REGULATORY REQUIREMENTS TO SUPPORT TRANSPORT CATEGORY AIRCRAFT
NOTE: The specific regulations, where they differ from those for all aircraft, are for Transport Category
Airplanes (14CFR Part 25), but there are similar requirements for all aircraft.
I. TYPE CERTIFICATE (all aircraft):
A. 14CFR section 21.41 defines the type certificate: Each type certificate is considered to include:
1. The type design (ref. 21.31);
2. The operating limitations (ref. Part 25, Subpart G, 25.1501 - 25.1587, including 25.1529);
3. The certificate data sheet:
4. The applicable sections of this subchapter with which the Administrator records compliance, and;
5. Any other conditions or limitations prescribed for the product in this subchapter.
B. TYPE DESIGN:
14CFR section 21.31 states that the type design for transport category aircraft consists of:
(a) The drawings and specifications, and a listing of those drawings and specifications, necessary to define
the configuration and the design features of the product shown to comply with the requirements of that part of this subchapter
applicable to the product;
(b) Information on dimensions, materials, and processes necessary to define the structural strength of the
(c) The Airworthiness Limitations section of the Instructions for Continued Airworthiness (ref. sections 21.50,
C. OPERATING LIMITATIONS:
Part 25, Subpart G - Operating Limitations and Information, establishes, and requires the availability of
operating limitations. Included in Subpart G (25.1501-25.1587) is 25.1529.
1. 14CFR section 25.1529 Instructions for Continued Airworthiness:
a. "The applicant must prepare Instructions for Continued Airworthiness in accordance with Appendix H to this
part that are acceptable to the Administrator."
II. INSTRUCTIONS FOR CONTINUED AIRWORTHINESS (Appendix H to Part 25)
(a) This appendix specifies requirements for the preparation of Instructions for Continued Airworthiness as
required by sect. 25.1529.
(b) The Instructions for Continued Airworthiness for each airplane must include the Instructions for Continued
Airworthiness for each engine and propeller (hereinafter designated "products"), for each appliance required by this chapter,
and any required information relating to the interface of those appliances and products with the airplane.
(c) The applicant must submit to the FAA a program to show how changes to the Instructions for Continued Airworthiness
made by the applicant or by the manufacturers of products and appliances installed in the airplane will be distributed.
(a) The Instructions for Continued Airworthiness must be in the form of a manual or manuals as appropriate
for the quantity of data to be provided.
(b) The format of the manual or manuals must provide for a practical arrangement.
The content of the manual or manuals must be prepared in the English language. The Instructions for Continued
Airworthiness must contain the following manuals or sections, as appropriate, and information:
(a) Airplane maintenance manual or section.
(1) Introduction information...
(2) A description of the airplane and its systems and installations including its engines, propellers, and
(3) Basic control and operation information...
(4) Servicing information...
(b) Maintenance instructions.
(1) Scheduling information for each part of the airplane and its engines, auxiliary power units, propellers,
accessories, instruments, and equipment that provides the recommended periods at which they should be cleaned, inspected,
adjusted, tested, and lubricated, and the degree of inspection, the applicable wear tolerances, and the work recommended at
these periods. (This is the source requirement for providing the FAA with an initial scheduled maintenance/inspection program.
(See Part II, following)) . ...The recommended overhaul periods and necessary cross references to the Airworthiness Limitations
section of the manual must also be included. In addition, the applicant must include an inspection program that includes the
frequency and extent of the inspections necessary to provide for the continued airworthiness of the airplane.
(2) Troubleshooting information...
(3) Information describing the order and method of removing and replacing products and parts...
(4) Other general procedural instructions including procedures for system testing during ground running, symmetry
checks, weighing, and determing the center of gravity, lifting, shoring, and storage limitations.
(c) Diagrams of structural access plates and information needed to gain access for inspections when access
plates are not provided.
(d) Details for the application of special inspection techniques including radiographic and ultrasonic testing
where such processes are specified.
