Some definitions part 2

M

Mag: Magnetic
Magnetic course: Intended horizontal direction, measured in degrees clockwise from the magnetic north.
Mach number: Ratio of true airspeed to the speed of sound. Mach 1 is the speed of sound at sea level. Its value is approximately 760 mph.
Manufacturer: Aircraft builder, such as Airbus, Boeing, Embraer, etc.
Mayday: The ultimate international radio distress call, indicating imminent danger to the life of the occupants onboard and requiring immediate assistance. Its slightly less prioritary equivalent is Pan Pan*. The anecdote says it comes from a French pilot who said over the radio "Venez m'aider" ("help me") to an English-speaking controller, who only understood "Mayday".
MLS: Microwave Landing System. A microwave-based instrument approach system intended to replace ILS in the 1990s and claimed to offer a number of advantages such as the ability to fly segmented and curved precision approaches.
MSL: Mean Sea Level
MSN: Manufacturer Serial Number. Internal number, for the use of the manufacturer* (see above), identifying a particular aircraft within the same model.
MTOW Maximum Take-Off Weight


N

NDB: Non-Directional Beacon. A medium-frequency navigational aid which transmits non-directional signals, superimposed with a Morse code identifier and received by an aircraft's ADF*.
NM: Nautical Miles.
Non-Revenue: Passenger flying free of charge, on a standby* basis, by presenting an airline/aviation employee pass. Non-Revenue passengers may or may not be on duty, therefore this expression also applies to repositioning* crew members. Also known as Non-Rev for short.
No-Show: Passenger with a confirmed reservation, who failed to check baggage or to present at the gate on time.
NOTAM: Notices To Airmen. Issued by the FAA or its equivalent to inform pilots of new or changed aeronautical facilities, services, procedures, or hazards, temporary or permanent.
NTSB: National Transportation Safety Board. U.S. government organisation in charge of investigating in the case of an accident. Its United Kingdom equivalent is the Air Accident Investigation Branch (AAIB) of the Department of Transport.


O-P

OAT: Outside Air Temperature
Pan Pan: International radio urgency call. It usually indicates a threat to the safety of an aircraft or its passengers. It is, however, less urgent than Mayday*. Pan Pan comes from the French word "Panne" which means "failure".
Pax: Passengers
Payload: Revenue passengers and/or cargo, or more specifically their combined weight.
PNR: Passenger Name Record. Another word for Reservation.
POB: Number of Persons On Board. Also SOB, Souls On Board.
POH: Pilot's Operating Handbook. It is the aircraft's "owner's manual".
psi: Pounds per Square Inch. Unit of measure for pressure.


Q
The following glossary terms are called Q-codes. It is a code system developed when air-to-ground communication was made with wireless telegraphy, reducing many routine phrases and questions to three letters, now obsolete, except for the following exceptions.


QDR: magnetic bearing from the station.
QFE: atmospheric pressure at aerodrome elevation. With its sub-scale set to the aerodrome QFE an altimeter will indicate height above that airfield.
QFU: magnetic orientation of runway in use.
QNE: reading in feet on an altimeter set to 1013.2 millibars (standard pressure) when the aircraft is at aerodrome elevation.
QNH: altitude above mean sea level based on local station pressure.
QTE: true line of position from a direction-finding station.
QUJ: true bearing


