From Aircraft Health Monitoring to

Aircraft Health Management

White Paper on AHM

1 From Aircraft Health Monitoring to Aircraft Health Management Feb 2022

Contents
1. Foreword .............................................................................................................................................................................................. 3
2. Aircraft Maintenance Milestones ................................................................................................................................................. 5
2.1. Aircraft Maintenance as Means to an End ................................................................................................................................. 5
2.2. Maintenance Life of the Aircraft ................................................................................................................................................... 6
2.3. Evolution of Aircraft Maintenance Concept ............................................................................................................................. 7
3. The AHM Paradigm ......................................................................................................................................................................... 10
3.1. Defining Vocabulary ........................................................................................................................................................................ 11
3.2. Searching Optimization of Aircraft Technical Availability .................................................................................................. 12
3.3. Securing the Benefits ..................................................................................................................................................................... 13
4. Industry Action Steps .................................................................................................................................................................... 15
4.1. Recognizing Foundations .............................................................................................................................................................. 15
4.2. Developing Capabilities ................................................................................................................................................................. 17
4.3. Creating Standards ......................................................................................................................................................................... 18
5. Regulatory Balancing Act ............................................................................................................................................................. 20
5.1. Addressing Necessity .................................................................................................................................................................... 20
5.2. Solving the AHM Puzzle ................................................................................................................................................................. 20
6. AHM Roadmap .................................................................................................................................................................................. 24
6.1. Starting Points ................................................................................................................................................................................... 24
6.2. Validation Gates and Criteria ....................................................................................................................................................... 24
6.3. Pursuing Implementation .............................................................................................................................................................. 25
7. Conclusions ....................................................................................................................................................................................... 27
Appendix 1 – Abbreviations ............................................................................................................................................................. 28
Appendix 2 - Suggested Readings ................................................................................................................................................. 30
Appendix 3 - Acknowledgements .................................................................................................................................................. 31

Figure 1: Reliability Bookmarks .................................................................................................................................................................... 5

Figure 2: Maintenance Taxonomy Excerpt .............................................................................................................................................. 6
Figure 3: Driving Factors in Scheduling Maintenance ......................................................................................................................... 8
Figure 4: Layered Setup of AHM Readiness ..........................................................................................................................................10
Figure 5: Uncertainty Matrix of Reality and Perception .....................................................................................................................15
Figure 6: Steps Marking the Life-Cycle ...................................................................................................................................................16
Figure 7: Integration and Capability Milestones ..................................................................................................................................17
Figure 8: Levels of Analysis in MSG-3 Logic .........................................................................................................................................19
Figure 9: Pieces of the Puzzle .....................................................................................................................................................................21
Figure 10: Steps to Take for AHM Implementation.............................................................................................................................25

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1. Foreword
Managing the technical availability of the aircraft is key in accomplishing your mission, whichever is your stakeholder
status vis-à-vis the aircraft asset: Airline Operator, Aircraft OEM, Aircraft MRO or Aircraft Owner/Lessor.
In assessing the potential impact of (un)availability, operators asserted that aircraft dispatch delays can cost $10K
(or more) per hour with flight cancellations imposing a financial penalty of $100K (and above) per instance.

Hovering consistently well above a 99% benchmark of aircraft technical availability implies a careful steering of the
aircraft maintenance with a sharp focus on preserving the capabilities and performance of the asset close to its “as
new condition”. Hence, the needed enabler for a 24/7 visibility on, awareness of, and action to maintaining the
required level of aircraft health.

Accomplishing the above is the main objective and direct result of a robust Aircraft Health Management (AHM).
The AHM means using aircraft and fleet generated data to promptly identify the individual aircraft’s needs for
maintenance work and trigger an effective and efficient maintenance action. This is an end-to-end comprehensive
process, which encompasses aircraft systems, data transfer and electronic processing, data analysis, and
subsequent informed decision on improved, re-defined, or alternative methods to maintenance tasks. Such a
process includes both “on-board” and “off-board” sequences and its results are highly relevant to planning and
executing the aircraft scheduled maintenance program or the ad-hoc required maintenance action. It is a dynamic
action-oriented approach and a consequential evolution of the already acknowledged albeit more “passive
witnessing” field of Aircraft Health Monitoring.

This White Paper is a quick review of what AHM implies and could possibly empower its adopters to perform, in the
not-too-distant future, towards ensuring the economically optimized technical availability of the aircraft.
While there is no substitute (at least not yet) to the aircraft maintenance action requiring the maintenance staff
“hands-on” presence for physical accomplishment of an aircraft part replacement or repair, implementing the AHM
approach would position the practitioner to make the optimum decision regarding such maintenance action.
Predictive maintenance employing health monitoring mechanisms is estimated to enable airlines around $3B per
year in maintenance cost savings.

The objective of this White Paper is to: a) familiarise the industry with the technological revolution that the use of
data collected from the aircraft can improve the levels of safety and efficiency, b) provide a roadmap to capitalize on
this data usage, and c) address challenges and opportunities that this will bring to the industry.

Empirical data indicate that, for the average operator, over 70% of its scheduled maintenance program “fault finding
tasks” resulted in “no findings”. This maintenance execution fact coupled with utilizing the alternative of AHM-based
tasks to enable a condition-based maintenance versus on-wing manual preventive maintenance tasks will result in:
a) significant cost reductions for the operator, and b) increased aircraft on-time performance and improved dispatch
reliability as real time data is either pro-actively or reactively used by operators to address aircraft systems or
structural issues before faults could develop into functional failures affecting the aircraft technical availability.

Adopting and operationalizing a refined AHM path will naturally lead civil aviation actors to also explore new ways of
guarding the safety level priority in the context of ever-growing complexity of aircraft and their operation.
Critically important for all entities in the aviation ecosystem is that Airworthiness regulatory authorities approving
and overseeing the AHM implementation do engage the industry and consider their feedback in designing the safest
and most efficient aviation framework.

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Recently manifested radical progress factors and technology disruptors like Big Data and Cloud Services, Industrial
Internet of Things, Artificial Intelligence and Machine Learning, Industry 4.0 and Digital Twins are all major potential
contributors to shape and empower the AHM.

This White Paper is an invitation for all industry stakeholders to consider the AHM ensuing benefits in building the
future success of the entities and communities they belong to.
Sharing AHM related ideas, initiatives, experiences, and results would benefit the entire aviation ecosystem and this
White Paper is intended to enhance the interest in that direction.

Looking forward to receiving any feedback at Techops@iata.org.

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2. Aircraft Maintenance Milestones
While not always visible to aircraft operation direct beneficiaries, aircraft maintenance is a constant presence
enabling the aircraft asset to deliver along its entire life the expected financial and business values without any
hindrance due to aircraft technical status. The recognition of aircraft technical availability key role is unanimous,
although one should always check the definition of this KPI for common acceptance basis and interpretation
awareness (see reference [1] in Appendix 2 for a detailed discussion).

