TEMPLATE
Note that throughout this Template, black font indicates the template framework and red
italic provides guidance material, offers options or suggests content and should be
overwritten. PT's must apply considered thought to the content of their SI Strategy
Document – simply replacing the red text with the platform name throughout would not result
in an acceptable strategy; likewise, the black text can be adjusted to suit the particular
platform.
PLATFORM NAME
STRUCTURAL INTEGRITY
STRATEGY DOCUMENT
Reference: XXXX/XXXX/XXX
Date: 12 Apr 2013
Approved and Issued by: Project Team Leader
Copy Number: ____ of ____
i
Intentionally Blank
ii
CONTENTS
Contents Page
Abbreviations
Record of Amendments
iii
v
vii
PART 1 - PLATFORM NAME SI STRATEGY DOCUMENT INTRODUCTION
Background
Aim
Scope
Strategy Document Usage Methodology
Strategy Document Relationship to Other Documents
Strategy Document Content
Ownership and Review Processes
SI Assurance Activities
Structural Integrity Meetings
Structural Integrity Plan
Structural Integrity Historical Evidence
PART 2
PLATFORM NAME SI STRATEGY DOCUMENT
Introduction
Establishing SI
Introduction
Type Records
Statement of Operating Intent (SOI)
Structural Qualification/Clearances
Identification and Classification of Structure
Sustaining SI
Introduction
Structural Monitoring and Individual Aircraft Tracking
Fatigue Meter Formula
Structural Examination
Structural Configuration Control
Validating SI
Introduction
Statement of Operating Intent and Usage (SOIU)
Type Records
Structural Sampling
Operational Loads Measurement/Operational Data Recording
Requirements
Maintenance Schedule Review
Ageing Aircraft Audit - Structural Sub-Audit
Recovering SI
Introduction
Structural Issues
Environmental Damage Prevention and Control (EDPC)
Compromised IAT
Repair Assessment Programme (MASAAG 106)
Exploiting SI
Introduction
Fatigue Conservation Measures
Structural Hazard-Risks
Exploiting In-Service Experience
iii
Life Extension Activities
Aircraft Disposal
PART 3 - PLATFORM NAME HISTORICAL SI ASSURANCE ACTIVITIES
Introduction
Aim
Historical Activities Summary Statements
ANNEXES:
Annex A – Structural Integrity Meetings Matrix
Annex B – Structural Integrity Meetings – Terms of Reference
Annex C – Structural Integrity Working Group Standing Agenda
Annex D – Platform Specific Structural Integrity Document References
iv
List of Abbreviations
(Delete abbreviations from this list if they are not used in the final document. Likewise, the
list can be added to)
AAA
AAMC
AASA
ac
AD
ADR
ADS
AEDIT
ALARP
ALI
AMC
AMM
AOA
AP
ASI
CAA
CADMID
DDH
Def Stan
DO
EASA
ED
EDPC
ESVRE
FAA
FDR
FH
FI
FLC
FMF
FSFT
FST
FTR
FWAMG
GAG
GARP
GM
HAMG
HRI
HUMS
IAT
IPT
IPTL
ISD
JAP
JSP
LEP
Ageing Aircraft Audit
Alternative Acceptable Means of Compliance
Ageing Aircraft Structural Audit (obsolete term – include in this list of your
platform had an AASA in the past)
Aircraft
Accidental Damage
Air Data Recorder
Aircraft Document Set
Aircraft Engineering Development Investigation Team
As Low as Reasonably Practicable
Airworthiness Limitation Item
Acceptable Means of Compliance
Aircraft Maintenance Manual
Aircraft Operating Authority
Air Publication
Aircraft Structural Integrity
Civil Aviation Authority
Concept, Assessment, Demonstration, Manufacture, In-service, and Disposal
Delivery Duty Holder
Defence Standard
Design Organisation
European Aviation Safety Agency
Environmental Damage
Environmental Damage Prevention and Control
Establish, Sustain, Validate, Recover, Exploit
Federal Aviation Authority
Flight Data Recorder
Flying Hour
Fatigue Index
Front Line Command
Fatigue Meter Formula
Full-Scale Fatigue Test
Forward Support Team
Fatigue Type Record
Fixed Wing Airworthiness Management Group
Ground-Air-Ground
Generic Aircraft Release Process
Guidance Material
Helicopter Airworthiness Management Group
Hazard Risk Index
Health and Usage Monitoring System
Individual Aircraft Tracking
Integrated Project Team
Integrated Project Team Leader
In-Service Date
Joint Air Publication
Joint Service Publication
Life Extension Programme
v
MAA
MAR
MASAAG
MDRE
MOD
MRCOA
MRP
NDE
NDI
NDT
NDTS
ODH
ODR
OLM
OSD
PA
PDS
PE
PHM
PSE
PSEP
PSWG
RA
RAP
RCM
RI
RN
RTS
RTSA
SDH
SEP
SoFS
SHM
SI
SIN
SI(T)
SIWG
SM
SME
SMM
SOI
SOIU
SPC
SPS
SSI
STR
TAA
TLM
TLMP
UAVASMG
UTI
WLC
Military Aviation Authority
Military Aircraft Release
Military Aircraft Structural Airworthiness Assurance Group
Manual Data Recording Exercise
Ministry of Defence
Military Registered Civil Owned Aircraft
MAA Regulatory Publications
Non-Destructive Examination
Non-Destructive Inspection
Non-Destructive Testing
Non-Destructive Testing Squadron
Operational Duty Holder
Operational Data Recording
Operational Loads Measurement)
Out of Service Date
Publication Authority
Post Design Services
Project Engineer
Prognostic Health Monitoring
Principal Structural Element
Project Safety & Environmental Panel
Project Safety Working Group
Regulatory Article
Repair Assessment Programme
Reliability Centred Maintenance
Regulatory Instruction
Regulatory Notice
Release to Service
Release to Service Authority
Senior Duty Holder
Structural Examination Programme
Safety of Flight Structure
Structural Health Monitoring
Structural Integrity
Schedule Identification Numbers
Special Instructions (Technical)
Structural Integrity Working Group
Service Modification
Subject Matter Experts
Structural Matters Meeting
Statement of Operating Intent
Statement of Operating Intent and Usage
Sortie Profile Code
Support Policy Statement
Structurally Significant Item
Static Type Record
Type Airworthiness Authority
Through Life Management
Through Life Management Plan
Unmanned Air Vehicle Airworthiness and Safety Management Group
Urgent Technical Instruction
Whole Life Costs
vi
Record of Amendments
To record the incorporation of an amendment list in this publication, sign against the
appropriate Amendment List number and insert the date of incorporation.
Amendment
List Number
Incorporated by
Name
Signature
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
vii
Date
PART 1
PLATFORM NAME
STRUCTURAL INTEGRITY STRATEGY DOCUMENT
INTRODUCTION
References:
A.
Def Stan 00-970, Design and Airworthiness Requirements for Service Aircraft.
B.
MRP RA 5720.
C.
Commission Regulation (EC) No 1702/2003 (Part 21) and Commission Regulation
(EC) No 2042/2003 Annex 1 (Part M).
1
BACKGROUND
The policy governing the activities required to achieve and maintain Structural Integrity (SI)
for MOD aircraft from their inception through to their eventual disposal are detailed in
References A and B. Similar requirements for civil ac types are contained in the regulations
at Reference C.
Note that the last sentence of the above paragraph is appropriate if the PT intends to adhere
to civil regulation in its management of the aircraft’s SI. However, if this is the case then the
PT needs to clearly communicate this decision in the lead paragraph. Furthermore, a
description of how the civil regulation compares with military regulation and a description of
any Exemptions, Waivers or Alternative Acceptable Means of Compliance (AAMC) agreed
with the MAA need to be added throughout the document.
Whilst the References define regulation for maintaining SI, the required activities are not
fixed throughout the life of the platform. Consequently, there is a need for a ‘living’ document
that is platform specific within which the PT can communicate its intentions, regarding
ongoing SI activities, to all stakeholders. This communication is particularly important, as it
will form part of the platform’s Through Life Management Plan (TLMP) and ultimately the
associated Safety Case. It will also act as a record of the rationale behind the SI decisions
taken throughout the life of the platform. Therefore, this document intends to outline the
strategy and detail the headline actions required to implement and maintain Structural
Airworthiness.
