Reference
PPL Glossary
A plain-English glossary of the aviation terms and acronyms you will meet across all seven CAAS Private Pilot Licence theory subjects. The terms are grouped by subject so you can revise one area at a time, and each definition is written at private-pilot theory level. The concepts here are general ICAO and aerodynamic principles; always confirm any Singapore-specific figures against the current CAAS syllabus.
Air Law & airspace
The rules of the air, the structure of the sky, and the documents and clearances that keep everyone separated.
- ICAO
- International Civil Aviation Organization — the United Nations agency whose Annexes set the global standards on which national rules, including the CAAS syllabus, are based.
- Airspace classes (A–G)
- ICAO divides airspace into classes A to G. Higher classes (A, C) carry more control and stricter entry and separation rules; lower classes (F, G) are uncontrolled. The class determines whether you need a clearance, what services you receive, and the visibility and cloud-clearance minima that apply.
- VFR
- Visual Flight Rules — flying by reference to the horizon and outside visual cues, only when the weather meets the minimum visibility and distance-from-cloud requirements (VMC) for the airspace you are in.
- IFR
- Instrument Flight Rules — flying primarily by reference to the instruments, used when conditions are below VMC or when required by the airspace or procedure.
- VMC
- Visual Meteorological Conditions — weather good enough (in terms of visibility and distance from cloud) to fly under VFR.
- NOTAM
- Notice to Airmen — a time-critical notice about hazards, closures, or changes (a closed runway, a temporary restricted area, an unserviceable navaid) that a pilot must check before flight.
- ATZ / CTR
- An Aerodrome Traffic Zone is the protected airspace immediately around an aerodrome; a Control Zone (CTR) is controlled airspace from the surface upward around a busier airport. Both require specific communication or clearance to enter.
Meteorology
The weather products and pressure concepts every pilot decodes before and during a flight.
- METAR
- A routine, coded observation of the actual weather at an aerodrome at a given time — wind, visibility, weather, cloud, temperature, dew point and pressure. It tells you what the weather is doing right now.
- TAF
- Terminal Aerodrome Forecast — a coded forecast of expected weather at an aerodrome over a defined period. Where the METAR reports the present, the TAF predicts the near future.
- QNH
- The altimeter sub-scale setting that makes the altimeter read height above mean sea level (altitude). With QNH set, the altimeter reads aerodrome elevation when you are on the ground.
- QFE
- The altimeter setting that makes the altimeter read height above a specific datum, usually the aerodrome — so it reads zero on the runway. Useful in the circuit for reading height above the field.
- QNE / standard pressure
- Setting the sub-scale to the standard 1013.25 hPa so the altimeter shows a flight level. Used above the transition altitude so all aircraft share a common pressure reference.
- ISA
- International Standard Atmosphere — an agreed model atmosphere (15 °C and 1013.25 hPa at sea level, with a fixed lapse rate) used as a reference for performance and altimetry calculations.
- Dew point
- The temperature to which air must be cooled, at constant pressure, for it to become saturated. When the air temperature and dew point converge, expect cloud, mist or fog.
- Front
- The boundary between two air masses of different temperature and humidity. Warm and cold fronts bring characteristic sequences of cloud, precipitation and wind shifts.
Navigation
The headings, errors and rules of thumb behind getting from A to B and knowing where you are.
- Variation
- The angle between true north and magnetic north at a given place. You apply variation to convert a true heading into a magnetic heading.
- Deviation
- The small compass error caused by magnetic influences within the aircraft itself. You apply deviation to convert a magnetic heading into a compass heading. The memory aid TVMDC (True, Variation, Magnetic, Deviation, Compass) captures the running order.
- 1-in-60 rule
- A navigation rule of thumb: being one mile off track after 60 miles equals roughly one degree of track error. It lets you estimate and correct heading errors quickly in the air.
- Dead reckoning
- Working out your position from a known starting point using heading, airspeed, wind and elapsed time, rather than from external fixes.
