ISO 20291-1:2021
(Main)Air cargo — Restraint slings — Part 1: Design and testing
Air cargo — Restraint slings — Part 1: Design and testing
This document specifies the design criteria and testing methods adequate to guarantee the ultimate strength and operational dependability of cargo restraint sling assemblies made of steel wire rope, with a 22,25 kN (5 000 lbf) rated ultimate load capability, as can be used by the airline industry in order to restrain on board civil transport aircraft during flight, including the following: — cargo loaded and tied down onto airworthiness approved air cargo pallets, themselves restrained into aircraft lower deck, main deck or upper deck cargo systems and meeting the requirements of ISO 8097 (NAS 3610) or ISO 21100, or — non-unitized individual pieces of cargo, or pieces of cargo placed onto an unrestrained ("floating") pallet into either lower deck, main deck or upper deck containerized cargo compartments of an aircraft, to be restrained onto aircraft structure attachment (tie-down) points. Two types of wire rope restraint slings are defined: a) type A: adjustable length restraint sling assemblies, including a tension retaining device and termination fittings attached to the wire rope end eyes; b) type B: fixed length restraint sling extensions, to be used in conjunction with a type A cable; extensions are usually terminated at both ends by eyes, without additional fittings, and can be attached through hooks or shackles. The cables specified in this document are intended exclusively for restraint purposes on board aircraft, and not for use as lifting slings.
Fret aérien — Câbles d'arrimage — Partie 1: Conception et essais
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 20291-1
First edition
2021-06
Air cargo — Restraint slings —
Part 1:
Design and testing
Fret aérien — Câbles d'arrimage —
Partie 1: Conception et essais
Reference number
ISO 20291-1:2021(E)
©
ISO 2021
---------------------- Page: 1 ----------------------
ISO 20291-1:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 20291-1:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Design requirements . 6
4.1 General . 6
4.2 Construction . 6
4.3 Tension retaining device . 8
4.4 End fittings . 8
4.5 Ultimate load .10
4.6 Elongation .10
4.7 Environment .10
4.8 Operator safety .11
5 Testing .11
5.1 General .11
5.2 Testing apparatus .12
5.3 Sleeves test .12
5.4 Ultimate load and elongation test .12
5.5 Cyclic load test .14
5.6 Test record .15
6 Quality control .15
7 Markings .15
8 Options .16
9 Manufacturer's instructions .17
10 Operating instructions .17
Bibliography .19
© ISO 2021 – All rights reserved iii
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ISO 20291-1:2021(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.
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 9, Air cargo and ground equipment.
A list of all parts in the ISO 20291 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 2021 – All rights reserved
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ISO 20291-1:2021(E)
Introduction
The aim of this document is to standardize the design and testing requirements for air cargo restraint
sling assemblies used as an alternate to restraint straps for tie-down of cargo on board civil transport
aircraft.
The civil aviation requirements referred to in this document are those relating to the design of transport
aircraft. They constitute the set of design requirements internationally agreed in the application of
International Civil Aviation Organization (ICAO) Annex 6, 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 of primary importance in providing safe air cargo restraint sling assemblies. Deviation
from the recommended criteria should only occur after careful consideration and thorough service
evaluation have shown that alternate methods can be used to provide an equivalent level of safety.
The requirements of this document are expressed in the applicable SI units, with approximate inch-
pound units conversion between brackets for convenience in countries using that system.
Sling or cable assemblies made of steel wire rope are intended to be used in lieu of cargo restraint
straps meeting the requirements of ISO 16049-1, where straps inherent elongation under tension
appears unadvisable for a given tie-down arrangement. Typical examples of loads where substitution
of cables for straps throughout a given tie-down arrangement can be advisable are those for which
even limited movement during flight can be hazardous, such as heavy vehicles, aircraft engine stands,
helicopters, machinery.
On the date of publication of this document, no airworthiness approval procedure by Civil Aviation
Authorities is applicable to restraint slings. Their use for cargo restraint, however, remains subject to the
requirements of the approved aircraft type or sub-type Weight and Balance Manual (see ISO 20291-2).
© ISO 2021 – All rights reserved v
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INTERNATIONAL STANDARD ISO 20291-1:2021(E)
Air cargo — Restraint slings —
Part 1:
Design and testing
1 Scope
This document specifies the design criteria and testing methods adequate to guarantee the ultimate
strength and operational dependability of cargo restraint sling assemblies made of steel wire rope,
with a 22,25 kN (5 000 lbf) rated ultimate load capability, as can be used by the airline industry in
order to restrain on board civil transport aircraft during flight, including the following:
— cargo loaded and tied down onto airworthiness approved air cargo pallets, themselves restrained
into aircraft lower deck, main deck or upper deck cargo systems and meeting the requirements of
ISO 8097 (NAS 3610) or ISO 21100, or
— non-unitized individual pieces of cargo, or pieces of cargo placed onto an unrestrained ("floating")
pallet into either lower deck, main deck or upper deck containerized cargo compartments of an
aircraft, to be restrained onto aircraft structure attachment (tie-down) points.