2.1. Aircraft Maintenance as Means to an End

Airline Operators are aware that aircraft maintenance, notwithstanding its “must have” regulatory status, is just the
means to support the desired end outcome of aircraft fleet operational readiness.

The perspective of a “self-healing” aircraft is still a distant one even if some of the edge research in self-diagnostics
and self-repair of complex structures is bringing such aircraft of the future out of the Science Fiction realm and closer
to aviation attainable goals.
In this context, the first step to ensure the desired technical availability of the aircraft is to set-up an appropriate
maintenance activity, which is focused on and supports the airworthiness, technical capability and performance of
each aircraft, as demanded by the airline’s operation schedule.

While clearly distinct from it, the aircraft technical availability relies first and foremost on the aircraft reliability.

Figure 1: Reliability Bookmarks

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The reliability which an operator could achieve for the aircraft (i.e., “individual tail reliability”) is lower than, or at best
equal to, the aircraft reliability performance intrinsically resulted from the design of the aircraft type and production
of the aircraft unit.

The aircraft “built-in” reliability threshold resulted from design and production is the maximum achievable level of
reliability in operation. Aircraft maintenance, however diligent and effective, would not result in exceeding that
threshold and operators should acknowledge it as a limitation which is out of their control and is dependent on the
aircraft design and production.
Only with a well-conceived and implemented Aircraft Maintenance Program (AMP) could the operator eventually
achieve that end level of reliability. Airlines are requested by regulation to have a Reliability Program for their fleet by
considering several sources of information (e.g., Pilot Reports – PIREPS, Maintenance Reports – MREPS) and
operationalizing a Failure Reporting, Analysis and Corrective Action System – FRACAS.

Additionally, operational relief mechanisms involving dispatch under Minimum Equipment List (MEL) and
Configuration Deviation List (CDL) are, in some circumstances, facilitating a limited technical availability of the
aircraft, albeit they are not intended to and could not address a lack of reliability issue.

AHM potentially becomes a key enabler of optimized AMP implementation; its direct impact on securing the aircraft
technical availability makes it an important tool for airlines in achieving the desired level of Dispatch Reliability (DR).

2.2. Maintenance Life of the Aircraft

The aircraft “maintenance life” is effectively starting once the production test flight of the aircraft is performed
although the clock and focus for technical, commercial, and regulatory compliance activities with aircraft
maintenance relevance is initiated “de jure” at the time of aircraft delivery to its first operator.

Exploring the taxonomy of aircraft maintenance types is a multi-layered exercise with numerous categories of
maintenance activity being distinguished based on the criteria considered to define them.
A non-exhaustive list of examples would include grouping by:

• location and complexity of activity execution during the aircraft operational life (i.e., line or base
maintenance).
• volume of activity committed and its optimization for the timing and duration of execution (i.e., equalized or
block maintenance).
• nature of activity in relation to the technical content of the executed maintenance tasks (i.e., preventive or
corrective maintenance).
• prior level of planning granularity/comprehensiveness governing the activity (i.e., scheduled or non-
scheduled maintenance).

Figure 2: Maintenance Taxonomy Excerpt

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Each criterion is capturing the dominant feature of that category of maintenance and the very same maintenance
task could be simultaneously identified as belonging, for example, to preventive, block and base maintenance.

The individual airline will always seek to build and adopt the AMP best suited to its own operational profile and fleet;
the resulting aircraft maintenance activity planning and execution will account for the specific constraints and
conditionalities. This could result in a very tailored packaging of maintenance tasks which accommodates to the best
possible level the particular operation.

Reviewing the frequency of aircraft parts’ failure, a series of patterns were identified in the attempt of linking the
occurrence of such failures to the operating time (or the relevant use control parameter) of the part. The conclusion
was that most functional failures (approx. 89% of them) in a complex machinery like the aircraft occur following a
deterioration model which is not “age related” but rather “random” (see reference [13] in Appendix 2 for more details).
The emergence of software parts which the configuration of modern aircraft comprises (e.g., currently, the B787
counts around 1400 instances of such parts in its listed configuration) seems to bring no major change to the above
conclusion which is based on legacy configuration aircraft (i.e., in-service by 1980).

While the conclusion drawn constitutes an important element which the AHM must consider, the corelations unveiled
by a continuous and detailed monitoring of parameters could be an AHM opportunity to pursue when attempting to
explore the previously observed randomness.

2.3. Evolution of Aircraft Maintenance Concept

In its history beginning phase, aircraft maintenance was mainly of corrective type – fix the equipment once it has
broken and failed to fulfil its intended function - with the addition of some servicing maintenance actions (e.g.,
cleaning and lubrication) and limited restoration of condition to “as if new” when the need to recover evident loss of
performance was identified.

This approach evolved later to include scheduled restoration, overhaul or replacement of equipment and parts. The
intent of such maintenance actions was preventive in nature with the scope of increasing reliability of subject
equipment and parts and it was based on the belief that the more maintenance the aircraft undergoes the better its
reliability will be.
This view resulted from across-the-board application of the “bathtub model” of failure and its assumed wear-out
zone while, at the same time, ignoring the failure rate injected into otherwise stable operating systems by
unnecessary maintenance actions.

The Maintenance Steering Group (MSG) became the aerospace industry driving force to introduce the systemic
engineering approach to aircraft scheduled maintenance development. This formalized a decision logic flow which
was permanently refined and reflected in the successive standards document MSG-1/ -2/ -3 with a notable
mechanism for periodic revisions of MSG-3.

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 Figure 3: Driving Factors in Scheduling Maintenance

The major step in this evolution was to recognize that performance of maintenance should be targeting function
preservation at the aircraft level rather than focusing on the component failure per se. This evolution resulted in:

• the system level and top-down approach for function identification, instead of a component level and
bottom-up approach.
• the consequence-driven approach, starting with the failure identification as “hidden” or “evident” to the flight
crew and “safety” or “non-safety” categorization to ensure specific addressing controls of the risk of failure.
• the function preservation instead of failure prevention, to ensure the system function and the availability of
protective devices.
• the task-oriented approach instead of a maintenance process-oriented approach to preparation of a
maintenance programme.

This evolution history started with embracing three types of maintenance processes:

Hard Time (HT) defined as the preventive process in which known deterioration of a system or component is limited
to an acceptable level by the maintenance actions which are carried out at periods related to time in service or other
corresponding control parameter (e.g., calendar time, number of cycles, number of landings). The prescribed actions
restore the system or component utility margin to the applicable control parameter limitation. Examples: overhaul
the landing gear; discard the cartridge of the engine fire extinguishing; discard cabin crew protective breathing
equipment.

On Condition (OC) defined as the preventive process that requires a system or component be inspected periodically
or checked against some appropriate physical standard to determine if it can continue in service between the
periodic maintenance actions. The standard ensures that the unit is removed from service or undergoes the
necessary maintenance action before failure in service. Examples: Lubrication tasks, Operational Checks, General
Visual Inspections.

