ISO 18387:2019

Aerospace - Linear hydraulic utility actuator - General specifications

This document establishes the general requirements for a linear hydraulic utility actuator, herein referred to as a "utility actuator", for use in flight vehicle hydraulic systems at pressures up to 35 000 kPa (5 000 psi). These requirements include: - design requirements; - test requirements. This document is intended to be used in conjunction with the detail specification that is particular to each application. NOTE Although Brake pistons and Landing Gear Bogie (Truck) Pitch Trimmers are utility actuators, they are outside the scope of this document. This is because these devices are considered to be specialist actuator devices due to their specific duty cycles requiring a separate set of tailored requirements.

Série aérospatiale — Actionneur hydraulique linéaire à usage général — Spécifications générales

General Information

• Status: Published
• Publication Date: 26-Sep-2019
• ICS: 49.080 - Aerospace fluid systems and components
• Technical Committee: ISO/TC 20/SC 10 - Aerospace fluid systems and components
• Drafting Committee: ISO/TC 20/SC 10/WG 9 - Hydraulic power and actuation equipment
• Current Stage: 9093 - International Standard confirmed
• Start Date: 14-Jan-2025
• Completion Date: 13-Dec-2025

Overview - What ISO 18387:2019 covers

ISO 18387:2019 defines the general requirements for linear hydraulic utility actuators used in aerospace flight-vehicle hydraulic systems up to 35 000 kPa (5 000 psi). It provides a baseline of design, performance and test requirements for utility actuators and is intended to be used together with a detail specification specific to each application. The standard clarifies scope (for example, brake pistons and landing‑gear bogie pitch trimmers are excluded as specialist devices) and supports airworthiness and qualification activities for aerospace hydraulic actuators.

Key technical topics and requirements

ISO 18387 organizes requirements across functional, strength, endurance and design areas. Key topics include:

• Functional requirements

  • Actuator types and features incorporated within utility actuators
  • Hydraulic fluid compatibility and cleanliness
  • Performance cases, leakage limits, seal and scraper friction
  • End‑of‑travel snubbing and locking means

• Endurance and testing

  • Duty cycle definition and endurance test expectations
  • Impulse fatigue and endurance verification under representative conditions

• Strength and structural requirements

  • Hydraulic proof pressure and ultimate (burst) pressure limits
  • Combined hydraulic and structural loading, buckling, limit and ultimate loads
  • Port strength, vibration and mechanical fatigue considerations

• Detail design and construction

  • Seals, scrapers, back‑up rings, gland finishes and lead‑in chamfers
  • Bearings, rod ends, threaded components, retainer and spring rings
  • Corrosion protection, materials selection and marking/nameplate requirements

• Environmental and airworthiness

  • Fluid and ambient temperature ranges, environmental testing and airworthiness documentation

Practical applications - who uses this standard

ISO 18387 is practical for:

• Aerospace actuator designers creating linear hydraulic utility actuators
• Systems and propulsion engineers specifying actuator requirements for flight systems
• Manufacturers and suppliers preparing detail specifications, test plans and product qualification
• Quality, test laboratories and certification authorities assessing compliance (proof pressure, endurance, leakage, fatigue)
• Procurement and maintenance teams referencing standard requirements during selection, inspection and overhaul

Related standards and usage

ISO 18387 is intended to be used alongside application‑specific detail specifications and other aerospace standards covering hydraulic fluids, sealing materials, corrosion protection and airworthiness certification. When specifying a component, reference ISO 18387 for general actuator requirements and add application‑specific documents to define duty cycle, interfaces and installation criteria.

Keywords: ISO 18387, linear hydraulic utility actuator, aerospace actuator specifications, hydraulic systems, endurance test, seal and scraper, proof pressure, actuator design.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 18387
First edition
2019-09
Aerospace — Linear hydraulic utility
actuator — General specifications
Série aérospatiale — Actionneur hydraulique linéaire à usage général
— Spécifications générales
Reference number
©
ISO 2019
© ISO 2019
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 © ISO 2019 – All rights reserved

Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 General requirements . 7
4.1 Order of precedence . 7
4.2 Hydraulic system characteristics . 7
4.3 Qualification . 7
4.4 Airworthiness requirements. 7
5 Functional requirements . 7
5.1 General . 7
5.2 Actuator type . 7
5.3 Features incorporated within the utility actuator . 8
5.4 Hydraulic fluid . 8
5.5 Performance . 8
5.5.1 General. 8
5.5.2 Performance cases . . 8
5.5.3 Leakage . 9
5.5.4 Seal and scraper friction .10
5.5.5 End of travel snubbing .10
5.5.6 Utility actuator locking means .10
5.6 Endurance .12
5.6.1 General.12
5.6.2 Duty cycle .12
5.6.3 Endurance test .12
5.7 Fluid and ambient temperature .12
5.8 Fluid cleanliness .13
5.8.1 Operation .13
5.8.2 Malfunction . .13
5.8.3 Equipment delivery .13
5.9 Environmental requirements .13
6 Detail design requirements .14
6.1 General .14
6.2 Prevention of incorrect assembly .14
6.3 Standard parts .14
6.4 Maintainability features .15
6.5 Seals and scrapers .15
6.5.1 General.15
6.5.2 Gland surface finishes.15
6.5.3 Static seals .15
6.5.4 Dynamic seals .16
6.5.5 Scraper rings .16
6.5.6 Back-up rings .16
6.5.7 Lead in chamfers .17
6.6 Fluid porting through interfacing surfaces .17
6.7 Lubrication of hydraulic elements .17
6.8 Orifices .17
6.9 Retainer (snap) rings .17
6.10 Spring rings .18
6.11 Secondary locking .18
6.12 Drainage .18
6.13 Drillings .18
6.14 Fillet radii .18
6.15 Rod ends .18
6.16 Bearings .19
6.16.1 General.19
6.16.2 Lubrication .19
6.16.3 Anti-roll feature .20
6.17 Threaded components .20
6.18 Electro-conductive bonding .20
6.19 Marking .20
6.19.1 Nameplate .20
6.19.2 Fluid identification .21
7 Strength requirements .21
7.1 Hydraulic .21
7.1.1 DOP definition .21
7.1.2 Proof pressure .21
7.1.3 Ultimate (burst) pressure .21
7.1.4 Impulse fatigue .21
7.1.5 Operation at full flow relief pressure .21
7.2 Loads . .21
7.2.1 Buckling load .21
7.2.2 Locking load (if applicable) .22
7.2.3 Limit load .22
7.2.4 Limit retraction and extension .22
7.2.5 Ultimate load .22
7.2.6 Bottoming loads .22
7.2.7 Stall load .22
7.2.8 Bench handling loads .23
7.3 Combined hydraulic pressure and structural loading .23
7.3.1 General.23
7.3.2 Design operating pressure and limit structural load .23
7.3.3 Proof pressure and ultimate structural load .23
7.4 Mechanical fatigue .23
7.5 Port strength .23
7.6 Vibration .24
8 Construction .24
8.1 Materials .24
8.1.1 General.24
8.1.2 Metals .24
8.2 Corrosion protection .25
8.2.1 General.25
8.2.2 Ferrous and copper alloys .25
8.2.3 Aluminium alloys .25
8.3 Forgings .25
9 Mass .25
10 Installation requirements.25
10.1 Space envelope .25
10.2 Overtravel .26
10.3 Adjustment .26
10.4 Dimensions .26
10.4.1 Retracted length .26
10.4.2 Extended length .26
10.5 Interface document .26
10.6 Installation drawing .27
10.7 Mounting of the actuator to structure .27
10.8 Hydraulic interfaces .28
iv © ISO 2019 – All rights reserved

10.9 Electrical interfaces (if applicable) .28
11 Instrumented utility actuator .28
12 Maintainability requirements .28
12.1 General .28
12.2 Maintenance concept .28
12.3 Service life limitations and storage specifications .29
12.4 Reparability .29
13 Reliability requirements .29
13.1 Requirements .29
13.2 Equipment compliance .29
14 Quality assurance provisions .29
14.1 Responsibility for inspection .29
14.2 First article inspection (FAI) .30
14.2.1 General.30
14.2.2 First article samples . .30
14.2.3 First article inspection report .30
14.2.4 Rejection .30
14.3 Classification of tests .30
14.4 Test stand requirements .30
15 Development tests .31
16 Acceptance tests .31
16.1 General .31
16.2 Examination of the product .31
16.3 Test programme and inspection methods .32
16.3.1 General.32
16.3.2 Mass .32
16.3.3 Run-in .32
16.3.4 Proof pressure .32
16.3.5 Leakage .32
16.3.6 Performance tests .33
16.3.7 Electro-conductive bonding .33
16.3.8 Storage and packaging .33
17 Qualification .34
17.1 Purpose .34
17.2 Qualification procedure .34
17.2.1 Qualification programme plan .34
17.2.2 Qualification test procedure .34
17.2.3 Similarity and analysis report .34
17.2.4 Qualification test report .34
17.2.5 Samples and programme of qualification tests .34
17.2.6 Acceptance tests .36
17.2.7 Dimensional check .37
17.2.8 Expanded envelope acceptance tests .37
17.2.9 Performance .37
17.2.10 Endurance test .40
17.2.11 Structural tests .41
17.2.12 Environmental tests .45
17.2.13 Post qualification tests .45
17.2.14 Supplementary tests .46
Bibliography .47
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
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electrotechnical standardization.
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This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 10, Aerospace fluid systems and components.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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vi © ISO 2019 – All rights reserved

