ISO 21785:2020

INTERNATIONAL ISO
STANDARD 21785
First edition
2020-02
Air cargo unit load devices — Load
distribution model
Unités de charge de fret aérien — Modèle de répartition des charges
Reference number
ISO 21785:2020(E)
©
ISO 2020

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ISO 21785:2020(E)

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ISO 21785:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Load distribution model . 2
4.1 Principle . 2
4.2 Application . 4
5 Operational C.G. trade-off . 4
5.1 General . 4
5.2 One direction trade-off . 4
5.3 Two directions trade-off . 5
5.4 Required precautions . 5
Bibliography . 7
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ISO 21785:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 9, Air cargo and ground equipment.
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.
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ISO 21785:2020(E)

Introduction
This document specifies a reference model for load distribution on air cargo unit load device (ULD)
bases, to reflect in a standardized manner maximum allowable centre of gravity (C.G.) eccentricity
limitations.
The civil aviation requirements referred to in this document are those concerning certification
of transport aircraft and appliances to be installed aboard them, and constitute the set of design
and operation requirements internationally agreed in application of International Civil Aviation
Organization (ICAO) Annex 8, Airworthiness of aircraft, to the Convention on International Civil
Aviation.
Throughout this document, the minimum essential criteria are identified by use of the key word "shall".
Recommended criteria are identified by use of the key word “should” and, while not mandatory, are
considered to be of primary importance in providing safe air cargo unit load devices. Deviation from
recommended criteria should only occur after careful consideration and thorough service evaluation
have shown alternate methods to provide an equivalent level of safety.
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INTERNATIONAL STANDARD ISO 21785:2020(E)
Air cargo unit load devices — Load distribution model
1 Scope
This document defines the industry agreed model for load distribution on air cargo unit load devices
(ULD) bases to apply the maximum allowable centre of gravity (C.G.) eccentricity.
Its purpose is to establish a common reference load distribution algorithm for:
a) comparable and repeatable ULD testing methods, or equivalent numeric simulations;
b) aircraft structure and cargo systems design assumptions, consistent with existing airframers
practices; and
c) definition of operators unit load devices utilization rules and cargo build-up training programs.
It applies to all types of unit load devices intended for use on board civil transport aircraft and
airworthiness approved in accordance with the performance requirements and testing parameters of
either ISO 21100 or, as applicable, ISO 8097.
It also applies to non-airworthiness approved (non-certified) containers as defined in ISO 4118,
the utilisation of which is controlled by the provisions of the aircraft type's Weight and Balance Manual
and other airframe manufacturer's documents.
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 8097, Aircraft — Minimum airworthiness requirements and test conditions for certified air cargo unit
load devices
ISO 10254, Air cargo and ground equipment — Vocabulary
ISO 21100, Air cargo unit load devices — Performance requirements and test parameters
3 Terms and definitions
For the purposes of this document, the terms and definitions of ISO 10254 and the following apply:
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
eccentricity
offset
plan view distance between the overall centre of gravity (C.G.) of the unit load
device and its contents and the geometric centre of its base, expressed in percentage of the base length
and width
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ISO 21785:2020(E)

3.2
homogeneous cargo
cargo of homogeneous density and of such a nature that the whole weight of each piece is evenly
distributed over the whole of that piece's footprint area
4 Load distribution model
4.1 Principle
4.1.1 Airworthiness approval of each type and size of unit load device includes maximum load centre
of gravity (C.G.) eccentricity (offset) allowances at unit maximum gross mass, that are part of its testing
and approval (see ISO 21100 or ISO 8097, as applicable, for unit load device configurations and ultimate
load criteri
...