Condition Monitoring (CM) defined as the process for systems or components that have neither HT nor OC
maintenance as their primary maintenance process. It is accomplished by appropriate means available to an
operator for finding and solving problem areas. This is not a preventive process, and the system or component are
permitted to remain in service without preventive maintenance until a functional failure occurs. The CM is often
abusively equated with “run-to-failure” or “fit and forget” philosophy, ignoring that many components maintained
under such a process are removed before their failure in service if related repair costs would justify removal.
Examples: maintenance of Passenger Convenience Items or Non-Essential Equipment and Furnishings.

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It should be noted that in-shop maintenance practice for off-wing components may be following what is sometimes
referred to as “soft-time intervals” philosophy which, for example in the case of an engine, retains in essence the
“on-condition” maintenance practice and minimizes the impact of additional module disassembly.

While in general these maintenance processes are not driving the aircraft maintenance concept anymore
(exceptions may be encountered for legacy fleets), it is worth emphasizing that CM is not linked to achieving OC
maintenance.

Another misleading association is to assume any commonality between CM and CBM.

Condition Based Maintenance (CBM) is a type of maintenance activity that determines the condition and remaining
useful life of the component/equipment and consists in maintenance performed based on evidence of need in order
to maximize the utilization of economic life of that component/equipment. The CBM, through its application and
integration of appropriate processes, technologies, knowledge-based and prognosis capabilities, represents a
major evolution of the OC type of maintenance and, by enabling the optimal failure management strategies
depending on system reliability characteristics and the intended operating context, it essentially fits under AHM.

Avoiding confusions associated with various interpretations is benefiting also from the evolution of MSG standards:
the MSG-3 departed from the HT, OC and CM concepts which were central to the MSG-2.

A significant evolution in the decision logic established for developing the aircraft scheduled maintenance would be
to accommodate the AHM implementation. Such development would be possible in the next MSG-3 revision
(envisaged for 2022) by including the optional level of analysis adopted through IP-180 (see section 4 for details).

Takeaway
• Aircraft maintenance shall be strictly supporting the technical availability of the aircraft asset for safe flight
operation and integrate the airline operator specific elements in the process of doing so in an effective and
efficient way.

• Implementation of AHM is a logic step to consider in the evolution of aircraft maintenance concepts,
especially as they apply to the new level of technology defining the recently certificated aircraft types.

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3. The AHM Paradigm
Engaging into AHM implementation is conditional to having both the DAH/OEM and the Operator successfully reach
the necessary readiness level and assume the AHM specificities consistent with their roles as recognized and
endorsed by the Regulator. The multi-layered essence of this required three-legged construct is summarized in the
figure below.

Figure 4: Layered Setup of AHM Readiness

Although robust addressing of safety remains the main driver, commercial considerations (e.g., costs and
contractual agreements) do have their role in some of the intra and inter layer connections implied in the above
figure.

While building the AHM readiness requires each stakeholder to explore and master new elements, a previous exploit
in aviation – consisting of the ETOPS/EDTO implementation - is a valuable procedural model to follow.

Several tenets worth be reminded for their relevance to the AHM paradigm:

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 • With a fundamental role in aircraft airworthiness and, thus, essential to aircraft flight safety, the aircraft
maintenance actions must be executed whenever necessary and shall always encompass the sufficient level
of detail. Thus, the maintenance action must meet both the necessity criterion and the sufficiency criterion.

• The AHM purpose is to produce the aircraft accurate health indicator which would constitute the evidence
of maintenance need and guide the granularity of work to be performed based on the condition and actual
use controlling parameter of the equipment instead of a specified calendar time or generic use limits.

• The key enabler in pursuing any maintenance credits for AHM is to identify and address the product
certification and operational authorization precursors in a way commensurate to the AHM use case.

• Implementation of AHM requires a capability level not only for the initial qualification phase (e.g., aircraft type
certification and production certification; airline infrastructure, processes, procedures, and personnel) but
also for the continued preservation of such qualification (e.g., in-service experience/data driven
revisions/updates).

• Portability between maintenance systems with and without AHM over the operational life of the aircraft asset
should be ensured and AHM should be viewed and developed as “the option” and not “the obligation” of
airline operators.

• Exploring the concept of certification of “AHM dependent product design” is a possible future direction
envisaged by OEMs.

3.1. Defining Vocabulary

The aircraft maintenance concepts, even when new and somehow disruptive approaches were adopted, has always
provided to its practitioners a cohesive evolution from one construct to the next and AHM is no exception. There is
however a certain level of on-going dynamics regarding the definition, acceptance and use of some of the
terminology or categorization involved in the emergence of AHM and related activities. This could generate
overlapping, duplication, or misalignments (even apparent contradictions) which the industry and regulatory
stakeholders are called upon limiting; flexibility is desired and would benefit AHM implementations, but vagueness
and/or lacking consistency would hamper any progress in AHM use.

Often enough, a close scrutiny of the wording used and the associated definitions may indicate more of a marketing
or trademark motivation rather than a substantial conceptual differentiation.

While a definitive coining of the AHM vocabulary is out of scope and would be an unattainable pursuit for this paper,
there are a few elements to highlight in support of a common understanding basis:

Aircraft Health Management (AHM) is the unified capability of using health monitoring of aircraft structure and
systems (including propulsion system) to control the scheduling of aircraft needed maintenance actions; could be
resumed to the process stages of Sense, Acquire, Transfer, Analyse and Act (SATAA).

Aircraft Health Monitoring is the technique of monitoring the output of a single and/or multiple condition indicators
during operating conditions used to diagnose faulty states and predict future degradation of the equipment; could
be resumed to the process stages of Sense, Acquire, Transfer and Analyse (SATA).

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Fault vs Failure should be understood as the anomaly identified in a component or system without impact on the
required functional output of the item or system vs the inability of a component or system to perform its functional
role within previously specified limits.

Potential to Failure (P to F) is an interval (expressed in functional use control parameter units), counted from the
presence of a defined identifiable condition at its earliest point of detection/diagnosis, at the end of which the
degradation process triggered by the condition leads to a functional loss of the component or system; it is a value
which once predicted remains constant for the entire degradation period.

Remaining Useful Life (RUL) is the remaining segment of the P to F at the time of discussion; it is a value which
decreases from the P to F value (if the time of discussion coincides with the origin of P to F) to zero (if the time of
discussion coincides with the functional loss).

Failure Mode vs Failure Cause vs Failure Effect should be understood as the way in which a component/system
can fail vs why the component/system failed in the observed mode vs the result/consequence which the failure of
the component/system has.

Condition Indicator vs Health Indicator should be understood as the result produced by an algorithm that
combines one or more features of a component or system and which is representative of the state of the component
or system vs the result of one or more condition indicator values cumulated to signal a need for a maintenance
action.

Predictive Maintenance is the maintenance process with the objective to answer “what and when” will happen with
the asset which is maintained. It consists in the prediction of future events based on historical and real-time collected
data; it employs sophisticated data analytics and automated maintenance workflow elements with possible AI tools.