Two types of wire rope restraint slings are defined:
a) type A: adjustable length restraint sling assemblies, including a tension retaining device and
termination fittings attached to the wire rope end eyes;
b) type B: fixed length restraint sling extensions, to be used in conjunction with a type A cable;
extensions are usually terminated at both ends by eyes, without additional fittings, and can be
attached through hooks or shackles.
The cables specified in this document are intended exclusively for restraint purposes on board aircraft,
and not for use as lifting slings.
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 2408, Steel wire ropes — Requirements
ISO 4117, Air and air/land cargo pallets — Specification and testing
ISO 4171, Air cargo equipment — Interline pallets
ISO 4346, Steel wire ropes for general purposes — Lubricants — Basic requirements
ISO 7166, Aircraft — Rail and stud configuration for passenger equipment and cargo restraint
ISO 7531, Wire rope slings for general purposes — Characteristics and specifications
ISO 7597, Forged steel lifting hooks with latch, grade 8
ISO 8097, Aircraft — Minimum airworthiness requirements and test conditions for certified air cargo unit
load devices
ISO 8793, Steel wire ropes — Ferrule-secured eye terminations
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ISO 20291-1:2021(E)
ISO 8794, Steel wire ropes — Spliced eye terminations for slings
ISO 9788, Air cargo — Double stud tie-down fittings — Design and testing requirements
ISO 10254, Air cargo and ground equipment — Vocabulary
ISO 17893, Steel wire ropes — Vocabulary, designation and classification
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 given in ISO 10254, ISO 17893 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
restraint sling assembly
type A
elementary tie-down (3.3) unit made of steel wire rope cable with end fittings (3.6) and tension retaining
device (3.5), used for restraint of cargo on board civil transport aircraft
Note 1 to entry: It consists of 1 (one) fixed length (3.8.1) end and one adjustable end and can be used in conjunction
with one or two extensions(s).
Note 2 to entry: See Figure 1.
Key
1 fixed end
2 adjustable end
3 end fitting
4 tension retaining device
l fixed length
GF
l adjustable length (3.8.2)
GL
l total length (3.8.3)
TG
Figure 1 — Adjustable (type A) restraint sling assembly
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ISO 20291-1:2021(E)
3.2
restraint sling extension
type B
fixed length (3.8.1) steel wire rope (cable) with end eyes but no tension retaining device (3.5), with or
without end fittings (3.6), used in conjunction with a restraint sling assembly (3.1) to extend usable
length between attachment points
Note 1 to entry: See Figure 2.
Key
1 ferrule
2 thimble
3 end fitting (ring)
4 end fitting (hook)
l length of restraint sling extension (3.9)
rse
Figure 2 — Fixed length (type B) restraint sling extensions
3.3
tie-down
fact of restraining cargo movements in relation to an aircraft's structure, throughout the range of
relative accelerations resulting from the allowable flight envelope, by means of an appropriate use of a
number of elementary devices against each direction of restraint
3.4
tensioning device
mechanical device inducing and maintaining a tensile force in the load restraint assembly
EXAMPLE Lever, ratchet, winch, cam, over-centre device, or equivalent.
3.5
tension retaining device
part connecting to the wire rope and retaining any force induced between the ends of the assembly
3.6
end fitting
connecting component
metallic device connecting a wire rope end to the attachment point on the aircraft structure, the pallet
edge track, another restraint element, or the load to be restrained
Note 1 to entry: See examples in Figure 3, D1 to D3.
Note 2 to entry: The end fittings most commonly used on air cargo restraint slings include:
a) retainer or latch equipped hook (see example in Figure 3, D1),
b) air cargo tie-down (3.3) double stud (male) fitting (see example in Figure 3, D4) conforming to ISO 9788,
connected to the cable directly or through an intermediate ring,
c) ring (see example in Figure 3, D2) or wire rope end loop (eye) compatible with hooks.
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ISO 20291-1:2021(E)
Key
A restraint sling assembly (complete) D connecting elements
A1 marking (label) D1 hook with retainer or latch
B tension holding element D2 end ring
B1 steel wire rope D3 shackle with steel pin
C tensioning device (3.4) (optional) D4 double stud tie-down fitting
C1 possible tension arrangement E1 tension force indicator (3.7)
C2 example of rope tensioner D connecting elements
Figure 3 — Examples of restraint sling equipment
3.7
tension force indicator
device that indicates the tensile force applied to the restraint sling assembly (3.1)
Note 1 to entry: See example in Figure 3, C.
3.8 length of restraint sling assembly
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ISO 20291-1:2021(E)
3.8.1
fixed length
l
GF
length of a fixed end, measured from the force bearing point of the end fitting (3.6) to the outer turning
radius of the connection of the wire rope to the tension retaining device (3.5)
Note 1 to entry: See Figure 1.
