Glossary

Every defined term used on the site, in plain words. Where a published lesson teaches a term, the entry links to it.

"Operations normal": Routine report showing the flight is progressing to plan. SERA.10001(b) Flight information service and alerting service
A-SMGCS / SMR: Surface surveillance systems that the tower uses to monitor and guide surface traffic. ATS.TR.245 Aerodrome control and visual separation near aerodromes
ACAS: Airborne collision avoidance system using SSR transponder signals. SERA Art. 2(17) Transponder operating procedures and phraseology
ACAS resolution advisory (RA): Collision-avoidance manoeuvre indication that the pilot follows even against ATC. SERA.11014 Emergencies, communication failure and contingencies
access control: Applying means by which entry of unauthorised persons or vehicles may be prevented. Reg. (EC) No 300/2008 Art. 3(10) Aviation security: aims and objectives
accident: Occurrence in the boarding-to-disembarkation window that causes a fatal or serious injury, qualifying damage, or a missing or inaccessible aircraft. Reg. (EU) No 996/2010 Art. 2(1) Accident and incident investigation
accredited representative: Qualified person designated by a State to take part in an investigation run by another State. Reg. (EU) No 996/2010 Art. 2(2) Accident and incident investigation
act of unlawful interference: A deliberate act that jeopardises the security of civil aviation. The regulation uses the term without defining it. Reg. (EC) No 300/2008 Art. 1, Art. 3 Aviation security: aims and objectives
ADS-B: Broadcast of position and other data from the aircraft (may share the Mode S transmitter). SERA Appendix 6 Item 10; Appendix 1 note to 2.3.10 Transponder operating procedures and phraseology
Advisory airspace / advisory route: Airspace or a route where air traffic advisory service is available SERA Article 2(3), (4) Air traffic services: definitions and general provisions
AeMC / AME / GMP: Aero-medical centre / aero-medical examiner / general medical practitioner (may issue LAPL medicals where national law allows). MED.A.040 Personnel licensing: Annex 1, Part-FCL and Part-MED
aerobatic flight: Intentional manoeuvres with abrupt attitude change, abnormal attitude or abnormal speed variation, not needed for normal flight or for licence/rating instruction (except aerobatic rating). SERA Article 2(5) Rules of the air: general rules
aerodrome: A defined area on land or water (or on a structure), with its buildings and equipment, intended for arrival, departure and surface movement of aircraft. SERA Article 2(6) Rules of the air: definitions and applicability
aerodrome beacon: Aeronautical beacon used to indicate the location of an aerodrome from the air. CS ADR-DSN.A.002 Aerodrome lights
aerodrome control service: ATC service for aerodrome traffic. SERA Art. 2(7) Aerodrome control and visual separation near aerodromes
aerodrome control tower (TWR): Unit providing ATC to aerodrome traffic. SERA Art. 2(8) Aerodrome control and visual separation near aerodromes
aerodrome elevation: Elevation of the highest point of the landing area. CS ADR-DSN.A.002; Annex 14 Ch. 1 Aerodromes: definitions and aerodrome data
aerodrome emergency plan (AEP): The aerodrome operator's plan that coordinates all organisations responding to an emergency at or near the aerodrome. ADR.OPS.B.005 Rescue and fire fighting, apron management
Aerodrome identification sign: ICAO-recommended sign showing the aerodrome name, readable from the air. Annex 14 5.4.5 Aerodrome signs
Aerodrome reference point (ARP): The designated geographical location of an aerodrome, near its (planned) geometric centre. Annex 14 Ch. 1; GM1 ADR.OPS.A.005 Aerodromes: definitions and aerodrome data
Aerodrome reference temperature: Monthly mean of daily maximum temperatures of the hottest month, averaged over five years, in °C. GM1 ADR.OPS.A.005 Aerodromes: definitions and aerodrome data
aerodrome RFF category: A number from 1 to 10 that states the level of fire protection normally available, based on the longest aeroplanes' length and fuselage width. AMC2 ADR.OPS.B.010(a)(2) Rescue and fire fighting, apron management
aerodrome traffic: Traffic on the manoeuvring area plus aircraft flying near the aerodrome, including those joining or leaving the circuit. SERA Art. 2(9) Aerodrome control and visual separation near aerodromes
aerodrome traffic circuit: The specified path for aircraft that operate in the vicinity of an aerodrome. SERA Article 2(10)
aerodrome traffic zone (ATZ): Airspace of defined dimensions around an aerodrome for the protection of aerodrome traffic. SERA Article 2(11)
Aeronautical beacon: Ground light visible at all azimuths, continuously or intermittently, designating a point on the earth's surface CS ADR-DSN.A.002 Aerodrome lights
aeronautical data: Formalised representation of aeronautical facts, concepts or instructions for communication, interpretation or processing. Reg. (EU) 2017/373 Annex I (9) Aeronautical information: AIP, NOTAM, AIRAC and AIC
aeronautical fixed service (AFS): The telecommunication service between fixed points, mainly for the safety of air navigation, used to distribute NOTAM. Reg. (EU) 2017/373 Annex I (11) Aeronautical information: AIP, NOTAM, AIRAC and AIC
Aeronautical ground light: Any light specially provided as an aid to air navigation, other than one on an aircraft CS ADR-DSN.A.002 Aerodrome lights
aeronautical information: Information resulting from assembling, analysing and formatting aeronautical data. Reg. (EU) 2017/373 Annex I (13) Aeronautical information: AIP, NOTAM, AIRAC and AIC
aeronautical information product: Aeronautical data or information provided as digital data sets or a standardised paper or electronic presentation, such as the AIP, AIC, charts and NOTAM. Reg. (EU) 2017/373 Annex I (117) Aeronautical information: AIP, NOTAM, AIRAC and AIC
aeronautical information service (AIS): The service that collects, processes, publishes and distributes aeronautical data and information for a State's territory. AIS.OR.105 Aeronautical information: AIP, NOTAM, AIRAC and AIC
aeroplane: A power-driven, heavier-than-air aircraft that gets its lift chiefly from surfaces that stay fixed in a given flight condition. SERA Article 2(16) Rules of the air: definitions and applicability
AFIS: FIS for aerodrome traffic provided by a designated ATS provider. Reg. (EU) 2017/373 Annex I (6) Flight information service and alerting service
AFIS / AFIS unit / AFIS aerodrome: FIS for aerodrome traffic; the unit giving AFIS and alerting service (suffix INFORMATION); an aerodrome where AFIS is provided Air traffic services: definitions and general provisions
AFIS aerodrome: Aerodrome where AFIS is provided in its associated airspace. Reg. (EU) 2017/373 Annex I (125) Flight information service and alerting service
AFIS unit: Unit providing AFIS and alerting service. Reg. (EU) 2017/373 Annex I (126) Flight information service and alerting service
AIC: A notice with information that does not qualify for a NOTAM or for inclusion in the AIP, but relates to flight safety, air navigation, technical, administrative or legislative matters. Reg. (EU) 2017/373 Annex I (115) Aeronautical information: AIP, NOTAM, AIRAC and AIC
aiming point marking: Two conspicuous white stripes, one on each side of the runway centre line, marking the point where a pilot aims to touch down. CS ADR-DSN.L.540(a), (c) Aerodrome markings
AIP: The State publication of aeronautical information of a lasting character essential to air navigation. Reg. (EU) 2017/373 Annex I (118); SERA Art. 2(13) Aeronautical information: AIP, NOTAM, AIRAC and AIC
AIP amendment: A permanent change to the information in the AIP. Reg. (EU) 2017/373 Annex I (119) Aeronautical information: AIP, NOTAM, AIRAC and AIC
AIP supplement (SUP): A temporary change to the AIP information, published on special pages. Reg. (EU) 2017/373 Annex I (120) Aeronautical information: AIP, NOTAM, AIRAC and AIC
Air Navigation Commission (ANC): Body of aeronautical experts appointed by the Council; prepares and recommends changes to the Annexes. Arts 56, 57 ICAO: objectives and composition
air traffic: All aircraft in flight or on the manoeuvring area of an aerodrome. SERA Article 2(26) Rules of the air: definitions and applicability
Air traffic advisory service: Service in advisory airspace that keeps IFR flights apart as far as practical; advice, not control SERA Article 2(27) Air traffic services: definitions and general provisions
air traffic control (ATC): The ATC service, which keeps controlled flights apart from each other and keeps aerodrome traffic orderly. ATS.TR.105(a) Air traffic services: definitions and general provisions
air traffic control (ATC) service: A service that prevents collisions between aircraft (and with obstructions on the manoeuvring area) and keeps traffic flowing in order. SERA Article 2(30) Rules of the air: definitions and applicability
air traffic services (ATS): The services that prevent collisions, keep traffic orderly, give advice and information, and alert the right organisations about aircraft needing assistance. SERA.7001; ATS.TR.100 Air traffic services: definitions and general provisions
Air Transport Committee: Council committee for air transport (economic) matters, chosen from Council representatives. Art. 54(d) ICAO: objectives and composition
air-to-ground signal: A manoeuvre or light signal made by an aircraft to show that a ground signal has been understood. Annex 12, Appendix 3 Search and rescue signals
AIRAC: A system of advance notification, based on common effective dates, of circumstances that need significant changes in operating practices. Reg. (EU) 2017/373 Annex I (121) Aeronautical information: AIP, NOTAM, AIRAC and AIC
aircraft: Any machine that can be supported in the atmosphere by reactions of the air, other than reactions of the air against the earth's surface. SERA Article 2(18) Rules of the air: definitions and applicability