Prescriptive Maintenance is the maintenance process elevating the prediction capabilities (see the predictive
maintenance process discussed above) by adding adaptation and optimization capabilities which enable it to not
only predict “what and when” for the event which will happen but also recommend “how” to resolve the event; it
employs sophisticated data analytics and automated maintenance workflow elements including AI tools.

3.2. Searching Optimization of Aircraft Technical Availability

Statistics indicate that, depending on the aircraft type and use category/destination/market, somewhere between
two thirds and four fifths of maintenance generated unavailability originate from planned maintenance with the rest
coming from unplanned maintenance activity. In general, due to operational considerations, from the airline
perspective the unavailability “unit cost” ends by being much higher for non-operating time due to unplanned
maintenance rather than planned maintenance.

The planned maintenance activity would benefit from AHM implementation through its inherent optimization since
maintenance resources would be focused on evidence of need provided by health indicators of the aircraft asset. In
essence, introducing AHM in the equation of the rationale driving the content of scheduled maintenance, the planned
maintenance can be optimized and implicitly the related unavailability contained to its feasible minimum.

Additionally, one of the main strengths of an AHM proposed approach and a major source of attracting the active
interest of airline operators, is to transform many unpredictable maintenance events into predictable ones and
properly plan for them. The capability of additionally reducing operational interruptions from unplanned maintenance
events is particularly appealing to airlines.

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AHM should provide visibility and knowledge of the aircraft actual usage with a sufficient level of detail and
supporting data.
Usage monitoring information comprising data regarding operational regimes, functional parameters and
operational environment would generate a refined actual usage identification spectrum of the aircraft structure,
systems and components.
The potential consequence would reach from improving the accounting of the maintenance control parameter
triggering the execution of a maintenance task up to influencing the decision if the life limit of an LLP was attained or
not.
The above-mentioned potential consequence is recognized as an opportunity already explored by engine DAHs with
the concept of Usage Based Lifing (UBL).
This would compensate for the unintended over-conservative effect of design and certification assumptions in the
case of a low severity usage.
The reversed situation could also happen, whereby AHM outcome safely compensates an under-conservative
assumption in the case of higher than design-assumed usage severity.

3.3. Securing the Benefits

Quantifying the value of AHM is a fundamental step for each category of stakeholder before engaging on the AHM
avenue and there are different weights attached to individual benefits depending on the stakeholder identity (e.g.,
airline, OEM, MRO).
The assessment should consider the potential safety, operational and economic benefits.

Enabling a constantly actualized characterization of the in-service condition of an aircraft system or component with
the real (or almost real) time continuous collection of data which the AHM entails, could become a significant benefit
in the aircraft operational safety equation. The potential of having a continuous monitoring versus a discrete interval
visibility, would enable moving the maintenance action promptitude and its time horizon on a different coordinate
with ensuing benefits to aircraft safety.

The AHM benefit pool comprises the categories of short-term ones – e.g., visibility and understanding of a
system/component deterioration enables to optimize the timing and the level of maintenance action to avoid
operational disruptions, and long-term ones – e.g., prioritize, relying on AHM, the component restoration or repair for
an economic optimum regarding the maintenance cost.

When deciding on any particular AHM implementation four questions will be asked from start by the airline
considering it:

• Does AHM solve some of the issues the airline is faced with and would it bring new opportunities to airline’s
operation?

• Is AHM technically feasible in airline’s organizational context and resources?

• Would AHM be a sustainable operation for the airline to engage-in?

• What is the level of regulatory involvement needed for approval and oversight, and could that be secured by
the stakeholders concerned?

Integrating the AHM basis in aircraft maintenance would unlock a broad range of benefits including higher
productivity, decrease in maintenance turn times, lower costs, increased quality of the process and would deliver
finally a better technical availability and enhanced dispatch reliability of the aircraft.

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It shall be recognised nevertheless that tailoring AHM for implementation on a targeted platform aircraft must
consider what is practical to implement versus attempting by default to apply AHM across the board for all
equipment / components which are part of the aircraft configuration.

AHM suitability relies essentially on the measured condition of aircraft systems, equipment or components and their
actual values of usage control parameters. Aircraft design configuration technical elements or airline operational
procedures inability to deliver such information would rule out AHM applicability.

Based on the typical use of classic scheduled maintenance tasks for all aircraft systems (i.e., including propulsion
systems) it is asserted that up to 90% of those tasks result in “no finding”. This statistic would lead to the rather
staggering conclusion that 90% of aircraft ground time for systems scheduled maintenance does not change the
condition of the aircraft. Is that a waste of labour and material resources?
Additionally, it is asserted that more than 60% of the systems’ functional failures (i.e., considering the total across all
FECs) had no scheduled maintenance tasks selected through the typical maintenance program development
process.
The potential to change the above through a robust implementation of AHM is a strong motivator for action.

Takeaway
• The willingness to address the burden of unnecessary labour and material resources resulted from the
typical scheduled maintenance development is a strong incentive for AHM implementation.

• While there are up-front costs involved by AHM implementation, and all categories of stakeholders should
assume their share, in general “the potential gain is worth the pain”.

• Individual scrutiny for feasibility and sustainability should be applied to each AHM use case.

• The AHM future requires a high level of automation with data science developed processing algorithms
running in an AI/ML setting made possible by AHM ready aircraft products and components.

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4. Industry Action Steps
Like most developments in civil aviation, the exploration of AHM concept emerged from the aviation industry push
to refine what and how to perform for aircraft maintenance once the asset commenced its service life.
While airlines are the ultimate enabler and user of the AHM implementation, hence their active role in building a
coherent and fit for purpose sustainable construct, developing the AHM path could not be envisaged as the effort
of a single category of stakeholders (see considerations presented in section 3) and outside of a wide-reaching
harmonization.
IATA is at the forefront of advocating and pursuing such harmonization and several of the status relevant elements
are summarized in sections 4 and 5.

This section is presenting some of the aviation industry debated elements and the successfully undertaken steps
by entities participating in forums like the (IATA) Engineering and Maintenance Group / Technical Operations Working
Group (EMG/TOWG), Maintenance Programs Industry Group (MPIG), and SAE International. Significant follow-up
steps are needed and expected from the industry to improve and implement the AHM approach promoted by the
forums mentioned above.

4.1. Recognizing Foundations

The AHM consists fundamentally in looping the aircraft health data through the process stages of Sense, Acquire,
Transfer, Analyse and Act (SATAA). The loop starts at the aircraft asset level with the physical sensing of one or
more parameters and eventually ends at the aircraft asset level with the physical execution of a maintenance action.

Each one of the stages is essential by itself and the AHM would be as robust as the weakest link of the SATAA chain.
For each stage there is a primary role assumed by one stakeholder, but the success of that stage delivery will always
depend on (at least one) secondary role fulfilled by another stakeholder (e.g., for S the aircraft configuration must
physically have the sensing capability – thus DAH/OEM is a primary stakeholder – but that capability/part must be
properly operated/maintained - thus Airline is a secondary stakeholder).