Note 2 to entry: This length can be zero, i.e., the end fitting directly attached to the tensioning device (3.4).
3.8.2
adjustable length
l
GL
maximum length of an adjustable end, measured from the tension device to the force bearing point of
the end fitting (3.6)
Note 1 to entry: See Figure 1.
3.8.3
total length
l
TG
sum of fixed length (3.8.1), adjustable length (3.8.2) and length of the tension retaining device (3.5)
3.9
length of restraint sling extension
l
rse
length measured between the force bearing points of each terminal, whether thimbles, hooks or rings
Note 1 to entry: See Figure 2.
3.10
breaking force
BF
maximum force that the restraint sling assembly (3.1) withstands when tested in a complete form, i.e.
with tension retaining device (3.5) and end fittings (3.6)
3.11
hand force
HF
force applied to adjust, latch, or unlatch the restraint sling assembly (3.1)
3.12
limit load
LL
maximum load to be expected in service
Note 1 to entry: See CAAC CCAR-25, CS-25, JAS Part 3 or 14 CFR Part 25, § 25,301 (a).
Note 2 to entry: It is two thirds of ultimate load (3.13), i.e. 14,8 kN (3 333 lbf) for a rated ultimate load of 22,2 kN
(5 000 lbf).
3.13
ultimate load
UL
limit load (3.12) multiplied by a safety factor of 1,5
Note 1 to entry: See CAAC CCAR-25, CS-25, JAS Part 3 or 14 CFR Part 25, § 25,303.
Note 2 to entry: It is used for computation of cargo tie-down (3.3) arrangements, based on the ultimate load
factors defined in the aircraft Weight and Balance Manual in each direction of restraint, throughout the certified
flight envelope of the aircraft type. The restraint sling assembly's (3.1) rated ultimate load must not exceed the
measured breaking force (BF) (3.10).
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ISO 20291-1:2021(E)
3.14
residual tension
tension force which can be measured in the rope of a cable assembly attached between two fixed points,
after its length was adjusted and it was operated and latched with the reference hand force (HF) (3.11),
prior to application of any external load
3.15
competent person
designated person, suitably trained, qualified by knowledge and practical experience and with the
necessary instructions to enable the required tests and examinations to be carried out
Note 1 to entry: A competent person can be suitably trained in accordance with ISO 9001:2015, 7.2.
4 Design requirements
4.1 General
4.1.1 Unless otherwise specified, the design requirements hereafter equally apply to type A and type B
restraint slings as defined in Clause 1.
4.1.2 This document specifies the design criteria for individual restraint sling assemblies but does
not intend to specify the way they are to be used aboard aircraft to ensure proper restraint throughout
the certified flight envelope. It is presupposed that tie-down arrangements meet all the applicable
requirements of the Weight and Balance Manual for the aircraft type or sub-type concerned, particularly
as regards, but not necessarily limited to, ultimate load factors to be taken into account to determine
the number of cables to be used in each direction of restraint, maximum angles to be observed with the
direction of restraint, minimum spacing and ultimate load capacity of attachment points, etc.
4.1.3 When restraint sling assemblies are attached to the edge rails of a certified air cargo pallet
meeting the requirements of ISO 8097 (NAS 3610) or ISO 21100 (AS 36100), operating instructions
should duly take into account the restraint net attachment point locations on the pallet edge rail and other
requirements defined by the appropriate ISO 8097 (NAS 3610) or ISO 21100 (AS 36100) configuration
drawing(s).
4.1.4 Subject to proper operating instructions per 4.1.2 and 4.1.3 being defined and complied with,
using restraint sling assemblies manufactured to an adequate design and a tested ultimate load capability
is nevertheless deemed necessary in order to ensure flight safety. General utilization guidelines and
calculation methods adequate to guarantee the effectiveness and ultimate load strength of the tie-down
arrangements performed with cables to restrain cargo on board civil transport aircraft can be found in
ISO 20291-2.
4.1.5 The restraint sling assembly shall be designed to be used on and compatible with:
a) the edge rails of air cargo pallets meeting the requirements of ISO 4117 or ISO 4171, airworthiness
approved according to ISO 8097 (NAS 3610, TSO C90c) or ISO 21100 (AS36100, TSO C90d), or
b) aircraft floor tracks or structural attachment points meeting the requirements of ISO 7166,
either directly or using ISO 9788 double stud tie-down fittings as intermediate attachment hardware.
4.2 Construction
4.2.1 Wire rope shall meet the requirements of ISO 2408, should be of ISO 2408:2017, Annex C
2
class 6x7-FC or 6x7-IWRC, grade 1 960 N/mm , 6 mm (0.25 in) diameter, of minimum breaking
force 23,4 kN or 25,3 kN, and should be galvanized (zinc-coated) or stainless steel, of a construction
appropriate to guarantee the required breaking force while keeping maximum flexibility.