2
AIM
The aim of this SI Strategy Document is to communicate how the Platform Name Project
Team, along with the key stakeholders, complies or intends to comply with the SI
management requirements contained in the MRP. The document also acts as a record of
significant historic SI actions and events.
Part 1 Page 1
3
SCOPE
This document is applicable to the aircraft structure of the Platform Name, where ‘Structure’
is defined in RA 5720 as:
Structure: Aircraft structure consists of all load-carrying members including wings,
fuselage (including some transparencies), empennage, engine mountings, landing
gear, flight control surfaces and related points of attachment, control rods, propellers
and propeller hubs if applicable and, for helicopters: rotor blades, rotor heads and
associated transmission systems. The actuating portion of items such as landing
gear, flight controls and doors must be subject to System Integrity Management
regulation (RA 5721) as well as Structural Integrity Management regulation.
‘Structural Integrity’ is similarly defined in RA 5720 as:
Structural Integrity: SI is the ability of an aircraft structure to retain its strength,
function and shape within acceptable limits, without failure when subjected to the
loads imposed throughout the aircraft’s service life by operation within the limitations
of the Release To Service (RTS) and to the usage described in the Statement of
Operating Intent (SOI) or the Statement of Operating Intent and Usage (SOIU).
3.1
PLATFORM DETAILS. Include a brief description and history of the platform,
procurement strategy, platform evolution, support strategy, its Designer/Design
Organisation, design methodology, intended/actual use, fleet size and geographical
locations as well as In-Service Date (ISD) and projected Out of Service Date (OSD).
The aim of this section is to identify those significant aspects of the origins, history and
development of the platform that could influence the SI programme for the remainder of the
in-service life, including any life extension. These aspects may include changes of role (from
a structural usage and environmental protection perspective) and major modifications to the
aircraft. For example, the role of the platform may have changed significantly from the
design assumptions (e.g. conversion from an air interceptor role to a ground attack role or
use of an aircraft designed for land-based operations in a maritime environment).
Additionally, aircraft designed under multi-national collaborative programmes may have been
designed to an amalgam of assumed usages; historically UK usage has tended to be more
severe than other nations in such programmes.
Moreover, aircraft designed for civil roles and certified to civil regulation are frequently used
within the military air environment and often with a usage significantly different to that
assumed in design (e.g. time at low level, operating at higher all-up mass or far more
frequent transition between flight conditions).
Also, aircraft have been introduced to service rapidly to support operational requirements
with limited certification evidence; these platforms may remain in service far longer than
originally expected. All of these examples can affect the SI measures needed to support the
platform significantly and need to be considered within the SI Strategy.
3.2
KEY SI STAKEHOLDERS. There are several organisations that are considered key
SI stakeholders for the Platform Name:
a.
Platform Name Project Team
Part 1 Page 2
b.
Designer/Design Organisation - Platform Design Organisation
c.
Independent Structural Airworthiness Advisors - e.g. QinetiQ/CAA/Cranfield
Aerospace
d.
Aircraft Operating Authority (AOA) - Details
e.
Release to Service Authority (RTSA) - Desk Officer Details
f.
Duty Holder Chain
(1)
(2)
(3)
g.
DDH - e.g. Stn Cdr RAF Waddington
ODH - e.g. AOC 1 Gp
SDH - e.g. CAS
CAA (MRCOA only)
Also, whilst not a Key Stakeholder, MAA-Cert-Structures 1-4 is able to provide
independent specialist regulatory advice.
4
STRATEGY DOCUMENT USAGE METHODOLOGY
4.1
STRATEGY DOCUMENT RELATIONSHIP TO OTHER DOCUMENTS
This SI Strategy Document provides the pivotal link between the activities of the PT,
stakeholders and the higher-level SI regulation. It should be closely coordinated with the SI
Plan. This document is in 3 parts: Part 1, an introduction that also contains the static SI
information; Part 2, the PT’s SI Strategy Document, and; Part 3, the historical perspective of
SI assurance activities. This document does not form part of the Topic 2(A/N/R)1 – General
Orders and Instructions - Support Policy Statement (SPS). Neither is it a leaflet in itself,
because it is a living document and the amendment process would be burdensome.
Consequently, the SI Strategy Document forms part of the suite of SI assurance actions and
is referenced from the Topic 2(A/N/R)1 – General Orders and Instructions - SPS. Diagram 1
shows the diagrammatic relationship of this strategy document to the SI Plan, SI processes,
working groups and other documents
Part 1 Page 3
H AMG
CA AMG
AS AMG
SAFETY CASE
TLMP
Platform 2*
Airworthiness
Review
Platform Air
System Safety
Working Group
PSEP
Topic 2(A/N/R)1
SI MEETINGS
SI DOCUMENTS
SI Strategy Doc
SIWG
Review
DOCUMENTARY
STRUCTURE
WORKING GROUP
STRUCTURE
Amendment
SI Plan
4.2
Structural Specialist
Meetings e.g EDPC
WG, SHM etc
Diagram
1 - Relationship
of SI Documents, Activities and Forums
STRATEGY
DOCUMENT
CONTENT
The Strategy Document content is structured as illustrated in Table 1 below:
Part
Title
Part 1
Platform Name SI Strategy Document Introduction
Part 2
Platform Name SI Strategy Document
Part 3
Platform Name Historical SI Assurance Activities (if included)
Annexes:
Annexes
Annex A – Structural Integrity Meetings Matrix
Annex B – Structural Integrity Meetings – Terms of Reference
Annex C – Structural Integrity Working Group Standing Agenda
Annex D – Platform Specific Structural Integrity Document Ref’s
Table 1 – Breakdown of Strategy Document Sections
4.3
OWNERSHIP AND REVIEW PROCESSES
Ownership and authority for this document lies with the Platform Name TAA. It will be
reviewed and amended periodically, then endorsed at the Structural Integrity Working Group
(SIWG) by the Structural Specialist Stakeholders. Reviews will be carried out when
necessary (pre-RTS ac) / every XX months (typically every 12 months for in-service ac).
5
STRUCTURAL INTEGRITY MEETINGS
RA 5720 mandate SI specific meetings. The schematic at Diagram 1 shows their relationship
with other documents and activities. Amend Diagram 1, and this paragraph, to reflect the
meeting hierarchy and titles used by the PT. This paragraph should include the PT’s
meetings policy, strategy, who will chair etc. Reference should be made to the appropriate
Annexes. RA 5720 also mandates the Environmental Damage Prevention and Control
Part 1 Page 4
(EDPC) Working Group. Make Reference to the following Annexes as appropriate:
A.
Structural Integrity Meetings Matrix
B.
SIWG Terms of Reference (Example TORs that could also be applied to other
meetings i.e. EDPC WG)
C.
SIWG Standing Agenda
6
STRUCTURAL INTEGRITY PLAN
The SI Plan for the Platform Name is maintained by the PT and can be found at hyperlink or
provide Reference. SI planning is a continuous ‘Sustaining SI’ activity, which ensures all
ESVRE activities are coordinated and the necessary SI actions are identified and adequately
resourced. Consequently, the SI Plan is a key document for through life planning and
underpins the SI aspects of the TLMP. The SI plan takes the form of a
spreadsheet/Microsoft project plan (as reqd) and is used to communicate when the SI
activities listed at Part 2 of this document are to be carried out. It also contains historical
data mentioned in paragraph 8 below. The SI plan is referenced from the Support Policy
Statement (SPS) contained within the Topic 2(A/N/R)1.
7
HISTORICAL STRUCTURAL INTEGRITY ASSURANCE ACTIVITIES
With the change over of personnel involved in maintaining the platform’s SI, the rationale
behind significant decisions and strategies is often lost. Therefore, as the existing strategy
evolves, it is essential to understand previous decisions and where the documentary
evidence has been placed. Therefore, Part 3 of this document contains the historical
perspective on SI assurance significant activities. (Adjust this paragraph if the platform is not
considered mature enough to require a separate history Part of the SI Strategy, so the
historical record is contained in Part 2)
Part 1 Page 5
PART 2
PLATFORM NAME
SI STRATEGY DOCUMENT
1
INTRODUCTION
This part of the Strategy Document communicates how the PT implements, or intends to
implement, the AMCs of RA5720. Where AAMC had been agreed with the MAA (iaw
MAA03), this is described in this Part of the document as well.
The responsibilities of key stakeholders are described, as are the major timelines for each
activity, cross referring to the SI Plan as required. Where documents are produced as a
result of this strategy, their reference and amendment state are recorded at Annex D of this
document.