Aircraft address: Unique 24-bit code per aircraft. SERA Art. 2(19) Transponder operating procedures and phraseology
Aircraft identification: Letters/figures equal to the call sign, sent by Mode S/ADS-B. SERA Art. 2(19a); SERA.13015 Transponder operating procedures and phraseology
Aircraft maintenance programme (AMP): The document that organises an aircraft's maintenance; declared by the owner or approved by the CAMO/CAO. ML.A.302 Airworthiness and the certificate of airworthiness
aircraft security check: An inspection of the passenger-accessible interior and the hold for prohibited articles. Reg. (EC) No 300/2008 Art. 3(29) Aviation security: aims and objectives
aircraft security search: An inspection of the interior and the accessible exterior of an aircraft. Reg. (EC) No 300/2008 Art. 3(30) Aviation security: aims and objectives
Aircraft stand taxilane: Apron portion designated as a taxiway giving access to stands only CS ADR-DSN.A.002 Aerodrome markings
airside: The movement area of an airport, adjacent terrain and buildings, access to which is restricted. Reg. (EC) No 300/2008 Art. 3(11) Aviation security: aims and objectives
Airway: Control area, or part of one, shaped as a corridor SERA Article 2(36) Air traffic services: definitions and general provisions
Airworthiness directive (AD): Mandatory action issued or adopted by EASA to restore safety when an unsafe condition is likely to exist in other aircraft of the type. 21.A.3B(a)–(b) Airworthiness and the certificate of airworthiness
Airworthiness review: Documented review of an aircraft's records plus a physical survey, done periodically to keep the airworthiness certificate valid. ML.A.901(a); ML.A.903(a) Airworthiness and the certificate of airworthiness
airworthiness review certificate (ARC): Certificate (EASA Form 15c) issued after a satisfactory airworthiness review; valid 1 year, extendable twice. ML.A.901(b); ML.A.902(a) Airworthiness and the certificate of airworthiness
Airworthy: Conforming to an approved design and in a condition for safe operation. 21.B.326(b) Airworthiness and the certificate of airworthiness
alert phase (ALERFA): Apprehension exists about the safety of an aircraft and its occupants. Reg. (EU) 2017/373 Annex I (135); ATS.TR.405(b)(1) Flight information service and alerting service
Alerting post: Facility acting as intermediary between a person reporting an emergency and an RCC/RSC. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
alerting service: Service notifying organisations about aircraft needing SAR aid and assisting them. SERA Article 2(37) Flight information service and alerting service
altitude: The vertical distance of a level from mean sea level (MSL). SERA Article 2(39)
AMC (acceptable means of compliance): EASA material, adopted by Executive Director decision, showing an accepted way to meet an implementing rule. SERA EAR, Note from the editor ATS phraseologies
Annex: A set of SARPs adopted by the ICAO Council, designated an Annex to the Convention for convenience. Art. 54(l), Art. 90 Chicago Convention, Part I: air navigation
anti-collision light: A light intended to attract attention to the aircraft. SERA.3215(a)(1)
Approach control service / unit: ATC for arriving or departing controlled flights / the unit giving it (suffix APPROACH) SERA Article 2(40), (41) Air traffic services: definitions and general provisions
appropriate authority: The single national authority that coordinates and monitors the implementation of aviation security. Reg. (EC) No 300/2008 Art. 9 Aviation security: aims and objectives
apron: A defined area for loading and unloading, fuelling, parking or maintenance of aircraft. SERA Article 2(42) Rules of the air: definitions and applicability
apron boundary: The published limit of the apron, shown on the aerodrome chart. ADR.OPS.D.005; AMC1 ADR.OPS.D.005 Rescue and fire fighting, apron management
apron management service (AMS): The service that manages aircraft and vehicle activities and movements on an apron. Reg. (EU) No 139/2014 Art. 2(5) Rescue and fire fighting, apron management
Area control centre (ACC) / area control service: Unit giving ATC to controlled flights in its control areas (suffix CONTROL) / the service itself SERA Article 2(43), (44) Air traffic services: definitions and general provisions
ARFF: Aircraft rescue and fire-fighting (aerodrome fire and rescue service). Signals
arrival report: A report made after landing to close a flight plan. SERA.4020 Rules of the air: general rules
ASDA: TORA plus the stopway, if provided. Reg. (EU) No 139/2014 Annex I (2) Aerodromes: definitions and aerodrome data
ASHTAM: A special-series NOTAM, in a specific format, on volcanic activity or an ash cloud. Reg. (EU) 2017/373 Annex I (29) Aeronautical information: AIP, NOTAM, AIRAC and AIC
Assembly: ICAO's body of all contracting States, one vote each; meets at least every three years; elects the Council. Arts 48, 49 ICAO: objectives and composition
ATC / FIS columns: The "Applicable to" columns showing whether a phrase is for an ATC function, an FIS function, or both. GM2 Appendix 1 to AMC1 SERA.14001 ATS phraseologies
ATC clearance: Authorisation for an aircraft to proceed under conditions that an ATC unit specifies. SERA Article 2(28) Rules of the air: definitions and applicability
ATC instruction: A directive from ATC that requires the pilot to take a specific action. SERA Article 2(29) Rules of the air: definitions and applicability
ATIS / Voice-ATIS / D-ATIS: Automatic provision of current routine information to arriving and departing aircraft, by continuous voice broadcast (Voice-ATIS) or by data link (D-ATIS). SERA Article 2(49) Flight information service and alerting service
ATS airspaces: Letter-designated airspaces with specified flight types, services and rules SERA Article 2(33) Air traffic services: definitions and general provisions
ATS reporting office (ARO): Unit receiving ATS reports and pre-departure flight plans SERA Article 2(34) Air traffic services: definitions and general provisions
ATS route: Specified route that channels traffic for ATS (airways, advisory routes, VFR routes, etc.) SERA Article 2(46); GM1 Article 2(46) Air traffic services: definitions and general provisions
ATS surveillance service: Air traffic service given directly by means of an ATS surveillance system SERA Article 2(34a) Radar services
ATS surveillance system: Umbrella term for ADS-B, PSR, SSR or comparable ground-based systems that allow aircraft identification Reg. (EU) 2017/373 Annex I (141) Radar services
ATS unit: ATC unit, FIC, AFIS unit or ATS reporting office. SERA Article 2(35) Flight information service and alerting service
autonomous aircraft detection system: A system that turns obstacle lights on only when an aircraft approaches. GM1 ADR-DSN.Q.840(d) Obstacles and restricted-use areas
aviation security: Measures plus human and material resources that safeguard civil aviation against acts of unlawful interference. Reg. (EC) No 300/2008 Art. 3(2) Aviation security: aims and objectives
background check: A recorded check of a person's identity, including any criminal history, used for unescorted access to SRAs. Reg. (EC) No 300/2008 Art. 3(15) Aviation security: aims and objectives
Barrette: Three or more closely spaced ground lights in a transverse line, appearing as a short bar CS ADR-DSN.A.002 Aerodrome lights
blind transmission: Transmission sent without contact or acknowledgement, prefixed "TRANSMITTING BLIND", and sent twice. SERA.14085(a) Emergencies, communication failure and contingencies
Cabotage: Carriage for payment between points within one State's territory. Art. 7 Chicago Convention, Part I: air navigation
CAMO / CAO: Approved organisations that can manage an aircraft's continuing airworthiness (CAO can also maintain). ML.A.201(e)–(f) Airworthiness and the certificate of airworthiness
catenary: The sagging curve of a wire between two towers. Its lowest point carries one high-intensity Type B light level. CS ADR-DSN.Q.852(d)(2) Obstacles and restricted-use areas
causes: Actions, omissions, events or conditions that led to an event. Identifying causes does not mean assigning fault. Reg. (EU) No 996/2010 Art. 2(4) Accident and incident investigation
CAVOK: Ceiling and visibility OK, spoken "CAV-O-KAY" Appendix 1 to AMC1 SERA.14001, 1.1.8 j ATS phraseologies
ceiling: The height above the ground or water of the base of the lowest cloud layer below 20 000 ft (6 000 m) that covers more than half of the sky. SERA Article 2(50)
certificate of airworthiness (CofA): Certificate (EASA Form 25) issued by the State of registry to an aircraft conforming to a type certificate; unlimited duration, valid only with a current ARC. 21.A.173(a); 21.B.325(a); 21.A.181 Airworthiness and the certificate of airworthiness
certificate of deregistration: Document confirming removal from a register and cancellation of the certificate of registration. Annex 7 9 Nationality and registration marks
certificate of registration: Document issued by the State of Registry, following the Annex 7 model, showing marks, aircraft and registered holder. Annex 7 8 Nationality and registration marks
Certificate of release to service (CRS): Statement issued after maintenance that the work was properly done; by certifying staff or, within limits, the pilot-owner. ML.A.801 Airworthiness and the certificate of airworthiness
certification specification (CS): EASA design standard against which an aerodrome is certified; worded "should". CS ADR-DSN.A.001 Indicators, signalling devices and markers
checklist NOTAM: A periodic NOTAM that lists the valid NOTAM of a series, together with the latest AIP amendments, supplements and AIC. AIS.TR.330(s)-(v) Aeronautical information: AIP, NOTAM, AIRAC and AIC
Chicago Convention: The Convention on International Civil Aviation, signed at Chicago on 7 December 1944 and in force from 4 April 1947. Doc 7300 Foreword, preamble note 1 Chicago Convention, Part I: air navigation
