BDCA CPL Knowledge Exam key terms

The speed shown on the airspeed indicator, derived from the pressure difference between pitot and static sources. It is uncorrected for instrument error, installation error or air density.

Indicated airspeed corrected for instrument and position (installation) error. It is close to true airspeed at sea level in standard conditions but diverges at altitude.

The actual speed of the aircraft through the surrounding air mass. It equals calibrated airspeed corrected for air density, so it rises with altitude for a given IAS.

The speed of the aircraft relative to the ground, found by combining true airspeed with the wind component along the flight path. It determines time en route and fuel used.

The aircraft plumbing that supplies ram air pressure from the pitot tube and ambient static pressure from static ports to the airspeed indicator, altimeter and vertical speed indicator.

The pressure value set on the altimeter subscale so that on the ground it indicates elevation above mean sea level. It is used below the transition altitude.

The fixed subscale setting of 1013.25 hPa or 29.92 inHg used at and above the transition level, giving pressure altitude and a common reference for all aircraft.

The altitude at or below which the altimeter is set to local QNH. Above it, pilots set standard pressure, and the change is made on climb and reversed on descent.

The lowest flight level available for use above the transition altitude. It is chosen so that adequate vertical separation exists between aircraft above and below the transition layer.

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

The angle of attack at which airflow separates from the wing and lift reaches its maximum. A wing always stalls at this angle regardless of speed, weight or attitude.

Drag created as a by-product of lift, caused by high pressure beneath the wing spilling around the tips to form vortices. It is greatest at low speed and high angle of attack.

The ratio of total lift to the aircraft's weight, expressed in g. It increases in turns and manoeuvres, raising stall speed and structural stress on the airframe.

The minimum airspeed at which the aircraft can maintain level flight before reaching the critical angle of attack. It increases with weight, load factor and altitude.

The point through which the total weight of the aircraft is considered to act. Its position affects stability and control and must remain within approved forward and aft limits.

Pressure altitude corrected for non-standard temperature. High density altitude reduces engine power, propeller thrust and lift, lengthening takeoff and landing distances.

The altitude indicated when the altimeter subscale is set to standard pressure. It is the basis for performance charts and for computing density altitude.

Disturbed air left behind an aircraft, dominated by wingtip vortices that are strongest when the generating aircraft is heavy, clean and slow. It poses a hazard to following aircraft.

A condition in which body tissues receive insufficient oxygen. In aviation it commonly results from high altitude, causing impaired judgement, euphoria and eventually unconsciousness.

The period after loss of oxygen supply during which a person can still perform useful tasks before becoming incapacitated. It shortens rapidly as altitude increases.

Rapid or deep breathing that lowers carbon dioxide in the blood, causing dizziness, tingling and confusion. Its symptoms resemble hypoxia but improve with controlled slower breathing.

A pilot's mistaken perception of the aircraft's position or motion, often caused by conflicting vestibular and visual cues in poor visibility. It can lead to loss of control.

A false sensation of pitching up or down caused by linear acceleration or deceleration, typically during takeoff or go-around. The pilot may wrongly push or pull the control column.

Weather conditions in which visibility, cloud and distance from cloud require flight under instrument flight rules. Pilots must rely on instruments rather than outside visual references.

Rules under which a pilot may operate primarily by outside visual reference, provided specified visibility and cloud separation minima are met. A clearance is required in controlled airspace.

A lettered category (A to G) defining the services, separation and clearance requirements within a volume of airspace. Classes determine whether VFR flight is permitted and what equipment is needed.

Airspace of defined dimensions within which air traffic control service is provided to flights in accordance with the airspace classification. Clearances are normally required to enter.

An authorisation for an aircraft to proceed under conditions specified by an air traffic control unit. It does not relieve the pilot of responsibility for safety or terrain clearance.

The pilot's repetition to the controller of a clearance or instruction to confirm it has been correctly received and understood. It is mandatory for safety-related instructions.

The standard set of spoken code words, such as Alfa and Bravo, used to identify letters clearly over the radio. It reduces misunderstanding caused by similar-sounding letters.

A four-digit octal code set on the transponder to identify the aircraft on secondary surveillance radar. Controllers assign discrete codes and may require specific emergency codes.

An airborne receiver and transmitter that replies to radar interrogations with identification and altitude information. It supports air traffic control surveillance and collision avoidance systems.

A radar system that interrogates aircraft transponders and displays the returned identification and altitude data. It gives controllers more information than primary radar alone.

A ground navigation beacon that transmits signals allowing an aircraft to determine the magnetic bearing from the station. It provides track guidance along defined airways.

A radio navigation aid that measures slant range from the aircraft to a ground station by timing signal exchanges. It is often paired with VOR or ILS installations.

The vector relationship between true airspeed, wind velocity and groundspeed that determines heading and drift. Pilots use it to calculate the heading needed to track a desired course.

A predetermined manoeuvre keeping an aircraft within a specified airspace while awaiting further clearance. It uses timed or distance legs and standard turns to remain predictable.

Ice forming in a carburettor due to fuel vaporisation and low pressure cooling, which can occur at outside temperatures well above freezing. It causes rough running and power loss.

The altitude at which the air temperature is zero degrees Celsius. Above it, visible moisture can cause airframe icing, and it is a key element of flight planning.