BDCA PPL Knowledge Exam key terms

A mandatory instruction issued by an aviation authority requiring inspection, repair, or modification of an aircraft or component to correct an unsafe condition. Compliance is legally required, and the directive is normally accomplished within a stated time or operating limit.

A document confirming that an individual aircraft conforms to its approved type design and is safe to operate. It remains valid only while mandatory maintenance, inspections, and airworthiness directives are complied with.

Weather conditions in which visibility and distance from cloud equal or exceed specified minimum values, allowing flight under visual flight rules. When these minima are not met, the flight must operate under instrument flight rules or not at all.

A set of regulations governing flight by visual reference to the ground, including weather minima, cloud clearance, and see-and-avoid responsibility. The pilot must remain clear of cloud and navigate by outside reference unless a specific clearance permits otherwise.

Regulations requiring flight by reference to instruments, with navigation and separation normally provided through air traffic control. Pilots must hold an instrument rating and follow clearances, reporting points, and prescribed procedures.

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

A four-digit octal code entered into the aircraft transponder so that air traffic control radar displays identify the flight. Codes are assigned by controllers, and specific codes signal emergencies, radio failure, or unlawful interference.

An airborne radio device that receives a radar interrogation and replies with an identification code and, in Mode S or C, pressure altitude. It allows controllers to identify aircraft and detect altitude discrepancies.

The point at which the aircraft's total weight is considered to act. Its position must remain within a certified range for safe control, stability, and performance in all phases of flight.

The process of calculating total aircraft mass and its distribution so that weight and center of gravity limits are respected. It uses weighed or assumed masses, arms, and moments for the empty aircraft, fuel, crew, passengers, and baggage.

The horizontal distance from a reference datum to a specified mass item, used to calculate its moment. Dividing total moment by total mass gives the center of gravity position.

The greatest mass at which an aircraft is certified to begin the take-off run. It may be limited by structural strength, runway length, climb performance, or obstacle clearance, whichever is most restrictive.

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

The altitude indicated by an altimeter set to the standard pressure of 1013.25 hectopascals. It is used for flight levels and performance calculations rather than for terrain clearance.

The local pressure value set on an altimeter so that it indicates height above a specified reference, usually mean sea level. Correct setting is essential for terrain clearance and for maintaining assigned altitudes.

The ratio of lift generated to the aircraft's weight. It increases in turns and maneuvers, raising stall speed and structural stress, and is limited by the aircraft's certified design category.

The angle between the wing chord line and the oncoming relative airflow. Increasing it raises lift up to the critical angle, beyond which the airflow separates and the wing stalls.

The lowest airspeed at which an aircraft can maintain level flight before exceeding its critical angle of attack. It increases with weight, load factor, and altitude, and is independent of airspeed alone.

Drag resulting from the generation of lift, caused by airflow deflection and wingtip vortices. It increases with angle of attack and decreases as airspeed rises, making it dominant at low speed.

The upward angle of the wings relative to the horizontal. It provides lateral stability by creating a rolling moment that tends to level the aircraft after a disturbance.

A system of pressure sources and lines supplying the airspeed indicator, altimeter, and vertical speed indicator. Blockages cause erroneous indications, so pilots must recognize symptoms and use alternate sources.

A simple instrument indicating magnetic heading, subject to turning and acceleration errors and to deviation from aircraft magnetic fields. It is used to check and reset the gyroscopic heading indicator.

Ice formation in the carburetor caused by fuel vaporization and pressure drop cooling, occurring even in warm, humid air. It progressively reduces engine power and is countered by applying carburetor heat.

A condition in which body tissues receive insufficient oxygen. Symptoms include euphoria, impaired judgment, and headache, and they may go unnoticed, so oxygen use and descent are essential at altitude.

A pilot's mistaken perception of aircraft attitude or motion, often caused by conflicting sensory inputs in poor visual conditions. Recovery depends on trusting instruments rather than bodily sensations.

Abnormally rapid or deep breathing that lowers blood carbon dioxide and causes dizziness, tingling, and faintness. It is easily confused with hypoxia, so treatment involves slowing the breathing rate.

A line on a weather chart joining places of equal mean sea level pressure. Closely spaced isobars indicate strong winds, and their pattern reveals highs, lows, ridges, and troughs.

The altimeter setting that makes an altimeter read height above mean sea level at the reporting station. It is used below the transition altitude to keep altitude references consistent with terrain elevations.

A cumulonimbus cloud producing lightning, heavy rain, hail, gusty winds, and severe turbulence. It forms where warm, moist, unstable air rises, and aircraft should avoid it by a wide margin.

A rapid change of wind speed or direction over a short distance, often near fronts, thunderstorms, or inversions. It can cause sudden airspeed loss close to the ground and is a serious hazard on approach.

The shortest path between two points on the surface of a sphere, lying in a plane through the sphere's center. It is the basis of long-distance navigation and appears curved on flat maps.

A line crossing all meridians at the same angle, appearing straight on a Mercator chart. It is easy to follow with a constant heading but is not the shortest route over long distances.

The angular difference between true north and magnetic north at a given location, changing slowly over time. It is applied when converting between true and magnetic directions on charts and in navigation.

A ground-based radio navigation aid transmitting signals that let an aircraft determine a bearing to or from the station. Distance is provided separately by DME or by crossing radials.

A satellite constellation providing position, velocity, and time worldwide. Aviation receivers support area navigation, but signals can be degraded or lost, so alternate means should be available.

A certification confirming that specified maintenance has been completed and the aircraft is fit for return to service. It must be issued by authorized personnel and kept in the aircraft records.

A systematic external and internal check of the aircraft before flight to detect defects, security issues, and configuration errors. It confirms fuel quantity, control freedom, and that required documents are on board.

A radio message giving an aircraft's location, time, altitude, and next estimated position to air traffic control. It supports separation in areas without radar coverage and confirms progress along the route.

The repetition by a pilot of a controller's clearance or instruction to confirm it was received correctly. It is required for safety-critical items such as runway, altitude, and heading instructions.