**\[4910-13\]**

**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.

**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: gregory.dunn@faa.gov.

**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 (§) 21.31]{.underline} ("Type design"): This section defines
and describes "type design."

[§ 21.33]{.underline} ("Inspection and tests"): This section,
specifically § 21.33(b), provides additional insight as to the contents
of the type design data package.

[§ 21.21]{.underline} ("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.

[§ 21.50]{.underline} ("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.

[§ 21.101]{.underline} ("Designation of applicable regulations") and [§
21.115]{.underline} ("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:]{.underline} As mentioned above,
the FAA has identified a number of recently submitted type design data
packages that did not meet the intent of § 21.31(a). Specifically, these
packages did not completely define the 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:]{.underline} 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:]{.underline} 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:]{.underline} 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:]{.underline} 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:]{.underline} 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."

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-   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:\..."

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-   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:\..."

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-   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:\...\"

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-   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.

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-   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."

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-   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:]{.underline} Type design data
packages should meet the intent of § 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.

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-   Installation drawings.

Installation drawings should identify the configuration. Such drawings
will typically identify:

-   Equipment locations.

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-   Wiring routings.

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-   Mounting and support details.

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-   Other such details of features.

[System Safety Assessment:]{.underline} 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.

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-   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 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:]{.underline} 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:]{.underline} As noted in § 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.

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-   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.

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-   Material.

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-   Production processes.

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-   Any other properties affecting strength or functionality of each
    part.

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-   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.

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-   Do a physical inspection of the airplanes to be modified to ensure
    compatibility.

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-   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:]{.underline} 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 § 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.

/s/Vi Lipski

Vi Lipski

Manager

Transport Airplane Directorate

Aircraft Certification Service