Oman CAA ATPL(A) Theory key terms

The speed by which a failure of the critical engine must be recognised so the pilot can either continue the take-off or stop the aircraft within the remaining runway. It is chosen before flight and drives take-off performance calculations.

The runway length needed to accelerate to V1 with all engines operating, then lose the critical engine and bring the aircraft to a full stop. It is one of the limiting cases used to establish required take-off distance.

The runway length at which the accelerate-stop distance equals the one-engine-inoperative take-off distance, so neither stopping nor continuing is penalised further. It represents the shortest field for a given weight and conditions.

The certified forward and aft limits of aircraft centre of gravity position, expressed as a range for each weight. Operating outside it invalidates handling, performance and structural assumptions.

The mass of the aircraft with all its permanently installed equipment, unusable fuel and full operating fluids, but without crew, passengers, baggage or usable fuel. It is the starting figure for load sheets.

The mass of the aircraft including crew, passengers, baggage and cargo but excluding usable fuel. It must remain below a certified maximum because it governs wing bending and landing loads.

The highest mass at which the aircraft is certified to begin the take-off run, limited by structure, climb performance and brake energy. It may be further reduced by runway, obstacle or temperature conditions on the day.

The chord of a reference rectangular wing having the same area and pitching moment characteristics as the real wing. CG position is often quoted as a percentage of this chord.

The angle between the wing chord line and the relative airflow approaching it. Lift rises with angle of attack until the critical angle is exceeded and the airflow separates.

The angle of attack at which airflow begins to separate from the upper surface and lift reaches its maximum. Exceeding it causes a stall at any speed, weight or attitude.

Drag created as a by-product of lift, caused by the rearward inclination of the lift vector and wingtip vortices. It increases with angle of attack and decreases with higher speed.

Drag that does not contribute to lift, made up of form drag and skin friction. It rises with the square of airspeed, unlike induced drag which falls as speed increases.

The free-stream Mach number at which airflow somewhere on the aircraft first reaches the local speed of sound. Beyond it shock waves and drag rise begin to appear.

A nose-down pitching tendency at high Mach numbers caused by rearward movement of the centre of pressure and reduced downwash on the tailplane. It can lead to steepening dive unless corrected.

The line on a speed-altitude diagram separating smooth airflow from the onset of airframe buffet. It marks the practical high-altitude speed limit before stall or shock stall.

A device giving an audible or tactile alert before the critical angle of attack is reached, typically a reed horn or stick shaker. It warns of impending loss of lift independent of airspeed.

The altitude at which an aircraft in a given configuration can no longer climb faster than a specified small rate, commonly 100 feet per minute for jets. It reflects engine and wing performance limits.

The pressure altitude corrected for non-standard temperature, representing the altitude the aircraft's performance feels. High temperature or low pressure raises it and degrades climb and take-off performance.

The altitude indicated when the altimeter subscale is set to the standard datum of 1013.25 hPa. It is used above the transition level and for performance calculations.

The lowest flight level available for use above the transition altitude, at which pilots change the altimeter from local pressure to standard pressure. Its value varies with the regional pressure setting.

A surface of constant atmospheric pressure related to the standard datum of 1013.25 hPa and expressed in hundreds of feet. Aircraft above the transition level are separated using flight levels.

A rule allowing aircraft to be separated by 1000 feet instead of 2000 feet between specified flight levels in designated airspace, provided altimetry and equipment requirements are met.

The convention assigning magnetic cruising levels according to track: easterly tracks use odd levels and westerly tracks use even levels. It provides vertical separation between opposing traffic flows.

The altimeter subscale setting that makes the instrument read elevation above mean sea level when on the ground at that location. It is used for approach and landing.

The altimeter subscale setting that makes the instrument read zero on the ground at the aerodrome reference point. It indicates height above that point rather than altitude.

A magnetic bearing from a VOR station, identified by the phase difference between reference and variable signals. An aircraft flying outbound on a radial has that radial as its track from the station.

