U.S. Spells Out Data Needed For Wiring-Related Mod Approvals

By Sean Broderick

02-Jul-2001 1:13 PM U.S. EDT

U.S. regulators, concerned that applicants who request certification of wiring-related modifications don't always submit required data, have clarified what they expect applicants to provide as part of their requests - including detailed maintenance information related to the changed systems.

The Federal Aviation Administration (FAA) policy statement reminds applicants seeking "type design, amended design, and supplemental design" changes affecting wiring in transport-category aircraft that they are required by the Federal Aviation Regulations (FARs) to submit packages that "completely define the certification configuration." This includes, but is not limited to, complete wiring diagrams with routing details, mounting details, and a system safety analysis of the proposed changes.

The policy stresses that applicants also are required to submit instructions for continued airworthiness, or the information about the system that maintainers of the system would need during repairs.

"A review of past certification projects indicates that the maintenance aspects of system wire external to the installed equipment is not being adequately addressed," FAA wrote. "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," the agency continued. "Equipment installers need to address any special maintenance requirements for the airplane wiring associated with equipment installation."

The document, generated by the agency's Renton, Wash., aircraft certification office, is considered "advisory material," which does not carry the same weight as a regulation. FAA is seeking comments on the statement through Aug. 1.

Airliner wiring issues have gained visibility due to their role in several accidents, most notably the 1996 in-flight explosion of a TWA 747-100 and the September 1998 crash of a Swissair MD-11 cause by an electrical fire. Those two accidents led to numerous studies - and some new rules - on wiring integrity, maintenance practices, and design issues.

FAA's certification process has also come under fire during the last five years. The U.S. National Transportation Safety Board, pointing to evidence uncovered in the TWA crash and a few others, called for a review of FAA certification for several years. Earlier this year, NTSB Chairman Carol Carmody said doing the study would become a top priority for the board, even though FAA planned to do its own probe.

See Also:

U.S. FAA Aging Transport Non-Structural Systems Plan (.pdf)
Photo Courtesy Joe Pries

from this link

[Federal Register: July 2, 2001 (Volume 66, Number 127)]
[Page 34983-34986]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]



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 policy statement; request for comments.


SUMMARY: This notice announces the FAA's policy with respect to the 
type design data needed for the certification of wiring installed on 
transport category airplanes. The policy is necessary to correct 
deficiencies associated with the submittal of design data and 
instructions for continuing airworthiness involving airplane system 
wiring for type design, amended design, and supplemental design 
changes. This notice advises the public, in particular applicants for 
type certificates, amended type certificates, supplemental type 
certificates, or type design changes, of the range and quality of type 
design data that the FAA will expect applicants to submit as part of 
any certification project. This notice is necessary to advise the 
public of FAA policy and give all interested persons an opportunity to 
present their views on the policy statement.

DATES: Send your comments on or before August 1, 2001.

ADDRESSES: Address your comments to the individual identified under FOR 

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)

[[Page 34984]]

227-1320; e-mail: gregory.dunn@faa.gov.


Comments Invited

    The FAA invites your comments on this proposed general statement of 
policy. We will accept your comments, data, views, or arguments by 
letter, fax, or e-mail. Send your comments to the person indicated in 
FOR FURTHER INFORMATION CONTACT. Mark your comments, ``Comments to 
Policy Statement ANM-01-04.''
    Use the following format when preparing your comments:
 Organize your comments issue-by-issue.
 For each issue, state what specific change you are 
requesting to the proposed general statement of policy.
 Include justification, reasons, or data for each change 
you are requesting.
    We also welcome comments in support of the proposed policy.
    We will consider all communications received on or before the 
closing date for comments. We may change the proposals contained in 
this notice because of the comments received.