2
ESTABLISHING SI (RA 5720(2))
2.1
INTRODUCTION
The Establishing phase is aimed at providing the evidence to substantiate the initial
clearances for the aircraft and ensure that the aircraft is safe to operate. Primarily, this
phase occurs during the platform’s procurement and entry into service; however, the
principles also apply during the introduction of any modifications or life extension activities.
2.2
TYPE RECORDS – (RA 5720(2) Para 39-43, RA 5103(1)Para 1.d and Annex A.2 )
Static Type Record. A Static Type Record (STR), or equivalent (RA5720(2) Para 40), is
mandated by RA 5720 and is, in effect, a collation of the static strength evidence necessary
to support the structural airworthiness of the platform. The STR, or equivalent, comprises
the following: a general arrangement and description of the aircraft, static design
assumptions, critical loading, shear force, bending moment, torque and mass distributions,
static reserve factors and summaries and references for all relevant supporting stress
reports, test reports, calculation files, aerodynamic and loads models.
The modern approach to aircraft design is likely to preclude the direct inclusion of all relevant
evidence within a STR. Therefore, the STR could be considered as a summary document
with all appropriate references identified. Where a platform does not have a constituted
STR, those documents, references and models that contain the requisite static evidence,
need to be clearly identified (in Annex D to the SI Strategy) and maintained through life in
the same way as a STR and this approach needs to be identified in the SI Strategy.
The initial static strength evidence for the platform should have been presented by the DO
and reviewed by the Independent SI Advisor in support of the initial RTS for the platform.
Any shortfalls identified in the evidence, outstanding recommendations for further work, or
failure to undertake an independent review of the static evidence in support of the RTS, may
need to be addressed within the platform SI Strategy.
Historical evidence has identified shortfalls in the through-life management of the static
Part 2 Page 6
strength of a number of platforms. In several cases this has been due to failure to
appreciate the significance of incremental mass increases on the static strength margin for
the aircraft due primarily to modifications. Hence the evidence contained in STR no longer
reflected the configuration of the aircraft in service. .
Fatigue Type Record. A Fatigue Type Record (FTR), or equivalent (RA 5309), is, in effect,
a collation of the fatigue evidence necessary to support the structural airworthiness of the
platform. The FTR, or equivalent, comprises details of the fatigue design philosophy,
materials, loading, principal fatigue critical structure, development and results for analytical
and test-based evidence, inspection requirements (for inclusion in the Topic 5A1), usage
monitoring requirements and references to all relevant test reports, models etc.
As with the STR, the modern approach to aircraft design is likely to preclude the direct
inclusion of all relevant evidence within a FTR. Therefore, the FTR could be considered as a
summary document with all appropriate references identified. Where a platform does not
have a constituted FTR, those documents, references and models that contain the requisite
fatigue-life related evidence, need to be clearly identified (in Annex D to the SI Strategy) and
maintained through life in the same way as a FTR and identified accordingly in the SI
Strategy.
The FTR may require updating on a routine basis through the life of the platform to take
account of modifications, changes in operational usage, usage monitoring programmes (e.g.
IAT/OLM/ODR) and further fatigue-related test results, all of which may generate revised
fatigue lives or inspection requirements.
As with the STR, the initial fatigue-life related evidence for the platform should have been
presented by the DO and reviewed by the ITE in support of the initial RTS for the platform.
Any shortfalls identified in the evidence, outstanding recommendations for further work, or
failure to undertake an independent review in support of the RTS, may need to be addressed
within the platform SI Strategy. In addition, for the introduction to service of a ‘new’ platform,
it is likely that some fatigue test evidence will be outstanding when the aircraft enters service
and may require FTR updates when complete.
Evidence has shown that the fatigue-life analysis, testing and documentation required to
support a platform in service becomes increasingly complex over time. This is often a
function of change of usage in service, life extension or arisings in service illustrating
inadequacies in the original approach (such as failures in service showing a shortfall in a
loading spectrum under test and analysis). Hence, the importance of ensuring a strategy for
development and control of the fatigue-related evidence through life cannot be over
emphasised.
2.3
STATEMENT OF OPERATING INTENT - (RA 5720(2) Para 44-46)
This section of SI Strategy relates to establishing the Statement of Operating Intent (SOI) as
part of the introduction to service of the platform. Once the platform has entered service and
sufficient usage data have been collected (usually not more than 3 years in service), the
document is transformed to become the Statement of Operating Intent and Usage (SOIU).
Development of the SOI (Topic 15S) is mandated in RA 5720. The principle aim of the SOI
is to communicate the intended usage of the aircraft to the DO. This will allow the DO to
review the design usage assumptions against the SOI and to evaluate the initial aircraft
clearances and maintenance periodicities, as appropriate.
It is essential that development of the initial SOI for a platform is led by or has significant
input from the Aircraft Requirements Manager to ensure an accurate understanding of the
Part 2 Page 7
intended usage of the platform is captured. Technical advice from SMEs can also be
invaluable in anticipating the potential implications for different usage assumptions for the
platform. For example, a significant low-level content in the usage spectrum for a civildesigned and certified aircraft could have significant implications for fatigue lives or
inspection regimes in service. In developing the initial SOI it is useful to view the Concept of
Operations for the new platform alongside SOI/SOIU for current or previous types
undertaking similar roles, bearing in mind the capability of the new platform may differ
significantly when compared with previous platforms used in this role. Guidance on how to
generate an SOI is contained in the Ac Usage Validation Process, which can be obtained
from MAA-Cert-Structures.
This paragraph needs to explain whether an SOI has been produced as well as describing
how often reviews are performed and who is involved in those reviews (post titles). If the
SOI has been replaced by an SOIU a single sentence explaining this and signposting the
reader to para 4.2 is all that is required.
2.4
STRUCTURAL QUALIFICATION/CLEARANCES – (Reference A)
Details of clearance and qualification methodologies, both static and fatigue, and the
responsibilities of all parties are explained within this paragraph.
The majority of the structural qualification and clearance information required for the platform
should be contained within the STR and FTR (or equivalents) (see Sections 2.2 above)
However, as detailed in Section 2.2, it is highly likely that outstanding work will be required to
compile the full fatigue-life evidence for the platform at introduction to service. Therefore,
this section should identify the strategy, developed in conjunction with the DO and SMEs, for
gaining the evidence to support full-life clearances and the mechanisms to be used to
provide updated fatigue-life clearances to the fleet, with appropriate safety factors pending
teardown or residual strength calculation / testing.
The approach taken in gaining the optimum structural clearance evidence (often from testbased programmes) early in the life of the platform can have significant airworthiness and
cost-of-ownership implications for the remainder of the service life, particularly if usage is
more severe than assumed in design (often the case) or if life extension is required. Test
articles and rigs in particular represent a significant capital investment and hence careful
consideration, involving the DO and SMEs to develop methods and approaches to gain the
most information possible from these programmes, including detailed evidence from
teardowns of test articles, can be hugely advantageous in the longer term.
Care needs to be taken to ensure clearances are correctly identified against different
standards of aircraft within the fleet (this also relates to Structural Configuration Control –
Section 3.5). These variations could be due to production structural standards, modification
or technical instructions standards, flight control system / software standards and these
issues can be further complicated by the ability or components to migrate between aircraft
within the fleet. The strategy for managing incremental fleet clearances needs to be
cognisant of these potential issues.
Understanding and recording the development of a platform’s clearances through life is
essential to preserve SI airworthiness. In the past, loss of corporate memory has led to
platforms being inadvertently flown significantly beyond their originally cleared life and at
unacceptable risk levels. Moreover, evidence that undoubtedly existed has had to be
regenerated as the information had been lost over time. Therefore, as developments in the
structural qualification and clearances of the platform develop, population of Section 3
(particularly with references) of this document can help ensure this information and the
significance of this information is not lost to future organisations.
Part 2 Page 8
2.5
IDENTIFICATION & CLASSIFICATION OF STRUCTURE - (RA 5720(2) Para 29-33,
JAP (D) 100C-22.)
The aim of this section of the SI Strategy is to detail the approach taken (or intended to be
taken) in the identification of Structurally Significant Items (SSI) and to identify all relevant
references.
SSIs are the foundation used for the development of the Structural Examination Programme
(SEP), undertaken within the preventative maintenance programme. SSIs are identified as
either safe-life SSIs or damage-tolerant SSIs and then their vulnerability to accidental
damage or environmental damage is assessed and appropriate maintenance actions are
defined accordingly (e.g. inspection, replacement etc).
