Volume 3 General technical administration
chapter 40 APPROVE A MAINTENANCE RELIABILITY
PROGRAM FOR 121/135
Section 1 Safety Assurance System: Approving Part
135 Reliability Programs
3-3781 REPORTING SYSTEM(S), SAFETY ASSURANCE SYSTEM (SAS) AUTOMATION.
This section is related to SAS Element 1.1.4, (AW) Reliability Program.
3-3782 OBJECTIVE. This chapter provides guidance for approving Title
14 of the Code of Federal Regulations (14 CFR) part
135 reliability programs and providing technical assistance to the certificate
A. Performing the Task. This task is performed by the Airworthiness
aviation safety inspectors (ASI) and needs to be closely coordinated between
both the maintenance and avionics specialties. Approving a reliability program
is one of the most complex duties of an Airworthiness ASI and special attention
must be given to every element of the proposed program.
B. Guidance Documents. Reliability programs establish the time
limitations or standards for determining intervals between overhauls, inspections,
and checks of airframes, engines, propellers, appliances, and emergency equipment.
Guidance on the program elements is listed in the current edition of Advisory
120-17, Maintenance Control by Reliability Methods; Maintenance Steering
Group—2nd Task Force (MSG-2), the Airline/Manufacturer Maintenance Program Planning
Document, and the Maintenance Steering Group—3rd Task Force (MSG-3); and/or
maintenance tasks. It is important that the ASI explains all of the program
requirements to the operator/applicant.
3-3784 PRIMARY MAINTENANCE PROCESSES.
A. MSG-2, Primary Maintenance Processes Definitions.
1) Hard-Time (HT), Overhaul Time Limit, or Part Life Limit. This
is a preventive primary maintenance process that requires a system, component,
or appliance to be either overhauled periodically (time limits) or removed from
service (life limit). Time limits may only be adjusted based on operating experience
or tests, in accordance with procedures in the operator’s approved reliability
2) On-Condition (OC). This is also a preventive primary maintenance
process that requires that a system, component, or appliance be inspected periodically
or checked against some appropriate physical standard to determine if it can
continue in service. The standard ensures that the unit is removed from service
before failure during normal operation. These standards may be adjusted based
on operating experience or tests, as appropriate, in accordance with an air
carrier’s approved reliability program or maintenance manual.
3) Condition Monitoring (CM). MSG-2 introduced CM. This process
is for systems, components, or appliances 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. The user must
control the reliability of systems or equipment based on knowledge gained by
the analysis of failures or other indications of deteriorations.
B. MSG-3, Maintenance Task Definitions.
1) Lubrication/Servicing (LU/SV). Any act of lubrication or servicing
for the purpose of maintaining inherent design capabilities. The replenishment
of the consumable must reduce the rate of functional deterioration.
2) Operational/Visual Check (OP/VC). Hidden functional failure
categories. An operational check is a task to determine if an item is fulfilling
its intended purpose. The check does not require quantitative tolerances, but
is a failure-finding task. A visual check is an observation to determine that
an item is fulfilling its intended purpose and does not require quantitative
tolerances. This is a failure-finding task that ensures an adequate availability
of the hidden function to reduce the risk of a multiple safety failures, and
to avoid economic effects of multiple failures and be cost‑effective.
3) Inspection/Functional Check (IN/FC), All Categories.
1. Detailed Inspection (DI). An intensive visual examination of a specific
structural area, system, installation, or assembly to detect damage, failure,
or irregularity. Available lighting is normally supplemented with a direct source
of good lighting at an intensity deemed appropriate by the ASI. Inspection aids
such as mirrors or magnifying lenses may be used. Surface cleaning and elaborate
access procedures may be required.
2. General Visual Inspection (GVI)(Surveillance). A visual examination
of an interior or exterior area, installation, or assembly to detect obvious
damage, failure, or irregularity. This level of inspection is made under normally
available lighting conditions, such as daylight, hangar lighting, flashlight,
or drop-light, and may require removal or opening of access panels or doors.
Stands, ladders, or platforms may be required to gain proximity to the area
3. Special Detailed Inspection (SDI). An intensive examination of a
specific item(s), installation, or assembly to detect damage, failure, or irregularity.
The examination is likely to make extensive use of specialized inspection techniques
and/or equipment. Intricate cleaning and substantial access or disassembly procedures
may be required.
b) Functional Check. A quantitative check to determine if one or more functions
of an item perform within specified limits. Reduced resistance to failure must
be detectable, and there must be a reasonably consistent interval between a
deterioration condition and functional failure.
