[Federal Register Volume 67, Number 24 (Tuesday, February 5, 2002)]
[Notices]
[Pages 5357-5360]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-2718]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration


Policy Statement Number ANM-01-04; System Wiring Policy for 
Certification of Part 25 Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of final policy.

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SUMMARY: In this document, the FAA addresses public comments that were 
submitted in response to a previously published general statement of 
policy that is applicable to the type certification process of 
transport category airplanes. The policy provides guidance to FAA 
certification teams for the type design data needed. The policy is 
necessary to correct deficiencies associated with the submittal of 
design data and instructions for continued airworthiness involving 
airplane system wiring for type design, amended design, and 
supplemental design changes.

FOR FURTHER INFORMATION CONTACT: Gregory Dunn, Federal Aviation 
Administration, Transport Airplane Directorate, Transport Standards 
Staff, Airplane and Flight Crew Interface Branch, ANM-111, 1601 Lind 
Avenue SW., Renton, WA 98055-4056; telephone (425) 227-2799; fax (425) 
227-1320; e-mail: [email protected].

SUPPLEMENTARY INFORMATION:

Background

    On July 2, 2001, the FAA published in the Federal Register (66 FR 
34983) a general statement of policy comprising guidance to FAA 
personnel for reviewing certain certification plans for transport 
category airplanes. Specifically, the policy statement provides 
internal guidance to FAA certification teams that will enable them to 
more thoroughly examine all required information submitted in the type 
design data package for compliance with wire installation safety 
standards. This policy will also advise applicants what information 
needs to be provided in their type design data package to avoid delays 
in the certification process caused by incomplete or ambiguous 
information.
    The safety standards for civil transport category airplanes are 
specified in Title 14, Code of Federal Regulations (CFR), part 25. If 
an applicant demonstrates that a particular design (i.e., a particular 
model) complies with these standards, the FAA issues it a design 
approval. The drawings and other data that describe that design are 
known as the ``type design.'' When an applicant submits the necessary 
documents required for type certification by the FAA, the compilation 
of those documents is known as the ``type design data package.''
    Based on certification projects submitted to the FAA for review in 
recent years, the FAA has become aware that there is some confusion 
among applicants as to the definition of ``type design,'' especially 
with respect to the inclusion of drawings and specifications necessary 
to define the wiring configuration associated with equipment 
installation. In a number of recent certification projects, type design 
data packages that were submitted did not include wiring diagrams 
showing the source and destination of all wire associated with the 
installation. Also, wire installation drawings showing airplane wire 
routing, grounding, shielding, clamping, conduits, etc., either were 
missing or lacked sufficient detail. The wiring diagrams and 
installation drawings did not contain the necessary information 
intended by the relevant regulations. These drawing packages did not 
adequately and clearly define the configuration of the model to be 
certificated. In addition, instructions for continued airworthiness, as 
required by the regulations, were not defined.

Current Regulatory Requirements

    The type and quality of data required for type design data packages 
and requirements for instructions for continuing airworthiness are 
indicated in the regulations. The pertinent sections of 14 CFR are as 
follows:
    Section (Sec. ) 21.31 (``Type design''): This section defines and 
describes ``type design.''
    Sec. 21.33 (``Inspection and tests''): This section, specifically 
Sec. 21.33(b), provides additional insight as to the contents of the 
type design data package.
    Sec. 21.21 (``Issue of type certificate: normal, utility, 
acrobatic, commuter, and transport category aircraft; manned free 
balloons, special classes of aircraft, aircraft engines; propellers''): 
This section lists pertinent requirements for a type certificate.
    Sec. 21.50 (``Instructions for continued airworthiness and 
manufacturer's maintenance manuals having airworthiness limitations 
sections''): This section requires applicants to submit instructions 
for continued airworthiness as part of their type design data package. 
Paragraph 21.50(b) is relevant to this policy statement.
    Sec. 21.101 (``Designation of applicable regulations'') and 
Sec. 21.115 (``Applicable requirements''): These sections make it clear 
that these data requirements apply to changes to type certificates.
    Procedures for accomplishing the evaluation and approval of 
airplane type design data can be found in FAA Order 8110.4B, ``Type 
Certification,'' dated April 24, 2000. This document gives 
comprehensive guidance on what constitutes a design package and what is 
necessary to make acceptable findings of compliance.