The degree of accuracy between the actual real condition/state of the asset and the one perceived or predicted is
at the core of AHM and the agreement/disagreement of the two is reflected in the Uncertainty Matrix.

Figure 5: Uncertainty Matrix of Reality and Perception

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Considering that a Health Indicator is positive when indicating a failure, the resulting errors in diagnosing the
system/component emerge as a False Positive (when the healthy system is perceived as failed) or a False Negative
(when the failed system is perceived as healthy) and would affect the predictive capability of AHM.
Parsing the uncertainty starts at the Sense stage but extends to the Analyse stage thus depending on the sensor as
much as on the predicting algorithm or modelling of the system/component.
The AHM with a robust predictive capability performance will generate a “TRUE” outcome subsequent to a
successfully executed diagnostics (process which corresponds to “perceived”) or prognostics (process which
corresponds to “predicted”).

AHM is relying on data reflecting the set of parameters of interest originating from the aircraft/systems.
The capability of processing the data and run it through algorithms which model the aircraft/systems supports the
predictive performance of AHM bridging from “Normal” to “Remaining Useful Life (RUL)”.

Figure 6: Steps Marking the Life-Cycle

Data generation and collection rates, latency of data availability and securing data quality (through appropriate
procedures for data cleansing and wrangling) are all raising several specific issues which must be addressed in each
one of the steps depicted above.

Some fundamental elements considered in the life cycle suggested process should be:

• There is a certain variability of normality in operation from one asset to the next; establishing the baseline of
normal functioning must be calibrated for the asset and it may also drift with usage in service.

• Any excursion of a parameter from its baseline is a deviation but not all qualify as anomalies; the context of
the deviation must be available for such a qualification to be made; having an anomaly detection system
does not equate with having a diagnostics system.

• The aircraft/systems modelling would identify which anomalies are symptoms representative of an incipient
failure and based on this potential to failure (P to F) the RUL could be predicted.

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 • The predicted RUL depends on the type of terminal event it accounts for (i.e., RUL to avoid damage; RUL for
economic repairability; RUL for loss of function) and is always affected by an uncertainty distribution curve
of its estimation.

The modelling of the aircraft/systems could be derived from engineering applied laws of physics or could be a data-
driven model; each of the two has pros and cons and adoption of one or the other is conditional to specifics of the
business case.

4.2. Developing Capabilities

The adoption of AHM should not be contemplated as a panacea to aircraft maintenance and it would always depend
on the capabilities of the solution proposed. Pondering applicability and effectiveness for maintenance tasks will be
the deciding criteria since measuring loss of performance, deterioration and condition with the aircraft in-service is
sometimes technically challenging and it could be cost prohibitive.

The table below summarizes the general discussion regarding the evolution of AHM capability sophistication and its
expected integration level with the aircraft asset. The table is an adapted partial excerpt from a more detailed matrix
and classification criteria proposed by SAE International (check reference [12] in Appendix 2).

Figure 7: Integration and Capability Milestones

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The accuracy of prediction is time-horizon dependent and only predicting with a reasonable variance would be of
interest to aircraft maintenance practitioners.

When discussing the capability of enacting AHM, a clear understanding and distinction between the diagnostic
phase (as representing a classification problem) and the prognostics/predictive phase (as representing a regression
problem) should be made.
Although any reliable prediction is dependent on the accurate/detailed diagnostics which precedes it, the latter is
not ensuring the existence of AHM in the true acceptance of the concept.

The role of modelling the component/system/aircraft to enable the in-service data-driven informed and credible
prognostics is essential to AHM.

The DAH/OEM models with first principles basis already passed the certification scrutiny and were used to explore
all corners of the aircraft flight envelope but they may not be available to operators.
Although the alternative of a post EIS data-driven model exists for the operators, we should note that data-driven /
data-derived models are merely a representation of their training data set; addressing a novelty in the operation
mode when triggered by airline business priorities (e.g., new flight profiles or flight environments) could be
challenging such a model.

Another important feature of the AHM capability discussion is the level of automation.
This permeates each step of AHM: starting from parameter sensing and data collection, following with the in-flight
real-time transmission to ground (rather than post landing download/transfer/access) continuing with the
processing and maintenance decision support systems which involve AI and ML techniques.

Automation is in fact the condition for viable scalability of AHM; ensuring a reliable, unaltered, and secure data flow
compliant with cybersecurity standards is paramount to the integrity and credibility of the AHM program. Given the
big data which the AHM handles and relies on, extended automation is the only way forward and a complete
automation is very likely to follow.

4.3. Creating Standards

The body of standardization work with AHM significance comprises on one hand provisions focused directly on the
design and integration of its functional elements as well as their subsequent operational use and on the other hand
provisions indirectly touching on features met by it.
In one category the bar is set by MPIG and SAE while the other category benefits from deliveries of RTCA and
EUROCAE.

Given its impact on the aircraft maintenance activity practitioners at the aircraft in-service level, which is where AHM
should make the difference, the synthesis of what is entailed by opening MSG-3 to AHM is mentioned below (check
reference [5] in Appendix 2 for more details).

The traditional MSG-3 logic flow which consists of two levels of analysis of the aircraft systems to select an
applicable and effective maintenance task is enhanced with a third level, entirely optional, to be applied for identifying
an alternate with AHM basis in eligible cases resulted from the previous logic flow level.

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 Figure 8: Levels of Analysis in MSG-3 Logic

To enable the execution of analysis at Level 3 the amount of additional work involves extensive preparatory material
to address AHM linked details, parameters, interfaces, functional description, P to F and software certification
elements. The systems/components part of the aircraft certificated configuration added for AHM purposes generate
themselves the dedicated MSI analysis.
The possible outcomes could lead to a full replacement of the classic task (in the case of the “alternative” selection)
or to a partial replacement of the classic task (in the case of “hybrid” selection) or to the confirmation that no
applicable and effective replacement would be possible on AHM basis.

The above resumes the discussion of what is conducive in the end to the MRBR with its potential enhancement
considering AHM capabilities.

It is important to note that whereby the AHM path may not be found applicable and effective within the MRBR
framework, the stakeholder (DAH) may still develop and offer AHM options outside the MRBR. As part of the AMP the
airline operator may decide to use such options or even pursue to develop them.

The SAE Aerospace Council Technical Committees with AHM related focus (i.e. AISCSHM for aerospace structures,
HM-1 for systems and E-32 for propulsion) released several materials to address standardized metrics,
recommended practices and design requirements linked to the design approach and integration of vehicle health
management systems (see references [7] to [12] in Appendix 2).

Takeaway
• Aviation industry started its evolution towards AHM capability and integration, and is envisaging a
breakthrough in this journey by future pervasive availability of remote data and use of health-ready
components/systems to enable reliable prognosis and prediction of their RUL.

