[Federal Register: November 8, 2007 (Volume 72, Number 216)]
[Rules and Regulations]
[Page 63363-63414]
[DOCID:fr08no07-18]

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Part III

Department of Transportation

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Federal Aviation Administration

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14 CFR Parts 1, 21, 25 et al.

 Enhanced Airworthiness Program for Airplane Systems/Fuel Tank Safety
(EAPAS/FTS); Final Rule

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 1, 21, 25, 26, 91, 121, 125, and 129.

[Docket No.: FAA-2004-18379; Amendment Nos. 1-60, 21-90, 25-123, 26-0,
91-297, 121-336, 125-53, 129-43]
RIN 2120-AI31

Enhanced Airworthiness Program for Airplane Systems/Fuel Tank
Safety (EAPAS/FTS)

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: This final rule amends FAA regulations for certification and
operations of transport category airplanes. These changes are necessary
to help ensure continued safety of commercial airplanes. They improve
the design, installation, and maintenance of airplane electrical wiring
systems and align those requirements as closely as possible with the
requirements for fuel tank system safety. This final rule organizes and
clarifies design requirements for wire systems by moving existing
regulatory references to wiring into a single section of the
regulations specifically for wiring and by adding new certification
rules. It requires holders of type certificates for certain transport
category airplanes to conduct analyses of their airplanes and make
necessary changes to existing Instructions for Continued Airworthiness
(ICA) to improve maintenance procedures for wire systems. It requires
operators to incorporate ICA for wiring into their maintenance or
inspection programs. And finally, this final rule clarifies
requirements of certain existing rules for operators to incorporate ICA
for fuel tank systems into their maintenance or inspection programs.

DATES: These amendments become effective December 10, 2007.

FOR FURTHER INFORMATION CONTACT: If you have technical questions about
the certification rules in this action, contact Stephen Slotte, ANM-
111, Airplane & Flight Crew Interface, Federal Aviation Administration,
1601 Lind Avenue, SW., Renton, WA 98057-3356; telephone<PHONE_NUMBER>;
facsimile<PHONE_NUMBER>, e-mail<EMAIL_ADDRESS>If you have
technical questions about the operating rules, contact Fred Sobeck,
AFS-308, Aircraft Maintenance Division, Federal Aviation
Administration, 800 Independence Avenue, SW., Washington, DC 20591;
telephone:<PHONE_NUMBER>; facsimile<PHONE_NUMBER>, e-mail
<EMAIL_ADDRESS>Direct any legal questions to Doug Anderson,

Office of Regional Counsel, Federal Aviation Administration, 1601 Lind
Avenue, SW., Renton, WA 98057-3356; telephone<PHONE_NUMBER>; facsimile
(425) 227-1007, e-mail<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

Authority for This Rulemaking

    The FAA's authority to issue rules regarding aviation safety is
found in Title 49 of the United States Code. Subtitle I, Section 106
describes the authority of the FAA Administrator. Subtitle VII,
Aviation Programs, describes in more detail the scope of the agency's
authority.
    This rulemaking is promulgated under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701, ``General
requirements.'' Under that section, the FAA is charged with promoting
safe flight of civil aircraft in air commerce by prescribing minimum
standards required in the interest of safety for the design and
performance of aircraft; regulations and minimum standards in the
interest of safety for inspecting, servicing, and overhauling aircraft;
and regulations for other practices, methods, and procedures the
Administrator finds necessary for safety in air commerce. This
regulation is within the scope of that authority because it
prescribes--
     New safety standards for the design of transport category
airplanes, and
     New requirements necessary for safety for the design,
production, operation, and maintenance of those airplanes, and for
other practices, methods, and procedures relating to those airplanes.

Contents

I. Executive Summary
II. Background
    A. Summary of the NPRM
    1. The Proposed Rule
    2. Related Activities
    B. Differences Between the NPRM and the Final Rule
    C. Summary of Comments
III. Discussion of the Final Rule
    A. Overview
    B. Design Approval Holder (DAH) Requirements (part 26)
    1. Requirements To Develop ICA
    2. Changes to Location of Design Approval Holder Requirements
    3. Interaction Between New Design Approval Holder Requirements
and Part 21
    4. Compliance Dates
    5. The Design Approval Holder Compliance Plan
    6. Defining the Representative Airplane
    7. Impact on Operators
    8. EZAPs Already Completed
    9. Wire Inspections
    10. Protections and Cautions
    11. Alignment of EWIS and Fuel Tank ICA
    12. Approval of ICA
    13. Rule Applicability
    14. Non-U.S. Manufacturers
    15. General Comments About Design Approval Holder Requirements
    16. Airplanes Excluded From Design Approval Holder and EWIS
Operating Requirements
    C. Electrical Wiring Interconnection System (EWIS) Certification
Rules (part 25 subpart H)
    1. New Subpart for EWIS
    2. The Definition of EWIS (Sec.  25.1701)
    3. Functions and Installation: EWIS (Sec.  25.1703)
    4. Systems and Functions: EWIS (Sec.  25.1705)
    5. System Separation: EWIS (Sec.  25.1707)
    6. System Safety: EWIS (Sec.  25.1709)
    7. Component Identification: EWIS (Sec.  25.1711)
    8. Fire Protection: EWIS (Sec.  25.1713)
    9. Electrical Bonding and Protection Against Static Electricity:
EWIS (Sec.  25.1715)
    10. Accessibility Provisions: EWIS (Sec.  25.1719)
    11. Protection of EWIS (Sec.  25.1721)
    12. Flammable Fluid Shutoff Means: EWIS (Sec.  25.1727)
    13. Powerplant and APU Fire Detection System: EWIS (Sec.
25.1731)
    14. Fire Detector Systems, General: EWIS (Sec.  25.1733)
    15. Engine, Nacelle, and APU Wiring
    16. Designated Fire Zones
    17. Goal of the New Wiring Subpart
    18. Harmonization
    D. Instructions for Continued Airworthiness: EWIS (Sec.  25.1729
and Appendix H)
    1. Requirements for EWIS ICA
    2. ICA as a Single Document
    3. Standard Wiring Practices Manuals
    4. Mandatory Replacement Times
    5. Wire Identification Method Information
    6. Electrical Load Data
    E. Continued Airworthiness and Safety Improvements Subparts for
Operating Rules (parts 91, 121, 125, 129)
    1. Establishment of New Subparts
    2. Continued Airworthiness Subparts and Airworthiness Directives
    3. Type and Scope of Requirements
    F. Operating Requirements for EWIS (parts 121 and 129)
    1. Requirements for Maintenance and Inspection Program Revisions
    2. ICA Developed by Design Approval Holders
    3. Different Requirements for Existing and Future Designs
    4. ICA for Alterations
    5. Alaska Operations
    6. EWIS Inspections
    7. Non-U.S. Registered Airplanes
    8. Taking Airplanes Out of Service
    9. Training
    10. Reporting Requirements
    G. Operating Requirements for Fuel Tank Systems (parts 91, 121,
125, and 129)

    1. Requirements for Maintenance and Inspection Program Revisions
    2. Airplanes Excluded From Fuel Tank System Operating
Requirements
    3. Change in Operator Compliance Date for Auxiliary Fuel Tank
ICA
    4. Original Configuration and Auxiliary Fuel Tanks
    5. Inspection and Maintenance Program Terminology
    H. Regulatory Evaluation
    1. Engine Costs
    2. Wiring System Safety Analysis for Engines
    3. Labor Rates
    4. The Regional Airplane Fleet
    5. Measure of Effectiveness
    6. Operational Impacts
    7. Training Costs
    8. Costs for EZAP Analysis and Inspection of Engines
    9. Engine Costs of Sec.  25.1362
    10. Wire Labeling Costs
    11. Additional Certification and Operator Costs
    12. Previous Rulemaking
    13. Relevance to the Current Fleet
    14. Accidents Indirectly Initiated by EWIS
    I. Harmonization Changes to Transport Category Certification
Rules (Part 25)
    1. FAA/JAA (Joint Aviation Authority) Harmonization
    2. Circuit Protective Devices (Sec.  25.1357)
    3. Precautions Against Injury (Sec.  25.1360)
    4. Electrical Supplies for Emergency Conditions (Sec.  25.1362)
    5. Electrical Appliances, Motors, and Transformers (Sec.
25.1365)
    J. Additional Certification Rule Changes (part 25)
    1. Rules Changed To Accommodate Subpart H
    2. Electrical Equipment and Installations (Sec.  25.1353)
IV. Regulatory Notices and Analyses
V. The Amendments

I. Executive Summary

    Safety concerns about wiring systems in airplanes were brought to
the forefront of public attention by a midair explosion in 1996
involving a 747 airplane. Ignition of flammable vapors in the fuel tank
was the probable cause of that fatal accident, and the most likely
source was a wiring failure that allowed a spark to enter the fuel
tank. All 230 people aboard the airplane were killed. Two years later,
an MD-11 airplane crashed into the Atlantic Ocean, killing all 229
people aboard. Although an exact cause could not be determined, the
presence of resolidified copper on a portion of a wire of the in-flight
entertainment system cable indicated that wire arcing had occurred in
the area where the fire most likely originated.
    Investigations of those accidents and later examinations of other
airplanes showed a collection of common problems. Deteriorated wiring,
corrosion, improper wire installation and repairs, and contamination of
wire bundles with metal shavings, dust, and fluids (which would provide
fuel for fire) were common conditions in representative examples of the
``aging fleet of transport airplanes.''
    The FAA has concluded that current maintenance practices do not
adequately address wiring components, wiring inspection criteria are
too general, and maintenance instructions do not describe unacceptable
conditions, such as improper repairs and installations, in enough
detail.
    With this final rule we are introducing new maintenance,
inspection, and design criteria for airplane wiring to address
conditions that put transport airplanes at risk of wire failures,
smoke, and fire. We are adding requirements for type certificate
holders and applicants for type certificates and supplemental type
certificates to analyze the zones of their airplanes for the presence
of wire and for the likely accumulation of contaminant materials. This
final rule also requires them to develop maintenance and inspection
tasks to identify, correct, and prevent wiring conditions that
introduce risk to continued safe flight. We are requiring that these
tasks be included in new Instructions for Continued Airworthiness for
wiring and that they be compatible with Instructions for Continued
Airworthiness for fuel tank systems. The EWIS ICA must not conflict
with the ICA for fuel tanks, and must avoid duplication and redundancy.
Too frequent disturbance to electrical wiring by repeated moving,
pulling, and flexing of the wire bundles will induce unnecessary stress
on the wiring and its components, which in turn could lead to
degradation, expedited aging, and failures. Thus it is important that
redundant tasks and unnecessary disturbances to the electrical wiring
be minimized. We are amending Title 14 Code of Federal Regulations
(CFR) parts 91, 121, 125, and 129 operating rules to require operators
of transport category airplanes to incorporate maintenance and
inspection tasks for wiring into their regular maintenance programs and
we are clarifying existing requirements for fuel tanks.\1\ We are
creating a new subpart of part 25 to contain the majority of the
certification requirements for airplane wiring, including new rules to
improve safety in manufacture and modification. Finally, we are
creating a new part 26 for design approval holder requirements relating
to continued airworthiness and safety improvements and new subparts in
parts 91, 121, 125, and 129 for the same types of requirements for
operators.
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    \1\ We are not amending 14 CFR part 135 because presently there
are only 20 airplanes with sufficient passenger or payload capacity
to be affected by this rule that fly in part 135 operations. Should
part 135 be amended to permit widespread usage of these larger
transport category airplanes, we may extend the operating
requirements of today's rule to part 135 at that time.
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    Accompanying this final rule are guidance materials in the form of
advisory circulars (AC), which present one way, but not the only way,
to comply with specific parts of these regulations.
    One of the ACs presents a suggested curriculum for electrical
wiring interconnection system (EWIS) training. Existing Sec.  121.375
requires that certificate holders or anyone performing maintenance have
a training program. This requirement ensures that anyone determining
the adequacy of maintenance work (including inspectors) is fully
informed about the procedures and techniques involved and is competent
to perform them. AC 120-94 provides guidance for complying with Sec.
121.375 as it applies to EWIS maintenance and inspection. In AC 120-94
we provide a suggested training program to address the informational
needs of the various people who come in contact with airplane EWIS, and
we encourage operators to include this training voluntarily. While the
Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) had
recommended some form of EWIS training be required for anyone likely to
come into contact with EWIS, we have determined the associated cost
would be unduly burdensome. There are 11 other ACs accompanying this
rule which provide guidance on different requirements contained here. A
few of them have been revised for clarification. In those instances,
this will be noted in section III. Otherwise, except for minor
editorial changes, the guidance accompanying this rule is being
published in the same form in which it was proposed and will not be
discussed here.
    Since the Notice of Proposed Rulemaking (NPRM), the National
Transportation Safety Board (NTSB) has issued Safety Recommendations A-
06-29 through -35 pertaining to fires on one particular model of
regional jet. In the 6 months between October 2005 and March 2006,
there were a total of 6 fires on regional jets. A seventh fire occurred
prior to that 6-month period. The NTSB stated that, in addition to the
danger posed by the fires, 2 of the incident airplanes temporarily lost
all flight displays. The NTSB's investigation