Identified Problems

Ambiguous Definition of Configuration

    As mentioned above, the FAA has identified a number of recently 
submitted type design data packages that did not meet the intent of 
Sec. 21.31(a). Specifically, these packages did not completely define 
the

[[Page 5358]]

certification configuration. For example, these packages did not 
completely define specific routing and installation of wiring on the 
airplane, which then left an inordinate portion of the installation to 
the discretion of the installer.
    The routing of wiring is an important aspect not only to the system 
being modified, but also to other systems that can be affected by that 
wiring. It is important that the routing of wiring strictly follow the 
criteria established by the FAA in the certification basis, as 
reflected in the holder's original or subsequently approved type 
design. This requires installation drawings and instructions that 
completely define the required routing and installation with sufficient 
detail to allow repeatability of the installation.

System Safety Assessment

    A system safety assessment is done as part of the installation of 
any equipment on the airplane. This typically consists of a functional 
hazard analysis, failure mode and effects analysis, zonal analysis, or 
other safety analyses appropriate to the system being installed. In the 
past, insufficient emphasis has been placed on an examination of 
failures of wiring external to the actual line replaceable units being 
installed. Failure of wiring in bundles due to chafing, contamination, 
or other causes may affect the continued safe operation of the 
airplane.

References to General Guidance

    Problems occur when applicants overly rely on ``standard 
practices'' or other general guidance for installation details. Often, 
type design data packages make references to FAA Advisory Circular (AC) 
43-13, ``Acceptable Methods, Techniques, and Practices--Aircraft 
Inspection and Repair,'' for installation instructions. That guidance 
is general in nature and offers applicants multiple options for 
compliance. Because the installer can choose from a number of options 
for installation details, it is difficult for the FAA to find that the 
configuration complies with the criteria established by the FAA in the 
certification basis for a previously approved type design. An installer 
could make inappropriate choices of method, depending upon his or her 
previous experience and training.
    The practice of referencing general guidance, on those occasions 
when safety assurances and certification criteria necessitate strict 
adherence to specified certification standards, could result in an 
incomplete definition of the installation configuration. This 
clarification of FAA policy does not mean that data packages cannot 
reference AC 43-13 or similar documents, but the applicant is required 
to provide installation instructions which are unambiguous.

Omission of Manufacturing Process Specifications

    There also have been cases where crucial manufacturing process 
specifications were omitted in the type design data packages pertaining 
to wiring installation details. This has led to insufficient control of 
the production of parts, and consequent airworthiness problems related 
to faulty parts manufacturing. This omission error frequently occurs 
when the type design approval holder routinely uses a complex process, 
but has not carefully defined the process in the type design data. As a 
consequence, it can result in approval of replacement parts that may 
not comply with necessary but undefined processing requirements.

Modifications Not Compatible With Original Type Design Standards

    Another common problem occurs when a modifier is unaware of, or 
does not specify, installation and routing practices that are 
compatible with the certification standards established for the 
original type design.
    Some manufacturers provide an abbreviated version of their 
installation and routing specifications in the maintenance manual that 
they prepare for their products. These specifications may not be 
readily available to modifiers. This can result in ``inadvertent non-
compliance'' with certification requirements. One example of this kind 
of inadvertent non-compliance would be the installation of a power wire 
for a modification in a wire bundle containing critical wiring that the 
original manufacturer was required to isolate from other systems. This 
type of situation can be prevented by the applicant using experienced 
design engineers, doing physical inspections of the airplanes to be 
modified to ensure compatibility, and using the original airplane 
manufacturer's wiring installation guidelines.

Instructions for Continued Airworthiness

    A review of past certification projects indicates that the 
maintenance aspects of system wire external to the installed equipment 
is not being adequately addressed. The integrity of the wiring is 
typically left to those doing general airplane maintenance that relies 
on visual inspections. However, visual inspections may not be adequate 
for wiring routed in metal or opaque conduits, wire in high vibration 
areas, or wire located in difficult to inspect areas. Equipment 
installers need to address any special maintenance requirements for the 
airplane wiring associated with equipment installation.