4) Restoration (RS), All Categories. That work necessary to return
an item to a specific standard. Since RS may vary from cleaning or replacement
of single parts to a complete overhaul, the scope of each assigned RS task has
to be specified.
5) Discard, All Categories. The removal from service of an item
at a specified life limit. Discard tasks are normally applied to so-called single-celled
parts such as cartridges, canisters, cylinders, engine disks, or safe-life structural
3-3785 NEW AIRCRAFT. The lack of real experience with new aircraft
requires a careful, detailed study of their characteristics to determine which
components or systems would probably benefit from scheduled maintenance (HT
A. Initial Maintenance Programs. Special teams of industry and
Federal Aviation Administration (FAA) personnel developed the initial maintenance
programs for the B-747, DC-10, and L-1011 aircraft. Using the MSG-2 decision
analysis, these teams identified potential maintenance tasks and determined
which of these tasks must be performed to ensure operating safety or determine
essential hidden function protection.
B. Additional Maintenance Process. The remaining tasks were evaluated
to determine if they were economically useful. This evaluation provided a systematic
review of the aircraft design so that, in the absence of real experience, the
best maintenance process could be employed for each component or system. The
B-747, DC-10, and L-1011 aircraft operating experience confirmed the effectiveness
of these procedures.
3-3786 DATA COLLECTION SYSTEM. Typical sources of data collection
include the following:
· Unscheduled removals,
· Confirmed failures,
· Pilot reports,
· Sampling inspections;
· Shop findings,
· Functional checks,
· Bench checks,
· Service Difficulty Reports (SDR),
· Mechanical Interruption Summaries (MIS), and
· Other sources the operator considers appropriate.
A. Availability of Additional Information. Not all of these sources
may be covered in each and every program. However, the availability of additional
information provides the operator with an invaluable source of operating history
for determining success or failure in meeting program goals.
B. Accuracy. Data collected must be accurate and factual to support
a high degree of confidence for any derived conclusion. It must be obtained
from units functioning under operational conditions and must relate directly
to the established levels of performance.
3-3787 DATA ANALYSIS AND THE APPLICATION TO MAINTENANCE CONTROLS.
The objective of data analysis is to recognize the need for corrective action,
establish what corrective action is needed, and determine the effectiveness
of that action.
A. Data Analysis Systems. Data analysis is the process of evaluating
mechanical performance data to identify characteristics indicating a need for
program adjustment, revising maintenance practices, improving (modifying) hardware,
etc. The first step in analysis is to compare or measure data against acceptable
performance levels. The standard may be a running average, tabulation of removal
rates for past periods, graphs, charts, or any other means of depicting a “norm.”
B. Programs Incorporating Statistical Performance Standards (“Alert”
1) Reliability programs developed under
and earlier criteria use parameters for reliability analysis such
as delays per 100 departures for an aircraft system. They incorporate performance
standards as described in paragraph 3-3788. These standards define acceptable
2) System performance data usually is reinforced by component
removal or confirmed failure data. The condition-monitored process can be readily
accommodated by this type of program.
C. Programs Using Other Analysis Standards (“Non-Alert” Programs).
Data compiled to assist in the day-to-day operation of the maintenance program
may be used effectively as a basis for continuous mechanical performance analysis.
1) MISs, flight record review, engine monitoring reports, incident
reports, and engine and component analysis reports are examples of the types
of information suitable for this monitoring method. The number and range of
inputs must be sufficient to provide a basis for an analysis equivalent to the
statistical programs standards.
2) Actuarial analysis should be conducted periodically to ensure
that the current process classifications are correct.
3-3788 PERFORMANCE STANDARDS.
A. Factors. The following factors are acceptable for establishing
or revising a reliability program’s performance standards:
1) Past and present individual operator and industry experience.
If industry experience is used, the program must include a provision for reviewing
the standards after the operator has gained 1 year of operating experience.
2) Performance analysis of similar equipment currently in service.
3) Aircraft or equipment manufacturers’ reliability engineering
4) History of experience where reliability standards were acceptable
to the airline industry.
B. Program Deviation. If the program does not incorporate statistical
performance standards or significantly deviates from the instructions in AC
1) Performance measurements expressed numerically in terms of:
· System or component failure,
· Pilot reports,
· Aircraft operating hours,
· Number of landings,
· Cycles, and
2) Standards adjusted to:
· Operator’s experience,
· Seasonal, and
3) Procedures for periodic review:
· Upward adjustment, and
· Downward adjustment.
C. Monitoring Procedure:
· New aircraft, and
· Computing performance standards.