revealed that all of the fires originated from the same electrical
component--an electrical contactor located in the avionics compartment
beneath the floor of the captain's seat. The fires were caused by
moisture-induced short circuits between the electrical terminals of the
contactors. We have issued airworthiness directives (AD) to correct
this unsafe condition. However, if the requirements in this final rule
had been in effect, the type of failure that caused these 7 fires would
not have occurred. This is because several of the new requirements
directly address design issues that led to the fires. This final rule
is meant to proactively address wiring conditions existing in the
transport airplane fleet that we now know affect safe flight and can be
detected, corrected, or prevented.
    We express present value benefits and costs using a 7% discount
rate. The total estimated benefits of this final rule, $801 million
($388 present value) over a 25-year period, are comprised of
operational benefits and safety benefits. The operational benefits are
estimated at $506.3 million ($237.5 million present value). The safety
benefits are estimated at $294.6 million ($150.6 million present
value). This final rule will prevent a portion of fatal and non-fatal
incidents and accidents while decreasing the impact that EWIS
discrepancies have on airline operations.
    The estimated total cost of this final rule is $416 million ($233
million present value) over 25 years. The majority of these costs
($292.2 million, or $147.6 million present value) will be borne by
operators. The remainder of the projected costs will be borne by
aircraft and engine manufacturers, and, to a much lesser extent, the
FAA Oversight Offices.

II. Background

A. Summary of the NPRM

1. The Proposed Rule
    On October 6, 2005 (70 FR 58508), the FAA published in the Federal
Register the Notice of Proposed Rulemaking (NPRM) entitled Enhanced
Airworthiness Program for Airplane Systems/Fuel Tank Safety (EAPAS/
FTS), which is the basis of this final rule.
    In that NPRM, we proposed development of Instructions for Continued
Airworthiness (ICA) for wiring systems and subsequent incorporation of
those ICA into operators' maintenance programs. We also proposed
alignment of the compliance times for operators to incorporate wire and
fuel tank system ICA into their maintenance programs.
    We proposed changes in the certification rules to require more
attention during the design and installation of airplane systems to
conditions that could compromise wire safety and accessibility. And we
proposed a new part 25 subpart that would be dedicated to current and
new regulations about airplane wiring systems.
    If you would like more details about the proposal, you can get a
copy by following the instructions under the Availability of Rulemaking
Documents heading at the end of this preamble.
2. Related Activities
    On July 12, 2005, the FAA published in the Federal Register a
statement of policy for future management of the shared responsibility
between design approval holders (DAH) and operators in achieving
certain types of safety objectives. That stated policy is reflected in
the requirements of this final rule for DAHs to develop ICA for
airplane wiring systems.
    Also published in the July 12, 2005 Federal Register was a
disposition of comments on a previous notice to extend the date for
operators to comply with special maintenance requirements for fuel tank
systems. That date was extended from December 6, 2004 to December 16,
2008.
    On July 7, 2006, we published notice in the Federal Register
stating that, although we had originally proposed to align compliance
times for operator incorporation of ICA for wiring and for fuel tanks,
we later found it impractical to do so. This notice notified operators
that their compliance date for incorporation of fuel tank ICA is still
December 16, 2008.
    Twelve draft ACs on different aspects of the rule accompanied the
NPRM and were made available for public comment at the same time. On
November 8, 2005, the comment period for the ACs was extended to
February 3, 2006, so that it would align with the comment period for
the NPRM.

B. Differences Between the NPRM and the Final Rule

    We have revised the numbering for 14 CFR part 25 subpart H
Electrical Wiring Interconnection Systems (EWIS). We did this to
harmonize as much as possible with the planned European Aviation Safety
Agency (EASA) version of these rules. As discussed later, the design
approval holder requirements proposed in the NPRM as subpart I are now
contained in new part 26, again to harmonize more easily with the
regulatory structure of other national airworthiness authorities. We
also have made some changes to the compliance planning sections of
those rules. In response to comments, we have increased the compliance
time for the design approval holder requirements to 24 months from the
effective date of this rule. We have increased the time for operator
compliance with the EWIS requirements to 39 months from the effective
date of this rule. Because our regulatory process exceeded the time we
had originally planned for issuance of this rule, it is no longer
practical to align the operator compliance dates for the EWIS ICA with
those for fuel tanks. Coordination of the timing of the maintenance
tasks within those ICA is still desirable and possible, so that aspect
of our proposal remains unchanged in the final rule. We have, however,
extended the date for operators to submit ICA for auxiliary fuel tanks
to the FAA Oversight Office.
    We have removed some airplanes from the exclusion lists of the DAH
requirements and the operating rules. This was either because they were
already excluded as a result of the definition of the affected
airplanes or because we have reconsidered the rationale for certain
exclusions. We have also made other, minor, changes in wording to the
proposed rules for the purposes of clarification or harmonization. We
discuss all of the changes in section III of this preamble.

C. Summary of Comments

    The FAA received 39 comment letters about the proposed rule and
guidance material. The comments covered a wide spectrum of topics and a
range of responses, which we discuss more fully below. There was much
support for the general intent of the rule and the guidance material.
There were also requests for changes and for clarification.

III. Discussion of the Final Rule

A. Overview

    This rule is a result of years of study, data gathering, and
collaboration with industry. It has been developed as a solution to the
problem of wire contamination and wire damage on airplanes, which can
result in system failures, smoke, and fire, and can threaten continued
safe flight.
    Examinations by the Aging Systems Task Force of representative
airplanes from the fleet of aging transports revealed wiring that was
deteriorated, corroded, improperly installed and repaired, and
contaminated with materials such as metal shavings, dust,

and fluids.\2\ The NTSB, as well as working groups of the FAA,
industry, and other Civil Aviation Authorities, found these conditions
to be common across the fleet, not just isolated instances of poor
maintenance. While systems have always been subject to careful scrutiny
of their safety and reliability during the certification process, the
wires that connect those systems had been considered appropriately
cared for when fitted and maintained according to standard industry
practices.
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    \2\ Transport Aircraft Intrusive Inspection Project final report
dated December 29, 2000.
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    Now we know that airplane wiring needs more attention. It needs to
be considered as a discrete system, and given the same careful scrutiny
as other systems. The design of wiring systems is important for
creating safe separation from other wires and systems and protecting it
from damage. Inspection and maintenance is important in uncovering and
repairing wire damage and preventing buildup of contaminants that can
cause damage and that also provide fuel for fire. Wire must be
inspected regularly and contaminant buildup must be prevented.
    In considering the problems found on transport category airplanes,
we explored various alternatives. One alternative was to do nothing.
But the result of that approach would be a continuation of incidents
and accidents caused by deteriorated wiring systems. Once we knew there
was a problem affecting safe flight, doing nothing was not really an
option. We could have asked for voluntary support. But voluntary
programs in the past have not always resulted in complete
participation, and a voluntary program could not guarantee the level of
safety we want to ensure. Accordingly, we decided to develop a rule to
correct potential safety problems with airplane wiring, and to require
compliance of all those whose participation is necessary to achieve
that goal.
    This rule enlists the aid of design approval holders in assessing
the wiring on their airplanes and in developing inspection and
maintenance tasks that operators can use to maintain wire safety. It
requires operators to incorporate into their inspection and maintenance
programs tasks for maintaining wire safety that are based on those
developed in accordance with requirements. It introduces new
certification rules for wire separation, identification, system safety,
protection from damage, access, and other aspects of wire safety. It
creates a new subpart in the certification rules for wire certification
so that the many existing requirements are more easily found. It also
requires that design approval holders align inspection and maintenance
tasks for wiring with those for fuel tank systems, to avoid duplication
and to ensure that the most rigorous task is accomplished. As an
example, if the EWIS ICA calls for a general visual inspection of a
certain wire and the fuel tank ICA calls for a detailed inspection of
the same wire, the general visual inspection task would be removed from
the EWIS ICA and the detailed inspection would be retained in the fuel
tank ICA, identified as both a fuel tank task and an EWIS task.

B. Design Approval Holder (DAH) Requirements (Part 26)

    For design approval holders this final rule differs from the
proposal in the following four ways.
     The physical location of the rule has changed, from the
proposed location in part 25, subpart I, to a new part 26.\3\
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    \3\ Since the comments refer to the NPRM, however, the
commenters' original references are retained, including references
to proposed ACs.
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     The compliance date has been changed from December 16,
2007, to 24 months after the effective date of the rule.
     Two changes were made to the compliance plan requirement.
     The definition of the ``representative airplane'' has been
clarified.