R

RAF: Royal Air Force. Is also used as a prefix for a Royal Air Force base, e.g. RAF Mildenhall.
RAS: Rectified Airspeed. Indicated airspeed (IAS*) corrected for instrument position error.
RDO: Radio
Repositioning: Flying from the point of destination to the next point of origin, without carrying any payload* (in the case of an aircraft) or without being responsible for payload (in the case of a crew member). Example: a scheduled U.S. airline operates a charter flight from Los Angeles to Lisbon. Then, payload-free, it flies to Paris, where it will board passengers and cargo for a scheduled flight back to Los Angeles. Also known as deadheading, ferry flight.
Roger: Commonly used word in aviation communications. Just like "10-4" in other types of communications, it means that the instruction has been understood. Also, to roger is to repeat the instruction as to make sure it has been clearly understood.
RMI: Radio Magnetic Indicator. A navigation aid which combines DI*, VOR* and/or ADF* display and will indicate bearings* to stations, together with aircraft heading.
RNAV: Area Navigation. A system of radio navigation which permits direct point-to-point off-airways navigation by means of an on-board computer creating phantom VOR/DME* transmitters termed waypoints*.
RON: Remain Overnight. Aircraft remaining overnight at the airport, either at the gate, remote parking stand or hangar. Airlines take advantage of RONs to perform maintenance, cleaning, etc. on the aircraft.
RVR: Runway Visual Range. A horizontal measurement of visibility along a runway.
rpm: Revolutions Per Minute.
RWY: Runway


S

SELCAL: Selective Calling. A high-frequency system enabling air traffic control to alert a particular aircraft, by means of flashing light or aural signal in the cockpit, for receipt of a message without the crew having to maintain a listening watch. Used on long-haul over-ocean airline routes and by intercontinental business jets.
SCT: See SOCAL* (below).
Shanwick: ATCC* located in Shannon (Ireland) and Prestwick (Scotland, UK), hence the name. Shanwick looks after traffic in the Northern Atlantic coast of Europe.
SID: Standard Instrument Departure. A standard IFR* departure route enabling air traffic controllers to issue abbreviated clearances and thus speed the flow of traffic.
SOB: Souls (persons) On Board. Also POB, Persons on Board.
SOCAL: Southern California TRACON*, the busiest approach control in the world, located in San Diego. Controls most arrivals for commercial, general aviation, or military airfields in Southern California. Also known as SCT for short.
Squawk (to): To transmit an assigned code via a transponder* (e.g. Delta 207 Heavy, Squawk 2044). The squawk is also the assigned code. Below are some standard special squawks:
0001: USA President is on board
1200: VFR flight
4000: Military IFR/VFR
7500: Hijack
7600: Loss of radio communication. First, the pilot tunes 7700 for 1 minute, then 7600 for 15 seconds.
7700: Emergency situation
7777: Military interception operations
SSR: Secondary Surveillance Radar. A radar system comprising a ground-based transmitter/receiver which interrogates a compatible unit in the aircraft (the transponder*), providing instant radar identification without having to manoeuvre. Assigned four-digit transponder codes are referred to as squawk* (see above) codes.
Standby: In radio communications, is a word to ask the other person to wait for further instructions. A standby reservation is conditional and is on a waiting list, in case of any no-shows*.
STAR: Standard Terminal Arrival Route, for inbound IFR* traffic.
STOL: Short Take-Off and Landing.
STOVL: Short Take-Off and Vertical Landing.


T

TACAN: Tactical Air Navigation system. An ultra-high frequency electronic navigation aid which provides suitably-equipped aircraft with a continuous indication of bearing and distance to the selected Tacan station. The distance element can be received by civilian DMF equipment, but otherwise Tacan is principally a military navaid.
TAS: True Airspeed. Rectified airspeed corrected for altitude and outside air temperature.
TCA: Terminal Control Area.
TCAS: Traffic alert and Collision Avoidance System. U.S. developed radar-based airborne collision avoidance system operating independently of ground-based equipment. TCAS-I generates traffic advisories only, TCAS-II provides advisories and collision avoidance instructions in the vertical plane.
Tailwind: Strong wind in the same direction as the motion of the aircraft.
TOGA: Take-off/Go Around. An autopilot setting activating take-off or go-around* thrust.
TRACON: Terminal Radar Approach Control. ATC* for departures and approaches.
Transition altitude (TA): Altitude in the vicinity of an aerodrome at or below which the vertical position of an aircraft is controlled by reference to altitude, e.g. with the aerodrome QNH* set on its altimeter. Above transition altitude QNE* is set and flight levels used. Also called transition level (TL) at which a descending aircraft changes from FL* to QNH.
Transponder: Airborne receiver/transmitter portion of the SSR* system which receives the interrogation signal from the ground and automatically replies according to mode and code selected. Modes A and B are used for identification, using a four-digit number allocated by air traffic control. Mode C gives automatic altitude readout from an encoding altimeter.
TWR: Tower
TWY: Taxiway