The current definition of an SSI (RA 5720(2), Para 30) is: any detail, element or assembly,
which contributes significantly to carrying flight, ground, pressure or control loads and whose
failure could affect the Structural Integrity necessary for the continued safe and controlled
flight of the aircraft.
Generally, the DO is best placed to develop a SSI list, with input from SMEs (including
scheduled maintenance specialists) and this section needs to include a description of how
the SSI list was (or is to) be developed, what organisations were involved, what references
were produced, how the SSI list is promulgated in the ADS (Topic 5A1) and the development
of a Topic 5V. In addition, the mechanism needs to be identified for reviewing the SSI list to
ensure through-life in-service experience or any aircraft modifications are accounted for or
incorporated, as appropriate.
However, the identification of SSIs has proven challenging on several platforms in the past.
In some cases the number of SSIs identified has been enormous and down to the level of
spacers, ignoring the consequences of failure criteria. In others the SSI list has been
identified at major component level and is therefore impractical for use as the basis for
deriving a SEP. Some of these issues may be because aircraft structure has traditionally
been classified using various terms such as Primary Structure, Class 1 Structure, Vital Parts
or ‘Grade A’ Parts, Principal Structural Element (PSE), Airworthiness Limitation Items (ALIs),
SSIs and Safety of Flight Structure (SoFS) and there has been no universally accepted
method for selecting or identifying important structure, or commonly accepted interpretation
of critical or significant in this context.
In such cases, the use of a specialist working group, with input from the PT, DO, SMEs
(structures, maintenance and RCM) can provide a useful mechanism for deriving a workable
SSI list, from an initial list of important or critical structure already used on the platform,
supplemented by on-aircraft physical surveys. Where such an approach is taken, clear
documentation is necessary to ensure the origins and development of the SSI list can be
understood.
3
SUSTAINING SI (RA 5720(3))
3.1
INTRODUCTION
The Sustaining Phase is aimed at monitoring the aircraft usage, ensuring that appropriate
structural examinations take place and maintaining structural configuration control. This
phase is required to ensure SI is maintained throughout the life of the platform.
3.2
USAGE MONITORING AND INDIVIDUAL AIRCRAFT TRACKING - (RA 5720(3)
Part 2 Page 9
Para 74-83)
The decision as to what usage monitoring methodology is required for a particular platform
needs to be developed during the design phase (for a new platform) or introduction to
service (for an existing platform). RA5720(3) Para 74 outlines broad requirements for a
usage monitoring system. However, these need to be tailored to the platform, likely usage
and structural clearance development (largely referenced in the STR and FTR or
equivalent).
For example, if a platform has the capability to experience exceedences significantly beyond
structural never exceed limits and operations are likely to be conducted near those limits, an
exceedence monitoring requirement may be necessary. Equally, if the loading action on a
critical structural feature is driven by ground-air-ground (GAG) cycles alone and the variation
in these cycles is not considered significant, counting of GAG cycles may be sufficient to
monitor that particular feature.
For procurement of existing platforms, the platform may be delivered with an existing
monitoring system package and in such cases, it is important to understand the design
drivers behind the system as well as its strengths and limitations.
For all monitoring systems this section needs to include a clear statement of which areas of
structure are considered to be monitored by the system and how this is achieved (this may
be referenced to an existing document and summarised here).
The strategy for developing the monitoring system, introduction into service, including any
phased capability development (hardware and software), initial on-aircraft and off-aircraft
support and equipment and training needs to be clearly identified in this section along with
division of responsibilities between Stakeholders. The development and introduction to
service of a successful monitoring system requires involvement of the DO, SMEs, PT and
FLC and dedicated personnel and a Working Structure is usually necessary to support
development of these systems. Experience has shown that the introduction of modern,
complex, aircraft monitoring systems has often been challenging and capability has often
fallen short of expectation. Failure of the monitoring system to meet requirements can have
significant implications for fleet life clearances and contingency strategies for complex
monitoring systems may be advisable.
In addition, the approach for lifetime management of the monitoring systems
(SHM/HUMS/IAT etc) should be detailed. This approach, ideally developed by the PT, DO,
SMEs and FLC using Specialist Working Groups, needs to address the day-to-day
management of the monitoring system, with clear divisions of responsibility identified
including: data management and reporting, system performance monitoring, calibration and
fault finding, recovery action (including spares provisioning).
Longer-term issues should also be considered including: hardware and software upgrades
and system life and replacement strategy (it is considered highly unlikely that a modern
monitoring system will be economically supportable for the life of a platform). Obsolescence
relatively rarely affects SI issues on a platform; however, the rapid pace of electronic
obsolescence can be significant for monitoring systems and hence the replacement strategy
may be driven by sub-components in the system, or may be mitigated by life-time buys for
example.
3.3
FATIGUE METER FORMULAE (RA 5720(3) Para 79)
NOTE: This paragraph should not be used for aircraft that do not use Fatigue Meter
Formulae e.g. rotary wing aircraft.
Part 2 Page 10
This paragraph should include details of what Fatigue Meter Formulae (FMF) exist (e.g.
Wing Fuselage, Fin etc) for the platform and how they will be used. However, the important
aspect is the maintenance of the FMF and how it will be validated and updated. The FMF
should be reviewed and updated following an OLM programme, a significant modification or
a change of usage; however, this is a PDS activity through the designer or through the
Independent Structural Airworthiness Advisor. If this process is neglected the fatigue
‘damage’ being accrued by the platform will not be accurately recorded and there is a risk
that the airworthiness will be compromised and the aircraft will not meet the required OSD.
3.4
STRUCTURAL EXAMINATION (RA 5720(3) Para 60-69)
Structural Examination of the platform is required to ensure that the threats to SI are
detected, countered and recovery initiated. This examination is covered by the Structural
Examination Programme (SEP), which is made up of flight servicing, scheduled
maintenance, teardown and structural sampling activities; the latter 2 being validating
activities. The scheduled maintenance element of examination of SSIs should be reported
upon by operating units and maintenance facilities as detailed in the Topic 5V. This para
should include a brief description of the methodology used to derive the SEP; it should also
briefly identify the organisations that execute the SEP as well as describing the reporting
procedures (eg Topic 5V returns) that those organisations comply with.
3.5
STRUCTURAL CONFIGURATION CONTROL (RA 5720(3) Para 70-72)
Retaining structural configuration control has been a military airworthiness requirement for
many years (it is currently an MRP requirement, but SCC was mandated in JAP100A-01
and, for RAF platforms, in AP100A-01 before that). However, many PT's cannot claim to
fully understand the SCC of the ac that they support, although MRCOA platforms tend to
have a better SCC record that the equivalent record for 'pure' military platforms.
Maintaining SCC is important for 3 main reasons:



When a structural repair is needed on an ac the repair designer can use the record to
see if any other repairs are located close to the area of damage.
To enable trending of structural occurrences. This could be done in a couple of ways
– if someone thinks that there is a recurring issue, the PT could investigate the SCC
database to provide evidence that that issue does actually exist, which will add
weight to the case for funding for a modification. Alternatively, during the AAA the
auditor would typically spend some time investigating the SCC database to see if
there are any trends emerging that nobody had previously realised.
During an Ageing Ac Audit the auditor would examine the SCC database to decide
whether the accumulation of modifications, SI(T)s, repairs and corrosion blends
affect the aircraft type's mass, CofG, and structural layout, which could alter load
distributions and so affect static strength and fatigue and damage tolerance
clearances.
The result of not maintaining SCC could on one hand result in the need for a fleet structural
survey to be identified (e.g. as a result of an Ageing Ac Audit or to support a Life Extension
Programme), which would probably be extremely costly, or on the other hand it could result
in airworthiness decisions being made with incomplete information, which could be
dangerous. Furthermore, careful identification of which structural components or parts are to
be tracked on the ac can be a significant issue in addressing this problem. For example, a
major MOD fleet was introduced to service with no component tracking requirements for fins
or tailplanes. When individual fatigue lifing of these components was required part way
Part 2 Page 11
through the aircraft’s life, records were patchy and unreliable. This resulted in costly
remedial action and necessary conservative assumptions of life consumed having to be
made.
Whilst the ideal method of retaining SCC is for a PT to provide a single computer-based
database that captures all aspects of SCC, such databases are rarely affordable. Instead,
SCC could be retained by an SI(T) log, a modifications log and a waivers/concession log (all
of which should be in existence as part of the PT's wider configuration control policy),
combined with an additional log or logs to track instances of corrosion and structural repairs.