We have also made minor wording revisions to section 26.11 for
clarification. They do not change the requirements.
1. Requirements To Develop ICA
    As discussed above, this rule introduces requirements for design
approval holders (DAH) to assess their airplanes in relation to wiring.
The assessment must be performed with an enhanced zonal analysis
procedure (EZAP), which is outlined in a part-25-series advisory
circular accompanying this rule entitled AC 25-27 ``Development of
Transport Category Airplane Electrical Wiring Interconnection Systems
Instructions for Continued Airworthiness Using an Enhanced Zonal
Analysis Procedure.'' This AC was originally titled AC 120-XX ``Program
to Enhance Aircraft Electrical Wiring Interconnection System
Maintenance.'' The material contained in that proposed AC is now
presented in two separate ACs. Guidance for carrying out an EZAP
analysis, as required in the new parts 25 and 26 regulations in this
final rule, is presented in the newly titled No. 25-27 AC named above,
which will be referred to in the rest of this document as the DAH EZAP
AC. Guidance for the operator requirements will be presented in a
separate 120-series AC titled ``Incorporation of Electrical Wiring
Interconnection System (EWIS) Instructions for Continued Airworthiness
into the Operator's Maintenance Program.''
    For each zone on the airplane that contains wiring, DAHs must
develop maintenance and inspection tasks to prevent contaminant buildup
on that wiring and maintain safety. They must then make those tasks
available to operators in the form of ICA readily identifiable as
pertaining to wiring. They must also assess those wiring ICA in
relation to ICA for fuel tank systems to make sure there are no
conflicts or redundancies between the two. The rule includes
requirements for the DAH to submit a compliance plan to the FAA
outlining how it intends to meet these requirements.
2. Changes to Location of Design Approval Holder Requirements
    In the NPRM, we noted that we had not decided on the final location
of the continued airworthiness and safety improvements design approval
holder requirements of part 25, subparts A and I. We requested comments
on this issue, and received 7 comments on the rule location. Transport
Canada and British Airways stated that they wanted the requirements in
part 21. This was to keep the procedural requirements of the new
subpart with the present procedural requirements of part 21 and out of
the airworthiness standards parts of the regulations. EASA, Airbus,
Boeing, Aerospace Industries Association, and the General Aviation
Manufacturers Association stated that they wanted the requirements in a
new part or in part 21. EASA said these requirements must be in a
mandatory part of its system and CS (Certification Specifications) -25,
its equivalent to our part 25, is not mandatory. Others who commented
wanted to maintain part 25 as strictly an airworthiness standard.
    Based on these comments and on discussions with Transport Canada,
EASA, and the Brazilian Agencia Nacional de Aviacao Civil, we decided
to create a new part 26 and move the enabling regulations out of part
25 and into part 21--Certification Procedures for Products and Parts.
We did this for several reasons.
    First, moving these requirements to a new part keeps part 25 as
strictly an airworthiness standard for new transport category
airplanes. This is important because it maintains

harmonization and compatibility among the United States, Canada, and
the European Union regulatory systems. Second, integrating the
requirements into part 21 improves the clarity of how the part 26
requirements will address existing and future design approvals.
    In creating the new part 26, we renumbered the previous sections of
part 25, subpart I, and we incorporated the changes discussed in this
preamble. A table of this renumbering follows:

 Table 1.--Relationship of Proposed Subpart I to Final Rules in Part 26
------------------------------------------------------------------------
                  Part 26                        Part 25, Subpart I
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Subpart A--General
    Sec.   26.1 Purpose and Scope.........  Sec.   25.1801(a) Purpose
                                             and definition.
    Sec.   26.3 Definitions...............  Sec.   25.1801(b) and
                                             25.1803.
    Sec.   26.5 Applicability Table.......  New.
Subpart B--Enhanced Airworthiness Program
 for Aging Systems
    Sec.   26.11 Electrical Wiring          Sec.   25.1805 Electrical
     Interconnection Systems (EWIS)          Wiring Interconnection
     Maintenance Program.                    Systems (EWIS) Maintenance
                                             Program.
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    As noted in the table above, we have added a new Sec.  26.5 to
provide an applicability table that will facilitate identifying those
provisions of part 26 that apply to affected persons at any given time.
As we add subparts to part 26, we will update this table to identify
the applicability of those new subparts. As with new subpart B of part
26 in this final rule, we will specify the details of applicability for
each new subpart in the new subparts themselves.
3. Interaction Between New Design Approval Holder Requirements and Part
21
    It was our intent to treat those provisions of the requirements
establishing standards for design changes and revisions to the ICA as
airworthiness requirements. Adding a statement to the new Sec.  26.1(a)
that the requirements of part 26 are airworthiness requirements clearly
integrates these requirements with the procedures specified in part 21.
The result of treating these requirements as airworthiness requirements
is that any design changes that may be required by part 26 rulemaking
become part of the type design of the aircraft. This makes clear that
the full flexibilities allowed in part 21, such as equivalent level of
safety findings and special conditions, may be applied. Also, we added
Sec.  26.1(c) to make a distinction in part 26 between type
certificates and supplemental type certificates. Typically, for
interpreting part 21, reference to type certificates includes
supplemental type certificates unless usage of that term clearly
indicates otherwise. While the usage of those terms in part 26 is
contrary to the usage in part 21, we did this to make clear
distinctions in requirements within part 26.
    To address the change to ``Special retroactive requirements''
originally proposed in Sec.  25.2(d) and to fully integrate the new
rule with part 21, we made four changes to part 21. First, Sec.  21.7
replaces proposed Sec.  25.2(d) by establishing the applicability of
continued airworthiness and safety improvement requirements. This
section establishes the general applicability of part 26 to design
approval holders, pending and future applicants for design approval,
and type certificate holders and licensees for newly produced transport
category airplanes.
    While Sec.  21.7 makes part 26 applicable to pending applications,
Sec.  21.17(a) clarifies this applicability by adding part 26 to the
exception list of those requirements of the subchapter that are not
established by date of application for a type certificate but by date
that the type certificate is issued.
    For changed products, in the case when the exceptions of Sec.
21.101(b)(1), (2) or (3) apply, new Sec.  21.101(g) makes clear that,
even if an applicant may use an early amendment to part 25, the
applicant must still comply with any applicable provisions of part 26.
For each applicable part 26 provision, an applicant may elect to comply
with a corresponding amendment to part 25 that is issued on or after
the date of the part 26 amendment. Under the normal application of
Sec.  21.101, if the exceptions of Sec.  21.101(b) do not apply, the
applicant would be required to comply with the latest amendments of
part 25 in lieu of the requirements of part 26.
    Sections 21.31 and 21.50 are revised to make it clear that the
Airworthiness Limitations section of the ICA is part of the type design
and that changes to the ICA generated under part 26 must be made
available as part of the total ICA.
    These changes to part 21 do not change or add any new requirements
to those proposed in the NPRM. Rather, they clarify the relationship
between existing part 21 and new part 26.
4. Compliance Dates
    Several commenters proposed changes to the DAH compliance dates for
subpart I (now part 26) requirements. The proposal would have required
DAHs of existing airplanes to submit ICA for approval to the FAA
Oversight Office by December 16, 2007. This was based on an expected
effective date of June 30, 2006 for the final rule, and would have
allowed DAHs 18 months to complete compliance. The proposed operator
requirements would have allowed operators 12 months from the date DAHs
completed their ICA to incorporate EWIS tasks into their maintenance
program. The compliance date for operators (again based on an expected
final rule effective date of June 2006) was December 16, 2008.
    Avions de Transport Regional (ATR), Aerospace Industries
Association and General Aviation Manufacturers Association (AIA/GAMA),
General Electric (GE), and Boeing requested a longer compliance time
for the DAH requirements. ATR specifically proposed 30 months because
it said it will need to review and update all of its maintenance
documentation. GE requested 36 months. Boeing and AIA/GAMA requested
the compliance time for DAHs be increased to 24 months. Boeing and AIA/
GAMA noted that industry, through ATSRAC, originally identified 24
months as the time needed to conduct the EZAP analysis for their
existing airplane configurations. But the FAA has now proposed
additional requirements, such as evaluating type certificate (TC)
holder changes mandated by airworthiness directives (AD) and compliance
plan activities. The commenters noted that the original schedule and
resource analysis did not account for these additional activities.
Additionally, Boeing and FedEx requested that the rule include required
time periods for FAA review and approval activities involved in the
compliance plans. Boeing and Airbus noted that the rules do not
currently limit the amount of time the FAA will take to review and
approve documents, which will negatively impact their compliance time.
Boeing stated that most DAHs will require the full 90 days for
developing a compliance plan, and will not initiate that plan until
they obtain FAA approval. So to ensure that they have an appropriate
time for compliance activities, they'll need FAA approval immediately,
which is impractical.
    Boeing and AIA/GAMA also said that the hard compliance dates and an
expected final rule issuance in early 2007 will leave DAHs with less
than 12 months to comply with the subpart I requirements. Along with
Airbus and GE, they requested that we revise the compliance dates to
represent a number

of months after the effective date of the rule, rather than a hard
date. AIA/GAMA noted that this approach would prevent our process and
schedule for issuing the final rule from impacting DAH compliance
dates.
    We agree with the commenters that additional time should be allowed
for DAH compliance with 26.11. While we understand that ICA for EWIS
have already been developed for a number of affected airplanes, we also
understand that not all DAHs have begun this activity. In addition, as
discussed later, DAHs that have already developed EWIS ICA may not have
addressed the ``representative airplane'' configurations, as required
by this rule. However, because DAHs would need to plan and coordinate
with the FAA anyway, we do not believe the requirements to do so will
significantly increase the amount of time needed to comply. In
consideration of these factors, we believe that 24 months will allow
sufficient time for DAHs to develop and submit the necessary compliance
plan, draft data and documents, and final data and documents to show
compliance with today's rule.
    We have made a minor revision to section 26.11(d)(3), (d)(4) and
(d)(5). This is to clarify that the affected pending or future
applicants must comply either by a date based on the effective date of
the rule, or by the date of approval of the related certificate. Even
though we specifically discussed the intent of these dates in the NPRM
preamble, we believe that using the term ``approval of the
application,'' which appeared in the proposal (in proposed Sec.
25.1805(c)(3), (c)(4), and (c)(5)) indicating dates for compliance, may
have caused confusion. So, we have replaced the term ``application''
with the term ``certificate'' in 26.11(d)(3), (d)(4) and (d)(5).
    We are not including FAA-required time periods for review and
approval of the required compliance plans. Instead, expectations for
FAA personnel have been defined in a new FAA order \4\ that directs the
Aircraft Certification and Flight Standards Services in their roles and
responsibilities for implementing these initiatives. The order includes
expected times (6 weeks) for reviewing and approving DAH compliance
plans, plans to correct deficiencies, and draft and final compliance
data and documents. To facilitate implementation, we will also train
affected personnel in their roles and responsibilities and provide in-
depth familiarization with requirements of the regulations and
associated guidance. The FAA's Aviation Safety organization's recent
registration as an ISO (International Organization for Standardization)
-9001-compliant organization will also facilitate standardized and
timely implementation of the review and approval process.
---------------------------------------------------------------------------

    \4\ Order 8110.26, ``Responsibilities and Requirements for
Implementing Part 26 Safety Initiatives,'' will be released
concurrently with this rule.
---------------------------------------------------------------------------