civil aviation: Air operations by civil aircraft, excluding State aircraft. Reg. (EC) No 300/2008 Art. 3(1) Aviation security: aims and objectives
Class 2 medical certificate: The minimum medical certificate for PPL privileges. MED.A.030(c)(2) Personnel licensing: Annex 1, Part-FCL and Part-MED
Class rating: Rating for a class of single-pilot aeroplanes that does not need a type rating, for example SEP(land). FCL.010; FCL.705 Personnel licensing: Annex 1, Part-FCL and Part-MED
clear of cloud: Out of cloud, with no specified distance from cloud. Used in Class F and G in the low band and for special VFR. SERA.5001, Table S5-1; SERA.5010(b)(1)
Clearance limit: The point to which a clearance is granted SERA Article 2(52) Air traffic services: definitions and general provisions
clearway: Defined rectangular area on the ground or water, under aerodrome control, over which an aeroplane may make part of its initial climb. Reg. (EU) No 139/2014 Annex I (15); CS ADR-DSN.A.002 Aerodromes: definitions and aerodrome data
closed marking: A marking, white on a runway and yellow on a taxiway, that shows a runway or taxiway, or part of one, is closed. CS ADR-DSN.R.855; ADR.OPS.B.071 Obstacles and restricted-use areas
Code (SSR) / squawk: Four-digit Mode A/C reply code; "squawk" = select a code (phraseology). SERA Art. 2(54); Appendix 1 to AMC1 SERA.14001, 2.3 Transponder operating procedures and phraseology
code 7601: EU-only Mode A code for an IFR flight with radio failure that continues in VMC. SERA.14083(c)(6) Emergencies, communication failure and contingencies
code pennant: A tapered flag with vertical red and white stripes; hoisted close up (fully raised) by a surface craft it means "understood". Annex 12, Appendix 1.2, Note Search and rescue signals
Colour safe: Able to readily distinguish the colours used in air navigation and identify aviation coloured lights. MED.A.010 Personnel licensing: Annex 1, Part-FCL and Part-MED
common basic standards: The EU-wide baseline security standards set out in Annex I to the regulation. Reg. (EC) No 300/2008 Art. 4(1), Annex I Aviation security: aims and objectives
common mark: Mark assigned by ICAO to a common mark registering authority for aircraft of an international operating agency registered on a non-national basis. Annex 7 Ch. 1 Nationality and registration marks
common mark registering authority: Authority keeping the non-national register for an international operating agency's aircraft. Annex 7 Ch. 1 Nationality and registration marks
Compacted snow: Snow pressed into a solid mass that tyres run on without further rutting. Reg. 139/2014 Annex I (38h)(a) Aerodromes: definitions and aerodrome data
competent authority: The authority a Member State designates to exercise the options SERA gives it. SERA (several points)
Complex motor-powered aircraft: For aeroplanes: above 5 700 kg MCTOM, or more than 19 passenger seats, or two-pilot minimum crew, or turbojet / more than one turboprop. Reg. (EU) No 748/2012 Art. 1(2)(ha) Airworthiness and the certificate of airworthiness
Conditional clearance: A clearance that applies only after a stated condition is met (e.g. after a landing aircraft passes) SERA.8015(ec) ATS phraseologies
conspicuity code: Code 7000, selected when not receiving air traffic services to improve detection by suitably equipped aircraft. SERA.13005(b)(3) Transponder operating procedures and phraseology
Contaminated runway: Runway covered in significant part by one of the surface condition descriptors. Reg. 139/2014 Annex I (15a) Aerodromes: definitions and aerodrome data
Contingency plan: A service provider's plan for significant degradation or interruption of its services. ATS.OR.135 Emergencies, communication failure and contingencies
continuing airworthiness: All processes keeping an aircraft compliant with airworthiness requirements and safe to operate throughout its life. Reg. (EU) No 1321/2014 Art. 2(d) Airworthiness and the certificate of airworthiness
Contracting State: A State party to the Convention. Doc 7300 (passim) Chicago Convention, Part I: air navigation
contributing factors: Factors whose removal would have made the event less likely or less severe. They imply no fault. Annex 13 Ch. 1 Accident and incident investigation
control area: Controlled airspace that starts at a specified limit above the earth. SERA Article 2(56) Rules of the air: definitions and applicability
control zone (CTR): Controlled airspace from the surface up to a specified upper limit. SERA Article 2(61)
controlled aerodrome: Aerodrome where ATC is provided to aerodrome traffic. SERA Art. 2(57) Aerodrome control and visual separation near aerodromes
controlled airspace: Airspace where ATC service is provided according to its class (Classes A–E). SERA Article 2(58); GM1 Article 2(58) Rules of the air: definitions and applicability
controlled flight: Any flight that is subject to an ATC clearance. SERA Article 2(59) Rules of the air: definitions and applicability
Cospas-Sarsat: International satellite system that detects 406 MHz distress beacons and passes alerts to RCCs via its Mission Control Centres and the SAR point of contact. Annex 12, 2.4.1(j), 3.2.5, 5.2.4(b) Search and rescue: definitions and pilot procedures
Council: Permanent ICAO body of elected States, responsible to the Assembly; adopts standards and recommended practices as Annexes. Arts 50, 54 ICAO: objectives and composition
Critical area / sensitive area: Areas around precision approach ground equipment where aircraft or vehicles would disturb the guidance signal. CS ADR-DSN.A.002 Aerodrome signs
critical parts of SRA: Parts of an SRA where all non-passengers are screened on entry. Reg. (EC) No 300/2008 Annex I points 1.1.2(d), 1.3.2 Aviation security: aims and objectives
cruising level: A level that an aircraft holds for a significant part of a flight. SERA Article 2(63)
Current / filed flight plan: Flight plan including later clearance changes / as originally filed SERA Article 2(64), (73) Air traffic services: definitions and general provisions
Customs airport: Airport designated by a State for customs and other examination of arriving and departing aircraft. Art. 10 Chicago Convention, Part I: air navigation
danger area: Airspace in which activities dangerous to flight may exist at specified times. SERA Article 2(65) Rules of the air: general rules
declared distances: TORA, TODA, ASDA and LDA published for each runway direction. Reg. (EU) No 139/2014 Annex I (18); GM1 ADR.OPS.A.005 Aerodromes: definitions and aerodrome data
demarcated area: An area separated by access control from the SRAs, or from the other SRAs when it is itself an SRA. Reg. (EC) No 300/2008 Art. 3(14) Aviation security: aims and objectives
Difference (from a Standard): A way in which a State's rules or practices depart from an international standard; must be notified to ICAO. Art. 38 Chicago Convention, Part I: air navigation
direction sign: Black-on-yellow sign naming a taxiway with an arrow showing its direction at an intersection. CS ADR-DSN.N.785(a)(8), (c)(7) Aerodrome signs
Discrete code: Four-digit SSR code whose last two digits are not 00 GM1 Annex IV (Part-ATS) Radar services
displaced threshold: Threshold not located at the physical end of the runway. CS ADR-DSN.A.002; Annex 14 Ch. 1 Aerodromes: definitions and aerodrome data
distance from cloud: The horizontal and vertical distance between the aircraft and cloud that VMC requires (1 500 m horizontally and 1 000 ft vertically in most bands of Table S5-1). SERA.5001, Table S5-1
distress: A state of grave and imminent danger that needs immediate assistance. Signals include MAYDAY, SOS, red lights and transponder code 7700. SERA App. 1, 1.2.1
distress beacon: Generic term for a transmitter that signals distress; Annex 12 does not define it. Annex 12, 5.6.2(c), 5.7.2 Search and rescue: definitions and pilot procedures
distress phase (DETRESFA): Reasonable certainty of grave and imminent danger, or need for immediate assistance. Reg. (EU) 2017/373 Annex I (174); ATS.TR.405(b)(1) Flight information service and alerting service
distress scene: Term used from 26 November 2026 for the place of a distress in the Annex 12 PIC procedures. Annex 12, 5.6 footnote 2 Search and rescue: definitions and pilot procedures
Ditching: Forced landing of an aircraft on water. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
Downstream clearance: Clearance from an ATC unit not yet controlling the aircraft SERA Article 2(68) Air traffic services: definitions and general provisions
Dry runway: Runway free of visible moisture and not contaminated. Reg. 139/2014 Annex I (18a) Aerodromes: definitions and aerodrome data
dual obstacle lighting system: A system that shows white lights by day and twilight, and red medium-intensity lights at night, near an aerodrome. GM1 ADR-DSN.Q.846(c) Obstacles and restricted-use areas
dumb-bell: A white ground signal shaped like a dumb-bell. Alone, it means use runways and taxiways only. With black bars, it means runways only for take-off and landing. SERA App. 1, 3.2.3
eAIP: Electronic form of the AIP, displayable on screen and printable. AIS.TR.305(a) Aeronautical information: AIP, NOTAM, AIRAC and AIC
ELA1 / ELA2 aeroplane: Non-complex aeroplane of 1 200 kg / 2 000 kg MTOM or less. Reg. (EU) No 748/2012 Art. 1(2)(i), (j) Airworthiness and the certificate of airworthiness
ELT (emergency locator transmitter): Distress beacon carried by an aircraft; Annex 12 does not define it and refers to Annex 6 (carriage) and Annex 10 Vol III (specifications); frequencies 121.5 MHz and 406.0–406.1 MHz. Annex 12, 2.6.4 Notes Search and rescue: definitions and pilot procedures
emergency access road: A road that lets RFFS vehicles reach parts of the aerodrome and its approach areas quickly. GM1 ADR-DSN.T.900 Rescue and fire fighting, apron management