Disposition of Comments

    The FAA received comments on the policy statement from four 
commenters: two representing industry groups, one an aviation safety 
inspector, and one a private citizen. The comments generally fall 
within four specific subject areas. These are addressed below.

1. Editorial Changes for Clarification of Meaning

    One commenter suggests that the terms ``complete'' and 
``completely,'' ``strictly,'' ``precise,'' and ``definitive,'' used in 
the Statement of FAA Policy could be regarded as an absolute 
requirement, overly precise, or unclear. The commenter also requests 
that certain sentences be reworded.
    The FAA accepts these comments with some modifications. The intent 
of this policy is to define the type design using drawings which are 
unambiguous with respect to important design details. It is not the 
intent of the FAA to require that these drawings contain every minute 
detail. Tests and analyses must be sufficiently detailed so that 
conformity can be accomplished.
    In response to this commenter:
     The following sentence in paragraph 1 has been deleted: 
``These packages should completely define the certification 
configuration.''
     The sentence in paragraph 2, which begins ``Installation 
drawings that completely define the configuration typically will 
identify: * * * '' has been changed to the following: ``Installation 
drawings should identify the configuration. Such drawings typically 
will identify: * * * ''
     The sentence in paragraph 7 which begins ``These tests and 
analyses require complete * * * '' is changed to ``These tests and 
analyses should define the parts so that: * * * ''
     The sentence in paragraph 8 that contains ``A complete 
definition * * * requires a drawing package that clearly and completely 
identifies: * * * '' is changed to ``The definition of the parts, 
including wiring and wire installation hardware, requires a drawing 
package that clearly identifies: * * * ''
     The word ``strictly,'' as used in the fourth sentence in 
the first paragraph, beginning ``It is important that the routing of 
wiring strictly follow the intent of the criteria * * * '' is deleted.

[[Page 5359]]

     The word ``definitive'' in the last sentence in paragraph 
5 is deleted and the rest of the sentence is rewritten for clarity. The 
sentence now reads, ``This, in turn, requires a knowledge of the 
configuration through design control and an understanding of the 
airplane manufacturer's relevant wire installation practices or 
procedures, especially any requirements that pertain to wire 
separation.''
     In paragraph 6, ``definitive drawings'' is changed to 
``engineering drawings'' in order to more accurately reflect the 
intended meaning, and, in the same paragraph, in the last sentence, the 
word ``precise'' is removed from ``precise location or routing of the 
wiring'' and the phrase now reads ``location or routing of the 
wiring.''
    A second commenter requests deletion, addition, or revision of 
sentences for clarification. Specifically, this commenter requests the 
following changes:
     Remove the following sentence in the ``Background'' 
section under ``One-Only Approvals'': ``The certification regulations 
for one-only approvals permit the use of photographs and other similar 
data to document the modification.'' The commenter notes that this 
sentence implies that photographs are not acceptable for multiple 
approvals.
    The FAA accepts this comment with modification. The sentence is 
revised as follows: ``The certification regulations for one-only 
approvals often use photographs and other similar data to document the 
modification.''
     Add the following sentence to the end of ``References to 
General Guidelines'' section: ``This clarification of FAA policy does 
not mean that data packages cannot reference AC 43-13 or similar 
documents, but the applicant is required to provide installation 
instructions which are unambiguous.''
    The FAA concurs and the sentence is added as submitted.
     Modify the last sentence of paragraph 5 of ``Statement of 
FAA Policy'' to read, ``This, in turn, requires definitive knowledge of 
the configuration through design control and an understanding of the 
airplane manufacturer's wire installation rules, especially any 
requirements that pertain to wire separation, as described by the 
airplane manufacturer in the maintenance manual.''
    The FAA does not concur. The purpose of this sentence is to address 
the need to understand the manufacturer's design as well as 
installation requirements. These requirements are not necessarily found 
in the maintenance manuals. However, as noted earlier, the sentence is 
revised to address a previous commenter's request to remove the word 
``definitive.''

