Alphabet soup – the not so mysterious language of aviation revealed!

Aviation is full of MLAs (multi-letter acronyms!). This guide will be a living document, because on the average working day the aviation industry dreams up about 196 new acronyms, fortunately not all of which are related to actual flying. All intelligent suggestions for inclusions in this part of the guide will be welcome, but please don’t overdo it because there are thousands of them.

For the uninitiated we also define a few of the more frequently used aviation words and expressions.

Throughout our flying training guide, we’ll provide links to these pages for those who may be unfamiliar with all the expressions used in the guide.

Naturally, there will be omissions; for example the few “V-speeds” we define are only a handful of the more commonly used definitions, because there are almost 200 in use in aviation.

A/H Artificial horizon – A gyroscopic flight instrument that pictures the attitude of the aeroplane with relation to the horizon, indicating whether it is flying straight and level, banking left or right, climbing, or descending.  
A/P Autopilot – automatic pilot. Modern autopilots, especially those directed by sophisticated flight management systems, can perform virtually any task of which a pilot is capable, including zero-visibility landings.  
ADF Automatic direction finder, or radio compass, a navaid which allows an aircraft to home on an NDB or radio broadcast stations, which transmit on the same frequency band.  
ADS – B Automatic dependent surveillance – broadcast: An avionics system which transmits continuous data to the ATC system on an aircraft’s GPS position, altitude, and other flight data, so that the aircraft and data paint on the ATC radar.  
Ailerons The hinged control surfaces on the wing’s outboard trailing edge, which rotate the aircraft around its longitudinal axis, either to keep the wings level, or to roll the aircraft into and out of a turn.  
AIP Aeronautical Information Publication – detailed information provided by Air Services Australia and related to all aspects of air navigation and air space usage in Australian air space.  
Altimeter Instrument that sense air pressure and expresses it as altitude in feet above sea level, or above a set reference point that can be adjusted on the instrument by turning a knob.  
APF Australian Parachuting Federation  
ASI Airspeed indicator: Indicates the aircraft’s speed through the air. This has to be corrected to account for reduced air density altitude, converting it to true airspeed (TAS).
Asymmetric A term used to describe differences in the thrust delivered by two or more power plants, for example in the case of an engine failure in a multi-engined aircraft.
ATO Approved testing officer – a pilot holding delegated CASA approval to flight test applicants for various aviation qualifications.
ATPL Airline transport pilot licence.
ATSB Australian Transport Safety Bureau – the government body which investigates transport safety accidents and incidents.
AWAL Australian Warbirds Association Limited – The self-administration organisation that acts as a CASA delegate for former military aircraft (“warbird owner/operators.)
AWI Airworthiness inspector (CASA)
CARs Civil Aviation Regulations – older regulations now being transitioned into the newly named CASRs
CASA The Civil Aviation Safety Authority is responsible for the oversight of all Australian civil aviation activities in terms of flight operations, maintenance, repair and overhaul, aircraft manufacture and certification, licensing, registration and regulatory compliance. CASA delegates some of this oversight to organisations like AWAL, RA-Aus, GFA and APF.
CASRs Civil Aviation Safety Regulations – new regulations, some of which have already come into effect as part of the regulatory reform process.
CFI Chief flying instructor
CIR Command instrument rating – a qualification to fly as pilot in command in IFR flight.
CofA Certificate of airworthiness – every operational civil aircraft must have a current one.
CPL Commercial pilot licence – the minimum level of licence required if you’re flying “for hire and reward.”
CSU Constant speed unit – a component of a variable pitch propeller which alters the pitch to maintain the same rpm (within limits) when power is increased or decreased.
DG Directional gyro – a conventional flight instrument that displays aircraft heading information.
DME A VHF navigation system providing precise distance between an aircraft and a ground-based DME transponder.
Drag The aerodynamic force of resistance to forward flight, which in level flight is balanced by thrust.
Elevators Hinged control surfaces at the trailing edge of the tailplane, used to raise or lower than those and cause the aircraft to climb, descend, or fly straight and level.
FAA Federal Aviation Administration – the (USA) equivalent of CASA.
Flaps Aerodynamic devices fitted to the trailing edges of most aircraft wings, which effectively alter the shape of the wing, providing improved six lift at low speeds.
FOI Flying operations inspector (CASA)
G/S Groundspeed: The actual speed of the aircraft over the ground, taking into account the wind speed and direction.
GFA Gliding Federation of Australia – the body that administers all gliding activities including operations, maintenance and registration.
GLS GPS landing systems – precision runway approach systems providing the same guidance as ILS, but more reliable, especially when used in conjunction with augmentation systems.
GPS Global positioning system – satellite-based, and rapidly becoming the prime radionavigation device for anything that moves.
HF High frequency radio, a lower frequency range than VHF, used for ultra-long distance communications, still in use but gradually being superseded by a satellite-based communications.
HSI Horizontal situation indicator – a display which integrates the functions of the DG and VOR for easier azimuth guidance.
IAS Indicated airspeed (see ASI)
IFR Instrument flight rules – all the rules pertaining to flying by total reference to instruments. This is available only to aircraft equipped for IFR operations and pilots holding an instrument rating.
ILS Instrument landing systems, a VHF based radionavigation aid which provides lateral and vertical guidance during precision runway approaches. Gradually being replaced by satellite based GLS systems.
Lift The aerodynamic effect of airflow over a wing, which provides a force that in straight and level flight is equal and opposite to the aircraft’s weight.
MTOW Maximum takeoff weight – The maximum permitted takeoff weight of a particular aircraft including fuel, crew and payload.
MZFW The maximum permitted weight of a particular aircraft, above which any additional the weight may only be fuel.
NDB Non-directional beacon – continuously low-frequency transmitting ground navigation aid with which ADF-equipped aircraft can determine a bearing to the station. Expected eventually to become redundant as VHF navaids and satellite navigation take over.
PF Pilot flying – as distinct from support pilot (or PNF – pilot not flying – in a crew of two or more.
PNF Pilot not flying – the pilot or copilot designated to act as support pilot at any particular phase of the flight .
PPL Private pilot licence: Required for any non-commercial flying in CASA-registered aeroplane or helicopter.
RA-Aus Recreational Aviation Australia – the body that administers recreational aviation activities including operations, maintenance and registration. This includes all ultralight aircraft as well as owners who choose to register their light sport aircraft with RA-Aus.
RAAA Regional Aviation Association of Australia.
TAS True airspeed: Indicated airspeed corrected for ambient air pressure and temperature to reflect the aircraft’s actual airspeed.
Thrust The power provided by an aircraft’s engine/engines to provide acceleration and sustained forward movement.
Transponder An on-board radio or radar transmitter-receiver activated for transmission by reception of a predetermined signal from ATC radar, providing an accurate indication of aircraft position and other flight data to air-traffic controllers.
Turn & bank