• The industry incremental transition to AHM will be conducive to partial validation of recommended practices
and standards through legacy fleet retrofits before a new clean-sheet design of a complete AHM-ready
aircraft type/model will emerge.

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5. Regulatory Balancing Act
The role of Aviation Regulators in the AHM construct is covering all the typical aviation industry certification,
authorization, and oversight activities which ensure the operation of a safe and reliable civil aviation ecosystem. The
opportunity which Regulators have for adopting an effective risk-based framework and guidance for AHM
implementation is dependent on the timely harmonization between regulatory systems and the industry
stakeholders leading the AHM evolution.

IATA is at the forefront of advocating and pursuing such harmonization and, given its status of non-commercial and
impartial airline industry association, is an active partner for AHM focused proceedings conducted by aviation
regulatory bodies present in the International Maintenance Review Board Policy Board (IMRBPB), ICAO Airworthiness
Panel (AIRP) and Maintenance Management Team (MMT).

This section is presenting some of the regulatory debated elements and highlights considerations which the
Regulators are called to ponder on in a timely manner as part of their AHM focused work with and guidance to
industry entities.

5.1. Addressing Necessity

Integration of AHM within the aircraft maintenance activity must have direct or indirect approval/acceptance by the
competent aviation authorities certifying /authorizing / licensing and overseeing the products, organizations,
personnel, processes and procedures involved.

While the required effective correlation between the typical “Certification / Initial Airworthiness” and “Flight
Standards / Continuing Airworthiness” parts of the regulatory house is not a novelty facing aviation authorities, the
details of a commensurate and risk-based action with AHM focus are sometimes challenging the customary
conventions.
This brings the opportunity of a data driven questioning each time a legacy approach to aircraft maintenance would
be prone to AHM based evolution.
Providing the SATAA core of AHM with some specific additional regulatory boundaries and guidance is an
incremental process for which the successful previous aviation exploit of developing and implementing
ETOPS/EDTO is a valuable procedural precedent.

The AHM construct is encompassing many widely recognized initiatives and functioning programs like: Aircraft
Health Monitoring, Engine Health Monitoring, Structural Health Monitoring, Aircraft Condition Monitoring System,
Engine Condition Monitoring, Rotorcraft Health and Usage Monitoring System.
This legacy of achievements is spanning over a few decades and that should facilitate a robust and timely
differentiation between added value regulatory intervention and ineffective or over-bureaucratic regulatory red tape.

A true AHM implementation involves crediting the right actors for executing decisional mechanisms that support the
aircraft safe operation as effective as the legacy processes and procedures which they constitute an alternative to.

5.2. Solving the AHM Puzzle

There are numerous questions to answer in the context of defining and implementing the AHM path and they concern
both the readiness of the present regulatory construct for the approach in general and options for addressing the
individual solutions in particular.

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It is important to raise the issues and ask the questions to incite the exploratory work with the Regulators even when
acknowledged that a definitive answer would not be practicable at the level of “one size fits all” generic discussion.

The issues are mainly emerging from reviews and analysis of:

• Suitability and readiness of the legacy regulation for certification and continued airworthiness regarding
AHM implications including the performant and secure data acquisition-transmission-analysis-storage.

• Eligibility or non-suitability of the AHM sequence to supplement, provide alternatives to or supersede

partially or completely the aircraft maintenance tasks.

• Consequences/impact of AHM on allocation of initial and continuing airworthiness responsibilities between

the DAH / OEM and the Airline Operator (including Engineering/CAMO and Maintenance/MRO related
activities).

• The architecture of the AHM approach and its on-board / off-board aircraft partitioning.

• Building AHM with resources (i.e., products, services, personnel) residing within or external to aircraft
Technical Operations organizational layers (e.g., Engineering, Maintenance and Supply Chain/Material
Management) and even to customary aviation domain organizational layers.

• Addressing the transfer/portability of the aircraft asset maintenance between an AHM solution and a non-
AHM (legacy) one: both in a temporary scenario requiring continuity/recovery of maintenance operations
(like a short-time unavailability of the AHM solution employed by the operator) and in a permanent transition
(like an aircraft transfer to another airline) from an “AHM operator” to a “non-AHM” one.

Figure 9: Pieces of the Puzzle

Depending on the acceptance of AHM as an “evolutionary” step or viewing it as a “revolutionary” change in aircraft
maintenance, a series of AHM specific or technical aviation broader subjects enter the regulatory focused
discussion spectrum.

Airline/Operator or DAH/OEM discussion is an area of recognition that, while there are independent individual
stakeholder attributes in AHM, the sought outcome can be achieved only by discharging the obligations of both

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categories mentioned; the airline could pursue an AHM approach only to a limited extent if the aircraft
structure/system/component is not designed and manufactured at a certain “AHM ready” level; the transfer of AHM
work execution between the two stakeholders’ camps could take place but regulatory responsibility transfer needs
clarification.

On-Board or Off-Board debate is due to the limited integration by the aircraft platform of the needed data
processing and analysis which leads to the decision on the maintenance action; the typical SATAA is still involving
major ground-based contribution in advance of the maintenance action itself; future technical developments may
shift much of that and regulatory provisions should accommodate all scenarios.

Qualify or Certify discussion acknowledges that, while many of the technical elements supporting the data
collection and analysis are part of aircraft configuration and are certified as such via the aircraft certification process,
the data analysis may be the result of non-aviation traditional resources which lack an aviation certification; ground-
based hardware and software involved in data analysis is “imported” to aviation; more parts of the maintenance
action decision making reside with data analysts who are not (and should not be) necessarily certified/licensed
maintenance personnel.

Aviation Source or COTS Source is linked to the previous theme by recognizing that, while there may be a need of
verifiable status and traceability elements, a form of “qualification” construct should suffice and be accepted by
Regulators; there are clear cases when a risk-based rationale would indicate that a strict aviation “certification”
process is not justified and its replacement with a “qualification” commensurate to the case would deliver the same
safety benefits.

Relying on AHM implementation for airworthiness determinations or maintenance program adjustments requires
regulatory authority acceptance and authorization. The required maintenance credits for the related AHM parts
would be integral to the process. If operators use data for monitoring self-imposed tasks that have no influence on
airworthiness, such express authorization may not be required.

For example, it is envisioned that for US-based operators, the FAA will grant maintenance program AHM
authorization through Ops Spec D302 “Integrated Aircraft Health Management (IAHM) Program”. The provision is
mentioned in the draft Advisory Circular (AC) 43-218 “Operational Authorization of Integrated Aircraft Health
Management Systems”. This publication, once sanctioned by the FAA, may provide a template for other national
regulatory authorities to emulate.

Another example of a recent development with relevance to AHM path is the FAA (AIR-621, AED) released generic
“Issue Paper on Qualification of a Structural Health Monitoring System for Detection of Damage in Structure”
available to interested applicants in connection with AC 25.571-1D.