U

UHF: Ultra-High Frequency. Radio frequencies in the 300-3,000 MHz band.
UNICOM: privately-operated advisory air-to-ground radio service at uncontrolled airfields, in the USA.
UTC: Co-ordinated Universal Time, formerly Greenwich Mean Time


V

V1: decision speed, up to which it should be possible to abort a take-off and stop safely within the remaining runway length. After reaching V1 the take-off must be continued.
VA: design manoeuvring speed. The speed below which abrupt and extreme control movements are possible (though not advised) without exceeding the airframe's limiting load factors.
VFE: maximum flap extension speed (top of white arc on ASI).
VMCA: minimum control speed (air). The minimum speed at which control of a twin-engined aircraft can be maintained after failure of one engine.
VMO: maximum operating speed. Also Mmo, Mach limit maximum operating speed.
VNE: never-exceed speed, 'redline speed' denoted by a red radial on an ASI.
VNO: normal operating speed. The maximum structural cruising speed allowable for normal operating conditions (top of green arc on ASI).
VR: rotation speed, at which to raise the nose for take-off.
VSO: stalling speed at MTWA, in landing configuration with flaps and landing gear down, at sea level, ISA conditions (bottom of white arc on ASI).
VX: best angle of climb speed on all engines.
VXSE: best engine-out angle of climb speed.
VY: best rate of climb speed on all engines.
VYSE: best engine-out rate of climb speed, 'blueline speed' (blue radial on ASIs of light twins)
VASIS: Visual Approach Slope Indicator System. A colored light system providing visual guidance to the glidepath of a runway.
VFR: Visual Flight Rules. Prescribed for the operation of aircraft in visual meteorological conditions (VMC). VMC is generally defined as 5 miles visibility or more and 1,000 feet vertical and one nautical mile horizontal clearance from cloud, but variations apply to aircraft operating below 3,000 feet AMSL*. Special VFR (SVFR) clearances are granted at the discretion of ATC for VFR flight through some controlled airspace where IFR* usually apply.
VHF: Very High Frequency. Radio frequencies in the 30-300 MHz band, used for most civil air-to-ground communication.
VIS: Visibility
VNAV: Vertical Navigation
VOR: Very high frequency Omnidirectional Range. A radio navigation aid operating in the 108-118 MHz band. A VOR ground station transmits a two-phase directional signal through 360°. the aircraft's VOR receiver enables a pilot to identify his radial or bearing from/to the ground station. VOR is the most commonly used radio navigation aid in private flying. Increased accuracy is available in Doppler VORs (DVOR) which have replaced some VORs in the UK system. Also VORTAC, combined VOR and TACAN, and VOT, VOR test facility.
VSI: Vertical Speed Indicator. One of the primary flight instruments showing rate of climb or descent.
V/STOL: Vertical and Short Take-Off and Landing.
VTOL: Vertical Take-Off and Landing.


W-X-Y-Z

Wake turbulence: Wingtip vortices generated behind a wing producing lift. Behind a large heavy aircraft they can be powerful enough to roll or even break up a smaller aircraft.
Willco: Will copy. See Roger.
Windshear: localised change in wind speed and/or direction over a short distance, resulting in a tearing or shearing effect, usually at low altitude, that can cause a sudden loss of airspeed with occasionally disastrous results if encountered when taking-off or landing.
XMSN: Transmission
XPDR: Transponder
Zulu: Used worldwide for times of flight operations, formerly Greenwich Mean Time, now Co-ordinated Universal Time (UTC). (e.g. 1500Z)