ISO 16049-1:2020

Air cargo equipment - Restraint straps - Part 1: Design criteria and testing methods

This document specifies the design criteria and testing methods adequate to guarantee the ultimate load and operational dependability of cargo restraint strap assemblies with a typical 22 250 N (5 000 lbf) rated ultimate tension load capability, as used by the airline industry. These restraint straps are used in civil transport aircraft during flight for: a) 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 b) 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, c) the same restraint strap assemblies can also be used in other applications such as: 1) non-containerized (bulk loaded) baggage and cargo compartments; 2) to ensure cargo restraint inside an airworthiness approved air cargo container. NOTE The ultimate loads allowable on the attachment points available in most aircraft bulk compartments and inside many air cargo containers are significantly lower than 22 250 N (5 000 lbf). This results in the restraint arrangements ultimate load capability being dictated by the weakest element, i.e. the attachment points: typical 22 250 N ultimate load restraint straps will therefore be in excess of the requirements for such applications. Compliance with this document provides one means of cargo restraint straps airworthiness approval by Civil Aviation Authorities under TSO/ETSO-C172a, in addition to the other requirements therein.

Équipement pour le fret aérien — Sangles d'arrimage — Partie 1: Critères de conception et méthodes d'essai

General Information

• Status: Published
• Publication Date: 13-Jan-2020
• ICS: 49.120 - Cargo equipment
• Technical Committee: ISO/TC 20/SC 9 - Air cargo and ground equipment
• Drafting Committee: ISO/TC 20/SC 9 - Air cargo and ground equipment
• Current Stage: 9060 - Close of review
• Completion Date: 02-Sep-2030

Relations

• Revises: ISO 16049-1:2013 - Air cargo equipment - Restraint straps - Part 1: Design criteria and testing methods
• Effective Date: 05-Aug-2017

Overview - ISO 16049-1:2020 (Air cargo restraint straps)

ISO 16049-1:2020 specifies design criteria and testing methods for air cargo restraint strap assemblies used in civil transport aircraft. It targets assemblies with a typical rated ultimate tension capability of 22 250 N (5 000 lbf) and covers straps used to secure unitized cargo on certified air cargo pallets, non-unitized pieces of cargo, floating pallets, bulk-loaded compartments and air cargo containers. Compliance with this standard is accepted as one route to airworthiness approval by Civil Aviation Authorities (for example under TSO/ETSO‑C172a).

Key topics and technical requirements

The standard defines minimum and recommended requirements across design, performance and verification, including:

• Design criteria

  • Ultimate load and breaking force expectations for complete assemblies
  • Requirements for webbing, stitching and end fittings
  • Limits for elongation and acceptable dimensions
  • Tensioning and tension‑retaining device characteristics
  • Flammability and environmental degradation considerations

• Testing methods

  • Ultimate load (breaking force) tests on complete assemblies
  • Elongation and webbing elongation tests
  • Cyclic load tests to verify durability under repeated loading
  • Flammability tests consistent with aircraft safety regulations
  • Optional abrasion and additional webbing tests
  • Test specimen preparation, apparatus and record‑keeping requirements

• Quality control and marking

  • Manufacturer quality processes, traceability and required product markings
  • Instructions for users and operators (manufacturer’s and operating instructions)

Practical applications and who uses this standard

ISO 16049-1 is used by stakeholders involved in design, manufacture, certification and operation of air cargo restraint systems:

• Manufacturers of restraint straps, tensioners, webbing and end fittings - for product design and testing programs
• Aircraft and cargo pallet OEMs - to ensure compatibility with cargo restraint systems
• Certification and conformity assessment bodies and Civil Aviation Authorities - to assess airworthiness and approve equipment under TSO/ETSO regimes
• Testing laboratories - to perform the specified mechanical, cyclic and flammability tests
• Airlines, cargo operators and MRO organizations - for procurement specifications, inspection, maintenance and safe loading procedures

Use cases include tie‑down of unitized cargo on ISO/airworthiness‑approved pallets, restraint of non‑unitized cargo in containerized or bulk compartments, and securing baggage or cargo inside approved air cargo containers.