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ISO 20291-1:2021(E)
2
NOTE Using steel grade 1 770 N/mm usually results in a lower breaking force.
4.2.2 In exception from ISO 7531, justified by airworthiness standards (e.g. CAAC CCAR-25, CS-25,
JAS Part 3 or 14 CFR Part 25, § 25,303) applicable aboard aircraft, the minimum breaking force of the
new unfinished wire rope shall be the rated ultimate load (UL) of the complete restraint sling assembly
(see 4.5).
4.2.3 All wire rope end eyes shall be secured with stainless steel crimped ferrules or swaging sleeves
in accordance with ISO 8793 (see Figure 2). Cable grips, clips or clamps, or splicing per ISO 8794 shall
not be used. The minimum length of plain rope between the inside ends of ferrules terminating a same
wire rope shall be 20 times the nominal rope diameter.
4.2.4 All wire rope end eyes shall be protected against direct contact of attached fittings with rope by
a thimble appropriate to the wire rope's diameter, preferably made of galvanized or stainless steel or
aluminium alloy, or otherwise protected against corrosion. Soft or spliced loops are not allowed.
4.2.5 Where a wire rope end has no eye loop, e.g. at a free end of the adjustable end of a type A cable, it
shall be fitted with a stainless steel crimped ferrule stop in order to avoid its disengagement and strands
unwinding.
4.2.6 Optionally, all (for type B fixed length extensions) or part (the fixed end of type A adjustable
length cables) of the wire rope may be enclosed in protective semi-soft, e.g. polyamide, PVC or similar,
non-load bearing tubing in order to protect it, the hands of the operators, and any piece of cargo an
extension can be passed around. If provided, such tubing shall be:
a) transparent in order to allow visual cable inspection and verification that it is not broken nor
unduly bent, and
b) rigid enough to ensure that the minimum bending radius the wire cable can withstand (see wire
rope manufacturer’s information) is exceeded around a piece of cargo up to at least the cable's
breaking force.
4.2.7 In order to allow length adjustment, the wire rope of the adjustable end (l ) of type A cables
GL
shall be fitted with stainless steel ferrules (sleeves) at regular intervals to allow catching by the load
retaining device, capable of withstanding the tension loads sustained during flight. See Figure 4 for the
dimensions required.
Key
a ø 6 mm (0.25 in)
b spacing 25 mm to 38 mm (1 in to 1.5 in)
c ≥ ø 12,7 mm (0.5 in)
d ≥ ø 8 mm (0.3 125 in)
Figure 4 — Type A restraint sling adjustable end sleeves
4.2.8 The load bearing ferrules (sleeves) shall meet the applicable requirements of ISO 8397.
In addition, each sleeve should be attached to the wire rope in such a manner as to be capable of
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ISO 20291-1:2021(E)
withstanding in either direction at least 1,25 times the nominal ultimate load of the cable assembly.
See 5.3 for verification testing.
4.3 Tension retaining device
4.3.1 Type A adjustable restraint sling assemblies shall include a tension retaining device at the free
end, opposite to the end fitting, of the fixed length (l ) not bearing sleeves.
GF
They do not require a tensioning device capable of inducing a wire rope pre-tension. This may
nevertheless be provided as an option (see 8.6), subject to meeting the device elongation requirements
(see 4.6).
The type of tension retaining and, if provided, tensioning devices of type A adjustable length restraint
sling assemblies is to be selected on agreement between the manufacturer and the purchaser.
4.3.2 The tension retaining device shall be equipped with means to catch a cable sleeve (see Figure 4)
in such a way that the sleeve and adjacent wire rope are fully enclosed. In addition, a positive, self-
engaging, locking system in the closed position shall be provided in order to prevent any risk of self or
inadvertent release whether or not the wire rope is under tension. The design shall provide an immediate
visual indication whether this lock is in the open or closed position. Consideration should be given to the
geometry of catching or locking parts filling any remaining gap in the spacing between 2 adjacent sleeves
whether this lock is in the open or closed position.
4.3.3 It shall be possible to latch and unlatch the tension retaining device with a hand force (HF) not
exceeding 100 N (22 lbf), regardless of any tension remaining in the cable.
Disengagement of the locking system shall be possible only by a deliberate hand action, without the use
of tool(s), regardless of the cable's residual tension.
4.3.4 The thickness of the tension retaining device when in its latched position, including the handle in
its stored position, shall be kept to a minimum consistent with its design principle, and should preferably
not exceed 38 mm (1.5 in).
4.3.5 Tension retaining devices shall present no sharp edges which may come into contact with the
steel wire ropes or the operator's hands.
4.3.6 The recoil travel of the end of the handle of the tension retaining device under residual tension
shall not exceed 150 mm (6.0 in) when opening the device. The design should aim at minimizing the
spring effect creating a hazard to the operator (see 4.8.2).