Introduction
Linear hydraulic utility actuators are designed to move structural elements of a flight vehicle from
one position to another to allow the functioning of various flight vehicle systems, such as landing gear,
cargo doors, in-flight refuelling probes, etc.
It is noted that, while ISO standards should normally refer only to SI units, large segments of the
aerospace industry refer to other measurement systems as a matter of common working practice.
All dimensions used in this document are in SI units with the non-SI units given in addition for the
convenience of those users more familiar with these.
It is further noted that the standard ISO decimal symbol “,” (comma) is not used as common working
practice for inch dimensions. A decimal point is used in the inch dimensions in this document as in
many other aerospace standards.
NOTE The use of non-SI units and the decimal point in this document does not constitute general acceptance
of measurement systems other than SI within International Standards.
INTERNATIONAL STANDARD ISO 18387:2019(E)
Aerospace — Linear hydraulic utility actuator — General
specifications
1 Scope
This document establishes the general requirements for a linear hydraulic utility actuator, herein
referred to as a "utility actuator", for use in flight vehicle hydraulic systems at pressures up to
35 000 kPa (5 000 psi).
These requirements include:
— design requirements;
— test requirements.
This document is intended to be used in conjunction with the detail specification that is particular to
each application.
NOTE Although Brake pistons and Landing Gear Bogie (Truck) Pitch Trimmers are utility actuators, they are
outside the scope of this document. This is because these devices are considered to be specialist actuator devices
due to their specific duty cycles requiring a separate set of tailored requirements.
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 2093, Electroplated coatings of tin — Specification and test methods
ISO 2669, Environmental tests for aircraft equipment — Steady-state acceleration
ISO 2671, Environmental tests for aircraft equipment — Part 3.4 : Acoustic vibration
ISO 3323, Aircraft — Hydraulic components — Marking to indicate fluid for which component is approved
ISO 7137, Aircraft — Environmental conditions and test procedures for airborne equipment
ISO 8078, Aerospace process — Anodic treatment of aluminium alloys — Sulfuric acid process, undyed coating
ISO 8079, Aerospace process — Anodic treatment of aluminium alloys — Sulfuric acid process, dyed coating
ISO 8625-1, Aerospace — Fluid systems — Vocabulary — Part 1: General terms and definitions related to
pressure
ISO 8625-2, Aerospace — Fluid systems — Vocabulary — Part 2: General terms and definitions relating to
flow
ISO 8625-3, Aerospace — Fluid systems — Vocabulary — Part 3: General terms and definitions relating to
temperature
ISO 11218, Aerospace — Cleanliness classification for hydraulic fluids
SAE AS4088, Aerospace Rod Scraper Gland Design Standard
SAE AS4716, Gland Design, O-Ring and Other Elastomeric Seals
SAE AS5781, Retainers (Backup Rings), Hydraulic and Pneumatic, Polytetrafluoroethylene Resin, Single
Turn, Scarf-Cut, For Use in AS 4716 Glands
SAE AS5782, Retainers (Backup Rings), Hydraulic and Pneumatic, Polytetrafluoroethylene Resin, Solid, Un-
Cut, For Use in AS 4716 Glands
SAE AS5857, Gland Design, O-ring and Other Elastomeric Seals, Static Applications
SAE AS5860, Retainers, (Back-Up Rings), Hydraulic and Pneumatic, Polytetrafluoroethylene Resin, Single
Turn, Static Gland
SAE AS5861, Retainers, (Back-Up Rings), Hydraulic and Pneumatic, Polytetrafluoroethylene Resin, Solid,
Static Gland
MIL-STD-810, Environmental Engineering Considerations and Laboratory Tests
MMPDS Metallic Materials Properties Development and Standardization Handbook
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8625-1, ISO 8625-2, ISO 8625-3
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
utility actuator
two-position hydraulic utility actuator that is controlled by an external selector valve
Note 1 to entry: The scope of this document is not limited to those utility actuator configurations shown in
Figures 1 to 6, as these are only examples.
3.2
single acting hydraulic utility actuator
utility actuator (3.1) that is hydraulically powered in one direction and returned to the other by a spring
or externally applied mechanical force
Note 1 to entry: A typical configuration of a single acting utility actuator is shown schematically in Figure 1.
Figure 1 — Single acting utility actuator
3.3
double acting hydraulic utility actuator
utility actuator (3.1) that is hydraulically powered in both directions
Note 1 to entry: Typical configurations of double acting hydraulic utility actuators are shown schematically in
Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6.
Note 2 to entry: Figure 3 shows an actuator with piston rods that are equal in diameter. However, this type of
actuator may have unequal rod diameters.
2 © ISO 2019 – All rights reserved