3-3789 EVALUATING PROGRAM DISPLAYS AND STATUS OF CORRECTIVE ACTION PROGRAMS
A. Corrective Action System. Corrective action should be positive
enough to restore performance effectively to an acceptable level within a reasonable
time. The corrective action system must include provisions for the following:
1) Notifying the organization responsible for taking the action.
2) Obtaining periodic feedback until performance reaches an acceptable
3) Encompassing established methods for the overall maintenance
program, such as work orders, special inspection procedures, Engineering Orders
(EO), and technical standards.
4) Critical failures in which loss of function or the secondary
effects of failure could affect the airworthiness of the aircraft.
B. Statistical Performance Standards System.
1) A performance measurement expressed numerically in terms of
system or component failure, pilot report, delay, etc. (bracketed by hours of
aircraft operation, number of landings, operating cycles, or other exposure
measurement); serves as the basis for the standard. Control limits or alert
values are usually based on accepted statistical methods, such as standard deviations
or the Poisson distribution.
2) Some applications use an average or baseline method. The standard
should be adjustable and should reflect the operator’s experience during seasonal
and environmental condition changes and variations.
3) The program should include procedures for periodic review
and adjusting the program as appropriate.
4) The program should include procedures for monitoring new aircraft
until sufficient operating experience is available to compute performance standards—normally
C. Data Display and Reporting System.
1) Operators with programs incorporating statistical performance
standards (“alert” programs) should develop a monthly report with appropriate
data displays summarizing the previous month’s activity. This report should
include the following:
a) All aircraft systems controlled by the program in sufficient depth to
enable the FAA and other recipients to evaluate the effectiveness of the total
b) Systems that exceeded the established performance standards and discussion
of what action the operator has taken or planned.
c) An explanation of changes that the operator made or planned in the aircraft
maintenance program, including changes in maintenance and inspection intervals,
and changes from one maintenance process/task to another.
d) A discussion of continuing over-alert conditions carried forward from
e) The progress of corrective action programs.
2) Programs using other analytical standards (“non-alert” programs)
should consolidate or summarize significant reports used in controlling their
program to provide for evaluating program effectiveness. These reports may be
computer printouts, summaries, or other forms. A typical program of this type
reports the following information:
· Mechanical Interruption Summary Reports (MISRS);
· Maintenance process/task and interval assignments (master specification);
· Weekly update to the maintenance process and interval assignments;
· Daily repetitive item listing by aircraft;
· Monthly component premature removal report, including removal
· Monthly engine shutdown and removal report;
· Quarterly engine reliability analysis report;
· Engine threshold adjustment report; and
· Worksheets for maintenance process/task and interval changes (not
provided to the FAA, but the FAA approves the process/task changes).
D. Program Review System. The program should include a procedure
for revision that is compatible with FAA approvals. The procedures should identify
organizational elements involved in the revision process and the authority.
The program areas requiring formal FAA approval include any changes to the program
that involve the following:
· Procedures relating to reliability measurement/performance standards;
· Data collection;
· Data analysis methods and application to the total maintenance
· Process/task changes;
· Adding or deleting components/systems;
· Adding or deleting aircraft types; and
· Procedural and organizational changes concerning administration
of the program.
3-3790 INTERVAL ADJUSTMENTS, PROCESS, AND/OR TASK CHANGES.
NOTE: An evaluation process should exist in the maintenance program
document for the review of new or revised Failure Effects Categories (FEC) 5
and 8 safety task.
A. Maintenance Interval Adjustment, Process Category, and/or Task
Change System. Reliability programs provide an operator with a method of
adjusting maintenance, inspection, and overhaul intervals without prior FAA
approval. This does not relieve the operator or the FAA of their responsibilities
regarding the effects of the program on safety.
NOTE: If the ASI has any doubt as to the soundness of a requested maintenance
interval adjustment or task change, the inspector should coordinate the request
with the appropriate Aircraft Certification Office (ACO).
B. Procedures. Procedures for adjusting maintenance intervals
must be included in the program. Maintenance interval adjustments should not
interfere with ongoing corrective action. There should be special procedures
for escalating systems or components whose current performance exceeds control
1) Typical considerations for adjusting HT or OC intervals include
· Actuarial studies;
· Unit performance,
· Inspector or maintenance findings, and
· Pilot reports.
2) Methods for adjusting aircraft/engine check intervals should
be included if the program controls these intervals. Sampling criteria should
C. Classifying the Maintenance Processes and/or Tasks. The program
should include procedures for the classification and assignment of maintenance
processes and/or tasks and for changing from one process and/or task to another.
See MSG-2 for maintenance processes and MSG-3 for maintenance tasks. It should
include the authority and procedures for changing maintenance specifications
and the related documents to reflect the interval adjustments or process and/or
3-3791 PREREQUISITES AND COORDINATION REQUIREMENTS.
