Cmr

Development of Certification Maintenance Requirements
and Instructions for Continuing Airworthiness
Melbourne – May 2013
Design and Manufacturing
Seminar

Development of Instructions for Continuing Airworthiness
 A process for ICA creation performed by the OEMs as a part of Type
Certification (FAR / CS 23/25/27/29 – 1529, MSG – 1/2/3).
 Regulatory and engineering principles used for creation of
Certification Maintenance Requirements.
 A process used for unique MEL items and Permissible
Unserviceability assessment and approval.
 MSG 3 approach.
 A process used for in house versus OEM maintenance data creation
and approval.
 Processes involved in TBO and maintenance task / schedule
frequency escalations and one-off escalations / overruns.

 Instructions for Continuing Airworthiness (ICA) are developed
during the Type Certification process of an aircraft in accordance
with relevant certification standards. ICA are usually provided
through MM, SRM, SBs, SLs, MPD, AFM, MEL, etc.
 Instructions for Continuing Airworthiness (ICA) are also
developed during the Supplemental Type Certification process
in accordance with relevant certification standards. In this case
ICA are usually provided through Supplements to MM, SRM,
MPD, AFM, MEL, etc. STC Holders could also publish SBs, SLs
related to their STCs.

 ICA are developed in accordance with relevant certification
standards. CASA accepts EASA CSs and FAA FARs as
acceptable relevant standards for Normal and Transport
Category Aircraft / Rotorcraft (ref. CASR Part 23/25/27/29)
 ICA are developed in accordance with relevant regulations
provided in the FAR / CS 23/25/27/29 section 1529 and
applicable appendices. Section 1529 and applicable appendices
set the basic requirements for ICA.

FAR PART 25—AIRWORTHINESS STANDARDS:
TRANSPORT CATEGORY AIRPLANES
Subpart G—Operating Limitations and Information
§ 25.1529 Instructions for Continued Airworthiness.
The applicant must prepare Instructions for Continued Airworthiness
in accordance with appendix H to this part that are acceptable to the Administrator.
The instructions may be incomplete at type certification if a program exists to
ensure their completion prior to delivery of the first airplane or issuance of a
standard certificate of airworthiness, whichever occurs later.
[Amdt. 25-54, 45 FR 60173, Sept. 11, 1980]

 EASA approach is almost identical to FAA
 Certification Specifications (CS) section 1529 deals
with ICA.
 For example: EASA CS 29 Certification Specifications
For Large Rotorcraft - OPERATING LIMITATIONS
Section 29.1529 states:
Instructions for continued airworthiness in accordance
with Appendix A to CS–29 must be prepared.

 NAA Policy Statements must be considered when ICA are developed.
 Regulation of the Configuration, Maintenance, and Procedures (CMP)
 Process for Developing SFAR 88-related Instructions for Maintenance and Inspection of
Fuel Tank Systems
 Some of other NAA documents may need to be considered:
 AC 25.1529-1A - INSTRUCTIONS FOR CONTINUED AIRWORTHINESS OF
STRUCTURAL REPAIRS ON TRANSPORT AIRPLANES
 AC 120-93 DAMAGE TOLERANCE INSPECTIONS FOR REPAIRS AND ALTERATIONS
 AC25.1581-1 - Airplane Flight Manual
 AC120-16F - Air Carrier Maintenance Programs
 AC120-42B - Extended Operations (ETOPS and Polar Operations)
 AC121-16 - Maintenance Certification Procedures
 AC121-16 - Maintenance Certification Procedures
 AC120-76B - Guidelines for the Certification, Airworthiness, and Operational Use of
Electronic Flight Bags
 AC 120-98A - Operator Information for Incorporating Fuel Tank Flammability Reduction
Requirements into a Maintenance or Inspection Program
 AC121-22C - Maintenance Review Boards, Maintenance Type Boards, and OEM/TCH
Recommended Maintenance Procedures

Some of applicable CASA regulations may need to be considered when
ICA are developed.
 Civil Aviation Order 20.4 (PROVISION AND USE OF OXYGEN AND PROTECTIVE
BREATHING EQUIPMENT)
 Civil Aviation Order 20.18 (Aircraft equipment — basic operational requirements)
 Civil Aviation Order 20.11 (Emergency and life saving equipment and passenger
control in emergencies)
 CASR 1998 Part 90 (Additional Airworthiness Requirements )
 CASR 1998 Part 90 Manual of Standards (MOS)
 CASA AC 90-1(0) (EXCLUSIONS AGAINST PROVISIONS IN CASR PART 90)
 AAC 1-116 Approved Single Engine Turbine Powered Aeroplane (ASETPA)

Lesson 7
Certification Maintenance Requirements (CMR) Principles
A CMR is a required scheduled maintenance task established during
the design certification of the airplane systems as an operating limitation
of the type certificate (TC) or supplemental type certificate (STC).
A CMR usually results from a formal, numerical analysis conducted
to show compliance with the requirements applicable to catastrophic
and hazardous failure conditions.
Compliance may also result from a qualitative, engineering judgment-based
analysis.