Examples of regulatory recognition of AHM precursors relevant to the AMP exist also in the form of references to
Aircraft Health Monitoring and Engine Health Monitoring in the Part-M and Part-CAMO issued by EASA.

The regulatory issues linked to AHM should be considered in a timely manner by Civil Aviation Authorities. Such
entities must instigate the establishment of an AHM approach governed by uniform ICAO-originated standards to
eliminate variability and ensure harmonization and consistency among national rulemaking, processes, procedures,
and regulation mechanisms.

While the aviation regulatory provisions are not called upon governing the commercial aspects of the developments
they regulate, and nor should they attempt doing that, there are contextual elements regarding ownership and

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intellectual propriety rights regarding data produced and exchanged for AHM purposes as well as the regarding
algorithms to process that data.

The Civil Aviation Authorities should be aware of such aspects and consider if they are recognized and agreed to in
a way that would not impede on the implementation and accountabilities of AHM stakeholders.

Takeaway
• A risk-based approach should timely drive the rationale to determine if AHM specific regulatory provisions
need to be established. Regulators should be transparent and closely engage with Aviation Industry
stakeholders to validate the need and to draft such provisions, as applicable.

• Regulatory guidance material is needed by AHM actors to drive their effort in a harmonized and level playing
field across all aviation jurisdictions. Regulators should closely cooperate with Aviation Industry
stakeholders when drafting such guidance.

• The development pace of the AHM path by Industry should instil a sense of urgency for Regulators in
addressing the above.

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6. AHM Roadmap
The AHM concept surpassed the phase of its brainstorming beginnings and, without denying the “in-flux” status for
some of its features, is reaching a maturity level justifying the dynamics of implementation phase.
This section presents several considerations relevant to mapping the implementation road of AHM.

6.1. Starting Points

The aviation industry has enacted in the last decades several successful aircraft structure and systems monitoring
programs which are considered, in a significant measure, precursors of the integrated AHM pursued today.

Monitoring of physical parameters like pressures, temperatures, vibration, mechanical loads, electric loads/currents
in a time series data flow which covers transitory as well as stabilized operation of aircraft systems/components is
enabling operators to estimate degradation or detect a fault before a functional failure would generate operational
disruptions to require unscheduled maintenance corrective action.

The main purpose of such monitoring programs was to enable a system of notifications and alerts which were
tailored for triggering actions to improve the operator dispatch reliability or optimize the cost of maintenance and
repairs. By far and large they were not used as the sole source to determine aircraft system condition for safe
operation. Such airworthiness determination was not permitted in the absence of another accepted practice use as
well (e.g., visual check or functional check).
There is a limited number of one-off cases when aircraft health monitoring techniques were given the maintenance
credit required to alter/replace a traditional industry-accepted practice.

Nevertheless, the sizeable experience gathered by exercising the SATAA specific steps in the type of programs
mentioned above (see also section 5) is of significant transferable value to the integrated AHM model.

6.2. Validation Gates and Criteria

The validation gates and criteria must be set considering the requirements for design approval (residing with the
DAH) and the operational authorization (residing with the Airline/Operator).

In meeting both categories of requirements it should be made clear that the definition of the set of requirements in
each category should be tailored to the content and complexity of the AHM implementation envisaged. A typical
example of such tailoring would be the use for AHM purpose of data and information identical in
origin(source)/form/format with the one already employed in the control and oversight (including the FDE) of the
aircraft system/equipment; this was already covered by certification of the aircraft design and, thus, additional
design approval expectation based on its off-aircraft use for AHM could be questioned by the applicant. Obviously
that any AHM dedicated system/component which is part of the aircraft certificated configuration will be submitted
to the aircraft certification process specifics to the extent applicable to the said AHM dedicated system/component.

The importance of an incremental progress towards establishing the AHM cannot be underestimated.
This incremental approach is particularly important for the operational authorization as well as the AHM induction of
“legacy aircraft types”. A clean-sheet design aircraft would give the opportunity of integrating the AHM readiness in
the initially certified configuration.

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6.3. Pursuing Implementation
The considerations presented in this section sketch a roadmap of what a successful implementation of AHM in the
airline industry should entail in the short, medium, and long-time horizon.

Figure 10: Steps to Take for AHM Implementation

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While each timing stage comprises identifiable prerequisites, which are a must in order to access the milestone
deliveries, quantifying the timeline of each one of the three time-horizons is inherently a challenging forecast.

Such challenge is additionally compounded by the context in which the aviation industry in general, and the airline
world in particular, started the 2020s decade with two years of unprecedented crisis during which existential
priorities took their toll on AHM envisaged steps by each stakeholder category and individual entity.

The good news would be that completing the short-term prerequisites is almost accomplished and checking the
respective stage milestone achievements was already started by AHM early adopters in each stakeholder category.

It is worth reminding some successful use cases and completed actions focused on implementation of AHM
elements:

• Airline identification and prediction for aircraft defect management performed in-house or with OEM support
(e.g. bleed air valves, flap skew sensors, filter condition monitoring, hydraulic level monitoring)

• AMOC issued to AD provisions on the basis of AHM procedures, with appropriate end to end definition
(including constraints, mitigating measures and analysis algorithm) to replace fixed periodicity requirements
for SDI maintenance action (e.g., engine HPT borescope inspection, pressure bulkhead NDT)

• Proposal of revised PPH to support the IP-180 implementation in the aircraft type MRBR

While AHM is mainly contemplated as an alternative at this time, its addressing could take place on applicability basis
at operator level via customized solutions or at the fleet-wide global level via appropriate DAH involvement; with the
former having the potential of a more agile time-response to adoption of AHM, the latter will always be a guarantee
for the AHM adoption coverage.

Takeaway
• Airlines have a significant experience with AHM type of actions scoped to improve their individual aircraft
operational reliability or to optimize the cost of individual aircraft maintenance and repairs.

• Incremental steps in adopting AHM should be timely progressed to the benefit of all stakeholders before the
advent of the next clean-sheet design aircraft.

• The active sharing of experience and examples between AHM stakeholders should be incessantly pursued
in all eligible fora with the view of a timely progress in this field benefitting Industry and Regulators alike.

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7. Conclusions
A significant body of knowledge and experience emerged from years of aircraft health and trend monitoring used to
enhance aircraft dispatch reliability (DR) rates. The span of successful use cases, encompassing aircraft systems
(including propulsion systems) and aircraft structure, constitutes a solid basis and strong motivator for developing
the AHM path. This would be an alternative applicable to many of the aircraft maintenance tasks and lead to a change
in the typical form and significance of execution thresholds and periodicity.

Introduction of the AHM option alternative, as an opportunity and not as an obligation, is needed to attain the scale
of economics potentially offered by the concept of aircraft “Maintenance of Tomorrow” in which true aircraft
condition-based maintenance (CBM) would rely on the implementation of both predictive and prescriptive analytics
capabilities.