    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 to the FAA for approval, the 
compilation of those documents is known as the ``type design data 
    Certification projects submitted to the FAA for approval generally 
fall into two different categories:
    1. Multiple Approvals: Multiple approvals are approvals for 
modifications that may be installed on any airplane of a specific type. 
These approvals require a data package that defines the installation so 
that it may be duplicated on another airplane by an installer. It is 
FAA's policy to require that type design data packages for multiple 
approvals include the following:
 A drawing package that completely defines the 
configuration, material, and production processes necessary to produce 
each part in accordance with the certification basis of the product.
 Any specifications referenced by the required drawings.
 Drawings that completely define the location, 
installation, and routing, as appropriate, of all equipment in 
accordance with the certification basis of the product. If the 
modification being approved is a change to a type certificated product, 
the modification must be equivalent to and compatible with the 
previously approved type design standards.
    In addition, any applicant for a type certificate (TC), 
supplemental type certificate (STC), or type design change must submit 
Instructions for Continued Airworthiness in accordance with Sec. 21.50 
(``Instructions for continued airworthiness and manufacturer's 
maintenance manuals having airworthiness limitations sections'').
    2. One-Only Approvals: Some modification approvals are specific to 
only one airplane by serial number. These modifications are often 
referred to as ``one-only approvals.'' For one-only approvals, 
duplication of the installation is not necessary and different (i.e., 
lesser) data standards may apply. The certification regulations for 
one-only approvals permit the use of photographs and other similar data 
to document the modification. The degree of compliance of the policy 
statement herein for one-only design approvals is left to discretion of 
the certification engineer.
    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 
    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 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.

[[Page 34985]]

    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 chaffing, contamination, or other causes may affect the 
continued safe operation of the airplane.
    References to General Guidance: Problems occur when applicants over 
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.
    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 
    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.

Statement of FAA Policy

    Unambiguous Definition of Configurations: Type design data packages 
should meet the intent of Sec. 21.31(a). These packages should 
completely define the certification configuration. Specifically, 
routing and installation of wiring on the airplane should be addressed. 
It is important that the routing of wiring strictly 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 that completely defines the configuration 
typically will identify:
 Equipment locations,
 Wiring routings,
 Mounting and support details, and
 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 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 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 
    Specific Installation Drawings Instead of General References: The 
FAA expects the applicant to provide definitive 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 precise 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 require 
complete definition of the parts so that:
 Conformity of the parts to the type design may be 
verified, and
 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. A complete definition 
of the

[[Page 34986]]

parts, including wiring and wire installation hardware, requires a 
drawing package that clearly and completely identifies:
 Production processes,
 Any other properties affecting strength or functionality 
of each part, and
 The arrangement of each part in the final assembly.
    As an example, the FAA expects drawings to identify the material 
specification, heat treat, 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, and
 Develop processes and procedures to address compatibility 
between the original installation and the modification.
    Modifiers and installers should use the airplane manufacture'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.
    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 

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 
    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 June 25, 2001.
Vi L. Lipski,
Manager, Transport Airplane Directorate, Aircraft Certification 
[FR Doc. 01-16602 Filed 6-29-01; 8:45 am]


NTSB To Push Certification Study, Roselawn Revisit

By Sean Broderick / WASHINGTON

16-Feb-2001 4:19 PM U.S. EST

Acting U.S. National Transportation Safety Board Chairman Carol Carmody is pushing to get her agency moving on a pair of long-standing, controversial matters: a wide-ranging study on aircraft certification and closing the book on a 1994 American Eagle ATR crash near Chicago.

"Certification has come up a number of accident investigations," Carmody told AviationNow.com Friday. "The board has told itself twice now to do a study of certification. That's one of my main priorities, to get that under way."

Certification issues were main parts in probes of the 1994 crash of USAir 427, a Boeing 737, near Pittsburgh and the 1996 in-flight explosion of TWA 800, a Boeing 747, off the Long Island, N.Y., coast. During each of those investigations - arguably the two most complicated and cumbersome air crash probes ever done - the board said it would do an independent study of U.S. Federal Aviation Administration (FAA) certification standards and practices.