Related standards and references

Normative references in ISO 16049-1 include:

• ISO 8097, ISO 21100 (air cargo unit load devices)
• ISO 4117, ISO 4171 (air cargo pallets)
• ISO 7166 (rail and stud configuration)
• ISO 9788 (double stud tie‑down fittings)
• ISO/TR 8647 (environmental degradation of textiles)
• ISO 10254 (vocabulary)

Adopting ISO 16049-1 helps ensure durable, test‑verified restraint straps that meet industry safety and airworthiness expectations.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 16049-1
Third edition
2020-01
Air cargo equipment — Restraint
straps —
Part 1:
Design criteria and testing methods
Équipement pour le fret aérien — Sangles d'arrimage —
Partie 1: Critères de conception et méthodes d'essai
Reference number
©
ISO 2020
© ISO 2020
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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Design criteria . 6
4.1 General . 6
4.2 Ultimate load . 7
4.3 Elongation . 7
4.4 Flammability . 8
4.5 Environmental degradation . 8
4.6 Dimensions . 9
4.7 Tensioning device . 9
4.8 End fittings .10
4.9 Webbing and sewing .11
4.10 Detailed design .11
5 Testing methods .12
5.1 Tests .12
5.2 Objective .12
5.3 Test specimens .12
5.4 Testing apparatus .12
5.5 Ultimate load test .13
5.6 Elongation test .14
5.7 Cyclic load test .14
5.8 Flammability test .15
5.9 Webbing elongation test (optional) .15
5.10 Webbing elongation test (optional) .15
5.11 Webbing abrasion test (optional) .16
5.12 Test record .16
6 Quality control .16
7 Markings .17
8 Options .18
9 Manufacturer's instructions .19
10 Operating instructions .19
Bibliography .21
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.
This third edition cancels and replaces the second edition (ISO 16049-1:2013), which has been
technically revised. The main changes compared to the previous edition are as follows:
— in Figure 1, deletion of items D5 and D6, required by TSO/ETSO-C172a, and amendment of item D2;
— in 4.4, updating of flammability requirement to the latest amended Regulations.
A list of all parts in the ISO 16049 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 2020 – All rights reserved

Introduction
This document specifies the design criteria and testing methods applicable to air cargo restraint straps
to be used for tie-down of unitized or non-unitized cargo on board civil transport aircraft.
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 restraint straps. Deviation from
recommended criteria should only occur after careful consideration, extensive testing, and thorough
service evaluation have shown alternate methods to be satisfactory.
The requirements of this document are expressed in the applicable SI units, with approximate inch-
pound units conversion between brackets for convenience in those countries using that system.
INTERNATIONAL STANDARD ISO 16049-1:2020(E)
Air cargo equipment — Restraint straps —
Part 1:
Design criteria and testing methods
1 Scope
This document specifies the design criteria and testing methods adequate to guarantee the ultimate
load and operational dependability of cargo restraint strap assemblies with a typical 22 250 N
(5 000 lbf) rated ultimate tension load capability, as used by the airline industry. These restraint straps
are used in civil transport aircraft during flight for:
a) 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
b) 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,
c) the same restraint strap assemblies can also be used in other applications such as:
1) non containerized (bulk loaded) baggage and cargo compartments;
2) to ensure cargo restraint inside an airworthiness approved air cargo container.
NOTE The ultimate loads allowable on the attachment points available in most aircraft bulk compartments
and inside many air cargo containers are significantly lower than 22 250 N (5 000 lbf). This results in the restraint
arrangements ultimate load capability being dictated by the weakest element, i.e. the attachment points: typical
22 250 N ultimate load restraint straps will therefore be in excess of the requirements for such applications.
Compliance with this document provides one means of cargo restraint straps airworthiness approval
by Civil Aviation Authorities under TSO/ETSO-C172a, in addition to the other requirements therein.
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 4117, Air and air/land cargo pallets — Specification and testing
ISO 4171, Air cargo equipment — Interline pallets
ISO 7166, Aircraft — Rail and stud configuration for passenger equipment and cargo restraint
1)
ISO 8097:2001 , Aircraft — Minimum airworthiness requirements and test conditions for certified air
cargo unit load devices
ISO/TR 8647, Environmental degradation of textiles used in air cargo restraint equipment
ISO 9788, Air cargo — Double stud tie-down fittings — Design and testing requirements
ISO 10254, Air cargo and ground equipment — Vocabulary
1) Endorsement of NAS 3610 revision 10, TSO/ETSO/CTSO/JTSO-C90c.
ISO 21100, Air cargo unit load devices — Performance requirements and testing parameters
3 Terms and definitions
For the purposes of this document, the terms and definitions given in 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
restraint strap assembly
elementary tie-down (3.2) unit consisting of flat woven textile webbing (3.3) (one fixed length (3.8.1) end
and one adjustable end), one tensioning device (3.4) and two end fittings (3.6), used for restraint of cargo
on board civil transport aircraft
3.2
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 tie-down devices against each direction of restraint
3.3
flat woven textile webbing
conventional or shuttle-less woven narrow fabric made of continuous textile fibres, generally with
multiple plies, and the prime function of which is load bearing
Note 1 to entry: A characteristic of webbing is its tight woven fabric selvedge.
3.4
tensioning device
mechanical device inducing a tensile force in the load restraint assembly
EXAMPLE Ratchets, winches, over-centre buckles, see examples in Figure 1, items C1 and C6.
3.5
tension retaining device
metallic part connecting the webbing by clamping action and retaining the force induced in the
tensioning device (3.4) by hand
EXAMPLE Cam buckles, sliding bar buckles, see example in Figure 1, item F.
3.6
end fitting
metallic device connecting the webbing or the tensioning device (3.4) to the attachment point on the
aircraft structure, the pallet edge rail or the load
Note 1 to entry: See examples in Figure 1, items D1 to D4.
Note 2 to entry: The end fittings most commonly used on air cargo restraint straps include:
a) retainer equipped flat hook (see example in Figure 1, item D1);
b) air cargo tie-down (3.2) double stud (male) fitting conforming to ISO 9788, connected directly (sewn to the
webbing, see example in Figure 1, item D3) or by an intermediate ring;
c) piece of aircraft restraint (female) rail conforming to ISO 7166.
2 © ISO 2020 – All rights reserved