Each separate log could be computer-based or it could be hardcopy, provided that a record
of every repair, modification, corrosion arising etc and the individual airframe it has been
experienced on has been kept and can be searched in the future. If computer-based
databases are used, experience has shown that they are more likely to be populated
accurately if single data entry methods are used, rather than information duplication.
Furthermore, the use of validation rules and data quality monitoring for data entry
dramatically reduces the risk of erroneous data entry which unchecked can cause the
system to lack credibility.
This section of the SI Strategy should contain details of the approach to retain structural
configuration control. The names and location of each database and/or hardcopy file needs
to be mentioned. Also required is a reference to the Topic 2(A/N/R)1 leaflet that mandates
reporting of in-service arisings (e.g. corrosion & repairs) so that those arisings are captured
on the appropriate database/hardcopy file.
4
VALIDATING SI (RA 5720(4))
4.1
INTRODUCTION
‘Validating SI’ activities are aimed at measuring the current usage and loading as well as
the condition of structure that is not regularly inspected to allow a comparison with design
assumptions and make adjustments to component lives and inspection periodicities where
necessary. The nature and complexity of this phase means that it is a periodic rather than
continuous activity.
4.2
STATEMENT OF OPERATING INTENT AND USAGE (RA 5720(4) Para 93-96)
The SOI (Section 2.3) is migrated to a Statement of Operating Intent and Usage (SOIU)
once ac usage has stabilised in service and once sufficient usage data has been captured.
Normally this transition begins 3 years after the Type's ISD, when a statistical review of the
most recent 12-18 months of usage data would begin. As mandated at References C and D,
the SOIU (Topic 15S of the aircraft Air Publication (APs)) is the document that formally
communicates the recent and intended usage of the aircraft to the DO.
The content of the SOIU is owned by the AOA, although the PT usually administers the
review and publication of the document on the AOA's behalf; however, it is ultimately the
AOA's responsibility to ensure that the content of the document reflects the current and
intended usage of the ac Type.
Annual reviews are a simple check to ensure that no substantial change in usage has
occurred but has not been documented and the implications assessed. Likewise, the annual
review is also a check of whether a significant change of usage is planned in the next 12
months e.g. as a result of a new capability. During the annual review a senior operator (e.g.
Staneval) should be consulted to establish whether or not the usage documented in the
SOIU reflects current operating practice. Likewise, the AOA should confirm that no
Part 2 Page 12
significant changes in usage are planned over the following 12 months. Annual reviews
should be simple activities that could be completed relatively quickly.
Triennial reviews incorporate a statistical review of a sample of representative usage data,
as well as formal aircrew and AOA staff interviews, all carried out by an independent
organisation. Normally an SOIU will be re-written and re-issued following a triennial review.
Further guidance on the conduct of annual and triennial SOIU reviews can be found in the
Ac Usage Validation Process (AUVP), which is available from MAA-Cert-Structures.
Following any changes incorporated to the SOIU as a result of an annual review, or following
re-issue of the document as a result of a triennial review, the PT must ask the DO to review
the document and comment on the fatigue and maintenance implications of the changes.
This review by the Design Organisation is essential to ensure that the FTR and associated
clearances are underpinned by valid assumptions, and, if necessary any changes to
maintenance periodicities and procedures are incorporated into the Aircraft Maintenance
Manual (AMM) by the PT.
In this section the PT should document:




What the current issue state of the SOIU is.
Who is consulted during annual SOIU reviews (post titles, not individuals)
When annual reviews are carried out (e.g. the 1st week of June every year).
A very brief description of the triennial review process:
o When the last triennial review was conducted.
o What period the usage data that was statistically analysed covered.
o When the next triennial review is due.
Experience has shown that PTs often do not know when the last SOIU review was
performed and when the next one is due.
For a platform with a sophisticated monitoring system where the data is relayed or managed
by the DO, much of the data traditionally reproduced within the SOIU is already available to
the DO. In such circumstances the PT may consider applying for an AAMC to the full SOIU
requirement, although a process to ensure feedback from the DO of the fatigue and
maintenance implications of usage would still need to be demonstrated, as would a process
for conveying the future intended usage of the ac Type to the DO.
4.3
STRUCTURAL SAMPLING - (RA 5720(4) Para 104-109)
Structural Sampling. Structural Sampling is an element of the Structural Examination
Programme (SEP) that is carried out on a sample of SSI components where the SSIs are not
inspected as part of the maintenance schedule. The sampling programme is carried out to
ensure that the maintenance policy assumptions that precluded certain SSIs from scheduled
inspections, due to a low probability of degradation due to the effects of AD/ED, were
correct. This para should detail how the items are to be inspected, how they will be
identified, and how the inspection will be carried out and reported (either via the Topic 5V
reporting proforma or equivalent). The PT rationale for dealing with the results needs to be
included also, including a summary of structural sampling undertaken. Guidance should be
provided on the opportunity for sampling of hidden structure e.g. from Cat 4/5 ac or life
expired components. Negative reporting can also be extremely relevant for structural
sampling as this can significantly improve the understanding of the onset of degradation
across the fleet.
Structural sampling may also be considered necessary where novel material or new
Part 2 Page 13
processes have been introduced to service with the platform and where there is little or no
experience of the longer-term performance of these materials or processes. Teardown (e.g.
destructive assessment) may be required as an alternative where structural sampling does
not provide sufficient information.
Teardown. Teardown of an aircraft is the inspection of a whole airframe or component in
order to determine whether the threats to SI are compromising the SI of the aircraft. The
teardown is a formal process that uses both destructive and non-destructive techniques,
often to a forensic level, to progressively inspect and determine the integrity of the structure,
in particular those areas that cannot be inspected as part of the scheduled examination
element of the SEP. Teardown of the full scale fatigue test article is a Def Stan 00-970
requirement (clause 3.2.16 of Part 1 for fixed wing aircraft), which is an Establishing SI
activity. The requirement to conduct teardown of an in-service ac is normally a
recommendation from an AAA or it is identified as being required to support a Life Extension
Programme (LEP). Where possible, in-Service or retired airframes or components selected
for teardown shall be representative of the harshest usage/environment experienced by the
fleet in order to provide an indication of the ‘worst case’ SI threats that are likely to exist
throughout the fleet. As teardown of an In-Service or retired aircraft is not mandated, this
para may detail the PT’s intentions and any planned activities or review of the teardown
requirement. Although not mandated, targeted teardown of in-service aircraft on an
opportunity basis has provided invaluable information to support platforms in their later lives,
particularly in identifying emerging risks when approaching life extension.
Teardown may also be considered necessary where novel material or new processes have
been introduced to service with the platform and where there is little or no experience of the
longer-term performance of these materials. This may be necessary when structural
sampling cannot provide sufficient information to support this assessment.
4.4
OPERATIONAL LOADS MEASUREMENT/OPERATIONAL DATA RECORDING
REQUIREMENTS - (RA 5720(4) Para 98-103)
The routine usage monitoring systems together with the SOIU provide some confidence that
the initial design assumptions were correct. However, they may not provide the level of
detail required to validate all of the initial design usage and loads assumptions throughout
the life of the aircraft. This higher level of detail can be essential in assuring continued SI,
life/fatigue clearances, validating Fatigue Meter Formulae (FMF) (as applicable), validating
RTS assumptions (e.g. time at flight level for gust analysis) as well as underpinning any
ageing aircraft audit or life extension programme. This detail can only be determined by
undertaking an OLM (for fixed wing aircraft) or ODR (for rotary wing aircraft).
This para needs to detail the PT’s approach to OLM/ODR and to detail the strategy including
data analysis being undertaken. The relationship, if any, to SHM/HUMS activities should
also be included. A history of OLM/ODR activities undertaken previously, the headline
outcomes and also details of any OLM/ODR exemptions or waivers granted needs to be
discussed here.
Detailed guidance on the conduct of OLM programmes (largely applicable to ODR also) is
provided by MASAAG Paper 109 (available from MAA-Cert-Structures). The principal
guidance provided in this document is to consider carefully the aims of the OLM/ODR
programme in detail at the outset. One size does not fit all. For example, the usage
validation requirement for a combat aircraft with a limited IAT system is likely to be
significantly different to a civil derivative aircraft used in a civil-type role. An OLM/ODR
programme may be considered to have started once: the recommendations of MASAAG
Paper 109 have been sentenced; once a project-specific OLM/ODR requirements document
has been issued; and once the design of a suitable system has begun.
