the time the aircraft reaches 35 ft above the take-off surface with one engine inoperative, and maintained to at least 400 ft. It guarantees minimum climb gradient and directional control.

The lowest speed at which directional control can be maintained with a sudden failure of the critical engine, the other engine at take-off thrust, and only aerodynamic controls used. It constrains V1 from below.

The minimum speed at which the aircraft remains controllable with the critical engine inoperative, the other at take-off thrust, gear up and maximum 5 degrees bank towards the live engine. It sets the floor for V2.

The runway length at which the accelerate-stop distance equals the accelerate-go distance, giving the shortest field from which a given take-off mass is permitted. Longer runways allow the take-off mass to be limited by climb or obstacle clearance instead.

A defined area beyond the runway end, under the operator's control, free of obstacles and sloping upward no more than 1.25 percent, which may be included in the take-off distance available to 35 ft. It cannot be used for ground run.

A rectangular area beyond the runway end, at least as wide as the runway, prepared so that an aircraft can be stopped on it after an abandoned take-off without structural damage. It adds to the accelerate-stop distance available.

On a multi-engine propeller aircraft, the engine whose failure produces the most adverse effect on performance and control, usually the one whose thrust acts furthest from the centreline. It determines Vmcg and Vmca in the certification rules.

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

The angle of attack at which the wing reaches maximum lift coefficient and stalls. It is essentially constant for a given aerofoil regardless of mass, speed, bank angle or density altitude.

Drag caused by the generation of lift, arising from wingtip vortices and the rearward inclination of the lift vector. It is greatest at high angle of attack and low speed, and is reduced by higher aspect ratio.

The ratio of the square of the wingspan to the wing area. High aspect ratio wings produce less induced drag for a given lift, which is why gliders and long-range airliners use slender wings.

The ratio of total lift to weight, expressed in g. It increases in level turns as one over the cosine of bank angle, raising the stall speed by the square root of that factor.

The lowest indicated airspeed at which the aircraft can be flown without exceeding the critical angle of attack in straight and level flight at a given mass. It rises with mass and with load factor.

The ratio of true airspeed to the local speed of sound. As it approaches 1, shock waves and flow separation produce Mach buffet and control changes; exceeding Mmo risks structural and handling problems.

The free-stream Mach number at which airflow somewhere on the airframe first reaches the speed of sound locally. Beyond it drag rises sharply and buffet begins, limiting high-altitude cruise speed.

The narrow band of altitude and speed where the low-speed stall margin and the high-speed Mach buffet margin converge. At high altitude the usable speed range between them becomes very small, demanding smooth and precise handling.

The upward angle of the wings from root to tip. It creates lateral stability by generating a sideslip-induced rolling moment that tends to level the wings after a disturbance.

A coupled oscillation in yaw and roll, usually with a short roll period, caused by strong lateral stability combined with weak directional stability. It is damped by a yaw damper, which is required on swept-wing aircraft.

An automatic system that senses yaw rate and deflects the rudder to oppose unwanted yawing, suppressing Dutch roll. It is typically part of the autopilot and must be serviceable for dispatch where required.

The maximum permitted difference between cabin pressure and outside ambient pressure, limited by the structural strength of the fuselage. It determines the maximum cabin altitude that can be maintained at a given flight level.

The equivalent pressure altitude inside the pressurised cabin. It is normally kept below 8,000 ft; if it exceeds about 10,000 ft, oxygen masks deploy automatically and the crew must descend.

A valve that regulates the rate at which air leaves the pressurised cabin, thereby controlling cabin altitude and rate of climb or descent. It opens fully during depressurisation and is modulated by the pressurisation controller.

The period after loss of oxygen at a given altitude during which a person can still take corrective action before becoming incapacitated. It falls from several minutes at 25,000 ft to seconds above 40,000 ft.

A deficiency of oxygen reaching body tissues. Symptoms include euphoria, impaired judgement and cyanosis; because judgement is affected early, the sufferer may not recognise the condition and needs prompt oxygen and descent.