CMR Principles
1
• The CMRs are required tasks, and associated intervals, developed to
achieve compliance with § 25.1309.
2
• A CMR is intended to detect safety-significant latent failures that would, in
combination with one or more other specific failures or events, result in a
hazardous or catastrophic failure condition.
3
• A CMR can also be used to establish a required task to detect an
impending wear-out of an item whose failure is associated with a
hazardous or catastrophic failure condition.
4
• Further reading FAA AC 25-19A - Certification Maintenance Requirements

CMR Principles
The CMRs verify that a certain failure has or has not occurred, indicate that
repairs are necessary if the item has failed, or identify the need to inspect
for impending failures (e.g., heavy wear or leakage).
In other words, there are two main drivers for CMRs
System Safety Analysis (1309
Analysis).
Impending wear-out of an item
that could lead to a hazardous or
catastrophic
failure condition.
In both cases latent failures must be considered in the analysis.

CMR Principles
The CMRs analysis is different from the MSG-3 analysis and although both
types of analysis may produce equivalent maintenance tasks and intervals,
it is not always appropriate to substitute a CMR with an MSG-3 task.
The CMRs are to be developed and managed separately from any
structural inspections programs that are developed to meet the inspection
requirements for damage tolerance, as required by§ 25.571, 25.1529, and
Appendix H25.4 (Airworthiness Limitations section).
Scheduled Maintenance Tasks Developments

Lesson 7
CMR Principles
System Safety Analysis or System Safety Assessment (SSA) (1309 Analysis).
Part 23/25/27/29.1309 Equipment, systems, and installations - General and main requirements
The requirements of this section, are applicable, in addition to specific design requirements of
part 23/25/27/29, to any equipment or system as installed in the airplane. This section is a
regulation of general requirements and does not supersede any requirements contained in
another section of part 23/25/27/29.

Lesson 7
CMR Principles
System Safety Analysis or System Safety Assessment (SSA) (1309 Analysis).
Part 23/25/27/29.1309 Equipment, systems, and installations - General and main requirements
The airplane equipment and systems must be designed and installed so that any equipment
and system does not adversely affect the safety of the airplane or its occupants, or the proper
functioning.
The airplane systems and associated components considered separately and in relation to
other systems, must be designed and installed so that each catastrophic failure condition is
extremely improbable and does not result from a single failure, each hazardous failure
condition is extremely remote and each major failure condition is remote.

CMR Principles
SSA (1309 Analysis)
The applicant is responsible for identifying and classifying each failure condition
and choosing the methods for safety assessment. The applicant should then obtain
early concurrence from NAA on the identification of failure conditions, their
classifications, and the choice of an acceptable means of compliance.

CMR Principles
Documentation and Handling of CMRs.
 The CMR data location should be referenced in the type certificate data
sheet (TCDS).
 The latest version of the CMR document should be controlled by a log of
pages approved by the NAA of the TC / STC holder or CASA.
 CMRs are functionally equal to airworthiness limitations. An acceptable
means is to include CMRs in the Airworthiness Limitations section of the
airplane maintenance manual.
 Any post-certification changes to CMRs should be reviewed by the same
entities that participated in the initial CMR selection and approval and must
be approved by the NAA of the TC / STC holder or CASA.

MEL / PU Items assessment / approval
MEL Assessment
An operator’s MEL must take into account
The aircraft configuration Type of operation and operating environment
An MEL condition or item is normally not less restrictive than the corresponding MMEL
Except where regulatory requirements
permit.
FAA AD 74-08-09R3
MEL is derived from the Master Minimum Equipment List (MMEL)
MMEL is developed by the TC Holder and its
NAA
MMEL is approved by the NAA of the TC
Holder

Items not covered in an MMEL - assessment / approval process
The following methods of justification can be used for those items not covered in an MMEL.
Optional Equipment - When optional equipment is fitted (over and above the
aircraft type certification equipment).
Redundant Items - If the purpose or function of a component or system can be
carried out by some other item(s) of equipment.
Passenger Convenience Items - Item(s) such as galley equipment, in flight
entertainment, overhead reading lamps etc which are not addressed in the MMEL.
Any Other Items will require Qualitative and / or Quantitative Safety Analysis.