A. Prerequisites. Previous experience with the type of equipment
the operator/applicant proposes to include in the program.
B. Coordination. This task requires coordination between the
Airworthiness ASIs, to include both maintenance and avionics. Further coordination
may be required with regional and national headquarters (HQ).
3-3792 REFERENCES, FORMS, AND JOB AIDS.
A. References (current editions):
Maintenance Control by Reliability Methods.
Service Difficulty Program (General Aviation).
· MSG-2 Documents.
· MSG-3 Documents.
· FAA Order
Volume 8, Chapter 2, Section 7, Maintenance Review Boards.
B. Forms. None.
C. Job Aids. Automated operations specifications (OpSpecs) checklists
A. Meet With Operator/Applicant. In addition to providing AC
120-17, inform the operator/applicant of the following program requirements:
· Program application;
· Organizational structure;
· Data collection system;
· Methods of data analysis and application to maintenance control;
· Procedures for establishing and revising performance standards;
· Definition of significant terms;
· Program displays and status of corrective action programs;
· Procedures for program revision; and
· Procedures for maintenance control changes.
B. Evaluate the Program Application Procedures. When the applicant
submits a formal program, ensure that the program document defines the following:
1) Components, systems, or complete aircraft controlled by the
program. Individual systems and/or components are identified by the Airlines
for America (ATA) Spec 100, Manufacturers Technical Data. A list of all components
controlled by the program must be included as an appendix to the program document
or included by reference (e.g., time limits, manuals, or computer report).
2) The portion of the maintenance program controlled by the reliability
program (e.g., overhaul and/or inspection, check periods).
C. Evaluate Organizational Structure. The structure must be described
adequately and address committee membership, if appropriate, and meeting frequency.
Ensure that the reliability program includes an organizational chart that shows
1) The relationships among organizational elements responsible
for administering the program.
2) The two organizational elements responsible for approving
changes to maintenance controls and specifying the duties and responsibilities
for initiating maintenance program revisions.
NOTE: One of the two organizations must have inspection or quality control
(QC) responsibility or have overall program responsibility.
D. Evaluate the Organizational Responsibilities.
1) Determine if the reliability program document addresses the
a) The method of exchanging information among organizational elements. This
may be displayed in a diagram.
b) Activities and responsibilities of each organizational element and/or
reliability control committee for enforcing policy and ensuring corrective action.
2) Ensure that authority is delegated to each organizational
element to enforce policy.
E. Evaluate the Data Collection System.
1) Ensure that the reliability document fully describes the data
collection system for the aircraft, component, and/or systems to be controlled.
The following must be addressed:
· Flow of information;
· Identification of sources of information;
· Steps of data development from source to analysis; and
· Organizational responsibilities for each step of data development.
2) Ensure that the document includes samples of data to be collected,
· Powerplant disassembly and inspection reports;
· Component condition reports;
· Mechanical delay and cancellation reports;
· Flight record reports;
· Premature removal reports;
· In-flight shut downs (IFSD);
· Confirmed failure reports;
· Internal leakage reports; and
· Engine shutdown reports.
3) Ensure that the reliability document includes a graphic portrayal
of program operations. It must be a closed loop and show source data, data collection,
F. Evaluate the Methods of Data Analysis and Application to Maintenance
Controls. Ensure that the data analysis system includes the following:
1) One or more of the types of action appropriate to the trend
or level of reliability experienced, including:
a) Actuarial or engineering studies employed to determine a need for maintenance
b) Maintenance program changes involving inspection frequency and content,
functional checks, overhaul procedures, and time limits;
c) Aircraft, aircraft system, or component modification or repair; and/or
d) Changes in operating procedures and techniques.
2) The effects on maintenance controls such as overhaul time,
inspection and check periods, and overhaul and/or inspection procedures.
3) Procedures for evaluating critical failures as they occur.
4) Documentation used to support and initiate changes to the
maintenance program, including modifications, special inspections, or fleet
campaigns. The program must reference the operator’s manual procedures for handling
5) A corrective action program that shows the results of corrective
actions in a reasonable period of time. Depending on the effect on safety, a
“reasonable” period of time can vary from immediate to an overhaul cycle period.
Each corrective action plan (CAP) or program must be made a matter of record
and include a planned completion date. Samples of forms used to implement these
actions must be included in the program document.
6) A description of statistical techniques used to determine
operating reliability levels.
G. Evaluate the Procedures for Establishing and Revising Performance
1) Ensure that each program includes one of the following for
each aircraft system and/or component controlled by the program:
· Initial performance standards defining the area of acceptable
· Methods, data, and a schedule to establish the performance standard.