In final report on the TWA crash, NTSB cited several design flaws. The most significant was putting heat-generating systems like air-conditioning packs directly under the 747 center fuel tank, which add heat to fuel vapors in the tank, boosting the chances that an explosive fuel-ignition combination could form.

The USAir 427 report questioned the 737 rudder design, which lacks adequate redundancy in a key system blamed for contributing to the crash and is being re-designed as a result.

In both probes, FAA's reasoning behind certifying the systems came under fire.

Several other major accidents, including Alaska Airlines Flight 261 in 1999 and the 1994 American Eagle crash, have led investigators to scrutinize certification issues.

In the past two years, the study has been pushed off due to higher-priority tasks, including wrapping up the TWA 800 probe and heading up the EgyptAir 990 investigation. With the TWA report out and EgyptAir close to final draft form, Carmody believes the certification probe's time is now.

"As we get into accident investigations, we keep coming back to questions about certification," Carmody said. "That indicates there's something we need to be doing."

Carmody, a 20-year industry veteran who spent time at FAA, in Congress, and at the International Civil Aviation Organization before joining the board last June, has heard that FAA is doing its own study. While she welcomes the agency's input, she stresses that FAA's efforts will not alter the board's plans.

"FAA seems to be doing its own certification study in hopes they can deflect us," she said. "But this is a case where we can't hold hands with FAA. We need to do our own. I'm not saying all the expertise is in this [NTSB headquarters] building, but we need to be in charge of the study."

Carmody was named NTSB vice chairman last month, and immediately became acting chairman when former Chairman Jim Hall's term expired and he left the agency. She expects to be the interim boss until the middle of the year at least. Until then, her main goals are to urge her people to keep their report-publishing schedule on track, tackle day-to-day issues as they arise, and see that the board is unified.

"I see myself as a caretaker," she said. "I want a board that moves together."

As far as major, potentially controversial decisions go, "I would probably defer them to the next chairman." She adds, however, that nothing fitting that description is on the board's plate right now.

While Carmody isn't looking to create controversy in her own agency, she has firmly established that during her tenure as boss, NTSB will push its single-focus agenda of safety improvement as forcefully as ever. Last week, NTSB sent FAA a strongly worded letter questioning a recent deal between FAA and an air traffic controllers' union that the board believes could shrink safety margins.

"I do think it is part of our role to, if you will, keep the heat on," Carmody said of NTSB's relationship with the regulatory agency. "FAA is under tremendous pressure from the industry right now, and FAA's under tremendous pressure from the Congress, on a variety of issues. I don't want the safety to take a back seat, I don't think FAA would do that deliberately, but we all respond to pressure. When there's huge pressure, I don't want our voice to be any softer than the others."

Internally, significant aviation-related issues that Carmody wants to keep the board moving on include final reports on Alaska 261, EgyptAir 990, and the Learjet crash involving pro golfer Payne Stewart.

Carmody said the board hopes to have a draft final report of the EgyptAir crash in the Egyptians' hands by March 15. A final report taking into account comments the Egyptians would have on the draft could be out by fall, she said. General target dates for Alaska and the Learjet crash final reports are mid-summer and fall, respectively.

Besides the certification study, her other bold initiative is putting to rest the long-unresolved reconsideration of the board's report on the American Eagle crash. In that accident, the ATR 72 was in a holding pattern awaiting clearance to land at Chicago O'Hare. During the wait, ice formed on the wings of the twin-engine ATR turboprop, sending it out of control and into a field in Roselawn, Ind.

The board cited oversights by ATR, French regulatory and safety authorities, and FAA as contributors to the crash, and generally concluded that the accident could have been prevented had the regulators and manufacturer communicated more effectively. ATR, France's DGAC regulatory agency, the country's BEA accident investigation bureau, and FAA sharply disagreed with the board's conclusions. ATR and the French government submitted petitions for reconsideration backed by additional technical analysis, and FAA added its input in the form of comments on the French government report.

"We want to get those reconsideration petitions resolved soon," Carmody said. "It needs to be done, and I will push to get it done."


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