ISO/FDIS 21384-4
(Main)Unmanned aircraft systems — Part 4: Vocabulary
Unmanned aircraft systems — Part 4: Vocabulary
This document defines terms and definitions relating to unmanned aircraft systems that are widely used in science and technology.
Aéronefs télépilotés — Partie 4: Vocabulaire
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ISO/TC 20/SC 16
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FINAL DRAFT
International
Standard
ISO/TC 20/SC 16
Unmanned aircraft systems —
Secretariat: ANSI
Part 4:
Voting begins on:
Vocabulary
Voting terminates on:
Aéronefs télépilotés —
Partie 4: Vocabulaire
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
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RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
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BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
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TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
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Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
Bibliography .10
Index .11
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 16, Uncrewed aircraft systems.
This second edition cancels and replaces the first edition (ISO 21384-4:2020), which has been technically
revised.
The main changes are as follows:
— several new terms, related to UAS, have been introduced.
A list of all parts in the ISO 21384 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
FINAL DRAFT International Standard ISO/FDIS 21384-4:2025(en)
Unmanned aircraft systems —
Part 4:
Vocabulary
1 Scope
This document defines terms relating to uncrewed aircraft systems that are widely used in science and
technology.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
aerodrome
defined area on land or water (including any buildings, installations and equipment) intended to be used
either wholly or in part for the arrival, departure and surface movement of aircraft
3.2
aerodrome pilot
remote pilot familiar with a defined aerodrome (3.1) or landing site, which transfers responsibility to
another pilot a few minutes after take-off or accepts responsibility for approach, landing and possibly taxing
and parking
3.3
airspace management
ASM
planning function with the primary objective of maximizing the utilization of available airspace by dynamic
time-sharing and, at times, the segregation of airspace among various categories of users based on short-
term needs, while securing aviation safety
3.4
ATS communication link
air traffic service communication link
digital or analogue communication link to transfer voice or data between remote crew members (3.55), air
traffic service, airspace users and other airspace users
Note 1 to entry: It includes air-ground, air-to-air and ground-ground links.
3.5
beyond visual line-of-sight
BVLOS
operation of a UAS (3.83) other than visual line-of-sight operation in which neither the remote pilot nor any
observer use visual reference to the uncrewed aircraft (3.80) in the conduct of flight
3.6
CNS
communications, navigation, and surveillance system
system employing digital technologies, including satellite systems together with various levels of automation
3.7
collision boundary
closest point of approach or minimum distance to be achieved between two aircrafts to ensure that a
collision is avoided taking account of any inaccuracies in the system
3.8
collision volume
cylindrical volume of airspace centred on the uncrewed aircraft (3.80) with a horizontal radius and vertical height
within which a collision is most likely and avoidance of a collision can only be considered a matter of chance
3.9
constituent
tangible objects such as hardware and intangible objects such as software upon which the provision of UAS
(3.83) traffic management (UTM) services depends
3.10
crew resource management
CRM
utilisation of all resources available to the remote crew members (3.55) to manage human error
3.11
down-link
direct or indirect data link from the uncrewed aircraft (3.80) to one or more peers
3.12
drone
uncrewed system which is remotely or autonomously operated and does not carry passengers
3.13
droneport
aerodrome (3.1), including vertiports (3.88), exclusively dedicated to landing, ground-handling and take-off
of uncrewed aircrafts (3.80)
Note 1 to entry: The droneport does not serve crewed fixed wings aeroplanes.