Excessive breathing rate or depth that washes out carbon dioxide, causing dizziness, tingling and muscle spasms. Its symptoms resemble hypoxia, so oxygen and controlled breathing are the standard response.

A false perception of position, attitude or motion relative to the earth, caused by misleading vestibular and visual cues in flight without external visual reference. Recovery depends on trusting instruments rather than sensations.

A false sensation of pitching up during acceleration or down during deceleration, caused by the otolith organs responding to linear acceleration as if it were gravity. It can lead to inappropriate pitch input after take-off or go-around.

The inner-ear organs, semicircular canals and otoliths, that sense angular and linear acceleration. They cannot distinguish acceleration from gravity and provide unreliable attitude information without visual reference.

The altimeter subscale setting that, when set, causes the altimeter to indicate elevation above mean sea level at the aerodrome. It is used for flight below the transition altitude and for terrain clearance.

The standard altimeter setting of 1013.25 hPa, used at and above the transition level so that all aircraft share a common pressure datum. The resulting indication is called flight level.

The altitude above the aerodrome at which aircraft change from QNH to standard pressure when climbing. It is published for each aerodrome and may differ between locations in the same flight information region.

The lowest flight level available for use above the transition altitude, chosen so that the transition layer is at least 1,000 ft. It varies with the aerodrome QNH and is given by air traffic control.

The leading edge of a retreating cold air mass that undercuts warm air, producing a steep frontal surface. It brings rapid passage, cumulonimbus cloud, heavy showers, squalls, turbulence and a marked wind veer.

A line of active thunderstorms along or ahead of a fast-moving cold front, often hundreds of kilometres long. It produces severe turbulence, hail, strong gusty winds and wind shear hazardous to all aircraft.

A change of wind speed or direction over a short distance, horizontally or vertically. Low-level shear on approach or departure can cause sudden airspeed and lift changes and is a major cause of accidents.

A small, intense downdraught that spreads out on reaching the ground, producing a headwind then tailwind reversal over a short distance. It can cause performance loss close to the ground and is detected by airborne or ground weather radar.

A circle on the earth's surface whose plane passes through the earth's centre, dividing it into two equal halves. The shorter arc between two points is the shortest surface distance and the basis of great-circle track.

A line on the earth's surface crossing every meridian at the same angle. It plots as a straight line on a Mercator chart but is longer than the great circle between the same two points.

The direction of the great-circle path at the point of departure, measured from true north. Because the track changes continuously along the route, it must be recomputed at each waypoint.

A flight instrument that displays the ratio of true airspeed to local speed of sound, derived from pitot-static pressure and static pressure. It warns of exceeding Mmo and shows the high-speed buffet margin.

A surveillance system in which the ground interrogator triggers a transponder reply carrying identity and altitude. It provides range and bearing plus Mode C or Mode S data, unlike primary radar which relies on skin reflection.

The four-digit octal code set on the transponder, assigned by air traffic control, which identifies the aircraft on secondary radar. Codes 7500, 7600 and 7700 signify unlawful interference, radio failure and emergency.

Traffic alert and collision avoidance system that interrogates nearby transponders and displays traffic. It issues traffic advisories and resolution advisories, the latter requiring prompt manoeuvre in the direction commanded.

A racetrack manoeuvre flown to absorb delay, with standard right-hand turns and a one-minute inbound leg at or below 14,000 ft. Entry depends on the aircraft's heading relative to the inbound track.

The altitude on a precision approach at which a missed approach must be initiated if the required visual reference has not been established. It is referenced to mean sea level, unlike decision height.

The lowest altitude permitted on a non-precision approach before the required visual reference is acquired. Descent below it is not allowed unless the runway environment is clearly visible.

The point on a non-precision approach at which a missed approach must be started if the required visual reference has not been established. It is defined by distance, a fix or a navigation aid.

Rules permitting twin-engine aircraft to fly routes more than a specified time from an adequate alternate aerodrome, subject to approved reliability and equipment. The diversion time, such as 120 or 180 minutes, is stated in the approval.