Note 3 to entry: The utility actuators can incorporate restrictors to control the extension and/or the
retraction time.
Note 4 to entry: The utility actuators can incorporate end of travel snubbing (3.5.2) at one or both ends of the
actuator stroke.
Note 5 to entry: If the utility actuator is an unequal area actuator, pressure can be applied at both ports to extend
the utility actuator by permitting the fluid to circulate from the annulus side to the piston side.
Figure 2 — Simple utility actuator with extend and retract port
Figure 3 — Double ended utility actuator
Figure 4 — Utility actuator with end of travel snubber (in extension and retraction)
Figure 5 — Utility actuator with end of travel snubber (in extension and retraction), extend lock
and lock indicator
Figure 6 — Utility actuator with a shuttle valve for alternate supply power extend actuation
3.4
non-bottoming utility actuator
utility actuator (3.1) that does not rely on internal end stops for positioning as the extended and/or
retracted positions of the utility actuator are dictated by external features such as mechanical stops on
structure
Note 1 to entry: For non-bottoming utility actuators, the loads are generated by the internal pressures of the
utility actuator only because the piston is floating.
3.5 Velocity damping and end of travel snubbing
3.5.1
velocity damping
incorporation of means to reduce the utility actuator (3.1) stroke velocity during extension and/or
retraction
3.5.2
end of travel snubbing
incorporation of means to reduce the utility actuator (3.1) stroke velocity towards the extension and/or
retraction end stop to reduce impact loads
3.5.3
end of travel velocity
rate of the utility actuator (3.1) upon reaching its mechanical end stop(s)
3.6 Design operating pressure (DOP)
3.6.1
system DOP
normal maximum steady pressure that is applied to the actuator from the hydraulic power
generation system
Note 1 to entry: Excluded from this are:
— reasonable tolerances and transient pressure effects such as may arise from acceptable pump ripple, or
— reactions to system functioning or demands that may affect fatigue.
3.6.2
actuator DOP
sustained pressure that is generated within the actuator due to pressure intensification, such as end of
stroke damping
3.7 Load
3.7.1
stall load
maximum load at which the external force applied to the utility actuator (3.1) in the opposing direction
to that in which the utility actuator is operating, equals the internal hydraulic force generated by the
utility actuator
Note 1 to entry: Beyond this point, the actuator may or may not be back-driven depending on the hydraulic circuit
configuration.
Note 2 to entry: This load also corresponds to a static hydraulic chamber pressure (hydraulic load) that the
actuator cylinder housing has to withstand.
4 © ISO 2019 – All rights reserved

3.7.2
limit structural load
maximum external load applied to the utility actuator (3.1) in either the extended or retracted position
at the extent of the normal (nominal or worst case) operating conditions
Note 1 to entry: The limit structural load also takes into consideration the combined effects of both axial and
bending loads, if applicable.
3.7.3
ultimate structural load
load that the utility actuator (3.1) withstands without buckling or structural failure, and normally
associated with system single failure cases or flight outside the normal flight envelope
Note 1 to entry: The ultimate structural load also takes into consideration the combined effects of both axial and
bending loads, if applicable.
3.7.4
break out seal and scraper friction load
load that the seals and the scraper(s) impose on the utility actuator (3.1) rod that has to be overcome
before the actuator can start moving
3.8 Temperature
3.8.1 Ambient temperature
3.8.1.1
maximum rated temperature
maximum continuous temperature of the air surrounding the utility actuator (3.1)
Note 1 to entry: This temperature is generally lower than the survival temperature (3.8.3).
Note 2 to entry: Temperatures are expressed in degrees Celsius.
3.8.1.2
minimum operating temperature
minimum temperature of the air surrounding the utility actuator (3.1)
Note 1 to entry: This temperature is generally higher than the survival temperature (3.8.3).
Note 2 to entry: Temperatures are expressed in degrees Celsius.
3.8.2 Hydraulic fluid temperature
3.8.2.1
maximum rated temperature
maximum continuous temperature of the hydraulic fluid within the utility actuator (3.1)
Note 1 to entry: This temperature is generally lower than the survival temperature (3.8.3).
Note 2 to entry: Temperatures are expressed in degrees Celsius.
3.8.2.2
minimum operating temperature
minimum temperature of the hydraulic fluid within the utility actuator (3
...