3.14
dual instruction time
time during which a person is receiving instruction from a properly authorized remote pilot at the controls
of the remote pilot station
3.15
elevation
vertical distance of a point or a level, on or affixed to the surface of the earth, measured from mean sea level
3.16
eVTOL aircraft
electric vertical take-off landing aircraft
aircraft which is crewed or uncrewed (remotely or autonomously) operated and carries cargo or passengers
or is used for aerial work
3.17
extended visual line-of-sight
EVLOS
operation beyond the unaided visual range of the remote pilot, but where the remote pilot is supported by
one or more visual observers (3.89)
3.18
external service
service and related provider, necessary for the safety of the UAS (3.83) flight, encompassing:
a) command and control link communication service provider (C2CSP);
b) other operation support services (3.43), whose purpose is to support a single flight but not to manage
traffic;
c) UAS traffic management (UTM) services
3.19
flight duty period
period which commences when the first remote crew member (3.55) reports for duty that includes a flight or
a series of flights and which finishes when the last remote crew member’s duty ends
3.20
flight manual
manual, acceptable by the local aviation authority, containing the order of actions in normal, abnormal and
emergency procedures, checklists, limitations, performance information, details of the aircraft systems
3.21
flight plan
specified information provided to air traffic service (ATS) units, relative to an intended flight or portion of a
flight of an aircraft
3.22
flight route
specified route designed for channelling the flow of traffic as necessary for the provision of UAS (3.83) traffic
management (UTM)
3.23
flight termination system
means and/or procedure triggered manually or automatically to initiate a pre-programmed action or a set of
actions designed to terminate UA (3.80) flight, minimising risks to third parties
3.24
flight time
total time from the moment the on-board systems are activated with the intent to perform a flight, until the
moment the on-board systems are de-activated
3.25
geo-limitation
entity that represents area surrounded by virtual boundary lines in the real world
3.26
geoid undulation
height of the geoid relative to a given ellipsoid of reference
3.27
height above ellipsoid
vertical distance of a point or a level, on or affixed to the surface of the earth, measured from World Geodetic
System 1984 (WGS 84) ellipsoid
3.28
heliport
aerodrome (3.1) or defined area on a structure intended to be used wholly or in part for the arrival, departure
and surface movement of helicopters of unlimited mass and performance [i.e. class C vertiport (3.88)]
Note 1 to entry: Vertiport is an infrastructure or system with supporting services and equipment intended for landing,
ground-handling and take-off of crewed or uncrewed vertical take-off and landing (VTOL) aircraft. Helicopters belong
to the VTOL family.
Note 2 to entry: EASA Special Condition SC-VTOL-01 defines a vertiport as an area of land, water, or structure used or
intended to be used for the landing and take-off of VTOL aircraft.
3.29
instrument approach
approach and landing operation using instruments for navigation guidance based on airborne, ground-
based or satellite-based equipment or combination thereof
3.30
instrument flight time
time during which a pilot is piloting (3.51) an aircraft (solely by reference to instruments and without
external reference points
3.31
international vertiport
vertiport (3.88) designated by a state in whose territory it is situated, as a vertiport of entry and departure
for international air traffic, where the formalities incident to customs, immigration, public health, animal
and plant quarantine and similar procedures are carried out
3.32
in-time system-wide safety assurance
ISSA
safety net utilising system-wide information to provide alerting and to trigger mitigation strategies in time
to address emerging risks. It is part of proactive safety management
3.33
intruder
aircraft within the surveillance volume (3.71) but outside the self-separation threshold
3.34
launch and recovery system
system from which or by means of which an uncrewed aircraft (3.80) is launched or by which it is recovered
3.35
lost link
loss of command and control link contact with the uncrewed aircraft (3.80) such that the remote pilot can no
longer manage the flight of the UA (3.80)
3.36
magnetic declination
angle on the horizontal plane between magnetic north and true north
3.37
crewed aircraft
aircraft which is intended or designed to be
...
ISO/TC 20/SC 16
Secretariat: ANSI
Date: 2025-01-03-14
Unmanned aircraft systems —
Part 4:
Vocabulary
Aéronefs sans pilote — télépilotés —
Partie 4: Vocabulaire
FDIS stage
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2025 – All rights reserved
ii
Contents
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
Bibliography . 12
Index . 13
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 16, UnmannedUncrewed aircraft systems.
This second edition cancels and replaces the first edition (ISO 21384-4:2020), which has been technically
revised.
The main changes are as follows:
— — several new terms, related to UAS, have been introduced.