2. Consideration for modifications in process

    One commenter requests that the policy give reasonable 
consideration to modification programs presently in process.
    The FAA concurs with this comment. It is the Transport Airplane 
Directorate's position that we will not impose new policy on an 
applicant for projects well on the way to completion, unless there is a 
safety concern that calls for an Airworthiness Directive. Consequently, 
the following sentence is added to the section entitled ``Effect of 
This Statement of Policy'': ``This policy applies to any new project 
initiated after July 2, 2001, the date of the original publication of 
this notice in the Federal Register. However, the applicant is 
encouraged to incorporate the guidance in this policy into any present 
project where feasible.''

3. Electrical Load

    One commenter suggests that the policy should address the need to 
improve the currency and quality of the airline operator's electrical 
load report.
    The FAA does not concur. The policy is meant to address only those 
aspects of Part 21 related to type design data and continuing 
airworthiness for Part 25 airplanes. It is not the intent of this 
policy to address all design aspects of wire installations on 
airplanes.

4. Wire Types and Inspections

    Another commenter submitted the following three comments relating 
to wire types and wire inspections:
     The policy should address approved wire types.
    The FAA does not concur. As required by other regulations, wire 
must meet its intended function, pass applicable qualification testing, 
not pose a hazard to the airplane, and be properly maintained.
     Issues relating to the mixing of wire types are not 
addressed.
    Mixing of wire types is not addressed in this policy statement. 
Wires in a bundle must be securely clamped and bound and be compatible 
with their environment (i.e., vibration, temperature, etc.). These 
details are addressed in the design and installation requirements of 
the wire. These requirements are called out in the installation 
drawings.
     Visual inspections were found to be totally inadequate in 
discerning wiring cracks.
    The FAA does not concur. Generally, visual inspections are a very 
valuable tool in assessing the condition of wire. Additional tools are 
necessary to detect microscopic wiring cracks. This is an area of 
research and, currently, non-destructive inspection (NDI) techniques 
are being developed and/or evaluated. The policy addresses the need for 
specific wire inspection requirements.

Additional Changes

    The words ``when available'' were added to the last sentence in the 
section on ``Process Specifications and Modifications Compatible with 
Original Standards,'' for clarification.

Conclusion

    After due consideration of the public comments submitted, the FAA 
has modified the general statement of policy to add clarification. The 
final policy, as modified, and without preamble, appears below.

Statement of FAA Policy

Unambiguous Definition of Configurations

    Type design data packages should meet the intent of Sec. 21.31(a). 
Specifically, routing and installation of wiring on the airplane should 
be addressed. It is important that the routing of wiring follow the 
intent of the criteria established by the FAA in the certification 
basis as reflected in the original or subsequently approved type design 
approval holder's design. The installer should provide with each 
application for design approval the following:
     Wiring diagrams showing source and destination of all 
airplane wiring associated with equipment installation.
     Installation drawings.
    Installation drawings should identify the configuration. Such 
drawings will typically identify:
     Equipment locations.
     Wiring routings.
     Mounting and support details.
     Other such details of features.

System Safety Assessment

    Certain airworthiness criteria require failure analyses (i.e., 
failure mode and effect analysis, zonal analysis, or other safety 
analysis) to demonstrate that a failure of the system under 
consideration:
     Does not, in itself, constitute an unacceptable hazard.
     Does not result in damage to other systems that are 
essential to safety.
    The system safety assessment should include an assessment of the 
effects of failures of the airplane wire and its associated wire bundle 
for equipment

[[Page 5360]]

installed on the airplane. The analysis should consider the possible 
effects wire system failures would have on systems required for safe 
flight and landing due to damage in collocated wiring bundles and the 
possibility of smoke and/or fire events.
    Failure of other systems must not damage a system being modified if 
the modified system is essential to safety. Such analysis requires that 
any possible interaction between systems be examined. This, in turn, 
requires a knowledge of the configuration through design control and an 
understanding of the airplane manufacturer's relevant wire installation 
practices or procedures, especially any requirements that pertain to 
wire separation.

Specific Installation Drawings Instead of General References

    The FAA expects the applicant to provide engineering drawings 
instead of merely statements such as ``install in accordance with 
industry standard practices,'' or ``install in accordance with AC 
43.13.'' The FAA considers such statements inadequate because the 
standard practices cannot define the location or routing of the wiring.