Part 2 Page 14
In addition to discrete OLM/ODR systems, the use of data from existing SHM / HUMS, Flight
Data Recorder (FDR) or Accident Data Recorder (ADR) systems on the aircraft can
potentially meet a significant proportion of the OLM/ODR data capture requirements.
Moreover, a Manual Data Recording Exercise (MDRE) can also reduce the instrumentation
requirement in certain circumstances and this can be implemented rapidly.
Management of OLM/ODR programmes, due to their complexity, cost and the number of
agencies involved can be a significant challenge and needs to be addressed carefully within
the SI Strategy accordingly.
4.5
MAINTENANCE SCHEDULE REVIEW (RA 5720(4) Para 110-111, MAP 01 Chap
8.1.1)
The outline strategy for maintenance schedule reviews for the platform needs to be identified
within this section.
From a SI perspective, it is essential that the fatigue or damage-tolerance basis for SSI
inspections is preserved during this review process. For example, an historical lack of
arisings for fatigue-related inspections does not necessarily mean these will not occur in the
future. Moreover, corrosion-related occurrences are likely to increase with the life of the
platform due to usage and the degradation of protective measures. Therefore, it is essential
that DO and Structures SME input into schedule reviews is included within the process.
The maintenance schedule review programme also needs to include the content of the SSI
list (see Section 2.5) to ensure the SSI list reflects in service experience. In addition, the
implications from any arisings from Topic 5V inspections (Structural Sampling) or any
teardown programmes outside of the scheduled maintenance programme need to be
collated and considered within the review. The review also needs to include assessment of
the effectiveness of the inspections or other maintenance activity in assuring structural
airworthiness (for example, is the inspection requirement achievable in practice at the level
of strip at this maintenance opportunity?).
In addition, it is essential that SI-related Schedule Identification Numbers (SIN) are either
retained or traceable across all schedule reviews for the life of the fleet, to allow collation of
arising information and traceability of SSI inspection.
Where Special Instructions (Technical) (SI(T)) (e.g. UTI) are to be incorporated into the
maintenance programme care needs to be taken to ensure that the fatigue or damagetolerance basis of the instruction are not lost in the incorporation into the schedule. Also
where NDT techniques were developed, often at short notice, to support an urgent
instruction, a review of the technique in light of in-service experience, before incorporation
into the schedule can prove extremely valuable and experience may allow greater leeway in
inspection periodicity. An explanation of the process the PT applies for reviewing such
techniques needs to be included in this section.
A schedule review will use historical maintenance data to support the review process.
Experience has identified a lack of confidence in the recording of maintenance information
on a number of platforms. Consequently, the SI Strategy needs to include measures to
assure that any maintenance data are fit for purpose when used to support a schedule
review.
4.6
AGEING AIRCRAFT AUDIT - STRUCTURAL SUB-AUDIT (RA 5720(3) Para 85
and RA 5723)
Part 2 Page 15
RA 5720 mandates that a periodic assessment of the SI activities, with particular emphasis
on those issues associated with ageing are carried out. (Also consult RA 5723) Details of
any MAA waiver, when the review is required, what activities are to be carried out and
details of who is to carry out the review are to be detailed here. Specialist TOR and
meetings may be required. These are to be detailed in Part 3.
In addition, where an AAA has been undertaken, the PT’s approach to addressing
recommendations and actions from the audit needs to be clearly identified within this
strategy.
5
RECOVERING SI (RA 5720(5))
5.1
INTRODUCTION
The Recovering SI phase covers the techniques required to deal with airframe damage or
compromised usage metrics. Furthermore, reductions in clearances released by the
Designer are also dealt with during this phase of ESVRE.
5.2
STRUCTURAL ISSUES (RA 5720(5) Para 118-121)
The recovery of damaged structure is an essential part of maintaining SI, consequently
procedures are required to ensure this activity is appropriately carried out and recorded.
This section contains the PT’s strategy for dealing with damage, repairs, structural
modifications and SI(T) and recording actions taken.
In addition, this section of strategy is extremely important for collating and retaining the SI
history of the platform throughout its service life. Experience has shown that loss of
corporate memory has had significant airworthiness and cost of ownership implications for
MOD air platforms. Historically, the DO has often been relied upon to provide the required
continuity and memory across the life of a platform but this cannot necessarily be relied upon
for the future. Therefore, summaries of significant structural issues and how they have been
addressed (technical instruction, modification etc) can be documented either in this section
or in Part 3 of SI Strategy when considered routine business or ALARP. This approach
could be invaluable in supporting life extension programmes or AAA, as well as providing
briefing material for new members of staff within the PT, DO or SMEs. In reality, the
additional burden on staff of developing this approach is small as much of the information
can be extracted directly from the minutes of SIWG or similar meeting structures.
5.3
ENVIRONMENTAL DAMAGE PREVENTION & CONTROL (EDPC) (RA 5720(5))
The level of environmental damage on an air platform is generally a function of time, usage
and maintenance; the presence of corrosion or other environmental damage can reduce the
static strength and fatigue life of materials and adversely affect the platform’s/component’s
airworthiness, Whole Life Costs (WLC), availability and life. Consequently, detection,
monitoring and reporting of environmental damage is a key SI assurance activity. This
section details the PT’s approach to managing EDPC and fulfilling the requirements of
Reference D, including EDPC Working Groups as required.
Historically, the effectiveness and management of EDPC in service has been mixed. EDPC
measures often improve for a period of time in response to the identification of in-service
arisings or as a result of a particularly motivated EDPC Representative on a Station or in the
PT.
Evidence suggests that EDPC issues are often treated as repeated ‘one offs’ rather than
Part 2 Page 16
being addressed proactively. Corrosion issues in particular often re-surface periodically
during the life of a platform, frequently as a result of the measures taken in response to the
initial arising not having been completely effective.
Moreover, proactive measures have often been restricted to the particular arising identified
without consideration of the wider issues. In such cases the risk to similar combinations of
structures, materials or configurations elsewhere on the platform may not have been
identified. For example, one would expect the identification of structurally significant
corrosion in the metal honeycomb structure or a flying control to generate a review of the risk
to other flying controls on the platform manufactured in a similar way. Therefore, the SI
Strategy could include a specific requirement to consider a wider review and identification of
similar risk areas, once the initial remedial action in response to an EDPC arising has been
taken.
5.4
COMPROMISED IAT - (RA 5720(5) Para 122-124)
Experience has shown that IAT data is likely to be compromised at some stage through the
life of the platform. This is true for the simplest systems of manual recording of post-sortie
feedback (eg lost MOD Form 724/725s) through to the advanced parametric and straingauge systems fitted to some newer ac types (eg corrupted or lost data on data transfer
devices, or unserviceable accelerometers/strain gauges).
Therefore, in this section the PT needs to summarise its process for keeping track of the
unmonitored sortie rate (this should be done at every SIWG for modern Structural Health
Monitoring Systems). The PT also needs to describe its process for gap-filling lost IAT data.
Finally, for those ac types that use an advanced parametric and/or strain gauge-based
system for IAT, a brief description of how often the system is calibrated and how that
calibration is performed (eg BIT, ground calibration, flight calibration) should be provided.
5.5
REPAIR ASSESSMENT PROGRAMME (MASAAG 106)
A Repair Assessment Programme (RAP) is employed to assure confidence in the continued
airworthiness of repairs through to OSD. A physical survey of the fleet is part of conducting
a RAP and so the exercise can also be used to regain repair configuration control. MAACert-Structures can provide current regulatory advice and guidance on RAP.
A RAP is currently required for in-service large aircraft. In addition, it is an AMC for large ac
types undergoing a LEP (RA 5724). Newer ac types may avoid the need to perform a RAP if
they have maintained exceptional structural configuration control and if all repairs (either
from the SRM or bespoke repairs) have had a fatigue assessment performed. Some Fast
Jet and RW PTs have decided to perform a RAP to ameliorate concerns about the quality
and increasing number of repairs on the fleet.
Although the RAP requirement was identified by the civil regulatory organisations,
experience from a number of military LEP identified significant shortfalls in the fatigue
substantiation of aircraft repairs. In addition, platforms with a usage history prior to operation
by the MOD have often had significant issues with fatigue substantiation of repairs and, in
such cases, it may be necessary to survey the fleet to baseline the repair data.