A list of all parts in the ISO 21384 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv © ISO 2025 – All rights reserved
iv
DRAFT INTERNATIONAL STANDARD
Unmanned aircraft systems —
Part 4:
Vocabulary
1 Scope
This document defines terms and definitions relating to unmanneduncrewed aircraft systems that are widely
used in science and technology.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
aerodrome
defined area on land or water (including any buildings, installations and equipment) intended to be used
either wholly or in part for the arrival, departure and surface movement of aircraft
3.2 3.2
aerodrome pilot
remote pilot familiar with a defined aerodrome (3.1(3.1)) or landing site, which transfers responsibility to
another pilot a few minutes after take-off or accepts responsibility for approach, landing and possibly taxing
and parking
3.3 3.3
airspace management
ASM
planning function with the primary objective of maximizing the utilization of available airspace by dynamic
time-sharing and, at times, the segregation of airspace among various categories of users based on short-term
needs, while securing aviation safety
3.4 3.4
ATS communication link
air traffic service communication link
digital or analogue communication link to transfer voice or data between remote crew members (3.55(3.55),),
air traffic service, airspace users and other airspace users
Note 1 to entry: It includes air-ground, air-to-air and ground-ground links.
3.5 3.5
beyond visual line-of-sight
BVLOS
operation of a UAS (3.83(3.83)) other than Visualvisual line-of-sight operation in which neither the remote
pilot nor any observer use visual reference to the uncrewedaircraft (3.80unmanned aircraft (3.80)) in the
conduct of flight
3.6 3.6
CNS
communications, navigation, and surveillance system
system employing digital technologies, including satellite systems together with various levels of automation
3.7 3.7
collision boundary
closest point of approach or minimum distance to be achieved between two aircrafts to ensure that a collision
is avoided taking account of any inaccuracies in the system
3.8 3.8
collision volume
cylindrical volume of airspace centred on the unmanneduncrewed aircraft (3.80(3.80)) with a horizontal
radius and vertical height within which a collision is most likely and avoidance of a collision can only be
considered a matter of chance
3.9 3.9
constituent
tangible objects such as hardware and intangible objects such as software upon which the provision of UAS
(3.83UTM) traffic management (UTM) services depends
3.10 3.10
crew resource management
CRM
utilisation of all resources available to the remote crew members (3.55(3.55)) to manage human error
3.11 3.11
down-link
direct or indirect data link from the unmanneduncrewed aircraft (3.80(3.80)) to one or more peers
3.12 3.12
drone
unmanneduncrewed system which is remotely or autonomously operated and does not carry passengers
3.13 3.13
droneport
aerodrome (3.1(3.1),), including vertiports (3.88(3.88),), exclusively dedicated to landing, ground-handling
and take-off of unmanneduncrewed aircrafts (3.80(3.80))
NOTE: Note 1 to entry: The droneport does not serve mannedcrewed fixed wings aeroplanes.