3.7
tension force indicator
device that indicates the tensile force applied to the restraint strap assembly (3.1) by means of the
tensioning device (3.4) and movement of the load acting on the load restraint device
3.8
length of restraint strap assembly

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 webbing to the tensioning device (3.4)
Note 1 to entry: See Figure 2.
Note 2 to entry: This length can be zero, i.e. the end fitting directly attached to the tensioning device.
Key
A restraint strap assembly (complete)
A1, A2 space for marking (label)
B webbing
C tensioning devices
C1 ratchet tensioner
C2 ratchet tensioner with tension force indicator (3.7) (see also E)
C3 sliding bar buckle
C4, C5 over-centre buckles
C6 lashing winch
D end fittings
D1 snap hook, flat, swivel or twisted, with retainer
D2 flat hook, with retainer
D3 double stud tie-down (3.2) fitting (directly sewn onto webbing)
D4 triangle, designed to engage with an anchorage
E tension force indicator (see also C2)
F tension retaining device (3.5) (cam buckle, sliding bar buckle)
Figure 1 — Examples of restraint strap equipment, including tensioning device C, end fitting D
and tension force indicator E
3.8.2
adjustable length
l
GL
length of an adjustable end, measured from the free end of the webbing to the force bearing point of the
end fitting (3.6)
Note 1 to entry: See Figure 2.
4 © ISO 2020 – All rights reserved