    Several operators also requested revisions to the DAH compliance
dates, noting the potential adverse impact on them because of the time
it could take for FAA review and approval. Air Transport Association
(ATA) recommended that Sec.  25.1805(c)(1) (now 26.11(d)(1)) be
rewritten to provide a reasonable period of time (90 days) for the
necessary FAA review and approval activities. ATA noted that the amount
of time the FAA will take to review and approve TC holders' EWIS/FTS
ICA could reduce operator compliance time significantly. FedEx made
similar comments and noted that compliance dates should acknowledge
time for approval of compliance documents, distribution of those
documents, operator planning for addressing the requirements, and final
release of the changes in the operator's program. Royal Dutch Airlines
(KLM) was also concerned about FAA review and approval impacting
operators' compliance time and requested that the operator compliance
date be one year after ICA are approved. Boeing, ATR and U.S. Airways
also stated that the compliance time for the operational rules should
be based on availability of needed data.
    Continental requested that operators be allowed 18 months rather
than 12 months to comply. It said a thorough training program would be
needed for maintenance personnel not familiar with wiring and its
components. This would require additional effort by the operator not
contemplated by simply having ICA incorporated into a maintenance task
or inspection program. Additionally, Continental stated that contract
maintenance personnel must also be trained for systems they maintain.
    The National Air Carrier Association (NACA) requested that
operators have two years for compliance, dependent on DAHs complying
with their requirements on time.
    Based on rationale the ATA provided for requesting the change, we
infer that ATA would like additional time (90 days) added to the
operator's compliance time rather than to the DAH's compliance time.
While it is inappropriate to put requirements for the FAA in a rule
applicable to DAHs, we have, as discussed previously, identified
expectations for FAA review and approval (including timeframes) in an
internal FAA order. The length of time to review plans, data, and
documents depends largely on the quality of the submittals. Acceptable
documents will take less time to review.
    We have structured the requirements of the DAH rule and developed
complementary guidance to facilitate timely review and approval of DAH
submittals (compliance planning, draft document reviews, etc.). We do
agree, however, that a modest increase in operator compliance time
would help ensure that operators are not impacted by the FAA review and
approval process. We have revised the EAPAS compliance date for
operators from 12 months to 15 months.
    Regarding the NACA request for a two-year compliance time, in the
past we have imposed numerous maintenance program revision requirements
through operational rules and ADs. Twelve months has been the typical
compliance time for these changes and has been sufficient for operators
to comply. The maintenance actions described in the maintenance program
changes would be accomplished sometime later, as specified in the
maintenance program. So operators will have sufficient time to plan and
conduct the necessary EWIS training.
    On July 30, 2004, (69 FR 45936), we extended the Fuel Tank Safety
Operational Rule compliance dates to December 16, 2008, for reasons
outlined in that final rule. Because of the similar timelines for
operator incorporation of the FTS and EAPAS maintenance actions into
their programs, we had determined that aligning the compliance dates
for the FTS and EAPAS maintenance program changes would allow operators
to revise their maintenance program once to address both safety
initiatives. However, given delays in issuing the EAPAS rulemaking
proposal and the expectation for industry to have the FTS ICA developed
for compliance with the EASA rule (December 2007) and the FAA rule
(December 2008), we have determined that the benefits of aligning the
FTS and EAPAS compliance dates are not substantial enough to justify
further delay in implementing FTS maintenance actions. As previously
discussed, we are not extending the FTS operational rule compliance
date in this final rule.

5. The Design Approval Holder Compliance Plan
    As noted above, in the NPRM we contemplated submission of a
proposed means of compliance, identifying all required submissions to
the FAA. The NPRM proposed submission of--
     A project schedule identifying all major milestones.
     A detailed explanation of how the proposed means of
compliance would be shown to comply if it differed from that described
in advisory material.
     A proposal for submitting a draft of all compliance items
no less than 60 days before the compliance due date.
     A proposal for how the approved ICA would be made
available to affected persons (operators and others required to comply
with this rule).
    The proposal stated that if the FAA notified the DAH of
deficiencies in its proposed compliance plan or in its implementation
of that plan, the DAH must submit a corrected plan to the FAA Oversight
Office within 30 days. All of these compliance plan requirements were
contained in proposed Sec.  25.1805(d) and (e).
    Airbus requested that Sec.  25.1805(d) and (e) be removed because,
it said, these requirements are unnecessary. Airbus believes the only
important compliance date is the final date for DAHs to submit the data
and documents necessary to support operator compliance. Boeing
recommended we remove the Sec.  25.1805(d)(3) requirement to identify
deviations to methods of compliance identified in FAA advisory material
because it does not agree that proposed methods of compliance should be
compared to other methods. Instead, it said, they should be evaluated
on their own merits.
    The FAA agrees that some provisions of proposed Sec.  25.1803(d)
and (e) could be removed without adversely affecting our ability to
facilitate TC holder compliance. Specifically, proposed paragraph
(d)(3) would require TC holders to identify intended means of
compliance that differ from those described in FAA advisory materials.
While this is still a desirable element of any compliance plan, we have
concluded that an explicit requirement is unnecessary and it is not
included in this final rule. As with normal type certification
planning, we expect that TC holders will identify differences and fully
discuss them with the Oversight Office early in the compliance period
to ensure that these differences will ultimately not jeopardize full
and timely compliance. Because we believe that timely review and
approval is beneficial and will save both DAH and FAA resources, the
advisory material recommends that if the DAH proposes a compliance
means differing from that described in the advisory material, the DAH
should provide a detailed explanation of how it will demonstrate
compliance with this section. The Oversight Office will evaluate these
differences on their merits, and not by comparison with FAA advisory
material.
    Similarly, proposed paragraph (e) contains provisions that would
have authorized the Oversight Office to identify deficiencies in a
compliance plan or the TC holder's implementation of the plan and
require specific corrective actions to remedy those deficiencies. While
we anticipate that this process will still occur in the event of a
potential non-compliance, we have concluded that it is unnecessary to
adopt explicit requirements to correct deficiencies and have removed
them from the final rule. Ultimately, TC holders are responsible for
submitting compliant EWIS ICA by the specified date. This section
retains the requirements to submit a compliance plan and to implement
the approved plan. If the Oversight Office determines that the TC
holder is at risk of not submitting compliant EWIS ICA by the
compliance date because of deficiencies in either the compliance plan
or the TC holder's implementation of the plan, the Oversight Office
will document the deficiencies and request TC holder corrective action.
Failure to implement proper corrective action under these
circumstances, while not constituting a separate violation, will be
considered in determining appropriate enforcement action if the TC
holder ultimately fails to meet the requirements of this section.
    Additionally, in reviewing the comment, we realized that the rule
text could more clearly state our intent to allow DAHs flexibility to
modify their approved plan if necessary. So the final text of proposed
Sec.  26.11(f) has been modified to read ``each affected person must
implement the compliance plan, or later approved revisions * * *.'' In
response to Airbus' comment that the only important compliance date is
the final date for DAHs to submit the data and documents, we must
reiterate that we believe a compliance plan is important. The purpose
of a 90-day compliance date for the compliance plan is to allow all
parties to be informed about how the DAH will be meeting its
requirements and to ensure that the all necessary data will be provided
to the operators on time. Early development of a compliance plan will
give assurance of development of all the necessary data in time for the
operators to comply with their requirements.
6. Defining the Representative Airplane
    Boeing requested that we define in advance of the final rule which
TC holder configuration changes mandated by ADs should be considered in
the EZAP. Boeing and AIA/GAMA noted that the DAH must consider airplane
configurations representative of each airplane model plus DAH-developed
modifications mandated by AD. Boeing stated that because ADs are
applicable to operators and not DAHs, and because most ADs are not
applicable to all airplanes within a specific model range, it is
difficult to define a representative airplane. Boeing does not believe
the proposed Sec.  25.1805 (now Sec.  26.11) compliance time allows
enough time to properly define the representative configuration.
    As previously discussed, we have increased the proposed DAH
compliance time for a number of reasons, one of which was to allow
sufficient time for the DAH to identify the representative
configuration for each affected airplane model.
    As discussed in the NPRM, the purpose of the requirement to address
all TC-holder-developed modifications mandated by AD is to make the
EZAP as complete and accurate as possible. It would serve no purpose to
require the TC holder to analyze an airplane configuration no longer in
service because an AD has mandated its modification. Therefore, TC
holders must assess all these modifications to determine whether they
affect the results of the EZAP. Because TC holders own the design data
for both the original configurations and these modifications, they are
the only entities capable of performing these assessments. When TC
holders develop AD-mandated modifications for airplanes still in
production, they normally incorporate these same modifications into new
airplanes. So this requirement imposes little additional burden for
these airplanes. At the same time, we recognize that it would be
unreasonable to require the TC holder to analyze modifications
developed by third parties. Accordingly, this requirement is limited to
TC-holder-developed modifications.
    In reviewing Boeing's comment, we recognized that the proposed
definition of ``representative airplane,'' i.e., ``the configuration of
each model series airplane that incorporates all variations of EWIS
used on that series airplane * * *,'' could be interpreted in different
ways. It could be interpreted as applying to all post-production

modifications, not just those mandated by AD and those DAH-developed
modifications introduced into production. It could also refer to
variations used for post-production modifications, as well as those
used in production. Boeing correctly understands that we intended to
require evaluation only of variations used in production and those
post-production modifications mandated by AD. Section Sec.  26.11(b)
has been revised to clarify this. For those design changes made in
production for which the TC holder has issued service bulletins
describing post-production equivalents, the ICA should identify those
service bulletins with the corresponding production configurations.
This will enable operators that have incorporated these service
bulletins to determine that the ICA for the production modification
also applies to them.
7. Impact on Operators
    Boeing asked that we separate the operational rule from DAH
requirements, with a separate comment period, so that defined service
information and associated costs can be evaluated by the operators.
Boeing contended that consolidating DAH and operational requirements
into one rulemaking action with one comment period prevents the FAA
from obtaining accurate cost estimates and prevents operators from
determining the true impact of the proposal on their operations. NACA
also expressed concern that operators cannot know the full impact of
this rule until DAHs develop the required ICA.
    We have decided against separating the operational rules from the
DAH requirements. Separating the rules would not change the technical
requirements contained in this final rule but would substantially delay
implementation of the EAPAS safety initiative. Thus, it is essential to
include both certification and operational requirements in the final
rule to ensure maximum safety benefits to the flying public.
    In addition to issues of timeliness, we note that while some
operators will not know the precise effects of the ICA developed by TC
holders on their maintenance programs, they should have a good
understanding of the nature and scope of the program from the NPRM and
the guidance material provided in the DAH EZAP AC (AC No. 25-27). As
discussed, both of these were derived from ATSRAC's recommendations,
which operators played a major role in developing. In addition, since
2004, multiple operators have been involved with several airplane
manufacturers in developing EWIS ICA using the EZAP analysis described
in the DAH EZAP AC. This has been accomplished by integrating EWIS ICA
development into the airplane manufacturer's normal maintenance
development program. Operators of the airplane model for which a
maintenance program is being developed (or revised) are always involved
in the development of that program. Therefore, these operators do know
the impact of integrating these new EWIS ICA into their maintenance
programs.
8. EZAPs Already Completed
    Boeing asked that we include a statement in the final rule
indicating that EZAP analyses conducted prior to the effective date of
the final rule, and resultant ICA, comply with subpart I (now part 26)
requirements. Boeing questioned the statement that the proposed time
frames are supported by experience gained by EZAPs already performed,
when the NPRM did not discuss the acceptability of those analyses. It
noted that several EZAP analyses were conducted using MSG-3 \5\
methods, which differ slightly from those contained in proposed AC 120-
XX (now the DAH EZAP AC, No. 25-27). Boeing noted that, for those
cases, it must show the FAA Oversight Office how the previous analyses
were conducted, make any necessary changes, obtain industry agreement,
and have the FAA approve the resulting ICA.
---------------------------------------------------------------------------