emergency authority: The pilot-in-command's right to act at once against the flight plan or clearance in an emergency, then tell ATS. SERA.8020(a); SERA.2010(a) Emergencies, communication failure and contingencies
emergency frequency 121.5 MHz: The VHF emergency frequency, to be used only for emergency purposes. SERA Article 4a; SERA.11015(b)(3)
emergency phase: Uncertainty, alert or distress phase. GM1 Annex IV (Part-ATS) to Reg. (EU) 2017/373 Flight information service and alerting service
emergency separation: Temporary vertical separation of half the normal minimum, used in an emergency when horizontal separation cannot be kept. AMC1 ATS.TR.210(c) Emergencies, communication failure and contingencies
Endorsement (Art. 39): A list, on or attached to a certificate of airworthiness or licence, of the respects in which it does not meet the international standard. Art. 39 Chicago Convention, Part I: air navigation
Enhanced taxiway centre line: Continuous yellow centre line flanked by yellow dashed lines before a runway-holding position, warning of a nearby runway CS ADR-DSN.L.570 Aerodrome markings
Essential local traffic: Aircraft, vehicle or person on/near the manoeuvring area, or traffic in the climb-out or final approach area, that may be a hazard Reg. (EU) 2017/373 Annex I (177) Aerodrome control and visual separation near aerodromes
extensive object: An object, or a group of objects such as a group of buildings or a wind farm, whose extent needs outlining with several lights. GM1 ADR-DSN.Q.847; CS ADR-DSN.Q.851(c)(2) Obstacles and restricted-use areas
fatal injury: Injury suffered in an accident that results in death within 30 days of the accident. Reg. (EU) No 996/2010 Art. 2(5) Accident and incident investigation
fireproof material: Material that withstands heat at least as well as steel, with dimensions suited to the purpose. Annex 7 Ch. 1 Nationality and registration marks
Fixed light: Light of constant intensity seen from a fixed point CS ADR-DSN.A.002 Aerodrome lights
Fixed message sign: A sign showing only one message. CS ADR-DSN.A.002 Aerodrome signs
flight information centre (FIC): Unit that provides FIS and alerting service. SERA Article 2(75) Flight information service and alerting service
flight information region (FIR): Defined airspace in which FIS and alerting service are provided. SERA Article 2(76) Flight information service and alerting service
flight information service (FIS): Service giving advice and information for safe and efficient flight. SERA Article 2(77) Flight information service and alerting service
Flight information zone (FIZ): Airspace where AFIS and alerting service for aerodrome traffic are provided Air traffic services: definitions and general provisions
flight level (FL): A surface of constant atmospheric pressure related to the pressure datum 1013.2 hPa, separated from other such surfaces by set pressure intervals. SERA Article 2(78) Altimeter setting procedures
Flight path monitoring: Use of surveillance to advise aircraft of significant deviations from their nominal path or clearance GM1 Annex IV (Part-ATS) Radar services
flight plan: Information given to ATS units about an intended flight or part of a flight. SERA Article 2(79) Rules of the air: definitions and applicability
flight recorder: Recorder installed in an aircraft to help investigations. Reg. (EU) No 996/2010 Art. 2(6) Accident and incident investigation
Flight time: From the aircraft first moving to take off until it finally comes to rest after the flight. FCL.010 Personnel licensing: Annex 1, Part-FCL and Part-MED
flight visibility: The visibility forward from the cockpit of an aircraft in flight. SERA Article 2(80)
FOD (foreign object debris): Loose objects on the movement area that can damage aircraft or be blown about. ADR.OPS.D.035(f); ADR.OPS.D.040(c) Rescue and fire fighting, apron management
FOLLOW-ME vehicle: A vehicle that leads an aircraft along its apron route. AMC1 ADR.OPS.D.015(a); ADR.OPS.D.080 Rescue and fire fighting, apron management
frangible object: Low-mass object designed to break, distort or yield on impact, which reduces the hazard to aircraft. CS ADR-DSN.A.002 Indicators, signalling devices and markers
general call: Unacknowledged transmission to all aircraft concerned. AMC1 ATS.TR.305(a)(1)(ii) Flight information service and alerting service
geometric height (GNSS): A height derived from satellite navigation, not from air pressure. ATS.TR.155(f); AMC2 ATS.TR.155(f) Radar services
GM (guidance material): EASA explanatory material that helps interpret a rule or AMC SERA EAR, Note from the editor ATS phraseologies
Graded area: Part of the strip cleared and graded to limit damage to an aircraft running off the runway. CS ADR-DSN.A.002 Aerodromes: definitions and aerodrome data
ground visibility: The visibility at an aerodrome, reported by an accredited observer or by an automatic system. SERA Article 2(82)
ground-air visual signal code: A set of large symbols laid out on the ground to pass messages to aircraft, one set for survivors and one for rescue units. Annex 12, Appendix 2 Search and rescue signals
handover point: A designated point where responsibility for an aircraft passes between apron management and ATS. ADR.OPS.D.010(a)(1) Rescue and fire fighting, apron management
hazard: Situation or object with the potential to cause injury, damage, loss or reduced ability to perform a function. Reg. (EU) No 376/2014 Art. 2(10) Accident and incident investigation
heading: The direction of the aircraft's longitudinal axis, in degrees from true, magnetic, compass or grid north. SERA Article 2(83) Rules of the air: definitions and applicability
heavier-than-air aircraft: Aircraft deriving lift in flight chiefly from aerodynamic forces. Annex 7 Ch. 1 Nationality and registration marks
height: The vertical distance of a level from a specified datum. SERA Article 2(84)
hot spot: Location with a history or risk of collision or runway incursion that needs extra attention. Reg. (EU) No 139/2014 Annex I (19b) Aerodrome control and visual separation near aerodromes
IAMSAR Manual: International Aeronautical and Maritime Search and Rescue Manual (ICAO/IMO Doc 9731); Volume III covers mobile facilities and also lists these signals. Annex 12, 5.6.5, Note Search and rescue signals
ICAO: International Civil Aviation Organization, created by the Chicago Convention; a United Nations agency with 193 Contracting States. Chicago Convention, Art. 43 ICAO: objectives and composition
IDENT: Transponder feature that highlights the aircraft on the controller's display; used only on request. SERA.13001(b); Appendix 1, 2.3.7 Transponder operating procedures and phraseology
Identification: An aircraft's position indication is seen on the display and positively identified Reg. (EU) 2017/373 Annex I (200) Radar services
identification beacon: Aeronautical beacon emitting a coded signal identifying a point of reference. CS ADR-DSN.A.002 Aerodrome lights
identification plate: Fireproof plate showing at least the nationality/common and registration marks, fixed near the main entrance. Annex 7 10.1-10.2 Nationality and registration marks
immediate take-off: Clearance to enter the runway and take off without stopping. GM1 SERA.8005(a)(3) Aerodrome control and visual separation near aerodromes
incident: Occurrence other than an accident that affects, or could affect, the safety of operation. Reg. (EU) No 996/2010 Art. 2(7) Accident and incident investigation
Information marking: Yellow-on-black (location) or black-on-yellow (direction/destination) surface inscription CS ADR-DSN.L.610 Aerodrome markings
information sign: Sign identifying a location or giving routing information; black on yellow, except location signs (yellow on black). CS ADR-DSN.N.785 Aerodrome signs
Instrument / non-instrument runway: Runway intended for instrument approach procedures / for visual approach procedures. Reg. 139/2014 Annex I (22), (34) Aerodromes: definitions and aerodrome data
instrument meteorological conditions (IMC): Weather conditions, described by visibility, distance from cloud and ceiling, worse than the VMC minima. SERA Article 2(91)
intercept control unit: The ground unit directing the interceptor, with which the intercepted aircraft may talk on 121.5 MHz. Interception of civil aircraft
intercepted aircraft: The civil aircraft being intercepted, which must follow the interceptor's instructions. SERA.11015(b)
intercepting aircraft (interceptor): The aircraft that carries out an interception and gives the signals. SERA.11015, Tables S11-1, S11-2
interception: The approach of a normally military aircraft to a civil aircraft, to identify it and, if needed, guide it or make it land. Interception is a last resort. SERA.11015(a); AMC1 SERA.11015(a); GM1 SERA.11015, 1.1
Intermediate holding position: Designated position for traffic control where taxiing aircraft and vehicles stop and hold until cleared, when ATC so instructs CS ADR-DSN.A.002 Aerodrome markings
International flag "N": A blue and white chequered square flag; from a ship in reply to the "follow me" signal it means "unable to comply". Annex 12, Appendix 1.2, Note Search and rescue signals
international flag N: A blue and white chequered square flag; from a surface craft in reply to the "follow me" signal it means "unable to comply". Annex 12, Appendix 1.2, Note Search and rescue signals
international NOTAM office (NOF): The office a State designates to exchange NOTAM internationally. Reg. (EU) 2017/373 Annex I (197) Aeronautical information: AIP, NOTAM, AIRAC and AIC
international operating agency: Agency of the kind allowed by Chicago Convention Art. 77 (jointly set up by two or more States). Annex 7 Ch. 1 Nationality and registration marks
investigator-in-charge: Qualified person responsible for organising, conducting and controlling a safety investigation. Reg. (EU) No 996/2010 Art. 2(9) Accident and incident investigation