Items not covered in an MMEL - assessment / approval process
Other
• Any Other Items
And/Or
• Qualitative Safety Analysis.
And/Or
• Quantitative Safety Analysis.
• The unserviceability may be accepted.

 Qualitative Safety Analysis
These analytical processes assess system and aircraft safety in a subjective, non-
numerical manner, based on experienced engineering judgement.
Consider the impact that the proposed inoperative item has on
all other aspects of the aircraft’s operation.
The impact on crew workload and operating environment.
The impact of invoking multiple PU or MEL items.
The impact of any other existing defects.
The complexity of maintenance and/or operational procedures.

Lesson 8
 Quantitative Safety Analysis
If the operation of aircraft with an item inoperative cannot be justified by the
previous means or criteria, then a safety analysis must be carried out. This
involves a quantitative analysis of the likely risk of the worst effects that could
result from additional failures, events and/or environmental conditions
occurring during a flight, with the particular inoperative item in question.
 Assessment techniques / analysis that should be employed in this case are
the same or similar to those used for SSA (1309 Analysis).

MAINTENANCE STEERING GROUP (MSG)
The development of maintenance programs
dates to FAA Aeronautical Bulletin 7E of May
15, 1930. In the past, each air carrier
proposed its own unique program.
Today, the process is a collaborative effort in which the
associated regulatory authorities, and industry work
together to develop the minimum scheduled
maintenance/inspection requirements for new and
derivative aircraft, aircraft engines, and propellers.
In 1968, the Maintenance Steering Group - 1st Task Force
(MSG-1) developed maintenance requirements decision
and analysis logic. MSG-1 introduced three broad
processes to classify the scheduled maintenance
requirements.
Hard Time (HT) On-Condition (OC)
Condition
Monitoring (CM)

Lesson 8

 The MRB process should be used for:
(1) Transport category airplanes designed to carry 10 or more people or having a
maximum weight of 33,000 lb or more,
(2) Transport category “A” helicopters, or
(3) Powered-lift aircraft.
 MRB may also be used for any aircraft by choice of the OEM/TCH.
 An MRBR contains the minimum scheduled tasking/interval requirements for a
particular aircraft and on-wing engine maintenance programs.
 MRBR should undergo an annual review by the OEM/TCH, Industry Steering
Committee (ISC), and the Maintenance Review Board (MRB) chairperson.

Scheduled maintenance, as such, cannot correct deficiencies in the inherent
safety and reliability levels of the aircraft. The scheduled maintenance can only
prevent deterioration of such inherent levels. If the inherent levels are found to
be unsatisfactory, design modification is necessary to obtain improvement.
The objectives of efficient aircraft scheduled
maintenance
To ensure
realization of the
inherent safety and
reliability levels of
the aircraft.
To restore safety
and reliability to
their inherent
levels when
deterioration has
occurred.
To obtain the
information
necessary for
design
improvement of
those items whose
inherent reliability
proves inadequate.
To accomplish
these goals at a
minimum total
cost, including
maintenance costs
and the costs of
resulting failures.

Lesson 8
Maintenance data creation and approval
 Maintenance data can also be developed outside the TC / STC process of an
aircraft. This is usually done by an operator or an AMO or a CASR Part 21M
Authorised Person in order:
 to facilitate more efficient work practices, or
 to address the unavailability of materials, parts or tools required by already
approved maintenance data and facilitate their substitution, or
 there is no existing maintenance data covering the particular maintenance, or
 to address a repair or modification of the aircraft / aeronautical product made
under CASR Part 21M approval.
 A development of alternative maintenance data and practices in order to cut
maintenance costs is usually not an acceptable reason to redevelop
maintenance data. A process used by the operators or AMOs or a CASR Part
21M Authorised Persons to develop maintenance data is essentially identical to
the process used by the TC / STC holders.

 Civil Aviation Regulations 1988
CAR 2A Approved maintenance data
(2) For the purposes of paragraph (1) (a), the maintenance data are:
(e) any other instructions, approved by CASA under subregulation (4) for the
purposes of this paragraph, relating to how maintenance on aircraft, aircraft
components or aircraft materials is to be carried out.
(4) CASA may, for the purposes of paragraph (2) (e), approve instructions relating to
how maintenance on aircraft, aircraft components or aircraft material is to be carried
out.
Only CASA can approve newly created maintenance data that are not
listed in or not created by persons identified in CAR 2A (2).