    \5\ Air Transport Association (ATA) Maintenance Steering Group 3
(MSG-3) is a document containing a logic process used by the
airlines and manufacturers to develop scheduled maintenance programs
for an airplane.
---------------------------------------------------------------------------

    We believe that work done before adoption of the rule will reduce
the level of effort required for DAHs to comply with the rule. But we
also recognize that some additional work may be necessary for DAHs to
show compliance. For example, EWIS ICA may not have been aligned with
FTS ICA or may not have been developed for the ``representative
airplane'' as defined in the rule. Therefore previous work cannot
automatically be considered compliant. Because we cannot say with any
confidence that no more work will be required, we are not adopting
Boeing's recommendation.
9. Wire Inspections
    The National Air Traffic Controllers Association (NATCA) called the
proposal inadequate because it relies on enhanced zonal inspections to
detect latent failures in the wiring system, and it said that zonal
inspections detect only visible deteriorated wire.
    The commenter said that without periodic or real-time monitoring of
airplane wiring, there is no way to predict a degraded state and
prevent future wire failures. NATCA recommended that we include
requirements for either continuous on-board detection of airplane
wiring faults, such as that provided by system self-test features, or
periodic maintenance tasks, to detect both visible and hidden
degradation in the wiring system.
    The requirements adopted today do not prevent use of wire
monitoring or fault detection technology. Multiple non-destructive
inspection (NDI) tools and real-time monitoring techniques are being
developed for use in aircraft wiring inspection. However, current NDI
reflectometry technology is not yet mature enough for its use to be
mandated by the FAA. Although real-time monitoring technology, such as
arc fault circuit breaker technology, is further along in development,
it too is not yet mature enough to address all circuit types. We expect
that these technologies, when available, may be relatively more
expensive than conventional methods, so the need for visual inspection
of EWIS would remain even if this technology were widely available. We
made no change based on this comment.
10. Protections and Cautions
    Boeing requested that we remove from subpart I (now part 26) the
requirement to include ICA instructions for protection and caution
information to minimize contamination and accidental damage during
maintenance activities. It suggested this language should be added to
the operating rule. Boeing considers the methods of protecting wiring
during maintenance to be best determined by the maintenance provider
and dependent on the type of maintenance activity underway. Boeing also
noted that operators who have already developed protection schemes
based on their experience will be required by the operational rules to
replace this with the one provided by the TC holder. Boeing does not
believe this is a positive step towards increased protection of EWIS.
    United Airlines stated its support for requiring airplane
manufacturers to include specific recommendations for when and how to
protect wire bundles from damage during different phases of
maintenance.
    We infer that Boeing is referring to the requirement in
H25.5(a)(1)(vi). That requirement applies both to new type certificates
complying with Sec.  25.1729

(proposed as Sec.  25.1739) and existing type certificates complying
with part 26. The requirement is consistent with ATSRAC's
recommendations. These recommendations were based on recognition that
the TC holder will have the best understanding of EWIS material
properties and vulnerabilities, and will be in the best position to
identify what protection and caution measures are needed. If operators
have developed their own instructions, they may be used as alternatives
or as supplements to those provided by the TC holder, if approved by
their Principal Inspector (PI). We have provided guidance to the FAA
field offices to allow for consideration of an operator's alternative
to that approved by the FAA Oversight Office. We made no rule change
based on this comment.
11. Alignment of EWIS and Fuel Tank ICA
    AIA/GAMA and GE requested that the last sentence of proposed Sec.
25.1805(b) (now Sec.  26.11(b)), requiring minimization of redundant
requirements between EWIS and fuel tank ICA, be deleted. The commenters
stated that this is an economic and customer service issue beyond the
scope of the FAA's safety interest.
    Boeing requested we include, within proposed Sec.  25.1805(b), the
levels of alignment of FTS and EWIS maintenance actions that will be
acceptable for compliance. While Boeing sees the benefit of eliminating
redundant maintenance activities, it considers itself unable to
determine how to show compliance with this requirement.
    Minimizing redundant requirements is not just an economic issue for
operators. One of ATSRAC's findings is that repeated disturbance of
EWIS during maintenance is itself a source of safety problems.
Therefore, while ensuring that all necessary maintenance is performed,
it is also our objective to minimize disturbance by eliminating
redundant requirements. Too frequent disturbance to electrical wiring
by repeated moving, pulling, and flexing of the wire bundles will
induce unnecessary stress on the wiring and its components, which in
turn could lead to degradation, expedited aging, and failures. Thus it
is important that redundant tasks and unnecessary disturbances to the
electrical wiring be minimized. Operators will review their maintenance
tasks and coordinate with the DAHs to ensure that tasks are
incorporated into their maintenance program for the highest level of
safety and performed in the manner most suitable for their operation.
    As discussed earlier, Boeing and other TC holders have been
required to develop ICA since 1981, and maintenance manuals even before
that. In developing ICA, TC holders routinely review individual tasks
to align them with other tasks being developed. This is done both to
avoid redundancy and to eliminate confusing or conflicting instructions
that could inadvertently lead to improper maintenance with unsafe
consequences. The purpose of the requirement to align the ICA is no
different. The intended ``levels of alignment'' are the same as would
be expected for ICA developed in connection with original type
certification. The MSG-3 and Maintenance Review Board (MRB) processes,
with which Boeing and other affected TC holders are familiar, have the
same objectives. The DAH EZAP AC, ``Development of Transport Category
Airplane Electrical Wiring Interconnection Systems Instructions for
Continued Airworthiness Using an Enhanced Zonal Analysis Procedure,''
No. 25-27, describes means of compliance that will achieve these
objectives. It provides a step-by-step process to assist applicants in
compliance with the electrical wiring interconnection system (EWIS)
maintenance requirements. This process includes a step requiring an
analysis of the related maintenance tasks to ensure that they are
consolidated and/or aligned to maximize effectiveness and eliminate
redundancies and duplications between the EWIS and fuel tank ICA.
    The airplane manufacturer will align the ICA requirements to the
greatest extent possible. No change to the final rule is necessary.
12. Approval of ICA
    Boeing and AIA/GAMA requested further clarification of proposed
Sec. Sec.  25.1739 (now Sec.  25.1729) and 25.1805(b) (now Sec.
26.11(b)) requirements that ICA prepared in accordance with paragraph H
25.5 of Appendix H be submitted to the FAA Oversight Office for
approval. AIA/GAMA, Airbus, and FedEx recommended that EWIS ICA be
accepted by the FAA, rather than approved, with the exception of any
applicable airworthiness limitation items (ALI), which should be
approved. The commenters were concerned that the proposed requirements
are not consistent with the current requirement in Sec.  25.1529 that
ICA be found acceptable to the FAA (except for ALI, which must be
approved). FedEx also stated that creation of separate ``FAA-approved''
ICA will lead to confusion and fragmentation of what should be an
integrated inspection program.
    As discussed earlier, one of the primary objectives of these DAH
rules is to ensure that operators have at least one source of FAA-
approved data and documents that they can use to comply with
operational requirements. This objective would be defeated if the
required data and documents were not, in fact, approved. Only by
retaining authority to approve these materials can we ensure that they
comply with applicable requirements and can be relied upon by operators
to comply with operational rules. We believe that there are differences
between EWIS ICA and other ICA that necessitate approval of EWIS ICA:
     EWIS ICA are the means for compliance with some of the
technical requirements of new subpart H (Sec.  25.1707 relating to
system separation and Sec.  25.1711, component identification).
     EWIS ICA contain highly technical information such as
electrical loads data and wiring practices standards that are more
complex than typical maintenance instructions.
     EWIS ICA require a degree of consistency and
standardization that may not be necessary for other ICA.
    We agree that further clarification is needed regarding FAA
Oversight Office approval of EWIS ICA. We do not intend to approve all
documents that contain EWIS ICA details, such as the airplane
maintenance manual. We do intend to review references in all documents
that are referred to in the EWIS ICA source documents. We have made
changes to the AC guidance information (AC 25.1701-1) to clarify
exactly what documents the FAA Oversight Office will approve. No change
to the final rule is necessary.
13. Rule Applicability
    Today's rule is applicable to airplanes with a passenger capacity
of 30 or more passengers or a payload capacity of at least 7,500 pounds
operating in parts 121 and 129. NATCA requested that we consider
revising the rule applicability to address all transport airplanes
regardless of size or type of operation. It stated that all transport
airplanes are subject to the same aging safety concerns, and passengers
should have one level of safety.
    The FAA has used these size criteria for the applicability of other
rulemakings because they capture the airplanes carrying the vast
majority of passengers and cargo. Similarly, by limiting applicability
of the EAPAS operational rules to parts 121 and 129, we focus these
requirements on the

airplanes that transport most passengers and cargo. Based on our
analysis, the additional safety benefit of extending the operational
requirements to all transport airplanes would not justify the
additional costs of doing so. We will continue to review this issue
and, as this rule is implemented, if we can demonstrate that it can be
applied cost effectively to smaller airplanes or other operators, we
may consider further rulemaking.
    Several commenters requested revisions and clarification of
applicability with respect to supplemental type certificates (STC).
EASA requested we revise the applicability of Sec.  25.1805 (now Sec.
26.11(d)) to include STCs that significantly affect EWIS.\6\ British
Airways stated its support for the existing applicability, agreeing
that the analysis performed by the DAH would cover the EWIS they are
responsible for as well as the wiring changed or added by others. FedEx
requested clarification on means of compliance for STCs.
---------------------------------------------------------------------------

    \6\ EASA plans to address STCs in its NPA.
---------------------------------------------------------------------------