2) Ensure that the performance standard is responsive and sensitive
to the level of reliability experienced and is stable without being fixed. The
standard should not be so high that abnormal variations would not cause an alert
or so low that it is constantly exceeded in spite of the best known corrective
3) Ensure that the procedures specify the organizational elements
responsible for monitoring and revising the performance standard, as well as
when and how to revise the standard.
H. Evaluate Definitions. Verify that each program clearly defines
all significant terms used in the program. Definitions must reflect their intended
use in the program and will therefore vary from program to program. Acronyms
and abbreviations unique to the program must also be defined.
I. Evaluate Program Displays and Status of Corrective Action Programs
1) Ensure that the program describes reports, charts, and graphs
used to document operating experience. Responsibilities
for these reports must be established and the reporting elements must be clearly
identified and described.
2) Ensure that the program displays containing the essential
information for each aircraft, aircraft system, and component controlled by
the program are addressed. Each system and component must be identified by the
appropriate ATA (FAA) Spec 100 system code number.
3) Ensure that the program includes displays showing:
· Performance trends;
· The current month’s performance;
· A minimum of 12 months’ experience; and
· Reliability performance standards (“alert” values).
4) The program must include the status of corrective action programs.
This includes all corrective action programs implemented since the last reporting
J. Evaluate the Interval Adjustments and Process and/or Task Changes
1) Review the change system procedures. Ensure that there are
special procedures for escalating systems or components whose current performance
exceeds control limits.
2) Ensure that the program does not allow for the maintenance
interval adjustment of any Certification Maintenance Requirements (CMR) items.
CMRs are part of the certification basis. No CMR item may be escalated through
the operator maintenance/reliability program. CMRs are the responsibility of
FAA engineering as far as approval and escalation.
3) Ensure that the program does not allow for deletion of any
MSG-3 FEC 5 or 8 safety task without the concurrence/approval of the FAA MRB
Chairman and the Original Equipment Manufacturer (OEM)/Type Certificate Holder
NOTE: The operator may not use its reliability program as a basis for
adjusting the repeat interval for its Corrosion Prevention and Control Program
(CPCP); however, the operator may use the reliability program for recording
data for later submission to the FAA to help substantiate repeat interval changes.
4) Ensure that the program includes provisions for notifying
the certificate-holding district office (CHDO) when changes are made.
K. Evaluate the Procedures for Program Revisions. The reliability
document must accomplish the following:
1) Identify and isolate areas which require FAA approval for
program revision, including the following:
· Reliability measurement;
· Changes involving performance standards, including instructions
relating to the development of these standards;
· Data collection system;
· Data analysis methods and application to maintenance program;
· Any procedural or organizational change concerning program administration.
2) If the operator proposes that the FAA approve all revisions
to the program document, isolation of those areas requiring FAA approval is
not required. However, the document must recognize each of the above requirements
and must contain procedures for adequately administering and implementing changes
required by these actions.
3) Identify the organizational element responsible for approving
amendments to the program.
4) Provide a periodic review to determine that the established
performance standard is still realistic.
5) Provide procedures for distributing approved revisions.
6) Reference the operator’s manual and provide the overhaul and
inspection periods, work content, and other maintenance program activities controlled
by the program.
L. Evaluate the Procedures for Maintenance Control Changes. Ensure
that the reliability program document addresses the following:
1) Procedures for maintenance control changes to the reliability
2) The organizational elements responsible for preparing substantiation
reports to justify maintenance control changes. At least two separate organizational
elements are required, one of which exercises inspection or QC responsibility
for the operator.
3) Processes used to specify maintenance control changes (e.g.,
sampling, functional checks, bench checks, decision tree analysis, and unscheduled
4) Procedures covering all maintenance program activities controlled
by the program.
5) Procedures for amending OpSpecs, as required.
6) Procedures to ensure that maintenance interval adjustments
are not interfering with ongoing corrective actions.
7) Critical failures and procedures for taking a corrective action.
8) Procedures for notifying the CHDO, when increased time limit
adjustments or other program adjustments are addressed.
M. Analyze Reliability Program Evaluation. Follow SAS guidance for
3-3794 TASK OUTCOMES.
A. Complete the Task. Successful completion of this task will result
in the approval of the operator/applicant’s reliability program and OpSpecs
in accordance with
Volume 3, Chapter 18, Section 6.
B. Document the Task. Follow SAS guidance for modules 4 and 5.
3-3795 FUTURE ACTIVITIES. Follow SAS guidance.
RESERVED. Paragraphs 3-3796 through 3-3810.