3.14 3.14
dual instruction time
time during which a person is receiving instruction from a properly authorized remote pilot at the controls of
the remote pilot station
2 © ISO 2025 – All rights reserved
3.15 3.15
elevation
vertical distance of a point or a level, on or affixed to the surface of the earth, measured from mean sea level
3.16 3.16
eVTOL aircraft
electric vertical take-off landing aircraft
aircraft which is mannedcrewed or unmanneduncrewed (remotely or autonomously) operated and carries
cargo or passengers or is used for aerial work
3.17 3.17
extended visual line-of-sight
EVLOS
operation beyond the unaided visual range of the remote pilot, but where the remote pilot is supported by one
or more visual observers (3.89(3.89))
3.18 3.18
external service
service and related provider, necessary for the safety of the UAS (3.83(3.83)) flight, encompassing:
a) a) command and control link communication service provider (C2CSP);
b) b) other operation support services (3.43(3.43),), whose purpose is to support a single flight but not to
manage traffic;
c) c) UAS traffic management (UTM) services
3.19 3.19
flight duty period
period which commences when the first remote crew member (3.55(3.55)) reports for duty that includes a
flight or a series of flights and which finishes when the last remote crew member’s duty ends
3.20 3.20
flight manual
manual, acceptable by the local aviation authority, containing the order of actions in normal, abnormal and
emergency procedures, checklists, limitations, performance information, details of the aircraft systems
3.21 3.21
flight plan
specified information provided to air traffic service (ATS) units, relative to an intended flight or portion of a
flight of an aircraft
3.22 3.22
flight route
specified route designed for channelling the flow of traffic as necessary for the provision of UAS (3.83UTM)
traffic management (UTM)
3.23 3.23
flight termination system
means and/or procedure triggered manually or automatically to initiate a pre-programmed action or a set of
actions designed to terminate UA (3.80(3.80)) flight, minimising risks to third parties
3.24 3.24
flight time
total time from the moment the on-board systems are activated with the intent to perform a flight, until the
moment the on-board systems are de-activated
3.25 3.25
geo-limitation
entity that represents area surrounded by virtual boundary lines in the real world
3.26 3.26
geoid undulation
height of the geoid relative to a given ellipsoid of reference
3.27 3.27
height above ellipsoid
vertical distance of a point or a level, on or affixed to the surface of the earth, measured from World Geodetic
System 1984 (WGS 84) ellipsoid
3.28 3.28
heliport
aerodrome (3.1(3.1)) or defined area on a structure intended to be used wholly or in part for the arrival,
departure and surface movement of helicopters of unlimited mass and performance [i.e. class C vertiport
(3.88)]
Note 1 to entry: Vertiport is defined in ISO 21384-4 as an infrastructure or system with supporting services and
equipment intended for landing, ground-handling and take-off of mannedcrewed or unmanneduncrewed vertical take-
off and landing (VTOL) aircraft. Helicopters belong to the VTOL family.
Note 2 to entry: EASA Special Condition SC-VTOL-01 defines a vertiport as an area of land, water, or structure used or
intended to be used for the landing and take-off of VTOL aircraft.
3.29 3.29
instrument approach
approach and landing operation using instruments for navigation guidance based on airborne, ground-based
or satellite-based equipment or combination thereof
3.30 3.30
instrument flight time
time during which a pilot is piloting (3.51(3.51)) an aircraft (solely by reference to instruments and without
external reference points
3.31 3.31
international vertiport
vertiport (3.88(3.88)) designated by a state in whose territory it is situated, as a vertiport of entry and
departure for international air traffic, where the formalities incident to customs, immigration, public health,
animal and plant quarantine and similar procedures are carried out
4 © ISO 2025 – All rights reserved
3.32 3.32
in-time system-wide safety assurance
ISSA
safety net utilising system-wide information to provide alerting and to trigger mitigation strategies in time to
address emerging risks. It is part of proactive safety management
3.33 3.33
intruder
aircraft within the surveillance volume (3.71(3.71)) but outside the self-separation threshold
3.34 3.34
launch and recovery system
system from which or by means of which an unmanneduncrewed aircraft (3.80(3.80)) is launched or by which
it is recovered
3.35 3.35
lost link
loss of command and control link contact with the unmanneduncrewed aircraft (3.80(3.80)) such that the
remote pilot can no longer manage the flight of the UA (3.80)
3.36 3.36
magnetic declination
angle on the horizontal plane between magnetic north and true north
3.37
3.37 manned
crewed aircraft
aircraft which is intended or designed to be operated with at least one human pilot on board
3.373.38 3.38
model aircraft
UA (3.80(3.80)) that is capable of sustained flight in the atmosphere and that is used exclusively for leisure
flights, air displays, sport or competition activities
3.383.39 3.39
monitoring
process of observing on a regular basis over a period of time
3.393.40 3.40
national aviation authority
government statutory authority in each country that oversees the approval and regulation of civil aviation
3.403.41 3.41
non-cooperative aircraft
aircraft that do not have an electronic means of conspicuity (i.e. a transponder) aboard or not operating such
equipment due to malfunction or deliberate action
3.413.42 3.42
operation plan
specified information provided UAS
...
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