jet blast / propeller slipstream: The high-speed air behind an engine or propeller that is on, which can blow over people, equipment and light aircraft. ADR.OPS.D.055 Rescue and fire fighting, apron management
Joint rescue coordination centre (JRCC): RCC for both aeronautical and maritime SAR. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
just culture: Approach in which front-line operators are not punished for actions that match their experience and training, while gross negligence, wilful violations and destructive acts are not tolerated. Reg. (EU) No 376/2014 Art. 2(12) Accident and incident investigation
Landing area: Part of the movement area intended for landing or take-off. CS ADR-DSN.A.002 Aerodromes: definitions and aerodrome data
landing T: A white or orange T-shaped ground signal that shows the landing and take-off direction, towards the cross arm. SERA App. 1, 3.2.5.1
landside: The parts of an airport, adjacent terrain and buildings that are not airside. Reg. (EC) No 300/2008 Art. 3(12) Aviation security: aims and objectives
Language proficiency endorsement: Licence entry that shows the language, the level and the validity date. The minimum level is Level 4. FCL.055 Personnel licensing: Annex 1, Part-FCL and Part-MED
LDA: Runway length declared available and suitable for the ground run of an aeroplane landing. Reg. (EU) No 139/2014 Annex I (24) Aerodromes: definitions and aerodrome data
level: A generic term for a height, an altitude or a flight level. SERA Article 2(93) Altimeter setting procedures
level of protection: The firefighting capability (agents, rates, vehicles, people) actually provided, stated as an RFF category. AMC2 ADR.OPS.B.010(a)(2); GM1 ADR.OPS.A.005 Rescue and fire fighting, apron management
light signal: A coloured, steady or flashing light directed from aerodrome control to an aircraft, vehicle or person, with a meaning set by the rules of the air signals. SERA App. 1, 3.1
lighter-than-air aircraft: Aircraft supported chiefly by buoyancy. Annex 7 Ch. 1 Nationality and registration marks
Limitation (medical): A condition on the medical certificate that must be complied with while flying. MED.A.010 Personnel licensing: Annex 1, Part-FCL and Part-MED
location indicator: The four-letter ICAO code for an aerodrome or FIR, from ICAO Doc 7910, used in NOTAM Item A. AIS.TR.330(n) Aeronautical information: AIP, NOTAM, AIRAC and AIC
location sign: Yellow-on-black sign naming the taxiway, runway or pavement the aircraft is on or entering; no arrows. CS ADR-DSN.N.785(c)(2), (c)(8) Aerodrome signs
long final: The report made when turning onto final more than 7 km (4 NM) from touchdown, or at 15 km (8 NM) from touchdown on a straight-in approach. Appendix 1 to AMC1 SERA.14001, 1.4.15 Note ATS phraseologies
low-/medium-/high-intensity obstacle light: Three families of obstacle light of increasing brightness. Each light type has a letter that shows its colour and whether it is fixed or flashing. CS ADR-DSN.Q.846(b); Table Q-1 Obstacles and restricted-use areas
lowest usable flight level: The lowest flight level that can be used where no transition altitude is established (term used, not defined, in SERA). SERA.3110 Altimeter setting procedures
magnetic track: The track that selects the VFR cruising level in SERA Appendix 3 (grid track in polar areas above 70° latitude, where prescribed). SERA Appendix 3, footnote 1
maintenance: Overhaul, repair, inspection, replacement, modification or defect rectification; not the pre-flight inspection. Reg. (EU) No 1321/2014 Art. 2(h) Airworthiness and the certificate of airworthiness
Mandatory instruction marking: White-on-red surface inscription replacing or supplementing a mandatory instruction sign CS ADR-DSN.L.605 Aerodrome markings
mandatory instruction sign: White-on-red sign marking a place a taxiing aircraft or vehicle must not pass without tower authorisation. CS ADR-DSN.N.780(a)(1), (c)(1) Aerodrome signs
manoeuvring area: Take-off, landing and taxiing areas, excluding aprons. SERA Art. 2(94) Aerodrome control and visual separation near aerodromes
marker: Object displayed above ground level to indicate an obstacle or delineate a boundary. CS ADR-DSN.A.002 Indicators, signalling devices and markers
marking: Symbol or group of symbols on the surface of the movement area that conveys aeronautical information. CS ADR-DSN.A.002 Indicators, signalling devices and markers
MAYDAY / PAN PAN: Radiotelephony signals that open the first message of a distress (MAYDAY) or urgency (PAN PAN) communication. SERA.14095(a)(2) Emergencies, communication failure and contingencies
Minimum fuel (minimum fuel/energy): Report that the flight is committed to one aerodrome and further delay could eat into final reserve; not an emergency. GM1 SERA.11012 Emergencies, communication failure and contingencies
Mode A / Mode C / Mode S: A: identity code; C: code + pressure-altitude; S: selective, with 24-bit address and aircraft identification. SERA Appendix 6 Item 10; Art. 2(19) (detail 060-08-02) Transponder operating procedures and phraseology
Mode C level verification: The check by ATS that the level displayed by the transponder is within the approved tolerance of the reported level. SERA.13010(b) Transponder operating procedures and phraseology
mountainous area: An area where terrain elevation changes by more than 900 m (3 000 ft) within 18.5 km (10.0 NM). SERA Article 2(95b) Rules of the air: definitions and applicability
movement area: Manoeuvring area plus aprons. SERA Art. 2(96) Aerodrome control and visual separation near aerodromes
MSAW: Minimum safe altitude warning: ground system warning of possible infringement of a minimum safe altitude GM3 ATS.TR.155(c)(9) Radar services
Multilateration (MLAT): Position derived from transponder signals received at several ground stations, mainly by time difference of arrival GM1 Annex IV (Part-ATS) Radar services
national civil aviation security programme: The State document that sets out security responsibilities and measures. Reg. (EC) No 300/2008 Art. 10 Aviation security: aims and objectives
nationality mark: Group of characters taken from the ITU radio call-sign series allocated to the State of Registry, placed first in the aircraft's marks. Annex 7 3.3 Nationality and registration marks
navigation lights: Lights intended to show an observer the relative path of the aircraft. SERA.3215(a)(2)
night: The time from the end of evening civil twilight to the start of morning civil twilight. Civil twilight ends or starts when the centre of the sun is 6° below the horizon. SERA Article 2(97)
Night rating: Rating that allows LAPL or PPL privileges in VFR at night. FCL.810 Personnel licensing: Annex 1, Part-FCL and Part-MED
No-entry bar: Row of red lights across an exit-only taxiway preventing wrong-way entry CS ADR-DSN.M.771 Aerodrome lights
Noise certificate: Separate certificate (EASA Form 45) showing the noise standard the aircraft meets. 21.B.425; Appendix VII Airworthiness and the certificate of airworthiness
Non-instrument runway: Runway for aircraft using visual approach procedures CS ADR-DSN.A.002 Aerodrome markings
non-load-bearing surface: A paved-looking surface, such as a taxiway shoulder, that can damage an aircraft that uses it. CS ADR-DSN.R.860(a) Obstacles and restricted-use areas
Non-precision approach runway: Instrument runway with visual aids and at least one non-visual aid, for landings after a type A instrument approach CS ADR-DSN.A.002 Aerodrome markings
Non-scheduled flight: A flight not part of a scheduled international air service; has rights of entry, transit and non-traffic stops under Art. 5. Art. 5 Chicago Convention, Part I: air navigation
normal code: A code selected as ATS instructs or, without instructions, the default code 2000 or the conspicuity code 7000. SERA.13005(b)(1)–(3) Transponder operating procedures and phraseology
NOTAM: A notice distributed by telecommunication about the establishment, condition or change of a facility, service, procedure or hazard, the timely knowledge of which is essential to people involved in flight operations. Reg. (EU) 2017/373 Annex I (73); SERA Art. 2(97a) Aeronautical information: AIP, NOTAM, AIRAC and AIC
NOTAMN / NOTAMR / NOTAMC: New, replacing and cancelling NOTAM. Annex VI Appendix 2 Aeronautical information: AIP, NOTAM, AIRAC and AIC
obstacle: A fixed or mobile object, or part of one, on a surface where aircraft move, above a protective surface, or outside those surfaces but assessed as hazardous. Reg. (EU) No 139/2014 Art. 2(13) Obstacles and restricted-use areas
obstacle limitation surface (OLS): A surface that defines how high objects may project into the airspace around an aerodrome. Reg. (EU) No 139/2014 Art. 2(14) Obstacles and restricted-use areas
obstacle protection surface: A surface that protects a visual approach slope indicator; new objects are not permitted above it unless shielded. Reg. (EU) No 139/2014 Art. 2(15) Obstacles and restricted-use areas
occurrence: Any safety-related event that endangers, or could endanger, an aircraft, its occupants or any other person. Includes accidents and serious incidents. Reg. (EU) No 376/2014 Art. 2(7) Accident and incident investigation
operating site: A site that the operator or pilot-in-command selects for landing, take-off and/or hoist operations. SERA Article 2(99) Rules of the air: definitions and applicability
overtaking aircraft: An aircraft that approaches another aircraft from behind, on a line forming an angle of less than 70° with the other aircraft's plane of symmetry. SERA.3210(c)(3)
PANS: Procedures for Air Navigation Services; ICAO documents alongside the Annexes (six exist). ICAO: objectives and composition
PAPI / APAPI: Precision approach path indicator (four light units) / abbreviated PAPI (two light units). CS ADR-DSN.M.645 Aerodrome lights
Part-FCL: Annex I to Reg. (EU) No 1178/2011: EU rules for pilot licences, ratings and certificates. Reg. (EU) No 1178/2011; FCL.005 Personnel licensing: Annex 1, Part-FCL and Part-MED