Process Specifications and Modifications Compatible with Original 
Standards

    As noted in Sec. 21.21, certain of the airworthiness requirements 
require analysis or tests to define the strength, durability, and life 
of components associated with the installation of wiring in the 
airplane (i.e., connectors, brackets, wire constraints, grommets, 
ground terminations, etc.). These tests and analyses should define the 
parts so that:
     Conformity of the parts to the type design may be 
verified.
     The characteristics of the parts important for test or 
analysis may be determined.
    The airplane wiring parts specification provides the basis for 
necessary stress, durability, and life analysis. The definition of the 
parts, including wiring and wire installation hardware, requires a 
drawing package that clearly identifies:
     Shape.
     Material.
     Production processes.
     Any other properties affecting strength or functionality 
of each part.
     The arrangement of each part in the final assembly.
    As an example, the FAA expects drawings to identify the material 
specification, heat treatment, corrosion protection or other finish, 
and any other important characteristic of each part subject to test or 
analysis for showing compliance with the airworthiness requirements. 
Much of this information can be provided by reference on the drawings 
to material or process specifications; the references then become part 
of the drawing and, consequently, part of the type design data package.
    Modifiers of aeronautical products should use practices that 
reflect the certification criteria applicable to the original airplane 
manufacturer (OAM). The applicant should demonstrate that installation 
specifications and routing practices for the wiring used by modifiers 
is either the same as, or compatible with, those that are used 
presently for showing compliance to the type design certification 
requirements. Specifically, wire separation, wire types, wire bundle 
sizes, brackets, and clamping should be consistent with the approved 
standards. This may require the applicant and/or modifier to:
     Obtain or determine the applicable OAM design standards 
and/or practices for a given installation.
     Do a physical inspection of the airplanes to be modified 
to ensure compatibility.
     Develop processes and procedures to address compatibility 
between the original installation and the modification.
    Modifiers and installers should use the airplane manufacturer's 
maintenance manuals, such as Maintenance Manual Chapter 20 (``Standard 
Practices Airframe''), Maintenance Manual Chapter 70 (``Standard 
Practices Engines''), or Chapter 20 (``Standard Practices Wiring'') as 
the primary source of wiring installation information, when available.

Instructions for Continued Airworthiness

    Paragraph 21.50(b) of the regulations requires that instructions 
for continued airworthiness (ICA) be supplied by the modifier for 
modifications to aircraft and related products. The ICA for any 
specific wiring maintenance should be addressed where Sec. 25.1529 is 
included in the certification basis.
    Assessment of wire condition relies heavily on visual inspection. 
Consequently, the ICA should address inspectability of wire in conduits 
and difficult to inspect areas of the airplane. Where wire cannot be 
inspected visually, the ICA should address wire removal for inspection, 
when necessary, and the use of inspection techniques that do not rely 
on visual inspection alone. For example, wire in metal conduits may 
require repeated inspections for wear.
    The FAA expects applicants for modifications to provide 
airworthiness instructions for the proposed changes in a format 
compatible with other maintenance instructions for the aircraft 
involved.

Effect of This Statement of Policy

    The general policy stated in this document is not intended to 
establish a binding norm. It does not constitute a new regulation and 
the FAA would not apply or rely upon it as a regulation. Those tasked 
with the responsibility of airplane certification should generally 
attempt to follow this policy, when appropriate. In determining 
compliance with certification standards, each certification office has 
the discretion not to apply these guidelines where it determines that 
they are inappropriate. However, the certification office should strive 
to implement this guidance to the fullest extent possible to facilitate 
standardization and ensure that wiring installation details are 
adequately addressed during certification. Applicants should expect 
that the certificating officials will consider this information when 
making findings of compliance relevant to certification actions. 
Applicants also may consider the material contained in this policy 
statement as supplemental to that currently contained in 14 CFR part 21 
when developing a means of compliance with the relevant certification 
standards.
    This policy applies to any new project initiated after July 2, 
2001, the date of the original publication of this notice in the 
Federal Register. However, the applicant is encouraged to incorporate 
the guidance in this policy into any present project where feasible.
    Finally, as with all advisory material, this statement of policy 
identifies one means, but not the only means, of compliance.

    Issued in Renton, Washington, on January 28, 2002.
Vi Lipski,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 02-2718 Filed 2-4-02; 8:45 am]
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