3.8.3
total length
l
total of l (3.8.1), l (3.8.2) and length of the tensioning device (3.4)
GF GL
Key
1 fixed end
2 adjustable end
3 end fitting (3.6)
4 tensioning device or tension retaining device (3.5)
Figure 2 — Two-piece restraint strap assembly (3.1)
3.9
breaking force
F
B
maximum force that the restraint strap assembly (3.1) withstands when tested in a complete form
Note 1 to entry: With tensioning device (3.4) and end fittings (3.6) according to 5.5.
3.10
hand force
F
H
force applied to the handle of the tensioning device (3.4), which creates the tensile force in the restraint
strap assembly (3.1)
3.11
limit load
LL
maximum load to be expected in service
Note 1 to entry: See CCAR-25, CS-25, JAS Part 3 or 14 CFR Part 25, paragraph 25.301 (a).
Note 2 to entry: It is two thirds of the ultimate load (3.12), i.e. 14 827 N (3 333 lbf) for a typical rated ultimate load
of 22 250 N (5 000 lbf).
3.12
ultimate load
UL
limit load (3.11) multiplied by a safety factor of 1,5
Note 1 to entry: See CCAR-25, CS-25, JAS Part 3 or 14 CFR Part 25, subclause 25.303.
Note 2 to entry: It is used for computation of cargo tie-down (3.2) arrangements, based on the ultimate load
factors defined in the Airworthiness Authorities approved Weight and Balance Manual, in each direction of
restraint, throughout the certified flight envelope of the aircraft type. The restraint strap assembly's (3.1) rated
ultimate load is guaranteed not to exceed the measured breaking force (F ) (3.9).
B
3.13
residual tension
tension force which can be measured in the webbing of a strap assembly attached between two (2)
fixed points, after its length was adjusted and its tension device was operated and latched with the
reference hand force (F ) (3.10), prior to application of any external load
H
3.14
competent person
designated person, with suitable training, 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, for example ISO 9001:2015, 6.2.2
or another equivalent quality management standard.
3.15
traceability code
series of letters and/or numbers marked on a component or an assembly which enables its
manufacturing and in-service history to be retraced, including webbing production batch identification
Note 1 to entry: See 7.2.
4 Design criteria
4.1 General
4.1.1 This document specifies the design criteria for restraint strap assemblies, but does not intend
specifying in any manner 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 Airworthiness Authorities approved 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 straps to be used in each direction of restraint, maximum
angles to be observed with the direction of restraint, minimum spacing of attachment points, etc.
4.1.2 When restraint strap assemblies are attached to the edge rails of a certified air cargo pallet
meeting the requirements of ISO 8097 (NAS 3610) or ISO 21100, operating instructions should 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 configuration drawing(s).
4.1.3 The use of reliable and guaranteed restraint strap assemblies is necessary but not sufficient to
ensure flight safety: this document is based on the assumption that straps will be used and tie-down
will be performed in accordance with operating instructions established by the aircraft manufacturer, by
competent, suitably trained personnel, for example, as defined in ISO 9001:2015, 6.2.2 or an equivalent
quality management standard.
4.1.4 Subject to proper operating instructions as per 4.1.1 and 4.1.2 being defined and complied with,
using restraint strap 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 to restrain cargo on board civil transport aircraft can be found in ISO 16049-2.
4.1.5 The restraint strap 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) or ISO 21100),
6 © ISO 2020 – All rights reserved

b) aircraft seat tracks or structural attachment points meeting the requirements of ISO 7166, either
directly, or using intermediate attachment hardware such as ISO 9788 double stud tie-down
fittings.
4.2 Ultimate load
The breaking force (F ) of the restraint strap assembly, when tested in accordance with 5.5, shall
B
guarantee a rated minimum ultimate tensile load to be specified at purchasing as well as through
operating instructions.
The rated minimum ultimate load most commonly specified in the airline industry is 22 250 N
(5 000 lbf). This is compatible with the best omni-directional performance obtainable from structural
attachment points and intermediary hardware. In the interest of overall economy and world-wide
standardization, users are encouraged to use this value.
NOTE An example of justified deviation is where dedicated restraint straps are designed for use with
ISO 7166 single stud tie-down fittings. Then, the rated ultimate load consistent with the fitting's is 8 900 N
(2 000 lbf).
4.3 Elongation
4.3.1 Care shall be taken in selecting the materials and design most appropriate to minimizing the
restraint strap assembly elongation under load, in order to improve its restraint capability.
4.3.2 The total elongation of the complete restraint strap assembly under load, as measured between
the force bearing point of the end fittings, i.e. the sum of webbing elongation and any longitudinal
deformation of the hardware (tensioning device or end fitting), shall not exceed 10 % when submitted to
the rated ultimate load (UL).
4.3.3 Webbing slippage through the tensioning device (see 4.7.5) is allowable only during pretension
(i.e. while the tensioning device is being actuated and latched), and if:
a) it does not exceed 0,5 % of the maximum total length of the complete restraint strap assembly,
when submitted to the residual tension force resulting from release of the tensioning device handle
in the closed position, and
b) it no longer occurs under any load between zero and the rated ultimate load (UL), after the
tensioning device handle has been latched.
4.3.4 The total elongation when submitted to intermediate loads shall not exceed the linear relationship
between the maximum values stated in 4.3.2 and 4.3.3. See Figure 3.
Key
E elongation
L load
F tensile force
R residual load at tension
UL ultimate load
A allowable area
NA non allowable area
Figure 3 — Allowable elongation range
4.4 Flammability
4.4.1 It is presupposed that the webbing, as used in the restraint strap assembly, i.e. including sewing
and any treatment, meets the flammability test criteria of applicable regulations, e.g. CCAR-25, CS-
25, JAS Part 3 or 14 CFR Part 25, Appendix F, Part I, paragraph (a)(1)(v); it may not have a burn rate
greater than 63 mm (2,5 in) per minute when tested horizontally with the apparatus and test procedures
required in Appendix F, Part I, paragraph (b)(5).
4.4.2 The flammability test shall be performed on a minimum of three samples, and the results
averaged. The results shall be recorded in a test report to be handed to the purchaser on or before
delivery of each production batch.
4.5 Environmental degradation
4.5.1 The available data concerning degradation of woven textile fibre performance when exposed to
environment factors, as provided in ISO TR 8647, shall be taken into account for webbing and thread
selection and treatment, commensurate with the expected storage and service life of the restraint strap
assembly.
4.5.2 An expiry date after which the rated performance may not be expected to be maintained shall be
provided to the purchaser at or before the time of delivery of each production batch, and shall be marked
on each strap as part of the required traceability code (see 7.2). The expiry date may take into account
8 © ISO 2020 – All rights reserved