(e) Information needed to apply protective treatments to the structure after inspection.
(f) All data relative to structural fasteners such as identification, discard recommendations, and torque
(g) A list of special tools needed.
H25.4 Airworthiness Limitations section.
(14CFR section 25.571, Damage-tolerance and fatigue evaluation of structure, requires that an evaluation of
the strength, detail design, and fabrication must be performed and must show that catastrophic failure due to fatigue, corrosion
(environmental), or accidental damage, will be avoided throughout the operational life of the airplane. Further, based on
the evaluations, inspections or other procedures must be established as necessary to prevent catastrophic failure,and must
be included in the Airworthiness Limitations section of the Instructions for Continued Airworthiness required by section 25.1529.)
The Instructions for Continued Airworthiness must contain a section titled Airworthiness Limitations that
is segregated and clearly distinguishable from the rest of the document. This section must set forth: 1.) each mandatory replacement
time, 2.) structural inspection interval, and 3.) related structural inspection procedure approved under sect. 25.571...This
section must contain a legible statement in a prominent location that reads: "The Airworthiness Limitation section is FAA
approved and specifies maintenance required under sections 43.16 and 91.403 of the Federal Aviation Regulations unless an
alternative program has been FAA approved."
III. CERTIFICATION PROCEDURES FOR PRODUCTS AND PARTS
A. 14CFR section 21.50 requires the holder of design approval to furnish at least one set of complete Instructions
for Continued Airworthiness, prepared in accordance with FAR section 25.1529 (for transport category aircraft) to the owner
of each type of aircraft upon its delivery, or upon issuance of the first standard airworthiness certificate for the affected
aircraft, whichever occurs later, and thereafter make those instructions available to any other person required by this chapter
with any of the terms of these instructions. In addition, changes to the Instructions for Continued Airworthiness shall be
made available to any person required by the FARs to comply with any of those instructions.
MAINTENANCE PROGRAM DEVELOPMENT
I. SOURCE REQUIREMENTS
A. The specific requirement for preparing an initial scheduled maintenance/inspection program is found in
Appendix H to Part 25, Instructions for Continued Airworthiness, paragraph H25.3, (b) (1), see Part I, item III, above.
B. FAA Advisory Circular AC No. 121-22A "provides guidelines which may be used in the development and approval
of initial maintenance/inspection requirements for a derivative or newly type-certificated transport category aircraft and
1. MAINTENANCE REVIEW BOARD (MRB).
When a transport type certification project is undertaken, the airframe designer/manufacturer applies to the
FAA Aircraft Certification Office (ACO) for a type certificate, or a major change to an existing type certificate, the FAA
Aircraft Evaluation Group (AEG) manager in the controlling FAA Directorate will assign a qualified specialist to assume the
responsibility of MRB chairman, except MRB members assigned to the engine/propeller functions, who will be selected by the
manager of the FAA's New England Region's Engine/Propeller AEG.
2. INDUSTRY STEERING COMMITTEE (ISC).
DAC or ISC is responsible for formally notifying the manager of the AEG of the controlling directorate of
its intention to develop a proposal for establishing initial maintenance/inspection requirements for new, or derivative, aircraft
The ISC activities should be coordinated with the MRB chairman.
The ISC should be composed of members from a representative number of operators and airframe and engine manufacturers.
The ISC establishes maintenance program policy, directs the activities of the working groups, and prepares the MRB report
proposal. (ref. AC 121-22A, Ch. 3., item 22.)
The MRB report proposal, once approved by the FAA, become the base or framework around which each operator
develops his own individual maintenance program. An operator's total maintenance program will be approved by the assigned
Principal Maintenance Inspector (PMI).
3. MAINTENANCE STEERING GROUP (MSG)
Maintenance program development dates back to Aeronautical Bulletin 7E of May 15, 1930 (see
"Aeronautical Bulletin 7E" link at top right, or page at bottom). The evolution has gone from individual operator's
proposing their unique maintenance programs to a process where the FAA and industry work together to formulate initial scheduled
The Air Transport Association of America (ATA) and industry developed Handbook MSG-1, Maintenance Evaluation
and Program Development, in 1968, for developing a maintenance program for the B-747.