4.3.7 Positive means shall be provided to prevent the adjustable wire rope length from getting free
from the tension retaining device at maximum length (see 4.2.5).
4.3.8 All devices shall be designed so that there are no crushing or shearing points which might lead to
the hands of the operator being injured during intended use.
4.3.9 No lubricant should be necessary for proper operation of type A restraint slings length
adjustment. If a lubricant is nevertheless deemed necessary for the tension retaining device, it shall be
permanent and meet the requirements of ISO 4346.
4.4 End fittings
4.4.1 Type A adjustable length restraint sling assemblies shall be equipped at each end with a fitting
(connecting component), which may be, for example, a hook with retainer or latch (see example in
8 © ISO 2021 – All rights reserved
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...
INTERNATIONAL ISO
STANDARD 20291-1
First edition
Air cargo — Restraint slings —
Part 1:
Design and testing
Fret aérien — Câbles d'arrimage —
Partie 1: Conception et essais
PROOF/ÉPREUVE
Reference number
ISO 20291-1:2021(E)
©
ISO 2021
---------------------- Page: 1 ----------------------
ISO 20291-1:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 20291-1:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Design requirements . 6
4.1 General . 6
4.2 Construction . 6
4.3 Tension retaining device . 8
4.4 End fittings . 8
4.5 Ultimate load .10
4.6 Elongation .10
4.7 Environment .10
4.8 Operator safety .11
5 Testing .11
5.1 General .11
5.2 Testing apparatus .12
5.3 Sleeves test .12
5.4 Ultimate load and elongation test .12
5.5 Cyclic load test .14
5.6 Test record .15
6 Quality control .15
7 Markings .15
8 Options .16
9 Manufacturer's instructions .17
10 Operating instructions .17
Bibliography .19
© ISO 2021 – All rights reserved PROOF/ÉPREUVE iii
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ISO 20291-1:2021(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.
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 9, Air cargo and ground equipment.
A list of all parts in the ISO 20291 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 PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 20291-1:2021(E)
Introduction
The aim of this document is to standardize the design and testing requirements for air cargo restraint
sling assemblies used as an alternate to restraint straps for tie-down of cargo on board civil transport
aircraft.
The civil aviation requirements referred to in this document are those relating to the design of transport
aircraft. They constitute the set of design requirements internationally agreed in the application of
International Civil Aviation Organization (ICAO) Annex 6, 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 of primary importance in providing safe air cargo restraint sling assemblies. Deviation
from the recommended criteria should only occur after careful consideration and thorough service
evaluation have shown that alternate methods can be used to provide an equivalent level of safety.
The requirements of this document are expressed in the applicable SI units, with approximate inch-
pound units conversion between brackets for convenience in countries using that system.
Sling or cable assemblies made of steel wire rope are intended to be used in lieu of cargo restraint
straps meeting the requirements of ISO 16049-1, where straps inherent elongation under tension
appears unadvisable for a given tie-down arrangement. Typical examples of loads where substitution
of cables for straps throughout a given tie-down arrangement can be advisable are those for which
even limited movement during flight can be hazardous, such as heavy vehicles, aircraft engine stands,
helicopters, machinery.
On the date of publication of this document, no airworthiness approval procedure by Civil Aviation
Authorities is applicable to restraint slings. Their use for cargo restraint, however, remains subject to the
requirements of the approved aircraft type or sub-type Weight and Balance Manual (see ISO 20291-2).
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INTERNATIONAL STANDARD ISO 20291-1:2021(E)
Air cargo — Restraint slings —
Part 1:
Design and testing
1 Scope
This document specifies the design criteria and testing methods adequate to guarantee the ultimate
strength and operational dependability of cargo restraint sling assemblies made of steel wire rope,
with a 22,25 kN (5 000 lbf) rated ultimate load capability, as can be used by the airline industry in
order to restrain on board civil transport aircraft during flight, including the following:
— cargo loaded and tied down onto airworthiness approved air cargo pallets, themselves restrained
into aircraft lower deck, main deck or upper deck cargo systems and meeting the requirements of
ISO 8097 (NAS 3610) or ISO 21100, or
— non-unitized individual pieces of cargo, or pieces of cargo placed onto an unrestrained ("floating")
pallet into either lower deck, main deck or upper deck containerized cargo compartments of an
aircraft, to be restrained onto aircraft structure attachment (tie-down) points.
Two types of wire rope restraint slings are defined:
a) type A: adjustable length restraint sling assemblies, including a tension retaining device and
termination fittings attached to the wire rope end eyes;
b) type B: fixed length restraint sling extensions, to be used in conjunction with a type A cable;
extensions are usually terminated at both ends by eyes, without additional fittings, and can be
attached through hooks or shackles.
The cables specified in this document are intended exclusively for restraint purposes on board aircraft,
and not for use as lifting slings.