    Additionally, the ATA requested we revise proposed Sec.
25.1805(c)(4) (now Sec.  26.11(d)) to clarify its applicability only to
new STCs issued after the effective date of the final rule and not to
existing STCs that may be modified after the effective date of the
rule. The ATA noted that some STCs are modified to expand the STC
effectivity as an operator's fleet grows and should not be evaluated
for compliance with Sec.  25.1805(c)(4).
    Section 26.11 will apply to future applicants for STCs and to
existing TCs. As explained in the NPRM, we decided not to include
existing STCs in this section for two reasons. First, most existing
STCs do not provide detailed instructions for wiring installation,
relying on the judgment and expertise of the individual installer. In
most cases it would not be possible for the current STC holder to
evaluate these wiring installations. Second, in most cases, installers
have followed the TC holder's wire routing and installed STC wiring in
or adjacent to existing wiring. In these cases, implementing the
maintenance programs developed by the TC holder should adequately
address the safety issues identified in this rule that may exist in the
STC wiring. Our conclusion here is consistent with ATSRAC's
recommendations.
    However, we will not revise Sec.  26.11 to exclude modifications to
existing STCs. As discussed, one reason we are not applying this rule
to existing STCs is that in many cases existing STCs do not include
data for EWIS that can be evaluated. As discussed in the NPRM, we
believe it is important that EWIS ICA be provided for all future STCs,
including changes to existing STCs. We have revised Sec.  26.11(d) to
clarify that ``if an existing STC is amended, this section would apply
to the amendment.''
    The extent of the review required for changes to existing STCs
would be limited to the newly proposed changes. Applicants would not be
required to evaluate the entire design change approved under their
existing STC. For example, if an applicant proposed to add additional
monitors to an existing in-flight entertainment STC, only the EWIS
supporting the additional monitors would need to be evaluated for the
impact to the ICA. If an applicant were merely adding airplane models
of the same configuration to an existing STC, they would not need to
evaluate their STC.
    Boeing Wichita asked whether it would be required to evaluate EWIS
for an entire airplane in order to comply with requirements of Sec.
25.1805 (now Sec.  26.11) when applying for an STC.
    We do not intend to require applicants for design changes approval
to evaluate the EWIS of the entire airplane. Rather, these applicants
must evaluate whether their proposed design change would require
revision of the ICA developed by the TC holder (and any previous STC
applicants) in compliance with Sec.  26.11 to correctly address the
design change. An example would be if an STC applicant proposed to add
EWIS to a zone that did not previously have EWIS. The applicant would
need to develop an ICA revision providing for any maintenance actions
within that zone that may be necessary to comply with Appendix H to
part 25. We have revised Sec.  26.11 by adding a new paragraph (c) to
clarify this requirement.
14. Non-U.S. Manufacturers
    Airbus also commented that proposed Sec.  25.1805 paragraphs (b),
(d), and (e) (now Sec.  26.11(b) and (e)) fail to acknowledge that non-
U.S. manufacturers will likely have to comply with similar regulations
issued by their own authorities. Airbus said that discussion of the
compliance plan and review of the compliance items should be delegated
to the relevant foreign authority, as far as permitted by existing
Bilateral Aviation Safety Agreements.
    We recognize the important role other national authorities are
likely to play in implementation of this rule. In addition to the on-
going efforts to harmonize these requirements, we have been working
closely with the other national authorities to define appropriate
roles, responsibilities, and relationships among all affected
authorities. As discussed in the NPRM, the compliance planning
provisions are equally important for foreign TC holders, and we expect
to have mutually agreeable arrangements with their authorities on how
this planning will be overseen.
15. General Comments About Design Approval Holder Requirements
    We received a number of general comments responding to the concept
of DAH requirements rather than to the DAH requirements in this
specific rulemaking. We responded to these types of comments in the
comment disposition document accompanying our policy statement titled
``Safety--A Shared Responsibility--New Direction for Addressing
Airworthiness Issues for Transport Airplanes.'' Both were published in
the Federal Register on July 12, 2005. As a result, we will not respond
to such comments again here. We have included them, and our responses,
in a separate document in the docket. That document is titled ``General
Comments about DAH Requirements Sent to Docket Number 18379.''
    Boeing and AIA/GAMA did not agree with our assessment that DAH
rules are necessary to support this initiative. They requested we
remove proposed Sec.  25.1805 (now Sec.  26.11) from the rule. They
contended that
     The required material is neither complex nor limited to
the DAH,
     Operators have the option of developing an enhanced zonal
inspection program without participation of the DAH, and
     Operators will not be required to adopt maintenance
programs developed by the DAH.
    Both commenters stated that developing EWIS ICA is not complex.
They noted the EZAP process is based on MSG-3 maintenance program
development procedures, which are neither complex nor limited to the
DAH. They believe that the DAH type design data needed for development
of maintenance tasks is also available to operators.
    Boeing and AIA/GAMA also said that use of the MSG-3 process by the
DAH alone will only account for airplane configurations certified by
the DAH and some, but not all, AD-mandated modifications. Unique
configurations that evolved after delivery will not be considered by
the DAH. Boeing contended that operators are capable of assessing their
airplane configurations using proposed AC 120-XX (now the DAH EZAP AC)
and developing an

enhanced zonal inspection program without DAH involvement.
Additionally, Boeing stated that operators could develop ICA more
efficiently because they could concurrently address the baseline
configuration and any configuration changes made in service.
    As discussed previously, the policy statement provides criteria for
deciding when DAH regulations are necessary.
    Appendix H paragraph H25.5(a)(1) identifies information required to
perform the analysis and develop maintenance tasks. While some of this
information may be available to operators without assistance from the
DAH, operators would not have access to all of it.
    Also, the methodology described in the AC may appear to be
relatively simple, but applying it properly requires considerable
expertise and judgment and can be quite complex. DAH involvement is
necessary to ensure it is applied properly. We believe that DAH
regulations are necessary for this safety initiative to ensure all of
the representative type design configurations are addressed in a timely
manner. The ``representative'' airplane is defined as the configuration
of each model series airplane that incorporates all the variations of
EWIS used on that model, and that includes all TC-holder-designed
modifications mandated by AD, as of the effective date of this rule.
    Existing regulations regarding ICA as adopted in Amendments 21-50
and 25-54 require DAHs to provide ICA for the airplane as a whole. This
rule simply applies that same policy to EWIS, which were not
specifically addressed by those amendments.
    We note that in the form in which the rules were proposed,
operators would be required to implement EWIS ICA based on those
``developed by the type certificate holder.'' That statement did not
clearly articulate our intent and we have corrected that language in
the final rule to reference ``in accordance with the provisions of
Appendix H of part 25 of this chapter applicable to each affected
airplane * * *.''
    Both Boeing and AIA/GAMA requested that we establish, within the
final rule, all requirements for the DAHs regarding consistency,
standardization of process and requirements, and technical guidelines.
They do not believe the rule or guidance material is comprehensive
enough to enable DAHs to comply. Boeing stated that the root cause of
past difficulties with voluntary compliance lies with unclear
regulatory requirements and lack of appropriate guidance. Boeing noted
that the FAA attempted to address this problem in the proposed rule,
but said those attempts have fallen short of what is needed. It quoted
draft AC 25-XX: ``* * * the Compliance Team, as soon as possible after
issuance of the safety initiative rule, will provide the DAHs with our
expectations for the required analysis content [and] describe to the
DAHs our expectations for the content and format of their data * * *
.'' Boeing contends that visibility of requirements, expectations, and
technical requirements would ensure uniformity of application and
inform operators of what information they would receive from DAHs.
    We partially agree. The program plan for the aging airplane rules
was to release associated guidance and policy for public comment upon
release of the NPRMs. We believe this approach should have helped
clarify our expectations of what is considered an acceptable approach
to compliance.
    For this initiative, both the performance standards and guidance
materials were developed by ATSRAC, which had representatives from the
affected industry. We must presume that industry, in helping to develop
these materials, understood what would be expected for new TCs. We
consider these same materials to be sufficient for application to
existing TCs.
    The comprehensiveness and level of detail of requirements and
related advisory material is at least equivalent to that for other ICA
currently in Appendix H, which DAHs have successfully complied with for
25 years. The purpose of compliance planning provisions is to ensure
that DAHs work closely with the FAA, as they do for initial
certification, in developing compliant data and documents. We made no
change to the rule due to this comment. However, we will clarify in AC
26-1 that the compliance team will meet with DAHs as soon as possible
after issuance of the final rule to ensure that guidance materials and
expectations related to rule implementation are clear.
16. Airplanes Excluded From Design Approval Holder and EWIS Operating
Requirements
    The DAH requirements and the EWIS requirements for operators do not
apply to the following airplane models:
(1) Lockheed L-188
(2) Bombardier CL-44
(3) Mitsubishi YS-11
(4) British Aerospace BAC 1-11
(5) Concorde
(6) deHavilland D.H. 106 Comet 4C
(7) VFW-Vereinigte Flugtechnische Werk VFW-614
(8) Illyushin Aviation IL 96T
(9) Bristol Aircraft Britannia 305
(10) Handley Page Herald Type 300
(11) Avions Marcel Dassault--Breguet Aviation Mercure 100C
(12) Airbus Caravelle
(13) Lockheed L-300

    The airplanes excluded from these rules are not currently operating
under parts 121 or 129, so there is no need for DAHs to develop data to
support the operational rules for these airplane models. The Vickers
Viscount airplane appeared on this exclusion list in the NPRM. But
since the Vickers Viscount was originally type certificated before
January 1, 1958, this airplane is not subject to these rules because of
the general exclusion of airplanes type certificated before that date.
Thus it has been removed from the exclusion list. Similarly, the
Convair and DC-3 models that have been modified to incorporate turbine-
powered engines are also covered by this general exclusion, so they too
have been removed from the originally proposed exclusion list. The
Lockheed L-300 has been added to the exclusion list. There is only one
qualified aircraft, which was modified, used, and later retired by the
National Aeronautics and Space Administration (NASA) in 1995. It would
not be cost effective to bring it into 121 operations. Thus it has been
excluded from the requirements of these rules.

C. Electrical Wiring Interconnection System (EWIS) Certification Rules
(Part 25 Subpart H)

1. New Subpart for EWIS
    This final rule creates a new subpart H within part 25 of 14 CFR
addressing electrical wiring interconnection systems (EWIS). Its
purpose is to be the single place in the regulations where the majority
of certification rules pertaining to transport airplane wiring can be
found. Many of the rules contained in this new subpart are previously-
existing requirements that have been moved from different parts of the
regulations. Some have been reworded to make it clear that they apply
to wiring. Several of the rules in subpart H are new. As a whole, the
rules in subpart H are meant to improve the safety of transport
airplane wiring by making sure that it is designed to be safe.
Individually, the rules address different aspects of wiring design
safety, and they are discussed individually below.
    To better harmonize with foreign airworthiness authorities, the
numbers of many of the rules in subpart H have been changed from those
originally proposed. The following table indicates the revised numbers.
Since commenters referred to the proposal when they

wrote to the FAA, however, their references below are the originally
proposed rule numbers. Similarly, if a commenter references a proposed
AC, the original draft AC number is retained, as used by the commenter.
Several of the proposed subpart H rules received no comments and remain
unchanged except for their numbers. Those will not be discussed here.
The following table indicates the rule number changes.