MSG-1 was updated and made universally applicable. MSG-2, Airline/Manufacturer Maintenance Program Planning
Document, was the result of the update.
In 1979 MSG-2 was reviewed and various areas were identified as candidates for improvement. The active participation
and combined efforts of the FAA, CAA/UK, AEA, U.S. and European aircraft and engine manufacturers, U.S. and foreign airlines,
and the U.S. Navy generated the document, MSG-3 Airline/Manufacturer Maintenance Program Development Document, issued September
30, 1980. Revision 1 to MSG-3 was approved by the FAA in 1988 for the development of today's and future aircraft and powerplant
C. MSG-3, Airline/Manufacturer MAINTENANCE PROGRAM DEVELOPMENT DOCUMENT
1. MSG-3 outlines the general organization and decision processes for determining scheduled maintenance requirements
initially projected for the life of aircraft and/or powerplant which will be acceptable to the regulatory authorities, the
operators, and the manufacturers. The remaining maintenance, i.e. non-scheduled or non-routine maintenance, consists of maintenance
actions to correct discrepancies noted during scheduled maintenance tasks, other non-scheduled maintenance, normal operation,
or data analysis.
2. The Industry Steering Committee (ISC) should see that the MSG-3 process identifies 100% accountability
for all Maintenance Significant Items (MSIs, see 4.a.iii., below) and Structural Significant Items (SSIs, see 4.b.ii., below),
whether ir not a task has been derived from the analysis.
3. The objectives of the maintenance program are:
a. To ensure realization of the inherent safety and reliability levels of the equipment; and
b. To restore safety and reliability to their inherent levels when deterioration has occurred.
Another way of saying the above: To determine the maintenance tasks required to preclude significant failures
of systems and structures, and to maintain the aircraft in an airworthy condition. Also, the maintenance program will determine
the intervals at which specific maintenance tasks are to be performed.
4. The MSG-3 process is broken down into three main parts:
a. Aircraft Systems/Powerplant (including components & APUs) Analysis Method (see also FAR 25.1309 Equipment,
systems, and installations)
i. Based on the item's functional failures, effect of the failure, and failure causes
ii. Identify Aircraft's significant systems and components
iii. Maintenance Significant Items (MSIs) are those items identified by the manufacturer whose failure:
a) could affect safety on the ground or in flight,
b) could be undetectable or are unlikely to be detected during operations (latent), and/or
c) could have significant operational impact, and/or
d) could have significant economic impact
b. Aircraft Structural Maintenance Program Development
i. The structural maintenance program is designed to relate the scheduled maintenance tasks to the effect
of structural damage remaining undetected. Each structural item is evaluated in terms of:
a) Its significance to continuing airworthiness;
b) Its susceptibility to any form of damage (accidental, environmental, fatigue);
c) The degree of difficulty involved in detecting such damage.
ii. Aircraft Structure defined per MSG-3 document (see also FAR 25.571):
...all load carrying members including wings, fuselage, empennage, engine mountings, landing gear, flight
control surfaces, and related points of attachment.
a) A Significant Structural Item (SSI) (primary) is any detail, element, or assembly, which contributes significantly
to carrying flight, ground, pressure, or control loads, and whose failure could affect the structural integrity necessary
for the safety of the aircraft.
b) Other Structure (secondary) is that which is judged not to be an SSI.
c. Zonal Inspection Program
i. Requires a summary review of each zone of the aircraft and normally occurs as the analysis of structures,
systems, and powerplants are being concluded. In cases where a general visual inspection is required to assess degradation,
the zonal inspection is an appropriate method
a) Divide the aircraft externally and internally into zones as defined in ATA 100.
b) Prepare a task listing work sheet for each zone including location, description, access notes, etc.