Part-MED: Annex IV to Reg. (EU) No 1178/2011: EU rules for aircrew medical certificates. MED.A.005 Personnel licensing: Annex 1, Part-FCL and Part-MED
PCN: Pavement classification number: the pavement-strength figure in the ACN-PCN report. GM1 ADR.OPS.A.005 Aerodromes: definitions and aerodrome data
PCR / ACR: ICAO pavement classification rating (pavement strength) / aircraft classification rating (aircraft's effect on a pavement); aircraft with ACR ≤ PCR may use the pavement. Annex 14 Ch. 1, 2.6.3 Aerodromes: definitions and aerodrome data
permit to fly: Authorisation (EASA Form 20a/20b) for an aircraft that does not meet or is not shown to meet airworthiness requirements to fly for set purposes under set conditions. 21.A.701; 21.A.711 Airworthiness and the certificate of airworthiness
person involved: Owner, crew member or operator of an aircraft in an accident or serious incident, and others linked to its maintenance, design, training or air traffic services. Reg. (EU) No 996/2010 Art. 2(11) Accident and incident investigation
PIB: A plain-language summary of valid NOTAM of operational significance and other urgent information, prepared for flight crews before flight. GM1 AIS.OR.405(b)(c); ICAO Annex 15 Ch. 1 Aeronautical information: AIP, NOTAM, AIRAC and AIC
PIC: Pilot designated as being in command and responsible for the safe conduct of the flight. FCL.010 Personnel licensing: Annex 1, Part-FCL and Part-MED
pilot-owner: Licensed pilot who owns (or co-owns) the aircraft and may release limited maintenance on a Part-NCO aircraft. ML.A.803 Airworthiness and the certificate of airworthiness
plain language: Ordinary language, used only when no standard phraseology can carry the intended message. SERA.14001; GM2 Appendix 1 to AMC1 SERA.14001 ATS phraseologies
Position indication: Symbol or blip on the situation display showing an aircraft's position Reg. (EU) 2017/373 Annex I (215) Radar services
PPL(A): Private pilot licence for aeroplanes. The holder acts as PIC or co-pilot without remuneration in non-commercial operations. FCL.205.A Personnel licensing: Annex 1, Part-FCL and Part-MED
Pre-flight altimeter check location: Published-elevation area (often the apron) used to check the altimeter before flight. GM1 ADR.OPS.A.005 Aerodromes: definitions and aerodrome data
pre-flight inspection: Inspection before flight to make sure the aircraft is fit for the intended flight; the PIC's responsibility. Reg. (EU) No 1321/2014 Art. 2(j); ML.A.201(d) Airworthiness and the certificate of airworthiness
pre-threshold area: A paved area before a threshold that is not suitable for normal aircraft use. It carries chevron marking when it is longer than 60 m. CS ADR-DSN.R.865 Obstacles and restricted-use areas
Precision approach runway (CAT I/II/III): Instrument runway with visual aids and at least one non-visual aid, for landings after a type B CAT I/II/III approach CS ADR-DSN.A.002 Aerodrome markings
preliminary report: Early communication of data from an investigation. Reg. (EU) No 996/2010 Art. 2(12) Accident and incident investigation
pressure-altitude: A pressure expressed as its altitude in the Standard Atmosphere. SERA Article 2(101) Altimeter setting procedures
Primary surveillance radar (PSR): Radar that detects aircraft from reflected energy; shown as a "PSR blip"; needs no aircraft equipment GM1 Annex IV (Part-ATS) Radar services
principal / complementary agent: Principal: foam (performance level A, B or C). Complementary: dry chemical powder or an equivalent, for fast knock-down of fuel fires. AMC4 ADR.OPS.B.010(a)(2) Rescue and fire fighting, apron management
procedure word: The defined words and phrases with fixed meanings, such as ROGER, WILCO, AFFIRM and STANDBY. SERA.14045(b) ATS phraseologies
Procedure words: The defined words and phrases with fixed meanings, such as ROGER, WILCO, AFFIRM and STANDBY. SERA.14045(b) ATS phraseologies
Prohibited area: Area over which a State restricts or prohibits flight for military necessity or public safety. Art. 9 Chicago Convention, Part I: air navigation
prohibited articles: Weapons, explosives or other dangerous devices, articles or substances that may be used to commit an act of unlawful interference. Reg. (EC) No 300/2008 Art. 3(7) Aviation security: aims and objectives
projected course: The track a surface craft will follow if it holds its present heading; the aircraft crosses it close ahead for "follow me". Annex 12, Appendix 1.1(b) (usage) Search and rescue signals
Provisional ICAO (PICAO): The interim organisation set up by the Interim Agreement signed at Chicago on 7 December 1944, before the Convention came into force. Art. 45 ICAO: objectives and composition
psychoactive substance: Alcohol, opioids, cannabinoids, sedatives and hypnotics, cocaine, other psychostimulants, hallucinogens and volatile solvents (not caffeine or tobacco). SERA Article 2(104) Rules of the air: definitions and applicability
pyrotechnic signal: A flare or rocket used as a signal, for example a red pyrotechnic meaning do not land for the time being. SERA App. 1, 1.2.1(d), (e); Table AP 1-1
QFE: The altimeter setting that makes the altimeter read height above the aerodrome QFE datum. GM1 SERA Article 2(84) Altimeter setting procedures
QNH: The altimeter setting that makes the altimeter read altitude above mean sea level. GM1 SERA Article 2(39) Altimeter setting procedures
Radar approach: Approach whose final phase is directed by a controller using radar GM1 Annex IV (Part-ATS) Radar services
Radar clutter: Unwanted signals shown on a situation display GM1 Annex IV (Part-ATS) Radar services
Radar contact: An aircraft's radar position is seen and identified on a situation display GM1 Annex IV (Part-ATS) Radar services
radio communication failure procedure: Fixed actions after failed attempts to re-establish contact, including code 7600, and for a VFR flight staying in VMC, landing at the nearest suitable aerodrome and reporting arrival. SERA.14083 Emergencies, communication failure and contingencies
radio mandatory zone (RMZ): Airspace where VFR flights in Class E, F or G keep a continuous listening watch and make an initial call before entry. SERA.6005(a)
RCAM: Runway condition assessment matrix, used to assign the RWYCC. Reg. (EU) No 139/2014 Annex I (38a) Aerodromes: definitions and aerodrome data
RDRS: Runway distance remaining sign: optional ICAO white-on-black sign beside the runway showing distance to go. Annex 14 5.4.8 Aerodrome signs
readback: Repetition by the pilot of an item, such as an SSR code, to confirm that it was received correctly. SERA.8015(e)(1)(iii) Transponder operating procedures and phraseology
Reduced runway separation minima (RRSM): Locally prescribed, daylight-only shorter runway spacing for light propeller types AMC9 ATS.TR.210(c)(2)(i) Aerodrome control and visual separation near aerodromes
registration mark: Letters and/or numbers assigned by the State of Registry (or common mark registering authority), following the nationality or common mark. Annex 7 3.5 Nationality and registration marks
reporter: Natural person who reports an occurrence or safety information. Reg. (EU) No 376/2014 Art. 2(1) Accident and incident investigation
Reporting point / significant point: Location against which position is reported / location defining a route or flight path SERA Article 2(110), (121) Air traffic services: definitions and general provisions
RESA: Runway end safety area; a symmetrical area beyond the end of the strip, mainly to reduce damage to an aeroplane that undershoots or overruns the runway. Reg. (EU) No 139/2014 Annex I (38d); CS ADR-DSN.A.002 Aerodromes: definitions and aerodrome data
Rescue: Operation to retrieve persons in distress, meet initial needs and deliver them to a place of safety. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
rescue and firefighting services (RFFS): The aerodrome service that responds to aircraft accidents and incidents at or near the aerodrome to save lives. ADR.OPS.B.010; GM1 ADR.OPS.B.010(a)(1) Rescue and fire fighting, apron management
rescue coordination centre (RCC): Unit that organises SAR services and coordinates SAR operations in a SAR region. Reg. (EU) 2017/373 Annex I (82) Flight information service and alerting service
Rescue subcentre (RSC): Unit subordinate to an RCC, set up to complement it. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
rescue unit: A unit (ground team, vessel or aircraft) taking part in a rescue; here, the ground team laying out the rescue-unit symbols. Annex 12, Chapter 1 Search and rescue signals
response time: Time from the initial call to the RFFS until the first vehicles can apply foam at at least 50 % of the required rate. AMC5 ADR.OPS.B.010(a)(2) Rescue and fire fighting, apron management
restricted area: Airspace over a State's land or territorial waters in which flight is restricted by specified conditions. SERA Article 2(111) Rules of the air: general rules
restricted certificate of airworthiness: Certificate (EASA Form 24, or 24B for declared designs) for an aircraft conforming to a restricted TC or specific airworthiness specifications; carries limitations for use. 21.A.173(b); 21.B.325(b); 21.B.327 Airworthiness and the certificate of airworthiness
RETILs: Rapid exit taxiway indicator lights: yellow 3-2-1 distance-to-go lights CS ADR-DSN.M.700 Aerodrome lights
retroreflective: Reflecting light back towards its source, such as an aircraft's taxi light. Indicators, signalling devices and markers
Revalidation / renewal: Revalidation extends a rating within its validity period. Renewal restores a rating after it lapses. FCL.010 Personnel licensing: Annex 1, Part-FCL and Part-MED
right-of-way: The priority one aircraft has over another under the rules of the air. The aircraft with right-of-way keeps its heading and speed. SERA.3210(a)
Road-holding position: Designated position where vehicles may be required to hold CS ADR-DSN.A.002 Aerodrome markings