Division 7 Exemptions from, and variations of, requirements
CAR 42ZS Granting of exemptions and approval of variations
(1) CASA or an authorised person must grant the exemption or approve the
variation if CASA or the authorised person is satisfied that granting the exemption or
approving the variation would not adversely affect the safety of air navigation.
(2) If CASA or the authorised person grants the exemption, or approves the
variation, the grant or approval may be made or given subject to such conditions as
CASA or the authorised person thinks necessary in the interests of the safety of air
navigation.

The process used for
justifying exemptions from or
amending (making variation)
to maintenance data is the
same as the process used
for creating maintenance
data (as a part of ICA)
during the TC process.
The justification must
demonstrate a sound
understanding of
certification requirements
for the aircraft, their relation
to and impact on the
affected maintenance data.
An assessment of the
impact of the exemption or
variation on the certification
requirements of the aircraft
should be performed.
The outcome of the
assessment should identify
necessary conditions for the
approval.
Approval can be granted
by CASA or a CAR 42ZS
authorised person.
 CAR 42ZS provides an opportunity to approve variation to or exemptions from
approved maintenance data.

Lesson 14
System of Maintenance
TBO and maintenance schedule frequency escalations and one-off overruns
Basic principles:
Source: CAAP 42M-1(0) Approved System of Maintenance for Class A Aircraft
 Airworthiness limitations are mandatory replacement times, structural inspection
intervals, and related structural inspection tasks. Airworthiness limitations are excluded
from any escalation process by the operator.
 Critical Design Configuration Control Limitations (CDCCL) - An Airworthiness
Limitation that preserves a critical feature of the aircraft needed for the Flammability
Reduction Means (FRM) or Ignition Mitigation Means (IMM) to perform their intended
function and prevent the occurrence of an unsafe condition.

Lesson 14
Basic principles:
 The maintenance task frequencies included in the initial SOM generally
reflect the recommendations (MRB Report, MPD, Chapter 5 of the
Maintenance Manual, etc.) issued by the aircraft certification authority or the
aircraft TC holder. Frequencies may be adjusted later in accordance with the
operator’s reliability program or as a result of the operator’s monitoring of the
effectiveness of the SOM and IAW previously approved procedures for
adjustment.

Lesson 14
Basic principles:
 Task intervals of CMRs, CDCCL, ALIs and any regulatory requirements are
not permitted to be varied without prior approval of CASA or an authorised
person.
 TC holders' recommendations or inspection program revisions do not, by
themselves, permit change to an SoM. Any change to an SoM must be justified
by the registered operator and approved by CASA or an authorised person.

Some of the engineering, maintenance and reliability considerations that must be
taken into account when preparing a justification for maintenance schedule frequency
escalations and one-off overruns are provided in FAA AC 121-22C Chapter 12 and Appendix
2. A summary of these considerations is provided below.
 Evaluation of in-service data, both scheduled and unscheduled maintenance findings
related to the intent of the Maintenance Steering Group (MSG) task.
 Weighing of the relevance and significance of findings.
 Ensuring of data quality, integrity, completeness, and clarity.
 Consideration of each task individually.
 A review of original design and engineering specifications, as required.

Lesson 14
Some of the engineering, maintenance and reliability considerations
 review of all information related to continuing airworthiness (e.g., Airworthiness
Directives, Service Bulletins (SB), in-service reports/letters, and
modifications/repairs).
 Basing MRBR task evolution/optimization or deletion/addition on worldwide
representative samples that span the operating environment and age groupings of
the aircraft.
 Application of statistical models to support the evolution/optimization or
deletion/addition exercise.
 Measurement of task effectiveness.

Lesson 14
The same FAA AC 121-22C in Chapter 12 also provides the following statement:
If this chapter is not followed, the OEM/TCH will be limited to no more than 10
percent escalation with approved data. Further escalation is not allowed until a
task is repeated and sufficient data are available.
Many OEM/TCH use this provision to incorporate one-off 10% extension option in
their ICA in order to allow for maintenance and operational scheduling flexibility.

Lesson 14
 The engineering, maintenance and reliability considerations and
principles that must be taken into account when preparing a justification for
maintenance schedule frequency escalations and one-off overruns for Class B
aircraft are essentially the same as those previously presented for Class A
aircraft.
EASA policy on escalations is provided in IP 44 Evolution-Optimization Guidelines
and Work Instruction “Maintenance Review Board team WI.MRB.00002-001” and
it is essentially the same as FAA approach.

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