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 2408, Steel wire ropes — Requirements
ISO 4117, Air and air/land cargo pallets — Specification and testing
ISO 4171, Air cargo equipment — Interline pallets
ISO 4346, Steel wire ropes for general purposes — Lubricants — Basic requirements
ISO 7166, Aircraft — Rail and stud configuration for passenger equipment and cargo restraint
ISO 7531, Wire rope slings for general purposes — Characteristics and specifications
ISO 7597, Forged steel lifting hooks with latch, grade 8
ISO 8097, Aircraft — Minimum airworthiness requirements and test conditions for certified air cargo unit
load devices
ISO 8793, Steel wire ropes — Ferrule-secured eye terminations
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ISO 20291-1:2021(E)
ISO 8794, Steel wire ropes — Spliced eye terminations for slings
ISO 9788, Air cargo — Double stud tie-down fittings — Design and testing requirements
ISO 10254, Air cargo and ground equipment — Vocabulary
ISO 17893, Steel wire ropes — Vocabulary, designation and classification
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 given in ISO 10254, ISO 17893 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
restraint sling assembly
type A
elementary tie-down (3.3) unit made of steel wire rope cable with end fittings (3.6) and tension retaining
device (3.5), used for restraint of cargo on board civil transport aircraft
Note 1 to entry: It consists of 1 (one) fixed length (3.8.1) end and one adjustable end and can be used in conjunction
with one or two extensions(s).
Note 2 to entry: See Figure 1.
Key
1 fixed end
2 adjustable end
3 end fitting
4 tension retaining device
l fixed length
GF
l adjustable length (3.8.2)
GL
l total length (3.8.3)
TG
Figure 1 — Adjustable (type A) restraint sling assembly
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ISO 20291-1:2021(E)
3.2
restraint sling extension
type B
fixed length (3.8.1) steel wire rope (cable) with end eyes but no tension retaining device (3.5), with or
without end fittings (3.6), used in conjunction with a restraint sling assembly (3.1) to extend usable
length between attachment points
Note 1 to entry: See Figure 2.
Key
1 ferrule
2 thimble
3 end fitting (ring)
4 end fitting (hook)
l length of restraint sling extension (3.9)
rse
Figure 2 — Fixed length (type B) restraint sling extensions
3.3
tie-down
fact of restraining cargo movements in relation to an aircraft's structure, throughout the range of
relative accelerations resulting from the allowable flight envelope, by means of an appropriate use of a
number of elementary devices against each direction of restraint
3.4
tensioning device
mechanical device inducing and maintaining a tensile force in the load restraint assembly
EXAMPLE Lever, ratchet, winch, cam, over-centre device, or equivalent.
3.5
tension retaining device
part connecting to the wire rope and retaining any force induced between the ends of the assembly
3.6
end fitting
connecting component
metallic device connecting a wire rope end to the attachment point on the aircraft structure, the pallet
edge track, another restraint element, or the load to be restrained
Note 1 to entry: See examples in Figure 3, D1 to D3.
Note 2 to entry: The end fittings most commonly used on air cargo restraint slings include:
a) retainer or latch equipped hook (see example in Figure 3, D1),
b) air cargo tie-down (3.3) double stud (male) fitting (see example in Figure 3, D4) conforming to ISO 9788,
connected to the cable directly or through an intermediate ring,
c) ring (see example in Figure 3, D2) or wire rope end loop (eye) compatible with hooks.
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ISO 20291-1:2021(E)
Key
A restraint sling assembly (complete) D connecting elements
A1 marking (label) D1 hook with retainer or latch
B tension holding element D2 end ring
B1 steel wire rope D3 shackle with steel pin
C tensioning device (3.4) (optional) D4 double stud tie-down fitting
C1 possible tension arrangement E1 tension force indicator (3.7)
C2 example of rope tensioner D connecting elements
Figure 3 — Examples of restraint sling equipment
3.7
tension force indicator
device that indicates the tensile force applied to the restraint sling assembly (3.1)
Note 1 to entry: See example in Figure 3, C.
3.8 length of restraint sling assembly
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ISO 20291-1:2021(E)
3.8.1
fixed length
l
GF
length of a fixed end, measured from the force bearing point of the end fitting (3.6) to the outer turning
radius of the connection of the wire rope to the tension retaining device (3.5)
Note 1 to entry: See Figure 1.
Note 2 to entry: This length can be zero, i.e., the end fitting directly attached to the tensioning device (3.4).
3.8.2
adjustable length
l
GL
maximum length of an adjustable end, measured from the tension device to the force bearing point of
the end fitting (3.6)
Note 1 to entry: See Figure 1.
3.8.3
total length
l
TG
sum of fixed length (3.8.1), adjustable length (3.8.2) and length of the tension retaining device (3.5)
3.9
length of restraint sling extension
l
rse
length measured between the force bearing points of each terminal, whether thimbles, hooks or rings
Note 1 to entry: See Figure 2.