runway condition report: Standardised report of runway surface condition and its effect on performance, using the RWYCC. Reg. (EU) No 139/2014 Annex I (38c) Aerodromes: definitions and aerodrome data
runway guard lights: Lights cautioning pilots and drivers that they are about to enter an active runway. CS ADR-DSN.A.002 Aerodrome lights
runway incursion: Incorrect presence of an aircraft, vehicle or person on the protected area of a landing or take-off surface. GM1 Annex IV (Part-ATS) Aerodrome control and visual separation near aerodromes
runway strip: Defined area that includes the runway and any stopway, reducing the risk of damage to aircraft that run off the runway and protecting aircraft flying over it. Reg. (EU) No 139/2014 Annex I (38f); CS ADR-DSN.A.002 Aerodromes: definitions and aerodrome data
Runway turn pad: Defined area next to a runway for completing a 180° turn CS ADR-DSN.A.002 Aerodrome markings
runway vacated sign: Black-on-yellow sign showing the pattern A holding-position marking; marks the edge of the protected area for an aircraft leaving the runway. CS ADR-DSN.N.785(a)(4), (c)(4) Aerodrome signs
runway-holding position: A designated point that protects a runway, where taxiing aircraft and vehicles stop and hold. SERA Article 2(114); GM1 Article 2(114)
Runway-holding position / holding point: Designated place protecting a runway, OLS or ILS area where traffic stops unless the tower authorises SERA Art. 2(114); GM1 Annex IV (Part-ATS) Aerodrome control and visual separation near aerodromes
runway-holding position marking: Yellow marking painted along a runway-holding position, in pattern A or pattern B. CS ADR-DSN.L.575(a) Aerodrome markings
Runway-in-use: Runway selected by the tower for take-off and landing ATS.TR.260 Aerodrome control and visual separation near aerodromes
RVR: Range over which a pilot on the runway centre line can see the runway markings or lights CS ADR-DSN.A.002 Aerodrome lights
RWSL (RELs, THLs): Runway status lights: automatic red runway entrance and take-off hold lights CS ADR-DSN.M.706 Aerodrome lights
RWYCC: Runway condition code; a number from 0 to 6 describing the effect of the surface on deceleration and directional control. Reg. (EU) No 139/2014 Annex I (38b) Aerodromes: definitions and aerodrome data
safety investigation: Process of gathering and analysing information, drawing conclusions and making safety recommendations, to prevent accidents and incidents. Reg. (EU) No 996/2010 Art. 2(14) Accident and incident investigation
safety investigation authority (SIA): Permanent, independent national body that conducts or supervises safety investigations. Reg. (EU) No 996/2010 Art. 4(1) Accident and incident investigation
safety pilot: A pilot licensed to act as PIC of the aircraft who keeps look-out and can take control during simulated instrument flight. SERA.3220(b); GM1 SERA.3220(b) Rules of the air: general rules
safety recommendation: Proposal by an SIA, intended to prevent accidents and incidents. It creates no presumption of blame or liability. Reg. (EU) No 996/2010 Art. 2(15), 17(3) Accident and incident investigation
safety-sensitive personnel: People who might endanger aviation safety if they do their job improperly (crew, maintenance, aerodrome, rescue and fire-fighting staff, controllers…). SERA Article 2(116) Rules of the air: definitions and applicability
SAR aircraft: Aircraft with specialised equipment for efficient SAR missions. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
SAR facility: Any mobile resource used for SAR, including designated SAR units. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
SAR point of contact (SPOC): Point designated by a State to receive Cospas-Sarsat distress data (24-hour from 26 Nov 2026). Annex 12, 3.2.5; Reg. (EU) 2017/373 (GM text, ear-atm-ans L15837) Search and rescue: definitions and pilot procedures
SAR services unit (EU): Generic term for RCC, rescue sub-centre or alerting post. Reg. (EU) 2017/373 Annex I (90) Search and rescue: definitions and pilot procedures
SAR unit: Mobile resource of trained people with suitable equipment for expeditious SAR operations. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
SARPs: International standards and recommended practices adopted by ICAO and designated as Annexes. Arts 37, 54(l) Chicago Convention, Part I: air navigation
screening: Applying technical or other means to identify or detect prohibited articles. Reg. (EC) No 300/2008 Art. 3(8) Aviation security: aims and objectives
Search: Operation, normally coordinated by an RCC/RSC, to locate persons in distress. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
search and rescue region (SRR): Area of defined dimensions, linked to one RCC, in which SAR services are provided. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
Search and rescue service: Distress monitoring, communication, coordination and SAR functions, initial medical assistance or evacuation, using public and private resources. Annex 12 Ch. 1 Search and rescue: definitions and pilot procedures
Secretary General: ICAO's chief executive officer, appointed by the Council; heads the Secretariat. Art. 54(h) ICAO: objectives and composition
security control: Any means by which the introduction of prohibited articles may be prevented. Reg. (EC) No 300/2008 Art. 3(9) Aviation security: aims and objectives
security occurrence / security incident: A security-related event that may reduce security. An incident is an occurrence that affects, or could affect, people's safety. Reg. (EC) No 300/2008 Annex II point 1.1(15)-(16) Aviation security: aims and objectives
security restricted area (SRA): The part of airside where access is restricted and further security standards also apply. Reg. (EC) No 300/2008 Art. 3(13) Aviation security: aims and objectives
SEP aeroplane: Single-engine, single-pilot aeroplane without type rating, driven by a piston, electric or hybrid engine system; class ratings SEP(land) and SEP(sea). Article 2(8c); GM1 FCL.010 Personnel licensing: Annex 1, Part-FCL and Part-MED
SEP class rating: Class rating for single-engine, single-pilot aeroplanes without a type rating. Valid for 2 years unless the operational suitability data (OSD) says otherwise. Article 2(8c); GM1 FCL.010; FCL.740(a)(1) Personnel licensing: Annex 1, Part-FCL and Part-MED
Sequenced flashing lights: Approach centre line flashing lights firing twice a second from outer to inner CS ADR-DSN.M.630(c)(7) Aerodrome lights
serious incident: Incident whose circumstances show a high probability of an accident, in the same window. Reg. (EU) No 996/2010 Art. 2(16) Accident and incident investigation
serious injury: Injury suffered in an accident that meets one of six criteria, such as a hospital stay of more than 48 hours starting within 7 days of the injury. Reg. (EU) No 996/2010 Art. 2(17) Accident and incident investigation
signal area: An area on an aerodrome where ground signals are displayed. SERA Article 2(120)
signal panel: Panel displayed in the signal area to convey a visual ground signal. GM1 ADR-DSN.K.505 Indicators, signalling devices and markers
signalling lamp: Hand-aimed lamp in the control tower that produces red, green and white light signals. CS ADR-DSN.K.500 Indicators, signalling devices and markers
signalman / marshaller: A trained, approved person who guides aircraft on the ground with standard hand signals. SERA.3301(c), (d); GM1 to App. 1(4.1)(d)
Situation display: Controller's electronic display of aircraft position and movement Reg. (EU) 2017/373 Annex I (233) Radar services
skeletal object: A lattice or open-frame structure, such as a pylon, that is marked with bands when it is over 1.5 m in one dimension. CS ADR-DSN.Q.845(b)(2)(ii) (term used, not defined) Obstacles and restricted-use areas
Skill test / proficiency check: Skill test demonstrates skill for the issue of a licence or rating. Proficiency check demonstrates skill to revalidate or renew. FCL.010 Personnel licensing: Annex 1, Part-FCL and Part-MED
Slippery wet runway: Wet runway with friction found to be degraded over a significant portion. Reg. 139/2014 Annex I (41a) Aerodromes: definitions and aerodrome data
Slush: Snow so saturated that water drains from it when picked up. Reg. 139/2014 Annex I (38h)(e) Aerodromes: definitions and aerodrome data
SMGCS: Surface movement guidance and control system: the aerodrome's system of guidance and control for surface movement, which signs support. CS ADR-DSN.N.775(b)(1) (term used, not defined in text read) Aerodrome signs
SNOWTAM: A special-series NOTAM, in standard format, that reports snow, ice, slush, frost or water on the movement area. Reg. (EU) 2017/373 Annex I (231) Aeronautical information: AIP, NOTAM, AIRAC and AIC
Sovereignty (airspace): A State's complete and exclusive authority over the airspace above its territory. Art. 1 Chicago Convention, Part I: air navigation
Special air-report: Met report from an aircraft in flight, issued against set criteria Reg. (EU) 2017/373 Annex I (95) Flight information service and alerting service
special code: A code with a fixed meaning, selected to indicate an emergency, radio-communication failure or unlawful interference (7700, 7600, 7500). SERA.13005(a)(1)–(3) Transponder operating procedures and phraseology
special VFR: A VFR flight with an ATC clearance to operate in a control zone (CTR) in weather below VMC. SERA Article 2(122); SERA.5010
Special VFR flight: A VFR flight cleared by ATC to fly in a CTR in weather below VMC. SERA Art. 2(122) Visual flight rules
Specially prepared winter runway: Dry frozen compacted-snow/ice runway treated (sand, grit or mechanically) to improve friction. Reg. 139/2014 Annex I (41c) Aerodromes: definitions and aerodrome data
squelch: Receiver control that mutes the audio until the incoming signal exceeds a threshold, so weak signals are not heard. Search and rescue: definitions and pilot procedures