the expected storage duration, providing the strap assemblies are delivered and stored in an ultraviolet
protective packaging, and any storage conditions requirements which might affect performance
degradation are specified.
4.5.3 For environmental degradation assessment, it should be assumed that the restraint strap
assemblies will be operated throughout temperature ranges of −40 °C (−40 °F) to 60 °C (140 °F) with
relative humidity between 20 % and 85 %, including ice, snow and occasional soaking in water.
4.5.4 In addition, the strap assembly components and materials should be selected in order to allow
separate recycling of the non-textile and webbing parts when the unit is out of use or after its expiry
date. Instructions for recycling should be provided by the manufacturer.
4.6 Dimensions
4.6.1 Length: the length of the fixed end (l ) and the adjustable end (l ) shall be specified by the
GF GL
purchaser.
The length of the fixed end (l ) can be zero (end fitting attached directly to the tensioning device,
GF
or forming an integral part thereof). However, the use of such restraint strap assemblies is not
recommended on air-land pallets meeting the requirements of ISO 4117, when equipped with vertical
mounted edge rail tie-down slots, due to the risk of interference with aircraft restraint systems or an
adjacent pallet during handling.
4.6.2 Width: the nominal width of the webbing, measured between the outer faces of selvedges, should
preferably be (51 ± 1) mm (2,00 ± 0,04) in for a strap with a 22 250 N (5 000 Ibf) ultimate load rating.
Width between 38 mm (1,5 in) and 63 mm (2,5 in) is acceptable for the same load rating.
4.7 Tensioning device
4.7.1 The type of tensioning or tension retaining device shall be selected on agreement between the
manufacturer and the purchaser. The types most commonly used in the air cargo industry are:
a) continuous tension devices (ratchet buckles), or
b) "flat" one stroke tension devices (over-centre, sliding bar buckles).
Unless otherwise mentioned, the design criteria hereafter apply regardless of the type of device
concerned.
4.7.2 The thickness of the device when in its latched position shall be kept to a minimum consistent
with its design principle. The following recommended maximum thicknesses should be considered:
a) 50 mm (2,0 in) for ratchet buckles,
b) 40 mm (1,6 in) for one stroke devices.
4.7.3 The loose end of the adjustable webbing shall be protected against fraying, and positive means
shall be provided to prevent it from getting free from the tension device at maximum length.
4.7.4 Tensioning devices of the "flat" one stroke types should provide, when actuated, a minimum
50 mm (2 in) tensioning length on the webbing.
4.7.5 Tensioning devices design shall aim at maximizing friction coefficients in order to obtain self-
blocking capability and eliminate any risk of slippage of the webbing against the device once latched,
including when the webbing was soaked in water, or when submitted in flight to repeated slack (zero
load)/tight cycles.
If some initial slippage is unavoidable during pretension (i.e. while the tensioning device is being
actuated and latched):
a) it shall not exceed 0,5 % of the maximum total length of the complete restraint strap assembly,
when submitted to the residual tension force resulting from latching the device handle in the closed
po
...