An instrument which tells the pilots two things – the direction (left or right) and the rate of turn, and whether it is a balanced turn, i.e not a side-slipping or skidding.
UHF Ultra-high frequency – a higher communications frequency range used mostly by the military.
V1 The calculated speed above which a multi-engined aircraft is committed to continue the takeoff even if an engine fails.
V2 Takeoff safety speed – the calculated speed at which the aircraft can normally become airborne with one engine inoperative.
VFE Maximum flap extended speed
VFR Visual flight rules –The rules governing non–instrument flight, i.e. solely by reference to visual cues.
VHF Very high frequency, the radio frequency range in commonest use in ATC communications and several radionavigation aids.
VLO Maximum landing gear operating speed – the maximum speed at which it is safe to extend or retract the landing gear on a retractable gear aircraft
VMCA The airspeed below which airflow over the flight controls does not provide sufficient control authority to maintain stable controlled flight with the critical engine inoperative.
VNE Never exceed speed.
VOR VHF omni bearing range – provides bearing information relative to the VOR station and magnetic North.
VS Stall speed – the nominated airspeed below which the angle of attack of a particular aircraft degrades its aerodynamic lift to a point where it cannot sustain normal flight.
VSI Vertical speed indicator, which indicates an aircraft rate of climb or descent in feet per minute.
Weight The actual total weight of an aeroplane at any given time during flight, which in straight and level flight is equally balanced by the lift developed by the wings.















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