3.10
breaking force
BF
maximum force that the restraint sling assembly (3.1) withstands when tested in a complete form, i.e.
with tension retaining device (3.5) and end fittings (3.6)
3.11
hand force
HF
force applied to adjust, latch, or unlatch the restraint sling assembly (3.1)
3.12
limit load
LL
maximum load to be expected in service
Note 1 to entry: See CAAC CCAR-25, CS-25, JAS Part 3 or 14 CFR Part 25, § 25,301 (a).
Note 2 to entry: It is two thirds of ultimate load (3.13), i.e. 14,8 kN (3 333 lbf) for a rated ultimate load of 22,2 kN
(5 000 lbf).
3.13
ultimate load
UL
limit load (3.12) multiplied by a safety factor of 1,5
Note 1 to entry: See CAAC CCAR-25, CS-25, JAS Part 3 or 14 CFR Part 25, § 25,303.
Note 2 to entry: It is used for computation of cargo tie-down (3.3) arrangements, based on the ultimate load
factors defined in the aircraft Weight and Balance Manual in each direction of restraint, throughout the certified
flight envelope of the aircraft type. The restraint sling assembly's (3.1) rated ultimate load must not exceed the
measured breaking force (BF) (3.10).
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ISO 20291-1:2021(E)
3.14
residual tension
tension force which can be measured in the rope of a cable assembly attached between two fixed points,
after its length was adjusted and it was operated and latched with the reference hand force (HF) (3.11),
prior to application of any external load
3.15
competent person
designated person, suitably trained, qualified by knowledge and practical experience and with the
necessary instructions to enable the required tests and examinations to be carried out
Note 1 to entry: A competent person can be suitably trained in accordance with ISO 9001:2015, 7.2.
4 Design requirements
4.1 General
4.1.1 Unless otherwise specified, the design requirements hereafter equally apply to type A and type B
restraint slings as defined in Clause 1.
4.1.2 This document specifies the design criteria for individual restraint sling assemblies but does
not intend to specify the way they are to be used aboard aircraft to ensure proper restraint throughout
the certified flight envelope. It is presupposed that tie-down arrangements meet all the applicable
requirements of the Weight and Balance Manual for the aircraft type or sub-type concerned, particularly
as regards, but not necessarily limited to, ultimate load factors to be taken into account to determine
the number of cables to be used in each direction of restraint, maximum angles to be observed with the
direction of restraint, minimum spacing and ultimate load capacity of attachment points, etc.
4.1.3 When restraint sling assemblies are attached to the edge rails of a certified air cargo pallet
meeting the requirements of ISO 8097 (NAS 3610) or ISO 21100 (AS 36100), operating instructions
should duly take into account the restraint net attachment point locations on the pallet edge rail and other
requirements defined by the appropriate ISO 8097 (NAS 3610) or ISO 21100 (AS 36100) configuration
drawing(s).
4.1.4 Subject to proper operating instructions per 4.1.2 and 4.1.3 being defined and complied with,
using restraint sling assemblies manufactured to an adequate design and a tested ultimate load capability
is nevertheless deemed necessary in order to ensure flight safety. General utilization guidelines and
calculation methods adequate to guarantee the effectiveness and ultimate load strength of the tie-down
arrangements performed with cables to restrain cargo on board civil transport aircraft can be found in
ISO 20291-2.
4.1.5 The restraint sling assembly shall be designed to be used on and compatible with:
a) the edge rails of air cargo pallets meeting the requirements of ISO 4117 or ISO 4171, airworthiness
approved according to ISO 8097 (NAS 3610, TSO C90c) or ISO 21100 (AS36100, TSO C90d), or
b) aircraft floor tracks or structural attachment points meeting the requirements of ISO 7166,
either directly or using ISO 9788 double stud tie-down fittings as intermediate attachment hardware.
4.2 Construction
4.2.1 Wire rope shall meet the requirements of ISO 2408, should be of ISO 2408:2017, Annex C
2
class 6x7-FC or 6x7-IWRC, grade 1 960 N/mm , 6 mm (0.25 in) diameter, of minimum breaking
force 23,4 kN or 25,3 kN, and should be galvanized (zinc-coated) or stainless steel, of a construction
appropriate to guarantee the required breaking force while keeping maximum flexibility.
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ISO 20291-1:2021(E)
2
NOTE Using steel grade 1 770 N/mm usually results in a lower breaking force.
4.2.2 In exception from ISO 7531, justified by airworthiness standards (e.g. CAAC CCAR-25, CS-25,
JAS Part 3 or 14 CFR Part 25, § 25,303) applicable aboard aircraft, the minimum breaking force of the
new unfinished wire rope shall be the rated ultimate load (UL) of the complete restraint sling assembly
(see 4.5).