There are aircraft certification aspects and continued airworthiness elements which must be addressed to fully
realize the attainable benefits of AHM. They require a phased and simultaneous timely evolution of the deliverables
by aviation industry and regulatory entities alike. This can be achieved with a prompt recognition of and commitment
to a realistic sense of urgency by all stakeholders involved in the AHM related work.

Providing an AHM option in future MSG-3 methodology will compel the timely motivation for new policies, derivative
procedures, and technology benefiting all air transport industry stakeholders. This may precipitate a methodological
upgrade establishing the basis of a future MSG-4 task development philosophy construct.

Using AHM data and analysis capabilities to define alternative means to accomplish a “classic” preventive
maintenance task is the next practicable opportunity to further enhance aircraft availability. The approach would also
require an appropriately revised set of criteria in the traditional area of No Fault Found (NFF) categorization used by
maintenance providers, since an operator may employ AHM prediction to remove aircraft components prior to their
in-service failure.

The AHM approach impact on the technical operation’s commercial practices and supply chains must be considered
as well. Such considerations will potentially reshape the terms of performance agreements both at the product (e.g.,
aircraft, engines) and component levels, and also trigger a reconsideration of how spare parts inventories are
defined and maintained to support aircraft fleet operations.

Benefiting from automation prone sequences of AHM, including prognostics’ active reliance on artificial intelligence
(AI) and machine learning (ML) techniques coupled with digital twinning of aircraft assets, constitute a priority for
viably achieving AHM scalability. The necessary level of digital transformation inherently requires addressing the
data ownership and cybersecurity concerns; they are altogether topics of a different important discussion.

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Appendix 1 – Abbreviations
Abbreviation Source Terminology
AD Airworthiness Directive
AED Aircraft Evaluation Division (FAA)
AHM Aircraft Health Management, Aircraft Health Monitoring
AI Artificial Intelligence
AIR Aircraft Certification Service (FAA)
AIRP Airworthiness Panel (ICAO)
AISCSHM Aerospace Industry Steering Committee on Structural Health Monitoring
AMOC Alternative Means Of Compliance
AMP Aircraft Maintenance Program
CAMO Continuing Airworthiness Management Organization
CBM Condition Based Maintenance
CDL Configuration Deviation List
CM Condition Monitoring
COTS Commercial (available) Off-The-Shelf
DAH Design Approval Holder
DR Dispatch Reliability
EASA European Union Aviation Safety Agency
EDTO Extended Diversion Time Operations
EIS Entry Into Service
EMG Engineering and Maintenance Group (IATA; it became TOWG as of 2021)
ETOPS Extended Range Twin-Engine Operations
FAA Federal Aviation Administration
FDE Flight-Deck Effect
FEC Failure Effect Category
FRACAS Failure Reporting, Analysis and Corrective Action System
FTOPS Flight and Technical Operations (IATA)
HPT High Pressure Turbine
HT Hard Time
IATA International Air Transport Association
IAHM Integrated Aircraft Health Monitoring
ICAO International Civil Aviation Organization
IMRBPB International Maintenance Review Board Policy Board
IP Issue Paper
KPI Key Performance Indicator
LLP Life Limited Part

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 MEL Minimum Equipment List
ML Machine Learning
MMT Maintenance Management Team
MPIG Maintenance Program Industry Group
MRBR Maintenance Review Board Report
MREPS Maintenance Reports
MRO Maintenance, Repair and Overhaul
MSI Maintenance Significant Item
MSG Maintenance Steering Group
NDT Non Destructive Test
NFF No Fault Found
OC On Condition
OEM Original Equipment Manufacturer
PIREPS Pilot Reports
PPH Policy and Procedures Handbook
P to F Potential to Failure
RUL Remaining Useful Life
SATAA Sense, Acquire, Transfer, Analyze and Act
SDI Special Detailed Inspection
SF Science Fiction
TC Type Certificate
TOWG Technical Operations Working Group (IATA; former EMG)
UBL Usage-Based Lifing

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Appendix 2 - Suggested Readings

[1] “Aircraft Operational Availability” – 1st Edition, 2018 – International Air Transport Association (IATA)

[2] Proceedings of “5th Paperless Aircraft Operations and RFID Conference” – 2018 – IATA

[3] Proceedings of “14th Maintenance Cost Conference” – 2018 – IATA

[4] “ATA MSG-3 Operator/Manufacturer Scheduled Maintenance Vol 1 – Fixed Wing Aircraft” – Revision 2018.1-
Airlines for America

[5] “IP180 - Aircraft Health Monitoring Integration in MSG-3” – 2018 – International MRB Policy Board

[6] “AC 43-218 - Operational Authorization of Integrated Aircraft Health Management Systems” – FAA Draft for
Public Comments – 2019

[7] “ARP6803 - IVHM Concepts, Technology and Implementation Overview” – 2016 – SAE International

[8] “ARP5987 - A Process for Utilizing Aerospace Propulsion Health Management Systems for Maintenance
Credit” – 2018 - SAE International

[9] “ARP6461 - Guidelines for Implementation of Structural Health Monitoring on Fixed Wing Aircraft” – Rev A -
2021 – SAE International

[10] “ARP6407 – IVHM Design Guidelines” – 2019 - SAE International

[11] “ARP6883 – Guidelines for Writing IVHM Requirements for Aerospace Systems” – 2019 - SAE International

[12] “JA6268 – Design & Run-Time Information Exchange for Health-Ready Components” – 2018 – SAE
International

[13] “Aerospace Predictive Maintenance: Fundamental Concepts” – Charles E. Dibsdale – SAE International 2020

[14] “Reliability-centred Maintenance” – Second Edition, 1997 – John Moubray

[15] “Aeronautical Design Standard Handbook ADS-79E-HDBK - Condition Based Maintenance for US Army
Aircraft” – Dec 2015

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Appendix 3 - Acknowledgements
This White Paper presents elements highlighted during the IATA Flight and Technical Operations (FTOPS) team’s
engagement on the AHM subject since late 2015.

While these considerations emerged from the FTOPS perspective on the presented topics, they would have not
been possible without the multiple meetings and discussions on the subject that took place in bilateral or multilateral
settings, primarily with Airlines, Aircraft OEMs, Engine OEMs and Civil Aviation Authorities, also involving other
stakeholders throughout the aviation industry.

Enumerating the individual partners of dialogue engaged by IATA on the AHM subject would generate a long and
likely incomplete list.

A sincere thank you is addressed to all participants in the following forums, with high appreciation for the open
debates, shared insights and productive work made possible since 2015:

• IATA Technical Operations Working Group / Engineering and Maintenance Group;

• Maintenance Programs Industry Group;
• SAE Committees for:
o Aerospace Propulsion Systems Health Management,
o Integrated Vehicle Health Management,
o Aerospace Industry Steering on Structural Health;
• International MRB Policy Board;
• Maintenance Management Team, and
• ICAO Airworthiness Panel

This White Paper was authored by:

Dragos Budeanu, IATA – budeanud@iata.org

Chris Markou, IATA – markouc@iata.org

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