Slant range in nautical miles from the aircraft to a distance measuring equipment transponder, derived from signal round-trip time. It reads slightly greater than ground distance when overhead the station.

The vertical guidance beam of an instrument landing system, typically set at about three degrees, giving the aircraft a descent profile to the runway touchdown zone. It is paired with localiser lateral guidance.

The lateral guidance component of an instrument landing system, transmitting on a frequency in the 108 to 112 MHz band. It defines the extended runway centreline for the approach.

The altitude on a precision approach at which a missed approach must be initiated if the required visual reference is not established. It is referenced to the altimeter with QNH set.

The point on a non-precision approach, defined by distance or a navigation aid, beyond which a missed approach must be flown if the runway is not in sight. It is published on the approach chart.

The largest circle that can be drawn on a sphere, its plane passing through the centre. The shortest path between two points on the Earth's surface lies along a great circle.

A line crossing every meridian at the same angle, appearing straight on a Mercator chart. It is a constant-heading track but not the shortest distance between two points.

The angle at which meridians meet toward the pole, equal to the change of longitude multiplied by the sine of the latitude. It explains why a constant heading does not follow a great circle.

A condition in which body tissues receive insufficient oxygen, causing impaired judgement, euphoria and eventually unconsciousness. Its insidious onset makes self-detection unreliable, especially at high cabin altitude.

The period after loss of oxygen supply during which a person can still take effective corrective action before becoming incapacitated. It shortens rapidly as cabin altitude increases.

A mistaken perception of the aircraft's position or motion relative to the Earth, usually when visual references are lost and the pilot misinterprets vestibular cues. Instrument reference is the reliable defence.

A false sensation of pitching up during forward acceleration, or pitching down during deceleration, caused by the otolith organs responding to linear acceleration. It is a hazard on take-off and go-around.

The altitude at which the air temperature falls to zero degrees Celsius. Above it, visible moisture may exist as supercooled water droplets that can cause airframe icing.

Liquid water droplets remaining unfrozen at temperatures below zero degrees Celsius. On impact with an aircraft surface they freeze rapidly, forming clear or rime ice.

Rough, opaque ice formed when small supercooled droplets freeze almost instantly on impact, trapping air. It is brittle and may be removed by de-icing boots.

Ice forming in a carburettor due to fuel vaporisation and venturi pressure drop cooling the mixture, most likely at temperatures between about minus ten and plus twenty degrees Celsius with high humidity.

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

A small, intense downdraught spreading out at the surface, producing a headwind then tailwind change over a short distance. It is a severe hazard during approach and departure.

Exhaust gas temperature, a key limit indicating the thermal stress on turbine components. It is monitored to keep the engine within certified limits during start, take-off and climb.

The ratio of turbine discharge pressure to compressor inlet pressure, used as a thrust indication on some turbojet and turbofan engines. It reflects thrust output more directly than fan speed alone.

The system supplying total and static pressure to the airspeed indicator, altimeter and vertical speed indicator. Blockages or leaks cause characteristic and potentially misleading instrument errors.

The property of a spinning rotor to maintain its axis fixed in space unless acted on by an external torque. It is the basis of attitude and heading indicators.

The apparent tilting of a spinning gyroscope's axis at right angles to an applied force. It is exploited in rate gyros and causes real and apparent drift errors in heading indicators.

The angle between the aircraft's flight path and the horizontal, determined by the excess of thrust over drag relative to weight. It governs obstacle clearance, while rate of climb governs time to height.

The vertical speed of the aircraft, determined by the excess power available over power required. Unlike angle of climb, it depends on the speed flown and engine power.

A mandatory instruction issued by a state authority requiring inspection, modification or limitation on aircraft, engines or equipment to correct an unsafe condition. Compliance is legally required for continued operation.

A document confirming that an individual aircraft conforms to its certified type design and is safe to operate within specified limits. It remains valid only while maintenance and directive requirements are met.

An approved document listing items of equipment that may be inoperative while the aircraft is still dispatched under specified conditions and limitations. It must not be less restrictive than the master minimum equipment list.