Source: https://www.federalregister.gov/documents/2002/02/05/02-2718/policy-statement-number-anm-01-04-system-wiring-policy-for-certification-of-part-25-airplanes
Timestamp: 2018-02-21 17:59:06
Document Index: 242383793

Matched Legal Cases: ['art 25', '§\u200921', 'art 21', 'art 25', '§\u200921', '§\u200921', '§\u200925']

5357-5360 (4 pages)
Ambiguous Definition of Configuration
References to General Guidance
Omission of Manufacturing Process Specifications
Modifications Not Compatible With Original Type Design Standards
1. Editorial Changes for Clarification of Meaning
2. Consideration for modifications in process
4. Wire Types and Inspections
Unambiguous Definition of Configurations
https://www.federalregister.gov/d/02-2718 https://www.federalregister.gov/d/02-2718
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.
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.
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.”
Section (§ ) 21.31 (“Type design”): This section defines and describes “type design.”
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 Start Printed Page 5358certification 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.
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.
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.
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.
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.
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.
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.
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. Start Printed 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.”
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.”
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.
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.
The words “when available” were added to the last sentence in the section on “Process Specifications and Modifications Compatible with Original Standards,” for clarification.
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.
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.
Installation drawings should identify the configuration. Such drawings will typically identify:
Wiring routings.
Mounting and support details.
Does not, in itself, constitute an unacceptable hazard.
The system safety assessment should include an assessment of the effects of failures of the airplane wire and its associated wire bundle for equipment Start Printed Page 5360installed 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.
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.
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.
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:
Any other properties affecting strength or functionality of each part.
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.
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.
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.
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.
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.
Issued in Renton, Washington, on January 28, 2002.
[FR Doc. 02-2718 Filed 2-4-02; 8:45 am]