Development of instructions for continuing airworthiness and aircraft logistic support analysis

Development of Instructions for
Continuing Airworthiness and
Aircraft Logistic Support
Analysis
Andrey N. Petrov
M. Gromov Flight Research Institute

Development of Instructions for Continuing Airworthiness
and Aircraft Logistic Support Analysis
 Civil and military aircraft historically have formally different
but in fact very similar requirements concerning the
airworthiness and supportability respectively
 Civil aircraft airworthiness requirements are a part of air law,
which include continuing airworthiness regulations within the
international standards of Annex 8 to Chicago Convention,
USA FAR / EU Part 21, USA FAR / EU CS 2X, USA FAR
12X / EU Parts M & OPS
 Military aircraft supportability requirements are a part of
military directives and standards, which include logistic
support analysis procedures within the USA DoD Directive
5000.1 &Instruction 5000.2, MIL-HDBK-1388-1 & -2,
DEF STAN 00-60
 There is a strong trend for integration of the airworthiness
and supportability efforts in the product life-cycle
management technologies
Regulatory Requirements

 Airworthiness - Aircraft or part fitness for flight
 Continuing Airworthiness - Aircraft or part safety monitoring,
maintenance, repair and modification
 Supportability - Aircraft or part fitness for support at the operation stage
 Logistic Support Analysis (LSA) - Techniques and processes to
analyze an aircraft type design in order to establish and comply effective
scheduled maintenance and other supportability requirements and
provisions throughout the life cycle of an aircraft
 Instructions for Continuing Airworthiness (ICA) - Set of
manufacturers’ documents, data and procedures to prevent, rectify and
restore possible failures which could endanger safety of flight
 Master Minimum Equipment List (MMEL) - List of equipment failures
not affecting safety of the intended flight under certain conditions
 Product Life-Cycle Management (PLCM) - Part of the development,
production, operation, maintenance (repair, modification), and disposal
(recycling) activities which include controlled influence on an aircraft type
design, production environment, operation and maintenance systems
intended to achieve an overall aircraft program effectiveness with a
reasonable level of a life cycle cost (LCC)
Aircraft Airworthiness and Supportability

Aircraft Airworthiness
ICA Development
Reliability and Safety
Assessment of a Type Design
Scheduling of Maintenance and
Airworthiness Limitations
ICA Set of Docs & Data
CONTINUING AIRWORTHINESS
ACTIVITIES
Airworthiness
Compliance to the Type Design Availability for the Intended Flight
ATA MSG-3

Aircraft Supportability
LSA Scope of works
Reliability and Safety
Assessment of a Type Design
Maintenance Scheduling
and Support Planning
LSA Records
(incl. Common Source Data Base - CSDB)
OPERATIONS FEEDBACK
Supportability

Airworthiness vs Supportability
SAFETY
based on ICA
FLEET MANAGEMENT
EFFECTIVENESS
based on LSA
FINANCE MANAGEMENT
Goal – safety and availability
Customer – aircraft operator
Product Support
Goal – profit or missions success
Customer – business operator
Customer Support

 Both ICA and LSA processes are aimed at operating
capabilities insurance (primarily availability and
maintenance scheduling and control) within the
airworthiness limitations and LCC target for an aircraft
 Both processes are based on the results of reliability
and safety assessment of an aircraft type design
 Joint reliability-maintenance model could be used in
both processes
 Joint electronic definition of the aircraft systems and
structure would be implemented
 Software tools should be unified as much as possible
Commonality Calls for Unified Methodology

 Low formalization of procedures and algorithms, which leads to the high
user qualification requirements and need for the special policy and
procedures handbooks
 Need to arrange special set of input data - “maintenance/structural
significant items - MSI/SSI” - instead of direct link to the database of the
qualitative and quantitative results of reliability and safety assessments
 MSI/SSI concept covers both systems and components, which leads to the
uncertainty whether you analyze a system or component FM
 MMEL considered as an input set of data (rather being one of the RCM
analysis expected results)
 Use of the indefinite “safety / operating capability / economic effects” of
MSI/SSI failures instead of certain failure conditions (incl. aborted take-offs
& in-flight diversions) all already known from the reliability and safety
assessments
 Lack of procedure to use data from the in-flight monitoring systems
(FDR/CMC) that can facilitate finding of failures
 Lack of quantitative methods for maintenance intervals optimization (just
general guidance is provided)
Current Methodology Deficiencies

 Reliability-Centered Maintenance (RCM) concept can be kept as
a basis after elimination of it’s known deficiencies
 RCM logic should be refined
 Tool for quantitative maintenance intervals optimization should
be added
 Analysis procedures should be defined more formally and clear
to decrease qualification requirements for engineers-analysts
 Tools for solving additional LSA tasks should be proposed taking
into account the need for integration of the whole methodology
with the same:
• math model
• set of initial data
• integrated output database
Unified Methodology Approach
 Manufacturer
 Operators
 Authorities

