ISO 24355:2023

Flight control system for civil small and light multicopter unmanned aircraft system (UAS) - General requirements

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.

Système de contrôle de vol pour les multicoptères civils télépilotés petits et légers — Exigences générales

General Information

• Status: Published
• Publication Date: 11-May-2023
• ICS: 49.020 - Aircraft and space vehicles in general
• Technical Committee: ISO/TC 20/SC 16 - Unmanned aircraft systems
• Drafting Committee: ISO/TC 20/SC 16/WG 6 - UAS subsystems
• Current Stage: 6060 - International Standard published
• Start Date: 12-May-2023
• Due Date: 16-Nov-2022
• Completion Date: 12-May-2023

Overview

ISO 24355:2023 - Flight control system for civil small and light multicopter unmanned aircraft system (UAS) - General requirements - defines the composition, functional and performance requirements for flight control systems (FCS) used on civil multicopter unmanned aircraft (UA) with a maximum take-off mass (MTOM) ≤ 25 kg. The standard targets UAS at levels I–IV (per ISO 21895) and explicitly excludes fully autonomous flights. ISO 24355:2023 is applicable to design and manufacture of FCS units and subsystems.

Key topics and technical requirements

• System composition: Defines typical FCS elements - flight control unit, navigation unit, fault diagnosis/management, power management, flight planning, flight recorder and interfaces (including communication with an RPS).
• Flight control functions:
  • Angular velocity (rate) control, attitude control, velocity control and position control (when appropriate navigation sensors are fitted).
  • Requirements to reach target values within allowable time and to resist disturbances from external forces.
• Navigation unit:
  • Core functions: compute latitude/longitude, altitude, ground speed, heading, IMU-derived attitude/rate/acceleration, barometric altitude and GNSS positioning.
  • Sensor calibration, fault diagnosis and optional features such as AGL sensing, relative positioning, geofencing interfacing, sensor redundancy management, covariance/accuracy estimation and environmental monitoring.
• Flight management:
  • Mode switching (manual, semi-automatic, automatic), ground/air detection, remaining endurance reporting, component fault detection, envelope protections, and mission guidance including waypoint sequencing (2D/3D/4D).
  • Take-off and landing management: pre-take-off checks, home-point recording, environmental monitoring, safe-landing triggers and configurable landing speeds.
• Flight recorder: mandated logging of navigation data, control modes, remote-control inputs, system faults/warnings and flight status at manufacturer-specified frequency.
• Safety, emergency management and interfaces: fault handling, protective measures and RPS/UTM interactions.
• Performance & support: manufacturer responsibilities for system accuracy, flight quality, navigation performance, firmware/version management, user configuration/tuning support, user manuals, identification, packaging, transport and storage.

Applications and users

ISO 24355:2023 is intended for:

• UAS and multicopter manufacturers designing FCS hardware and software
• System integrators and avionics suppliers
• Test labs and certification bodies assessing compliance for small/light UAS (MTOM ≤ 25 kg)
• Fleet operators and service providers implementing safe take-off/landing and mission management workflows

Practical uses include FCS design specification, supplier contracts, verification test plans, and operational procedures for civil multicopter UAS.

Related standards

• ISO 21895 (UAS Levels I–IV)
• ISO 21384‑4 (UAS vocabulary)
• ISO 5491 (vertiport information exchange)
• ISO 23629‑12 (operational plan preparation / UTM service references)

Keywords: ISO 24355:2023, flight control system, multicopter UAS, FCS, navigation unit, flight recorder, MTOM ≤ 25 kg, unmanned aircraft system.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 24355
First edition
2023-05
Flight control system for civil small
and light multicopter unmanned
aircraft system (UAS) — General
requirements
Système de contrôle de vol pour les multicoptères civils télépilotés
petits et légers — Exigences générales
Reference number
© 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.
ISO copyright office
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Phone: [phone]
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Published in Switzerland
ii
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
Foreword
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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
INTERNATIONAL STANDARD ISO 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 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 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
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.
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
command;
b) withstand 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) adjust the aircraft velocity to the target value in a certain time according to the velocity command;
b) withstand 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:
a) control the aircraft to the target position;
b) keep the p
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