ISO 24355:2023

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 24355
ISO/TC 20/SC 16
Flight control system for civil small
Secretariat: ANSI
and light multicopter unmanned
Voting begins on:
2023-02-14 aircraft system (UAS) — General
requirements
Voting terminates on:
2023-04-11
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 24355:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023

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ISO/FDIS 24355:2023(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 24355
ISO/TC 20/SC 16
Flight control system for civil small
Secretariat: ANSI
and light multicopter unmanned
Voting begins on:
aircraft system (UAS) — General
requirements
Voting terminates on:
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
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.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: +41 22 749 01 11
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: copyright@iso.org
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 24355:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
  © ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023

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ISO/FDIS 24355:2023(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 1
5 Systems and functions .2
5.1 System composition . 2
5.2 Flight control unit . 2
5.2.1 Angular velocity control . 2
5.2.2 Attitude control . 3
5.2.3 Velocity control . 3
5.2.4 Position control . 3
5.3 Navigation unit . 3
5.3.1 General . 3
5.3.2 General requirements . 3
5.3.3 Optional function . 3
5.3.4 Flight management . 4
5.4 Flight recorder . 5
5.5 Safety and emergency management. 5
5.6 Interface . 6
5.7 Communication with RPS . 6
6 Performance requirements . .7
6.1 Performance requirements for FCS manufacturer . 7
6.1.1 System accuracy requirements . 7
6.1.2 Flight quality requirements . 7
6.2 Performance requirements of the navigation system . 7
7 Requirements and recommendations of support and maintenance .7
7.1 Firmware upgrade and version management . 7
7.2 User configuration and tuning support . 8
7.3 User manual . 8
8 Identification, packaging, transportation and storage . 8
8.1 General . 8
8.2 Identification . 8
8.3 Packaging . 9
8.4 Transportation and storage . 9
Bibliography .10
iii
© ISO 2023 – All rights reserved

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ISO/FDIS 24355:2023(E)
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 non­governmental, 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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
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, Unmanned aircraft systems.
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 2023 – All rights reserved

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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 24355:2023(E)
Flight control system for civil small and light multicopter
unmanned aircraft system (UAS) — General requirements
1 Scope
This document specifies the composition, functional and performance requirements of flight controls
for civil multicopter unmanned aircrafts (UAs) with the maximum take-off mass (MTOM) less than or
equal to 25 kg corresponding to unmanned aircraft systems (UAS) at levels I, II, III and IV as graded in
ISO 21895 which does not include fully autonomous flights.
The flight control system in this document consists of flight control unit, navigation unit, fault diagnosis
and management unit, flight planning, flight recorder, etc. This document is applicable to the design
and manufacture of other UA flight control systems or subsystems.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 21384­4, Unmanned aircraft systems — Part 4: Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21384-4 and the following
apply.
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
attitude control mode
flight control system mode that controls the attitude of the aircraft, but not the position of the aircraft
3.2
hover state
function or mode of keeping the position and height of an aircraft relatively unchanged in position mode
without receiving any external control instructions
4 Abbreviated terms
AGL above ground level
C2 command and control
FCS flight control system
GNSS global navigation satellite system
ICAO International Civil Aviation Organisation
1
© ISO 2023 – All rights reserved

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ISO/FDIS 24355:2023(E)
IMU inertial measurement unit
MTOM maximum take-off mass
RNP required navigation performance
RTK real time kinematic
RPS remote pilot station
UA unmanned aircraft
UAS unmanned aircraft system
5 Systems and functions
5.1 System composition
The FCS of multicopter UAS usually includes aircraft motion control unit, navigation unit, fault diagnosis
and management unit, power management unit and flight recorder. The typical information flow of the
FCS is described in Figure 1.
Figure 1 — Typical information flow of the FCS
5.2 Flight control unit
5.2.1 Angular velocity control
The FCS shall have the following angular velocity control functions:
a) respond to angular velocity commands in pitch, roll and yaw directions based on navigation
information;
b) control the UA angular velocity to reach the target angular velocity within the allowable time;
c) when the angular velocity control command is zero, the system should maintain current attitude
angle unchanged.
2
  © ISO 2023 – All rights reserved

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ISO/FDIS 24355:2023(E)
NOTE Angular velocity control is also called rate control in many cases.
5.2.2 Attitude control
The FCS shall have the following attitude control functions:
a) adjust the aircraft attitude to the target value in a certain time according to the attitude angle
com
...

ISO/DISFDIS 24355:2022(E)
ISO/TC 20/SC 16/WG 6
Secretariat: ANSI
2022-10-23

Fight Control SystemDate: 2023-01-31
Flight control system for Civil Smallcivil small and Lightlight
multicopter unmanned aircraft system (UAS) — General
requirements
FDIS stage
© ISO 2023 – All rights reserved

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ISO 21384-3:20XX/FDIS 24355:2023(E)
© ISO 20xx2023
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
maycan be requested from either ISO at the address below or ISO'sISO’s member body in the country of the
requester.
ISO Copyright Officecopyright office
CP 56 - 401 • Ch. de Blandonnet 8
CH-12111214 Vernier, Geneva 20
Phone: + 41 22 749 01 11
Fax: + 41 22 749 09 47
EmailE-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
ii © ISO #### 2023 – All rights reserved

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ISO/FDIS 24355:2023(E)
Contents

Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 1
5 Systems and functions . 2
5.1 System composition . 2
5.2 Flight control unit . 3
5.2.1 Angular velocity control . 3
5.2.2 Attitude control . 3
5.2.3 Velocity control . 3
5.2.4 Position control . 3
5.3 Navigation unit . 4
5.3.1 General . 4
5.3.2 General requirements . 4
5.3.3 Optional function . 4
5.3.4 Flight management . 4
5.4 Flight recorder . 6
5.5 Safety and emergency management . 6
5.6 Interface . 7
5.7 Communication with RPS . 7
6 Performance requirements . 7
6.1 Performance requirements for FCS manufacturer . 7
6.1.1 System accuracy requirements . 7
6.1.2 Flight quality requirements . 8
6.2 Performance requirements of the navigation system . 8
7 Requirements and recommendations of support and maintenance . 8
7.1 Firmware upgrade and version management . 8
7.2 User configuration and tuning support . 8
7.3 User manual . 8
8 Identification, packaging, transportation and storage . 9
8.1 General . 9
8.2 Identification . 9
8.3 Packaging . 9
8.4 Transportation and storage . 9
Bibliography . 10

© ISO 2022 2023 – All rights reserved iii

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ISO 21384-3:20XX/FDIS 24355:2023(E)
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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received (see www.iso.org/patents).
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.
Field Code Changed
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 16, Unmanned aircraft systems.
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.
Field Code Changed
iv © ISO #### 2023 – All rights reserved

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ISO/DISFDIS 24355:20222023(E)
Flight Control Systemcontrol system for Civil Smallcivil small and
Lightlight multicopter unmanned aircraft system (UAS) — General
requirements
1 Scope
This document specifies the composition, functional and performance requirements of flight controls for
civil multicopter unmanned aircrafts (UAs) with the maximum take-off mass (MTOM) less than 25kgor
equal to 25 kg corresponding to unmanned aircraft systems (UAS) at Levellevels I, II, III and IV as graded
in ISO 21895:2020 which does not include fully autonomous flights.
The flight control system in this document consists of flight control unit, navigation unit, fault diagnosis
and management unit, flight planning, flight recorder, etc. This document is applicable forto the design
and manufacture forof other UA flight control systems or subsystems.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 21895:2020, Categorization and classification of civil unmanned aircraft systems
ISO 21384-2:2021 Unmanned aircraft systems — Part 2: UAS components
ISO 21384-4:2020ISO 21384-4, Unmanned aircraft systems — Part 4: Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21384-4 and the following
apply.
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
attitude control mode
flight control system mode that controls the attitude of the aircraft, but not the position of the aircraft
3.2
hover modestate
function/ or mode of keeping the position and height of an aircraft relatively unchanged in position mode
without receiving any external control instructions
4 List of abbreviatedAbbreviated terms
AGL above ground level
C2 command and control
FCS flight control system
GNSS global navigation satellite system
AGL Above Ground Level
C2 Command and Control
FCS Flight Control System
© ISO 2022 2023 – All rights reserved 1

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ISO #####-2:2015/FDIS 24355:2023(E)
GCS Ground Control Station
GNSS Global navigation satellite system
ICAO International Civil Aviation Organisation
IMU Inertial measurement unit
IEC International Electrotechnical Commission
MTOM Maximum Take-off Mass
RTK Real Time Kinematic
RPS Remote Pilot Station
UA Unmanned Aircraft
UAS Unmanned Aircraft System
IMU inertial measurement unit
MTOM maximum take-off mass
RNP required navigation performance
RTK real time kinematic
RPS remote pilot station
UA unmanned aircraft
UAS unmanned aircraft system
5 Systems and functions
5.1 System composition
The flight control system (FCS) of multicopter UAS usually includes aircraft motion control unit,
navigation unit, fault diagnosis and management unit, power management unit and flight recorder. The
typical information flow of the FCS is described in Figure 1Figure 1.
Onboard sensor data
Autonomous Flight
Mission，Navigation
Sensor data
processing
Position setpoint
Flight mode
IMU data
Position Controller
switching mechanism
Attitude setpoint Position and Attitude
Estimator
Attitude and rate
controller
external position from
Actuator Control
GNSS /Vision Sensor, etc.
Output Driver

2 © ISO #### 2023 – All rights reserved

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ISO/DISFDIS 24355:20222023(E)

Figure 1 — Typical information flow of the FCS
5.2 Flight control unit
5.2.1 Angular velocity control
The FCS shall have the following angular velocity control functions:
a) a) Respondrespond to angular velocity commands in pitch, roll and yaw directions based on
navigation information;
b) b) Controlcontrol the UA angular velocity to reach the target angular velocity within the allowable
time;
c) c) Whenwhen the angular velocity control command is zero, the system should maintain current
attitude angle unchanged.
NOTE : Angular velocity control is also called rate control in many cases.
5.2.2 Attitude control
The FCS shall have the following attitude control functions:
a) a) Adjustadjust the aircraft attitude to the target value in a certain time according to the attitude
angle command;
b) b) Withstandwithstand the unexpected change of aircraft attitude angle caused by external forces
during the flight.
5.2.3 Velocity control
When equipped with navigation sensors for velocity measurements/estimation, the FCS shall have the
following velocity control functions:
a) a) Adjustadjust the aircraft velocity to the target value in a certain time according to the velocity
command;
b) b) Withstandwithstand the unexpected change of aircraft speed caused by external forces during
the flight.
5.2.4 Position control
When equipped with navigation sensors for position measurements/estimation, position control should
have the following functions:
© ISO 2022 2023 – All rights reserved 3

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ISO #####-2:2015/FDIS 24355:2023(E)
a) a) Controlcontrol the aircraft to the target position;
b) b) Keepkeep the position of the aircraft when the position control command remains unchanged.
5.3 Navigation unit
5.3.1 Subclause 5.3General
This subclause applies to the FCS with navigation capability.
5.3.15.3.2 General requirements
The navigation unit shall have the following functions:
a) a) Calculatecalculate all or some of other values such as th
...