Concept of Failure-Related Safety
• Failures considered to be a
MMEL items
• Acceptable failure probability
with MMEL-flights taken into
account
• Scheduled checks not
needed because of the flight
data use for failure monitoring
• Scheduled maintenance
need to be applied
• Acceptable failure
probability with maintenance
intervals taken into account
• Scheduled operational
checks of redundant/safety
components and systems
• Acceptable failure
probability
• Warning and crew
support systems
• Scheduled functional
checks (if possible and
effective)
Non-Critical / Redundant Parts Failures
EVIDENT HIDDEN
Critical ("single")
Failures / EVIDENT
Common Source Data Base
MMEL ICAAFM

 An aircraft has a number of systems each may be regarded as
consisting of a number of elements each having limited number
of failure modes (FM) with constant failure rates
 Failures are detected in flight and on the ground and are
corrected during maintenance
 Corrective maintenance (repair) after the failure finding assures
system restoration in a specified time
 For highly reliable aircraft systems repair time considered
negligible with respect to mean time between failures (MTBF)
 The inspections are nearly perfect (most failures under control
are detected and fixed with no new failures introduced as a result
of maintenance)
Under these assumptions the Markov homogeneous process
may be used in the math model for the aircraft systems
safety/reliability assessment and maintenance planning
Math Model Basics

 General technical data on aircraft systems & parts design and operation
(electronic design & functions definition, logistic aircraft breakdown etc.)
 Results of the aircraft failure mode and effect analysis:
• expected failure modes (FM) for the systems & elements (components)
• average probability per flight hour (FH) for each expected FM
• effect of each expected FM on the aircraft operation: failure condition in flight
and dispatch reliability effect (DRE)
• actual data/prognosis for each expected FM allowing to decide if its probability
is a flight hour dependent (FHD) or not
• each component FM functionality parameter (FP) reflecting the component
redundancy
 Initial data on the systems maintainability to evaluate and accept the
following analytical decisions:
• primary maintenance processes (PMP)
• systems' maintenance tasks: operational/functional checks, lubrication/servicing
& restoration tasks
• mandatory redesign measures if needed for any reasons: Redesign Mandatory -
Safety Accident (RMSA); RM - Safety Incident (RMSI); RM - Dispatch Reliability
(RMDR); RM - Operational Check (RMOC); RM - Functional Check (RMFC); RM -
Lubrication/Servicing (RMLS); RM - Restoration of an Item (RMRI)
Input Data

 Aircraft scheduled maintenance analysis covers:
• PMPs and maintenance tasks selection for each component taking into account
possible failures
• intervals optimization for the developed scope of maintenance tasks
• MMEL development as a compliment to the maintenance schedule
 Maintenance tasks development requires three levels of RCM-type
decision logic analysis (level 1 deals with systems failures, levels 2 & 3 deal
with components failures):
• level 1 - categorize all possible FM for the particular system into four
functionality effect categories (FEC, depending on severity of the FM
consequences) and evaluate the necessity of the system scheduled operational
checks which allow for timely finding of failures and timely system restoration
• level 2 - categorize each component failure significance (SC) in accordance with:
FM effect on system and aircraft operation (use FEC), redundancy level (use FP),
anticipated probability & physical nature of the FM (use FHD & DRE), - in addition
components PMPs (hard time, on-condition, failure monitoring) have to be
selected for logistic optimization & supply planning within the LSA process
• level 3 - components design evaluation to select necessary scheduled
maintenance tasks which preventing failures or timely finding failures out and
timely restoring the component airworthiness taking into account the SC for each
component's FM
Analysis Process (1)

 Possible redesign to be proposed at all levels of analysis if system or
component design and/or installation are not in compliance with the
airworthiness & operational requirements (RMSA, RMSI, RMDR, RMOC
categories) or component design and/or installation are not allow for
accomplishment of required maintenance tasks (RMOC, RMFC, RMLS, RMRI)
 Maintenance intervals optimization for redundant components checks
divided in three steps (other intervals need expert assessment) :
• determination of the unreliability functions for each system FM and maintenance
cost function for the system using following data: component FM & their
probabilities; typical flight & its phases duration; parameters of unknown
maintenance task intervals to be optimized; scheduled and unscheduled
maintenance tasks known or expected costs
• optimization of the individual maintenance tasks intervals using LaGrange's
method for convex functions case based on the proposed math model
• if necessary there is a possibility to form maintenance packages with associated
rational maintenance intervals adopted from the optimized individual task interval
values using known base maintenance intervals (A, B, C, D - checks structure)
 MMEL development is based on the same methodical approach and math
model, it is aimed at instructions to an aviation personnel on how to prepare
a flight with certain known failures on-board not affecting safety
Analysis Process (2)

RCM-type Decision Logic Diagram for
System Failures Analysis
Note:
RMOC – Redesign Mandatory to allow Operational Check