c) During analysis of systems, structures, and powerplants, list any general visual inspections which could
be conducted as part of the zonal inspection program.
d) Include the interval from the original analyses on the zone work sheet.
e) As the analysis covering items in a zone are completed, the zone should be reviewed to consolidate inspection
requirements and assign accomplishment intervals. Document in the work sheets any System/Powerplant or Structural general
visual inspections replaced by the zonal inspection tasks.
iii. Zonal Task Intervals:
Accomplishments are based on hardware, susceptibility to damage, the amount of activity in the zone, and operator
and manufacturer experience with similar systems, powerplants, and structures. When possible, intervals should correspond
to those selected for targeted scheduled maintenance checks.
A. The challenge and a maintainability program is to enhance and improve maintainability of the aircraft.
1. Maintainability is best served when it takes a holistic approach, treating maintenance as a whole system
rather than seemingly unrelated parts. Maintainability needs to be integrated into a coherent program where every opportunity
to address and improve maitainability will be siezed.
2. The opportunity to enhance and improve maintainability occurs throughout an aircraft's entire life cycle,
i.e. design, certification, manufacturing, and post delivery aircraft maintenance operation.
A. The top level process begins with two questions regarding each defined maintenance task;
1. Is the task necessary?, and if so,
2. What can be done to make the defined task easier, less time consuming, less dependent on special tools,
equipment, and processes; in general what will make the accomplishment of the task more efficient, and thereby less costly?
B. A maintenance task is composed of one or several major elements; inspection, test, servicing, replacement,
or repair, the purpose of which:
1. Ensures the safety and reliability of systems, equipment, and structure (inspections and tests);
2. Identifies deterioration in safety and reliability; and
3. Restores safety and reliability to their inherent levels when deterioration has occurred (servicing, replacing,
or repairing the deteriorated system, equipment, or structure).
A. The process is applied to the following elements:
1. Maintenance tasks required by 14CFR sections 25.571 for Airworthiness Limitation items (ALIs), and 25.1309
for Certification Maintenance Requirements (CMRs) will be identified.
i. Review each CMR and ALI for familiarization and concurrence (answer the first maintainability question,
"Is the task necessary?"), and to;
ii. Establish the mandatory replacement time, inspection interval, and inspection procedure (answer the second
maintainability question, "What can be done to make the defined task easier, less time consuming, less dependent on special
tools, equipment, and processes; in general what will make the accomplishment of the task more efficient, and thereby less
costly?") for each CMR and ALI.
b. Other maintenance tasks may be added in the development of the initial scheduled maintenance program.
2. Master Minimum Equipment List (MMEL):
a. The type certificate holder is responsible for developing a list of equipment and functions which need
not be operative for safe flight and landing based on stated compensating precautions that should be taken, e.g. operational
or time limitations, or flight crew or ground crew checks. This list is allowed in accordance with 14CFR section 25.1309 and
becomes the basis for the Master Minimum Equipment List (MMEL). The TC holder develops the related MEL Procedures Manual.
3. Maintenance Manuals, following, will be reviewed, and the maintainability question will be asked; "What
can be done to make the defined tasks easier, less time consuming, less dependent on special tools, equipment, and processes,
in general what will make the accomplishment of the task more efficient, and thereby less costly?":
a. The Maintenance Manual and changes thereto.
b. Vendor/supplier Component Maintenance Manuals and changes thereto .
c. Any other manuals necessary in the pursuit of improving maintainability.
4. Engineering/Design Drawings will be reviewed:
a. Analyze systems in accordance with maintainability enhancement objectives in accordance with established
b. Approve/sign-off as is, or
c. Recommend changes necessary to enhance maintainability.
5. Physical review - M&SR will:
a. Observe selected procedures during manufacture/assembly.
b. Participate in maintainability demonstration/manual verification at TC holder, and at Vendors/Suppliers.
c. Participate in maintainability investigations at airline customer's facility.
d. Monitor fleet maintainability issues and concerns, and
e. Recommend improvements/enhancements whenever feasible.