In this paragraph the PT should describe whether a RAP is considered necessary (either for
regulatory compliance or if the decision has been taken to perform a RAP on an ac type for
which it is not mandatory) and the minutes of the meeting at which the decision was taken
should be referenced. If a RAP has been performed (or will be performed in the future), a
brief description of when the RAP was performed and what the scope of the RAP was (eg
pressure fuselage only, whole ac structure etc) should be added.
Part 2 Page 17
6
EXPLOITING SI (RA 5720(6))
6.1
INTRODUCTION
The Exploiting phase covers the techniques required to determine if an increased life or
capability can be gained from a fleet. Indeed, the exploitation techniques can, if applicable
and appropriate, be used to decrease the maintenance required and thereby increase
availability.
6.2
FATIGUE CONSERVATION MEASURES (RA 5720(5) Para 130)
This section of the SI Strategy includes details of any fatigue conservation measures
implemented or planned for the platform and identifies mechanisms in place to identify when
conservation measures may be required.
Experience has shown that fatigue conservation measures are often introduced too late in
the platform’s life to be effective or they are not as effective as expected when introduced.
There are a number of reasons for this. Too much reliance can be placed upon using
average fatigue consumption rates for prediction models, whereas invariably fleet leaders
have above average fatigue consumption rates. Fleets-within-fleets issues are often the
cause of a wide range of fatigue consumption rates across the fleet and unless the required
operational capability is available on alternative platforms conservation measures are likely
to be ineffective. Often aircrew are provided with poor or limited advice on how to meet the
operational requirement but with reduced fatigue consumption. Also, blanket limitations
alone can be less effective than expected. For example, reducing the normal acceleration
(Nz) limit for a fleet can have limited effect if the way the mission profiles are flown is not
changed.
Therefore, fatigue consumption needs to be monitored carefully, drivers for that fatigue
consumption need to be understood (in conjunction with the DO, SMEs and aircrew) and
realistic expectations for conservation measures identified and the performance of
conservation measures needs to be monitored.
6.3
STRUCTURAL HAZARD-RISKS (RA 5720(5) Para 133-137)
Structural risks/incidents are subjected to a safety/risk assessment iaw the platform’s Safety
Case and Safety Management Plan. This paragraph contains details of how SI risks will be
determined and managed. This may involve referencing where the data to carry out an
assessment may be obtained from (for example) SHM, HUMS, hardcopy usage data, SOIU,
SME advice etc.
Although the process for risk management of structure is no different to the remainder of the
platform, assessing structural risks and apportioning probabilistic assessments, usually
identified as a Hazard Risk Index (HRI), can be particularly challenging for structures.
It can be extremely valuable to document in the SI Strategy the approach taken to identify
the initial HRI, which organisations are to be involved in the process, and what measures
can be implemented to mitigate the level of risk with confidence over time.
Although different identifiers and classification systems for assessing the HRI are used, all
Part 2 Page 18
require an assessment of the consequence of the failure and the probability of that failure
occurring.
Generally, an assessment of the consequence of failure of a structural item can be made
(usually with DO and SME support). The approach may vary slightly but it is expected that
consideration would be given as to whether the item was an SSI (or equivalent) or not.
Thereafter, the damage mechanism would be identified (e.g. fatigue) and an assessment
made of the residual strength, stiffness or deformation (depending on its function) and a view
of the likely in-service loads compared with the design case. An assessment would be made
as to: whether the component would collapse or fail to perform its function under expected
loads; whether that would lead to a structural collapse; and what the implications of any
structural collapse in terms of loss of aircraft would be.
However, the probability of occurrence of that failure has historically proved more difficult to
assess with confidence. The likelihood of events such as bird strike or lightning strike are
routinely assessed probabilistically and mitigations such as time at flight level or weather
restrictions can be used. However, the majority of structural failures occur (in systemsparlance) in the wear-out phase of the life of the item and hence figures of mean time
between failures, for example, are of little value. Hence, assessments of the probability of
occurrence, with confidence in the result, require considerable specialist knowledge (DO and
SMEs). Where practicable a visual or relatively simple NDT inspection can provide initial
confidence in the condition of the remainder of the fleet and provide a time window to
undertake a more detailed assessment of the HRI.
6.4
EXPLOITING IN-SERVICE EXPERIENCE (RA 5720(5) Para 144)
There may be other users of the platform both within UK and other nations and valuable
information may be gained from sharing SI information with them. Consequently, this
paragraph could detail the interaction (eg regular attendance at Type Operators'
Conferences, description of bi-lateral agreements etc) between these organisations that may
include but not be limited to Designer, Other operators or National Authorities including
Safety Investigation Organisations. This paragraph could also discuss the requirement to
provide feedback for the platform and the wider aircraft engineering and operating
communities on features, novel materials, maintenance methodologies etc.
6.5
LIFE EXTENSION ACTIVITIES (RA 5720(3) Para 138-143 RA 5724)
RA 5724 AMC identifies that a LEP should be undertaken when it is identified that an aircraft
type needs to be extended beyond its current certified life measured in any applicable lifing
parameter (such as calendar time, flying hours, fatigue Index (FI), landings or pressure
cycles). Additionally, the potential requirement for a life extension should be considered no
later than 10 years before the original Out-of-Service Date (OSD) and should be reviewed
annually thereafter.
This AMC is based firmly upon experience of LEP where programmes have suffered from
creeping incremental life extension requirements and OSD extension requirements identified
too late to allow suitable evidence to support continuing airworthiness to be assembled.
RA5724(2) states “When required to extend the certified life of a UK military ac type in any
parameter, the TAA shall develop and implement a LEP to underwrite the airworthiness of
the ac type for its extended life”. From this it is clear that any extension to OSD, no matter
how small, must be considered as a life extension and that TAAs are to develop a LEP in
order to remain compliant with the MRP. One of the AMCs to RA 5724(2) requires TAAs to
deliver a LEP Certification and Assurance Strategy to the MAA’s Certification Division; the
Strategy should explain how the TAA will demonstrate compliance with the other AMCs of
Part 2 Page 19
RA 5724.
7
AIRCRAFT DISPOSAL
This section provides details of the disposal plans for the fleet at drawdown or as individual
aircraft are retired. This should include any policy for the requirement, assessment and
recovery of structural items for spares parts, provision of teardown articles, onward sale to
non UK MOD users and the documentation that would be provided with them etc.
Part 2 Page 20
PART 3
PLATFORM NAME HISTORICAL STRUCTURAL
INTEGRITY ASSURANCE ACTIVITIES
1 INTRODUCTION
With the change over of personnel involved in maintaining the platform’s SI, the rationale
behind significant decisions and strategies is often lost. However, even if the current
strategy has progressed it is often useful to understand ‘how we got to where we are’.
Therefore, Section 3 of this document contains this historical perspective in terms of the
significant decisions made and the rational and methodology behind them.
2 AIM
To satisfy the requirements of RA 5720, there is a need to maintain a historical record of
significant SI assurance activities, the methodology and rationale behind SI decisions and
the significant SI issues encountered throughout the life of the aircraft.
RA 5720(3) puts emphasis on the need for this document to act as an accountable record of
the evidence and rationale behind the SI decisions such as MAA waivers for OLM
programmes or termination of full-scale fatigue testing, taken throughout the life of the
aircraft. Other suggested examples are as follows; Changes in design philosophy, Life
extensions, Modification to structure that may affect SI, Structural occurrences (significant
cracking, corrosion or other defects), Findings of the structural sub-audits of an AAA (or
findings of AASAs (now an obsolete term)), and Findings of Teardown activities.
It is suggested that this Section provides summaries of relevant SI activities, under the
ESVRE headings, with concise cross referencing to supporting documentation (files, letters,
publications etc) to provide accountability as well as Referencing to the platforms own SI
Plan as appropriate.
3 ESTABLISHING SI
4 SUSTAINING SI
5 VALIDATING SI
6 etc
Some PTs, in particular those that support younger ac types, may prefer to place the
historical record of structural integrity activity in Pt 2 of the Strategy. That would be
acceptable – the important part is that the historical decisions are documented and the
appropriate evidence is referenced.