4.2.3 All wire rope end eyes shall be secured with stainless steel crimped ferrules or swaging sleeves
in accordance with ISO 8793 (see Figure 2). Cable grips, clips or clamps, or splicing per ISO 8794 shall
not be used. The minimum length of plain rope between the inside ends of ferrules terminating a same
wire rope shall be 20 times the nominal rope diameter.
4.2.4 All wire rope end eyes shall be protected against direct contact of attached fittings with rope by
a thimble appropriate to the wire rope's diameter, preferably made of galvanized or stainless steel or
aluminium alloy, or otherwise protected against corrosion. Soft or spliced loops are not allowed.
4.2.5 Where a wire rope end has no eye loop, e.g. at a free end of the adjustable end of a type A cable, it
shall be fitted with a stainless steel crimped ferrule stop in order to avoid its disengagement and strands
unwinding.
4.2.6 Optionally, all (for type B fixed length extensions) or part (the fixed end of type A adjustable
length cables) of the wire rope may be enclosed in protective semi-soft, e.g. polyamide, PVC or similar,
non-load bearing tubing in order to protect it, the hands of the operators, and any piece of cargo an
extension can be passed around. If provided, such tubing shall be:
a) transparent in order to allow visual cable inspection and verification that it is not broken nor
unduly bent, and
b) rigid enough to ensure that the minimum bending radius the wire cable can withstand (see wire
rope manufacturer’s information) is exceeded around a piece of cargo up to at least the cable's
breaking force.
4.2.7 In order to allow length adjustment, the wire rope of the adjustable end (l ) of type A cables
GL
shall be fitted with stainless steel ferrules (sleeves) at regular intervals to allow catching by the load
retaining device, capable of withstanding the tension loads sustained during flight. See Figure 4 for the
dimensions required.
Key
a ø 6 mm (0.25 in)
b spacing 25 mm to 38 mm (1 in to 1.5 in)
c ≥ ø 12,7 mm (0.5 in)
d ≥ ø 8 mm (0.3 125 in)
Figure 4 — Type A restraint sling adjustable end sleeves
4.2.8 The load bearing ferrules (sleeves) shall meet the applicable requirements of ISO 8397.
In addition, each sleeve should be attached to the wire rope in such a manner as to be capable of
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ISO 20291-1:2021(E)
withstanding in either direction at least 1,25 times the nominal ultimate load of the cable assembly.
See 5.3 for verification testing.
4.3 Tension retaining device
4.3.1 Type A adjustable restraint sling assemblies shall include a tension retaining device at the free
end, opposite to the end fitting, of the fixed length (l ) not bearing sleeves.
GF
They do not require a tensioning device capable of inducing a wire rope pre-tension. This may
nevertheless be provided as an option (see 8.6), subject to meeting the device elongation requirements
(see 4.6).
The type of tension retaining and, if provided, tensioning devices of type A adjustable length restraint
sling assemblies is to be selected on agreement between the manufacturer and the purchaser.
4.3.2 The tension retaining device shall be equipped with means to catch a cable sleeve (see Figure 4)
in such a way that the sleeve and adjacent wire rope are fully enclosed. In addition, a positive, self-
engaging, locking system in the closed position shall be provided in order to prevent any risk of self or
inadvertent release whether or not the wire rope is under tension. The design shall provide an immediate
visual indication whether this lock is in the open or closed position. Consideration should be given to the
geometry of catching or locking parts filling any remaining gap in the spacing between 2 adjacent sleeves
whether this lock is in the open or closed position.
4.3.3 It shall be possible to latch and unlatch the tension retaining device with a hand force (HF) not
exceeding 100 N (22 lbf), regardless of any tension remaining in the cable.
Disengagement of the locking system shall be possible only by a deliberate hand action, without the use
of tool(s), regardless of the cable's residual tension.
4.3.4 The thickness of the tension retaining device when in its latched position, including the handle in
its stored position, shall be kept to a minimum consistent with its design principle, and should preferably
not exceed 38 mm (1.5 in).
4.3.5 Tension retaining devices shall present no sharp edges which may come into contact with the
steel wire ropes or the operator's hands.
4.3.6 The recoil travel of the end of the handle of the tension retaining device under residual tension
shall not exceed 150 mm (6.0 in) when opening the device. The design should aim at minimizing the
spring effect creating a hazard to the operator (see 4.8.2).
4.3.7 Positive means shall be provided to prevent the adjustable wire rope length from getting free
from the tension retaining device at maximum length (see 4.2.5).
4.3.8 All devices shall be designed so that there are no crushing or shearing points which might lead to
the hands of the operator being injured during intended use.
4.3.9 No lubricant should be necessary for proper operation of type A restraint slings length
adjustment. If a lubricant is nevertheless deemed necessary for the tension retaining device, it shall be
permanent and meet the requirements of ISO 4346.
4.4 End fittings
4.4.1 Type A adjustable length restraint sling assemblies shall be equipped at each end with a fitting
(connecting compo
...
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