Defining Significance Categories –
Mechanical Failures (damage or jam)
Probability of
failures &
combinations
there of
System failure mode with FEC I
System FM
with FEC II
System FM
with FEC III
System FM
with FEC IV
FP=1 FP=2
EI+
FP=2
EI
FP3 FP=1 FP2 FP=1 FP2 FP=1 FP2
EI 1 1 3 3 3 3 3 3 3 3
ER RMSA 1 3 3 3 3 3 3 3 3
R RMSA 1 3 3 2 3 3 3 3 3
P RMSA 1 3 3 2 3 2 3 3 3
P+ RMSA 1 3 3 2 3 2 3 3 3
Notes:
1 Probabilities thresholds (average, per 1 FH): probable (P) - 1·10
-4
... 1·10
-2
, remote (R) - 1·10
-7
... 1·10
-5
,
extremely remote (ER) - 1·10
-9
... 1·10
-7
, extremely improbable (EI) - less than 1·10
-9
2 For each system FM of certain FEC (I, II, III и IV) a number of elements FM combinations to be
considered each having its own functionality parameter FP (1, 2 & more, 3 & more)
3 For double failures causing FEC I system FM two cases to be considered:
1) when combination of 2 elements failures is not more than EI (FP=2
EI
) and
2) when ore probable (FP=2
EI+
)
4 All mechanical failures are considered as a flight hour dependent (FHD)
5 System considered to be redesigned if established analysis criteria are not met

Defining Significance Categories –
Non-Mechanical Failures (electrical, electronic, etc.)
Probability of failures
& combinations
there of
System failure mode with FEC I
System FM
with FEC II
System FM
with FEC III
System FM with
FEC IV
FP=1 FP=2
EI+
FP=2
EI
FP3 FP=1 FP2 FP=1 FP2 FP=1 FP2
ER
FHD RMSA 1 3 3 3 3 3 3 3 3
Non-FHD RMSA RMSA 3 3 3 3 3 3 3 3
R
FHD RMSA 1 3 3 2 3 3 3 3 3
Non-FHD RMSA 1 3 3 RMSI 3 3 3 3 3
P
FHD RMSA 1 3 3 2 3 3 3 3 3
Non-FHD RMSA 1 3 3 RMSI 3 3 3 3 3
P+
FHD RMSA 1 3 3 2 3 3 3 3 3
Non-
FHD
Non-
DRE
RMSA RMSA 3 3 RMSI 3 RMSI 3 3 3
DRE RMSA RMSA RMDR RMDR RMSI RMDR RMSI RMDR RMDR 3
Notes:
1 Probabilities thresholds (average, per 1 FH): probable (P) - 1·10
-4
... 1·10
-2
, remote (R) - 1·10
-7
... 1·10
-5
,
extremely remote (ER) - 1·10
-9
... 1·10
-7
, extremely improbable (EI) - less than 1·10
-9
2 For each system FM of certain FEC (I, II, III и IV) a number of elements FM combinations to be
considered each having its own functionality parameter FP (1, 2 & more, 3 & more)
3 For double failures causing FEC I system FM two cases to be considered:
1) when combination of 2 elements failures is not more than EI (FP=2
EI
) and
2) when ore probable (FP=2
EI+
)
4 System considered to be redesigned if established analysis criteria are not met

 Above defined categories of system failure effect (FEC) and
component significance (SC) are necessary to define components
PMP and depends on the inherent system/component reliability &
physical nature of possible failures
 Four kinds of FECs for systems FM shows system failures influence
on the airworthiness and flight safety from more (I) to less (IV)
 Three kinds of SCs for components shows component-level failure
influence on the airworthiness and flight safety from more (1) to
less (3)
 For all three significance categories both hard time and on-
condition component maintenance could be applicable and
effective with certain maintainability and testability requirements
 Condition monitoring maintenance is only applicable for the
components having SC 3
Failure Significance Category and Primary
Maintenance Processes

 Maintenance tasks development and optimization of maintenance
intervals is not presented in detail for the following reasons:
• Proposed decision logic for components failures analysis are very
similar to those of ATA MSG-3 with some additions (like more detail
decisions on functional vs operational checks)
• Decision logic for the airframe structural elements analysis is well-
defined in ASD S4000M, no additions proposed at the moment
• Proposed methodology of maintenance intervals optimization is a mix
of traditional expert approach for all tasks except those to find & fix
redundant components failures which covered by proposed quantitative
optimization technique to be discussed in details separately
• MMEL development is an optimization task for the restoration intervals
of anticipated evident FM of redundant components and methodically
problem is completely similar to hidden failures restoration policy (to be
covered by scheduled maintenance) with changing the maintenance
check interval with the restoration interval for evident failure (details of
this process are out of the frames of the presentation)
 Nevertheless, the overall methodical approach is comprehensive
and allows logical integration of ICA development and LSA
processes
Maintenance Tasks and Intervals Optimization

 There are two coherent approaches in place:
1) to develop aircraft ICA as an airworthiness tool for civil aircraft and
2) to accomplish LSA as a supportability tool mostly for military aircraft
 Commonality of both approaches calls for unified methodology to
achieve the goals of both processes
 Unified methodology is proposed, which is based on the proven
RCM concept with elimination of its known deficiencies
 The methodology supports integration of existing and new tools for
solving ICA/LSA tasks using common:
• math model allowing quantitative optimization
of certain maintenance tasks intervals
• set of unified initial data
• integrated output database (LSAR/CSDB)
Conclusion

Development of instructions for continuing airworthiness and aircraft logistic support analysis

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