SSR: Radar system of ground interrogators and airborne transponders. SERA Art. 2(118) Transponder operating procedures and phraseology
stand (aircraft stand): A designated parking position on an apron, allocated to suit the aircraft type. ADR.OPS.D.025 Rescue and fire fighting, apron management
Standard (standardised) phraseology: The fixed words and phrases set out for a situation, which must be used whenever they exist. SERA.14001; Appendix 1 to AMC1 SERA.14001 ATS phraseologies
standard phraseology: The fixed words and phrases set out for a situation, which must be used whenever they exist. SERA.14001; Appendix 1 to AMC1 SERA.14001 ATS phraseologies
standard setting: The subscale setting of 1013.2 hPa, at which the altimeter reads flight levels. GM1 SERA Article 2(78) Altimeter setting procedures
Standing water: Water deeper than 3 mm. Reg. 139/2014 Annex I (38h)(f) Aerodromes: definitions and aerodrome data
State aircraft: Aircraft used in military, customs and police services; outside the Convention. Art. 3(b) Chicago Convention, Part I: air navigation
state of design / state of manufacture: The State responsible for the organisation that holds the type design, or in which final assembly takes place. Annex 13 Ch. 1 Accident and incident investigation
state of occurrence: The State in whose territory the accident or incident occurs. Annex 13 Ch. 1 (used in Reg. (EU) No 996/2010 Art. 9) Accident and incident investigation
State of registry: The State in whose register the aircraft is entered; issues or validates its certificates and crew licences. Arts 17, 31, 32 Chicago Convention, Part I: air navigation
state of the operator: The State of the operator's principal place of business or, if none, permanent residence. Annex 13 Ch. 1 Accident and incident investigation
STCA: Short-term conflict alert: ground system alert of potential or actual separation infringement GM2 ATS.TR.155(c)(9) Radar services
stop bar: Lights at a holding position. Stop and hold at a lit stop bar; guidance says never to cross one that is lit. SERA.3210(d)(3); GM1 SERA.3210(d)(3)
stopway: Defined rectangular area on the ground at the end of the TORA, prepared for stopping an aircraft in an abandoned take-off. Reg. (EU) No 139/2014 Annex I (42); CS ADR-DSN.A.002 Aerodromes: definitions and aerodrome data
strayed aircraft: Aircraft significantly off its intended track, or reporting that it is lost. SERA Article 2(123) Emergencies, communication failure and contingencies
surface craft: A ship or boat on the water (as opposed to an aircraft), which may be directed to, or itself be, a craft in distress. Annex 12, Appendix 1 (usage) Search and rescue signals
surface in sight: The pilot sees the ground or water. SERA gives no definition; this is a plain-language explanation, not a defined term. SERA.5001, Table S5-1; SERA.5005(c)(3)(iii)
taxi side stripe marking: Two solid lines, each 15 cm wide and 15 cm apart, in the colour of the taxiway centre line marking. It marks the edge of the load-bearing pavement. CS ADR-DSN.R.860 Obstacles and restricted-use areas
Territory: A State's land areas and adjacent territorial waters under its sovereignty, suzerainty, protection or mandate. Art. 2 Chicago Convention, Part I: air navigation
threshold: Beginning of the part of the runway usable for landing. CS ADR-DSN.A.002; Annex 14 Ch. 1 Aerodromes: definitions and aerodrome data
threshold marking: A pattern of identical white longitudinal stripes placed symmetrically about the runway centre line at the threshold. CS ADR-DSN.L.535(a)-(b) Aerodrome markings
TODA: TORA plus the clearway, if provided. Reg. (EU) No 139/2014 Annex I (43) Aerodromes: definitions and aerodrome data
TORA: Runway length declared available and suitable for the ground run of an aeroplane taking off. Reg. (EU) No 139/2014 Annex I (44) Aerodromes: definitions and aerodrome data
Touchdown zone: Part of the runway beyond the threshold where landing aeroplanes are meant to touch down first. CS ADR-DSN.A.002 Aerodromes: definitions and aerodrome data
track: The projection of the aircraft's path on the earth's surface; direction in degrees from true, magnetic or grid north. SERA Article 2(130) Rules of the air: definitions and applicability
Traffic avoidance advice: ATS advice on manoeuvres to avoid a collision SERA Article 2(131) Air traffic services: definitions and general provisions
Traffic information: ATS information alerting a pilot to nearby known or observed traffic, to help avoid collision SERA Article 2(132) Radar services
Transfer of control point: Point where ATC responsibility passes to the next unit or position SERA Article 2(133) Air traffic services: definitions and general provisions
transition altitude: The altitude at or below which the vertical position of an aircraft is controlled by reference to altitudes. SERA Article 2(134)
transition layer: The airspace between the transition altitude and the transition level (term used, not defined, in SERA). SERA.8015(eb)(1) Altimeter setting procedures
transition level (TL): The lowest flight level available for use above the transition altitude. SERA Article 2(135) Altimeter setting procedures
Transponder: Airborne part of SSR that replies to interrogations (with code, altitude, identity depending on mode). Transponder operating procedures and phraseology
transponder mandatory zone (TMZ): Airspace where all flights carry and operate a Mode A+C or Mode S transponder. SERA.6005(b)
trigger NOTAM: A NOTAM that announces an AIP amendment or supplement published under AIRAC, in force from the same date and time as that change. AIS.OR.510(b); AIS.TR.510(f)-(j) Aeronautical information: AIP, NOTAM, AIRAC and AIC
Type certificate (TC): EASA's approval of a design, including its operating limitations and instructions for continued airworthiness. 21.A.41 Airworthiness and the certificate of airworthiness
uncertainty phase (INCERFA): Uncertainty exists about the safety of an aircraft and its occupants. Reg. (EU) 2017/373 Annex I (251); ATS.TR.405(b)(1) Flight information service and alerting service
unidentified aircraft: An aircraft seen or reported in an area whose identity has not been established. SERA Article 2(137) Interception of civil aircraft
unlawful interference: Interference with an aircraft that the pilot signals with code 7500; code 7700 can be used instead when circumstances warrant. SERA.13005(a)(3) Transponder operating procedures and phraseology
unserviceability marker / light: A cone, flag or striped board (marker), or a steady red light of at least 10 cd (light), that outlines an unserviceable or closed area. CS ADR-DSN.R.870 Obstacles and restricted-use areas
unserviceable area: A part of a taxiway, apron or holding bay that is unfit for aircraft movement, but that aircraft can safely go around. It is shown by unserviceability markers and lights. AMC1 ADR.OPS.B.070(c)(5); CS ADR-DSN.R.870 Obstacles and restricted-use areas
urgency: A state of difficulty, or a very urgent safety message, without need for immediate assistance. Signals include PAN PAN and XXX. SERA App. 1, 1.3
UTC: Coordinated Universal Time, the time standard used in aviation, on the 24-hour clock. SERA.3401(a) Rules of the air: general rules
Variable message sign: A sign able to show several predetermined messages, or none. CS ADR-DSN.A.002 Aerodrome signs
variable white: White used for lights whose intensity is varied. CS ADR-DSN.U.930(c)(3) Aerodrome lights
Vectoring: Navigational guidance as specific headings, based on surveillance Reg. (EU) 2017/373 Annex I (253) Radar services
VFR flight: A flight flown under the visual flight rules. SERA Article 2(140)
VFR on top: VFR flight above a cloud layer. At night it is possible above the low band, after the pilot considers the GM factors. GM1 SERA.5005(c)(3)(iii)
VHF emergency frequency: 121.500 MHz, reserved for genuine emergency purposes. SERA Art. 4a; ATS.OR.405 Emergencies, communication failure and contingencies
visibility: The greater of two distances - the distance at which a suitable black object near the ground is seen and recognised against a bright background, and the distance at which lights of about 1 000 cd are seen and identified against an unlit background. SERA Article 2(141); GM1 Article 2(141)
Visual aids: Indicators and signalling devices, markings, lights, signs and markers, or combinations of them. CS ADR-DSN.A.002 Aerodrome signs
visual docking guidance system: A stand system that guides the pilot onto the stand and shows where to stop. AMC1/AMC2 ADR.OPS.D.035(b); GM1 ADR.OPS.D.025(b)(2) Rescue and fire fighting, apron management
visual meteorological conditions (VMC): Weather conditions, described by visibility, distance from cloud and ceiling, at or better than the specified minima. SERA Article 2(142)
VOLMET / VOLMET broadcast: Meteorological information for aircraft in flight / continuous voice broadcast of current METAR, SPECI, TAF and SIGMET. Reg. (EU) 2017/373 Annex I (257), (258) Flight information service and alerting service
Wake / astern: The disturbed water behind a moving vessel / behind the vessel; the aircraft crosses it close astern for "no longer required". Annex 12, Appendix 1.2 (usage) Search and rescue signals
Wake turbulence category: Grouping of aircraft types (J, H, M, L) by MCTOM for wake minima AMC1 SERA.8012 Aerodrome control and visual separation near aerodromes
Wet runway: Runway with visible dampness or water up to and including 3 mm deep. Reg. 139/2014 Annex I (49) Aerodromes: definitions and aerodrome data
wind direction indicator: Fabric truncated cone on a pivot that shows the surface wind direction and a general indication of wind speed. Also called a wind sleeve, wind cone or windsock. CS ADR-DSN.K.490 Indicators, signalling devices and markers
Wing bar: Group of at least five green lights extending outward from each side of the threshold CS ADR-DSN.M.680(d) Aerodrome lights