                  Table 2.--Subpart H Rule Renumbering
------------------------------------------------------------------------
                                                 Final rule      NPRM
              Title in subpart H                  section      section
------------------------------------------------------------------------
Definition....................................      25.1701      25.1701
Functions and Installation: EWIS..............      25.1703      25.1703
Systems and Functions: EWIS...................      25.1705      25.1719
System Separation: EWIS.......................      25.1707      25.1709
System Safety: EWIS...........................      25.1709      25.1705
Component Identification: EWIS................      25.1711      25.1711
Fire Protection: EWIS.........................      25.1713      25.1713
Electrical Bonding and Protection against           25.1715      25.1717
 Static Electricity: EWIS.....................
Circuit Protective Devices: EWIS..............      25.1717      25.1721
Accessibility Provisions: EWIS................      25.1719      25.1725
Protection of EWIS............................      25.1721      25.1727
Flammable Fluid Protection: EWIS..............      25.1723      25.1729
Powerplants: EWIS.............................      25.1725      25.1731
Flammable fluid shutoff means: EWIS...........      25.1727      25.1733
Instructions for Continued Airworthiness--EWIS      25.1729      25.1739
Powerplant and APU fire detector system: EWIS.      25.1731      25.1737
Fire detector systems, general: EWIS..........      25.1733      25.1735
[Reserved]....................................      deleted      25.1707
[Reserved]....................................      deleted      25.1715
Instruments using a power supply: EWIS........      deleted      25.1723
------------------------------------------------------------------------

2. The Definition of EWIS (Sec.  25.1701)
    Section 25.1701 is a new requirement. It defines electrical wiring
interconnection systems (EWIS). The final rule differs from the
proposal in the addition of the words ``and external wiring of
equipment,'' discussed below.
    Boeing commented that EWIS is not limited to the numbered items in
Sec.  25.1701(a). EWIS components might also include terminal blocks,
circuit protective devices, and contactors. Boeing requested we
indicate that EWIS may include these and other items as well.
    We agree with Boeing that the EWIS components listed in Sec.
25.1701(a) are not a comprehensive list. There may be other devices
that would be considered part of an EWIS, as indicated by the phrase in
the lead-in sentence to the list of Sec.  25.1701(a)(1)-(13); ``* * *
this includes:'' A determination of whether a component is considered
to fall under the definition of EWIS must be made on specific design
details of a certification program.
    Airbus commented that the phrase ``and external wiring of
equipment'' should be added to the list in proposed Sec.  25.1701(b) of
components covered by the EWIS definition. Airbus stated that for
completeness and consistency, external wiring of equipment should be
considered, since it can be part of the aircraft installation (e.g.,
galley connection wiring and seat connection wiring). Continental asked
if wire installed in seats is covered by the proposal.
    We have added the phrase ``and external wiring of equipment'' to
the list of equipment in Sec.  25.1701(b). We consider this a
clarification of what constitutes an EWIS component and not an increase
in scope over the proposal. If an airplane component, such as a galley
or a seat, is manufactured with connection cables external to it, then
the external connection cables would be considered an EWIS component.
    An individual commenter stated that the word ``interconnection'' in
the phrase ``electrical wiring interconnection systems'' is redundant
and should be eliminated. This commenter also requested that we cite
the numerous examples of airplane electrical wiring systems that are
not a part of the EWIS. This commenter further requested that we define
the term EWIS in the definition section and cite examples of components
included in and excluded from the system.
    We do not concur with the request to remove ``interconnection''
from the term ``electrical wiring interconnection system'' (EWIS). The
EWIS certification and operational requirements in the final rule apply
to wires that ``interconnect'' airplane systems, as opposed to wiring
located solely within the enclosure of a piece of avionics equipment,
for example. Thus the word interconnection is integral and important in
describing what electrical wiring interconnection system means.
    The definition of EWIS contained in Sec.  25.1701 does include
examples of airplane wiring and its associated components that are not
part of the EWIS. We believe that these examples are sufficient to
adequately articulate the regulatory definition of EWIS and that
further examples are unnecessary. We made no change due to this
comment.
    We do not agree with the commenter's proposal to define EWIS in the
definition section. Although not specifically identified by the
commenter, we are assuming that he wants the definition to appear in 14
CFR part 1. Section 25.1701 contains the EWIS definition and clearly
states that the definition applies to ``The Chapter.'' This includes
all applicable certification and operational subchapters such as parts
25, 121, and 129 where the EWIS requirements are located. We have
revised the final rule to include a reference to Sec.  25.1701 in Sec.
1.2.
    Continental Airlines quoted Sec.  25.1701 (definition) and the
preamble discussion to emphasize the following statements:

    The term EWIS means any wire, wiring device, or combination of
these, including termination devices, installed in the airplane for
transmitting electrical energy between two or more termination
points * * *
    * * * but any electrical connection used to support power and/or
signal transmission that is part of the airplane TC, and that is
used for the laptop or other carry-on items, is covered by the
proposed definition.

    The commenter requested that the phrase ``signal transmission'' be
defined.
    As used in the context of the proposal, signal transmission refers
to data transmitted through wired means, as opposed to wireless signal
transmission.
    GE and AIA/GAMA commented that proposed Sec.  25.1701(c), which
provides for exceptions to the definition of an EWIS, means that the
equipment inside shelves, panels, etc. will have to show compliance
with EWIS requirements even if they are qualified to the standards of
Radio Technical Commission for Aeronautics (RTCA) document number RTCA/
DO-160. These commenters believe this would be the opposite of the
rule's intended meaning. They request that the following phrase be
deleted from the final rule: ``Except for the equipment indicated in
paragraph (b) of this section''.
    As discussed in the NPRM, the definition of EWIS includes
electrical wiring interconnection system components inside shelves,
panels, racks, junction boxes, distribution panels, back-planes of
equipment racks including circuit board back-planes, and wire
integration units. This EWIS, unlike wiring within avionics equipment,
is typically designed and made for a particular airplane model or
series of models. Avionics components must be sent back to their
manufacturer or a specialized repair shop for service. But this type of
equipment is maintained, repaired, and modified by the same personnel
who maintain, repair, and modify the other EWIS in the airplane. In an
electrical distribution panel system, for example, separation must be
designed and maintained within the panel just as in the EWIS leading up
to that panel. Identification of components inside the panel is just as
important as for those outside the panel since the wiring inside the
panel is treated much the same. We have retained the first sentence of
proposed Sec.  25.1701(c).
3. Functions and Installation: EWIS (Sec.  25.1703)
    Section 25.1703 (whose number is unchanged from that in the
proposal), is essentially derived from requirements of existing Sec.
25.1301. It requires that applicants select EWIS components that are of
a kind and design appropriate to their intended function. Factors such
as the components' design limitations, functionality, and
susceptibility to arc tracking and damage from moisture must be
considered in selecting EWIS components.
    The final rule differs from the proposal in that words were changed
to clarify meaning and words inadvertently left out of the proposal
were put back in. We also removed the word ``adequately'' in response
to a comment from Boeing, as noted in the discussion elsewhere under
the heading System Separation (Sec.  25.1707).
    Boeing commented that proposed Sec.  25.1703(a)(3) states that EWIS
must ``function properly when installed.'' Boeing proposed the final
rule be rewritten to say that EWIS must ``perform the function for
which it was intended without degrading the airworthiness of the
airplane.''
    The commenter stated that it has had difficulty in the past with
the term ``function properly'' when applied to complex or non-essential
systems. It stated the suggested revision will help clarify the
regulation's intent.
    We agree that in the past the term ``function properly'' has been
applied to complex or non-essential systems in a nonstandardized
manner. We have revised the final rule text as proposed.
    Airbus, Boeing, General Electric, and Honeywell requested that we
add the words ``in the fuselage'' to Sec.  25.1703(c) so it is
consistent with the original regulation, Sec.  25.869 (a)(3). They said
that this will ensure that the requirements of Sec.  25.1703(c) are
consistent with the original requirement.
    We agree. We mistakenly omitted the phrase ``in the fuselage'' in
the proposed wording. We have revised the final rule to include it.
    EASA and Airbus commented that ATSRAC recommended that Sec.
25.1703 include the following requirement:

    Electrical wiring interconnection system modifications to the
original type design must be designed and installed to the same
standards used by the original aircraft manufacturer or other
equivalent standards acceptable to the Administrator (for 14 CFR)/
authorities (for JAR).

    EASA stated that this requirement will be included in the EASA
notice of proposed amendment (NPA) that will propose to adopt ATSRAC's
recommendations. Airbus said such a requirement is consistent with the
proposal's preamble and advisory material (reference proposed AC
25.17XX, paragraph 5.b.(8)(b)). Airbus said that including this
language in the final rule will ensure EWIS minimum compatibility for
modifications made after an airplane is delivered.
    Similarly, the International Aviation Safety Association (IASA)
commented that airplane and wiring manufacturers should be required to
approve the type of wiring used in modifications to an approved type
design.
    To add this additional requirement would essentially delegate to
the type certificate holder authority to establish standards that go
beyond the minimum safety standards required by part 25. The FAA does
not have legal authority to make such a delegation. As with other
airworthiness standards, an applicant who shows compliance with our
standards is entitled to design approval (reference Sec.  21.117). The
rationale for this is that our standards provide an acceptable level of
safety, so exceeding them is not necessary for safety. However, the
referenced advisory material does contain the following statement:

    Only the components listed in the applicable manual or approved
substitutes should be used for the maintenance, repair, or
modification of the aircraft. EWIS modifications to the original
type design should be designed and installed to the same standards
used by the original aircraft manufacturer or other equivalent
standards acceptable to the FAA. This is because the manufacturer's
technical choice of an EWIS component is not always driven by
regulatory requirements alone. Sometimes specific technical
constraints would result in the choice of a component that exceeds
the minimum level required by the regulations.

We believe such a statement meets the intent of the ATSRAC
recommendation. Therefore, we made no changes based on this comment.
    Airbus requested that the term ``hazard'' replace ``hazardous
effects'' in proposed Sec.  25.1703(d). Airbus said this would
eliminate ambiguous interpretation due to inappropriate use of what is
a system safety classification term in Sec.  25.1309(b). Airbus stated
that the effect on the component itself needs to be covered instead of
the effect on the function.
    We infer from this comment that Airbus objects to the phrase
``hazardous effects'' because it believes this phrase implies that a
numerical probability analysis would be necessary to show that moisture
on EWIS components in known areas of moisture accumulation would not
create a hazard not shown to be improbable. A numerical probability
analysis is not necessary when demonstrating compliance with Sec.
25.1703(d). The intent is that good engineering and manufacturing
judgment be used when designing and installing EWIS components in areas
of known moisture accumulation to minimize potential for moisture to
cause an EWIS component failure. Such a failure could in turn lead to a
functional failure of the system it is associated with. Or it could
lead to accelerated

degradation of the component and localized electrical arcing could
occur. This in itself could lead to a hazardous condition. It is
important to protect the EWIS component from moisture damage. But it is
the possible safety hazard from failure of the component that the rule
is addressing, and not strictly the effect on the component, or its
function. The advisory material for Sec.  25.1703(d) states, in part,
the following:

    This section requires that EWIS components located in areas of
known moisture build-up be adequately protected to minimize
moisture's hazardous effects. This is to ensure that all practical
means are used to ensure damage does not occur from fluid contact
with components.