- Track vs heading
- Track is the path the aircraft actually follows over the ground; heading is the direction the nose points. The difference between them is the drift caused by wind.
- VOR / NDB / DME
- Ground-based radio navigation aids: a VOR gives a bearing to or from a station, an NDB is a non-directional beacon you home to with the ADF, and DME gives slant-range distance from a station.
Principles of Flight
The aerodynamics that explain why and how an aeroplane flies — and stops flying.
- Angle of attack (AoA)
- 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 airflow separates and the wing stalls — regardless of airspeed or attitude.
- Stall
- The loss of lift that occurs when the critical angle of attack is exceeded and airflow separates from the upper surface of the wing. A stall is about angle of attack, not simply low speed.
- Four forces
- Lift, weight, thrust and drag. In steady level flight lift balances weight and thrust balances drag; changing one requires balancing the others.
- Load factor
- The ratio of lift to weight, expressed in g. It rises in turns and pull-ups, increasing the stall speed and the structural load on the airframe.
- Centre of gravity (CG)
- The point through which the aircraft’s weight acts. It must stay within published forward and aft limits for the aircraft to remain controllable and stable.
- V-speeds
- Standardised reference speeds such as Vs (stall), Vx (best angle of climb), Vy (best rate of climb) and Vne (never-exceed). Knowing them is essential for safe handling and performance planning.
Human Performance
How the body and mind cope — and sometimes fail to cope — with the flight environment.
- Hypoxia
- A deficiency of oxygen reaching the body’s tissues, most commonly from reduced pressure at altitude. Early signs include impaired judgement and euphoria, which makes it dangerous because the sufferer may not notice.
- TUC
- Time of Useful Consciousness — the period after the oxygen supply is cut or pressure drops during which a pilot can still take meaningful corrective action. It shortens sharply with altitude.
- Hyperventilation
- Over-breathing that flushes out too much carbon dioxide, causing dizziness, tingling and anxiety. It is often triggered by stress and can mimic hypoxia.
- Spatial disorientation
- A false sense of attitude, position or motion that arises when the senses are deprived of reliable visual references, for example in cloud. Trusting the instruments over bodily sensations is the defence.
- IMSAFE
- A personal pre-flight fitness checklist — Illness, Medication, Stress, Alcohol, Fatigue, Emotion (or Eating) — used to decide honestly whether you are fit to fly.
Aircraft General Knowledge & Radio Telephony
The systems that keep the aircraft running and the standard language that keeps the radio clear.
- Carburettor icing
- Ice that forms in the carburettor from the temperature drop as fuel vaporises and air accelerates, restricting airflow and causing a power loss. It can occur even in warm, humid conditions; carburettor heat is the cure.
- Magneto
- An engine-driven generator that produces the high-voltage spark for the ignition independently of the aircraft’s electrical system. Light aircraft typically carry two for redundancy.
- Pitot-static system
- The system that feeds ram and static air pressure to the airspeed indicator, altimeter and vertical speed indicator. A blockage in either source produces characteristic, and potentially dangerous, instrument errors.
- MAYDAY
- The spoken distress signal, said three times, used when an aircraft is threatened by grave and imminent danger and requires immediate assistance. It takes absolute priority on the frequency.
- PAN-PAN
- The spoken urgency signal, said three times, used for a serious situation that does not yet pose immediate danger to life — for example a minor technical problem you want to flag without declaring an emergency.
- Phonetic alphabet
- The ICAO spelling alphabet (Alpha, Bravo, Charlie …) used to spell out letters unambiguously over the radio, where similar-sounding letters could otherwise be confused.
- Squawk / transponder code
- The four-digit code set on the transponder so air traffic control can identify the aircraft on radar. Reserved codes signal emergencies: 7700 (general), 7600 (radio failure) and 7500 (unlawful interference).
Turn definitions into recall
Reading a definition is not the same as being able to retrieve it under exam pressure. Take a quick practice quiz to see which of these terms you can actually apply.
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