Part 3 Page 1
ANNEXES
ANNEXES:
Annex A – Structural Integrity Meetings Matrix
Annex B – Structural Integrity Meetings – Terms of Reference
Annex C – Structural Integrity Working Group Standing Agenda
Annex D – Platform Specific Structural Integrity Document References
Annexes Page 1
ANNEX A TO
XXX/XXX/XXX/XXX
DATED XXXXXX
STRUCTURAL INTEGRITY MEETINGS MATRIX
Meeting
SI Working Group
SIWG or similar meeting
is mandatory. All other
meetings are
discretionary
Requirement
Reference
RA 5720(3) Para
54
Frequency
Chair
Minimum twice per
year
Minimum of
Airworthiness LoD
holder or by
exception, a SO1
or B2 that holds an
appropriate LoAA
Core Members (as applicable)
PT
Designer
Independent Advisors
Front Line Command /
Aircraft Operating
Authority
Release to Service
Authority
Service Provider
Other UK Platform
Users
Airworthiness LoAA
Holder (Chair)
Head of Structures
Structures Desk Officer
Fleet Manager
AEDIT/FST
Structures Section
Stress Office
e.g. QinetiQ
CAA
Requirements Manager
Engineering Rep
Aircrew Rep
RTSA Desk Officer
e.g. QinetiQ
Engineers/Aircrew
Whilst MAA-Cert-Structures desk officers are not core members of any PT meetings, they should be invited to all Structural Integrity–related
meetings.
A-1
Meeting
Environmental Damage
Prevention and Control
(EDPC) Working Group
Requirement
Reference
RA 5720(3) Para
54.
RA 4507
Frequency
As required
(typically twice per
year in align with
the SIWG)
Chair
PT Structures
Desk Officer
RA 5720(4) Para
98.
As Required
PT Structures
Desk Officer
MASAAG Paper
109
Manual Data Recording
Exercise (MDRE)
Ageing Aircraft Audit
(AAA) Structural SubAudit
RA 5720(3) Para
85.
As Required
PT
Designer
MAP-01, Chap
11.6
Operational Loads
Measurement (OLM)
or
Operational Data
Recording (ODR)
Core Members (as applicable)
PT Structures
Desk Officer
RA 5723.
Independent Advisor
Front Line Commands /
Aircraft Operating
Authority
Units
PT
Designer
Independent Advisor
Front Line Commands /
Aircraft Operating
Authority
Units
PT
Designer
Independent Advisors
Auditor
A-2
Structures Desk Officer
AEDIT/FST
Structures Section
Customer Support
e.g. QinetiQ
Engineering Rep
Corrosion Control Reps
Structures Desk Officer
Structures Section
e.g. QinetiQ
Engineering Rep
Chief Instructor (for
MDRE only)
Head of Structures
Structures Desk
Officers
Structures Section
Stress Office
e.g. QinetiQ
Meeting
Structural Health
Monitoring (SHM)
or
Health and Usage
Monitoring System
(HUMS)
Requirement
Reference
RA 5720(3) Para
74.
As Required
Chair
PT Structures
Desk Officer
MAP-01, Chap
11.2
Structural Matters
Meetings
Teardown/Structural
Sampling
Frequency
RA 5720(4) Para
104
Core Members (as applicable)
PT
Designer
System OEM
Independent Advisor
Front Line Commands /
Aircraft operating
Authority
As required
(typically twice per
year in align with
the SIWG)
PT Head of
Structures
As Required
PT Head of
Structures
PT
Designer
Independent Advisors
PT
Designer
Independent Advisors
Other meetings as
required
A-3
Structures Desk Officer
Structures Section
System Specialist
System Specialist
e.g. QinetiQ
Engineering Rep
1710 NAS
Head of Structures
Structures Desk Officer
Structures Section
Stress Office
e.g. QinetiQ
Head of Structures
Structures Desk Officer
Structures Section
Stress Office
e.g. QinetiQ
ANNEX B TO
XXX/XXX/XXX/XXX
DATED XXXXXX
STRUCTURAL INTEGRITY WORKING GROUP
TERMS OF REFERENCE
Example TORS show SIWG, but could also be applied to EDPCWG etc
Reference:
A.
MRP RA 5720
1
INTRODUCTION
The requirement for SI specific meetings is mandated in Reference A. The frequency,
chairmanship and core membership of the Platform Name Structural Integrity Working Group
(SIWG) are detailed at Annex A.
2
AIM
The aims of the meeting are:
a. To review the level of compliance with Structural Integrity regulations.
b. To identify, review, discuss and formally record the risks to structural
airworthiness and to accept and endorse the strategies and plans to mitigate
those risks.
c. To report to the PSEP (or equivalent meeting) any unmitigated or unquantified
risks.
d. To report to the AS/CA/H AMG any specific structural integrity risks as well as the
overall level of structural airworthiness risk.
3
SCOPE
The SIWG will consider and ensure progress on the SI activities detailed in the Standing
Agenda Annex C.
4
PERFORMANCE MEASUREMENT
The meeting performance will be assessed against agreed output plans and hard targets
agreed within the action matrix. Minutes will be issued within XXX working days and the
agenda will be issued XXX working days prior to the next meeting.
5
ADMINISTRATION
The meetings will be held at the company premises/MoD Abbey Wood and paid for under
the PDS contract. The secretariat for the meeting will be provided by XXX.
B-1
ANNEX C TO
XXX/XXX/XXX/XXX
DATED XXXXXX
STRUCTURAL INTEGRITY WORKING GROUP
STANDING AGENDA
1 Introduction
2 Fleet Planning
3 Establishing SI
4 Sustaining SI
5 Validating SI
6 Recovering SI
a. Introduction.
b. Actions arising from previous minutes and not covered
under items 3 to 7.
a. Fleet Statistics.
b. Fleet Size.
c. Fleet Disposition.
a. SI Strategy Document and SI Plan.
b. SOI.
c. Release to Service – SI aspects.
d. Structural Design Certification:
(1)
Classification of Structure & review of SSI list.
(2)
Static Type Record.
(3)
Fatigue Type Record.
e. Fatigue Test Clearances.
f. SARC Assessment.
a. Usage Monitoring – method of Individual Aircraft Tracking
(IAT); fatigue monitoring/budgeting/formulae; structural and
transmission Health and Usage Monitoring Systems.
b. Structural Examination Programme (SEP) (to include
discussion on structural examination to counter threat
posed by hazardous incidents, corrosion, erosion and other
environmental degradation).
(1)
SEP Reporting Process (Topic 5V).
(2)
Scheduled maintenance plan (Topic 5A1).
c. Structural Configuration Control.
d. OSD.
e. Obsolescence Management Plan.
f. SIWG Frequency and Composition.
g. SARC Assessment.
a. SOIU Review.
b. OLM/ODR/MDRE.
c. Structural Sampling.
d. Teardown.
e. Maintenance schedule review (Including Topic 5V returns).
f. Review of Type Records.
g. NDT Technique Review
h. Ageing Aircraft Measures.
i. SARC Assessment.
a. Structural Problems.
(1)
Review Contents of Structural Arising Database.
(2)
Review EDPC WG/Database.
b. Modifications with SI implications.
c. Special Instructions Technical SI(T) with SI implications.
d. Repair Assessment Programme (MASAAG
C-1
7 Exploiting SI
8 Ac Disposal Plan
9 AOB
10 SARC Score
11 New SI Risks
12 Upward Reporting
13 Next Meeting
106)(mandatory for large ac only).
Compromised IAT.
SARC Assessment.
Review of Structural Hazards or -Risks.
Fatigue Conservation Measures.
Exploiting In-service experience.
Life/OSD Extension Programme.
Exploitation of OLM/ODR/HUMS/SHM/MDRE data.
Aircraft Disposal Plan
AOB
Overall SARC Assessment.
Consideration of new SI Risks that should be registered
within Risk Management system
a. Actions from and reports to HAMG/CA AMG/AS AMG
a. Arrangements for next meeting
e.
f.
a.
b.
c.
d.
e.
a.
a.
a.
a.
C-2
ANNEX D TO
XXX/XXX/XXX/XXX
DATED XXXXXX
PLATFORM SPECIFIC STRUCTURAL INTEGRITY DOCUMENT REFERENCES
Document
Statement of Operating Intent and Usage (SOIU)
Reference
AP101B-XXXX-15S
Structural Qualification/Clearances
Static type records
Fatigue type records
Fatigue meter formula
Scheduled maintenance plan
Ageing Aircraft Audit (AAA) Structural Sub-Audit
OLM/ODR Documents
D-1
Date
XXXX
Amendment State
Issue XX AL XX