We believe that this statement prevents confusion about whether or not
a numerical probability analysis is required for demonstrating
compliance with this requirement. It is not. We made no changes due to
this comment.
    Boeing and AIA/GAMA commented that the preamble discussion of Sec.
25.1703(d) states that the rule proposes to ensure that ``all practical
means'' are used to prevent damage due to fluid contact. They noted
that one could interpret this guidance to mean that multiple means must
be used. Another interpretation could be that all practical means must
be considered and the most appropriate method used to address potential
for fluid impinging on wiring. For purposes of clarification, Boeing
requests that the term ``used'' be changed to ``considered.''
    This rule is meant to require that all practical means be
considered and the most appropriate method used to address potential
damage from fluid contact with EWIS components. The advisory material
for this requirement has been clarified to state this.
4. Systems and Functions: EWIS (Sec.  25.1705)
    Section 25.1705 was proposed as Sec.  25.1719. This section adds to
the regulations the concept that EWIS associated with systems required
for type certification or by operating rules must be considered an
integral part of those systems and considered in showing compliance
with all applicable requirements. In addition to this general
requirement, the rule lists other specific certification rules (for
example Sec.  25.773 Pilot compartment view and Sec.  25.981 Fuel tank
ignition prevention) for which the applicant must include consideration
of the EWIS that is part of the subject system in demonstrating
compliance.
    There are two differences between the proposal and the requirement
as adopted: The section number has been changed, and a reference to
Sec.  25.1331(a)(2) (as discussed below) has been added.
    EASA and Airbus requested that Sec.  25.1723 be deleted and
references to Sec. Sec.  25.1303(b) and 25.1331(a)(2) be moved to Sec.
25.1719 (now Sec.  25.1705).
    We partially agree to this request. There is no need to list both
rules in Sec.  25.1705(b). It is necessary to refer to Sec.
25.1331(a)(2) because that requirement specifically applies to
instruments required by Sec.  25.1303(b). To list both Sec. Sec.
25.1303(b) and 25.1331(a)(2) would be redundant. Therefore we have
revised Sec.  25.1705(b) to include 25.1331(a)(2) and we have deleted
proposed Sec.  25.1723 from the final rule.
    EASA suggested that references to Sec. Sec.  25.854 and 25.858 be
included in Sec.  25.1719 (now Sec.  25.1705). The subjects of these
two requirements are lavatory fire protection and cargo or baggage
compartment smoke or fire detection systems, respectively. EASA stated
that if we add Sec. Sec.  25.854 and 25.858 to Sec.  25.1719(b), Sec.
25.1735 can be deleted, because its intent would be addressed in Sec.
25.1719(a) and (b).
    Requirements of Sec.  25.1705(a) apply to EWIS associated with
systems required for type certification or by operating rules. This is
slightly different from those in Sec.  25.1735, which apply to EWIS
associated with any installed fire protection system, whether or not it
is required for type certification or by operating rules. Therefore, we
cannot delete Sec.  25.1735. We have revised it, however, to include
references to Sec. Sec.  25.854 and 25.858. We included these two
requirements in the preamble discussion for the proposed Sec.  25.1735
and to avoid future confusion we believe they should be referenced
within the final rule.
5. System Separation: EWIS (Sec.  25.1707)
    Section 25.1707 System Separation: EWIS was proposed as Sec.
25.1709. This rule requires applicants to design EWIS with appropriate
separation to minimize possibility of hazardous effects upon the
airplane or its systems.
    Aside from the section number change, the difference between the
proposal and this final rule is that word changes have been made to
clarify meaning, and the reference in paragraph (a) has been changed.
    EASA commented that proposed Sec.  25.1709 (now Sec.  25.1707) uses
the phrase ``any EWIS component failure'' in several places throughout
the requirement. EASA believes this implies that an exhaustive list of
possible EWIS component failures not related to the design under review
would have to be produced. It believes this goes beyond the intent of
the rule, and states that the equivalent EASA requirement will use the
wording ``an EWIS component failure * * *'' as was recommended by
ATSRAC. EASA recommended that the final rule language be revised to
adopt ATSRAC's recommended wording.
    We have made the change EASA requested. The intent of the
requirement is that applicants assess all EWIS components that could
have a reasonable likelihood of failing in such a manner as to create a
hazardous condition. We believe the revised rule language is clearer
and will not cause an applicant to unreasonably consider EWIS component
failures that could not adversely impact required separation.
    Boeing requested that the words ``adequately'' be removed from the
text of proposed Sec.  25.1703(d) (rule number unchanged) and
``adequate'' from Sec.  25.1709 (a), (c), (d), (e), (f), (g), (k), and
(l) (Sec.  25.1709 is now Sec.  25.1707). Boeing contends that
inclusion of these terms does not enhance interpretation of the rules.
It requested that we either delete them or add performance criteria
that define the term ``adequate.''
    We believe the word ``adequate'' is necessary to the intent of
Sec.  25.1707. Paragraph (a) of that section provides objective
criteria outlining how adequate physical separation must be achieved.
We have also described various means of providing adequate physical
separation in the associated advisory material. Because each system
design and airplane model can be unique, and because manufacturers have
differing design standards and installation techniques, Sec.  25.1707
does not mandate specific separation distances. The advisory material
provides the criteria each airplane manufacturer should consider when
developing adequate physical separation for EWIS. These criteria
include the following factors:
     The electrical characteristics, amount of power, and
severity of failure condition of the system functions performed by the
signals in the EWIS and adjacent EWIS.
     Installation design features, including the number, type,
and location of support devices along the wire path.
     The maximum amount of slack wire resulting from wire
bundle build tolerances and other wire bundle manufacturing
variabilities.
     Probable variations in the installation of the wiring and
adjacent wiring, including position of wire support devices and amount
of wire slack possible.

     The intended operating environment, including amount of
deflection or relative movement possible and the effect of failure of a
wire support or other separation means.
     Maintenance practices as defined by the airplane
manufacturer's standard wiring practices manual and the ICA required by
Sec.  25.1529 and Sec.  25.1729.
     The maximum temperature generated by adjacent wire/wire
bundles during normal and fault conditions.
     Possible electromagnetic interference, high intensity
radiated fields, or induced lightning effects.

Although not related to this comment, we believe that the requirements
of Sec.  25.1707(c) could be stated more clearly. We have revised Sec.
25.1707(c) in the final rule to state that

    * * * damage to circuits associated with essential functions
will be minimized under fault conditions.

    We have removed the word ``adequately'' from Sec.  25.1703(d). As
used in proposed Sec.  25.1703(d), that word does not add clarity to
the requirement's intent and is therefore unnecessary.
    GE suggested that for clarification we revise proposed Sec.
25.1709(l) (now Sec.  25.1707(l)) to read as follows:

    Sec.  25.1709(l) Each EWIS must be designed and installed so
there is adequate separation between it and other aircraft
components, in order to prevent abrasion/chafing, vibration damage,
and other types of mechanical damage.

    We agree with GE that the wording of this rule could be improved to
help clarify its requirements. We have revised Sec.  25.1707(l) to
state that

    * * * EWIS must be designed and installed so there is adequate
physical separation between it and other aircraft components and
aircraft structure, and so that the EWIS is protected from sharp
edges and corners, to minimize potential for abrasion/chafing,
vibration damage, and other types of mechanical damage.

    Boeing requested that the reference to Sec.  25.1309(b)(1) and
(b)(2) in Sec.  25.1709(a) (now Sec.  25.1707(a)) be deleted. It
commented that the applicable guidance material does not include a
numerical probability analysis. EASA commented that proposed Sec.
25.1709(a) limits applicability of Sec.  25.1309 to EWIS addressed by
subparagraphs (b)(1) and (b)(2). EASA believes that for administrative
purposes the final Sec.  25.1709(a) should simply reference Sec.
25.1309 because Sec.  25.1309 could be revised in the future or the
requirements of those paragraphs could be moved to a different
paragraph within Sec.  25.1309, making it necessary to also change
Sec.  25.1709. It stated that the equivalent EASA requirement will just
reference Sec.  25.1309.
    We agree with Boeing's request to delete the reference to Sec.
25.1309(b)(1) and (b)(2) and do not agree with EASA's request to modify
the reference. The intent of the reference to failure conditions as
defined by Sec.  25.1309(b)(1) and (b)(2) was to require that an EWIS,
under normal and failure conditions, would not create an unsafe
condition. The failure conditions we were intending to reference are
``hazardous'' or ``catastrophic,'' used in EASA CS-25.1309 and in Sec.
25.1709. In reviewing the text of the proposal, however, we realized
that this reference could cause confusion as to the intent of the
requirement and that the reference to the ``catastrophic'' failure
condition is not necessary for the purposes of this requirement. To
better align the requirement of paragraph (a) with the requirements of
paragraphs (e) through (j), and to ensure adequate separation between
EWIS and other airplane systems not specifically addressed by those
paragraphs and paragraph (k), we have revised the first sentence of
25.1707(a). That sentence now reads: ``Each EWIS must be designed and
installed with adequate physical separation from other EWIS and
airplane systems so that an EWIS component failure will not create a
hazardous condition.'' We discuss the term ``hazardous condition'' in
our response to the next two comments.
    General Electric and Honeywell commented that the wording of Sec.
25.1709 (now Sec.  25.1707) should be revised to clarify the meaning of
``hazardous conditions,'' so that a contained and detectable engine
nacelle or auxiliary power unit (APU) enclosure fire is clearly
distinguished from a fire within the pressurized fuselage as not being
hazardous. In a similar comment, Airbus requested that the language for
Sec.  25.1709(b) (now Sec.  25.1707(b)) be revised to reflect the
original ATSRAC recommendation as follows:

    Each EWIS must be designed and installed so that any electrical
interference likely to be present in the airplane will not result in
hazardous effects upon the airplane or its systems unless shown to
be extremely remote.

    Airbus stated that the ATSRAC-proposed words ``unless shown be to
extremely remote,'' should not be removed unless it can be interpreted
that the word ``likely'' excludes cases that are extremely remote and
this is expressed in the advisory material.
    In our NPRM preamble discussion of this issue, we said that the
phrase ``hazardous condition'' in Sec.  25.1709 (now Sec.  25.1707) is
used in a different context than it is when associated with the EWIS
safety analysis requirements of Sec.  25.1705 (now Sec.  25.1709.)
While that statement remains true, we now realize that framing the
discussion around what a hazardous condition means in different rules
may have caused confusion. The meaning of the term ``hazardous
condition'' remains the same, whether used in Sec.  25.1707, in Sec.
25.1709, in current Sec.  25.1353, or in CS 25.1309. Here is the
definition for a hazardous failure condition, and also for a
catastrophic failure condition.
    Hazardous Failure Condition:
    Failure condition that would reduce the capability of the airplane
or the ability of the flightcrew to cope with adverse operating
conditions to the extent that there would be, for example:
     A large reduction in safety margins or functional
capabilities; or
     Physical distress or excessive workload such that the
flightcrew cannot be relied upon to perform their tasks accurately or
completely; or
     Serious or fatal injuries to a relatively small number of
persons other than the flightcrew.
    Catastrophic Failure Condition:
    Failure condition that would result in multiple fatalities, usually
with the loss of the airplane.
    Hazardous and catastrophic failure conditions are descriptive terms
for situations that could occur in the airplane because of failures
(safety margins reduced, the flightcrew unable to perform accurately
because of adverse operating conditions, injuries to passengers, etc.).
These are situations that result from unsafe conditions and must be
avoided. Therefore, when an airplane is certified, the applicant must
show that the kinds of failures that could result in these kinds of
situations have been considered, and measures put in place to prevent
them.
    In the System Separation rule, Sec.  25.1707, separation distances
or a barrier must be used to ensure that none of the types of failures
described in the rule will create a situation that would fit the
definition of a hazardous condition. The operative term in this rule is
that such failures will not create a hazardous condition. To show that
a given failure, such as fuel leakage onto EWIS components, will not
create a hazardous condition, the applicant may use a qualitative
analysis, consisting of expert engineering judgment, manufacturing
judgment, and an assessment of any relevant service history.
    In the EWIS System Safety rule, Sec.  25.1709, the applicant must
show that each EWIS system is designed and installed so that each
hazardous failure

condition is extremely remote. The definition of a hazardous failure
condition remains the same. In this rule, however, a numerical
probability is required to demonstrate that the possibility for such an
occurrence is extremely remote.
    Section Sec.  25.1709 uses both the terms ``hazardous'' and
``catastrophic'' and says that the applicant must not only show that
each hazardous failure condition is extremely remote, but that each
catastrophic failure condition is extremely improbable and does not
result from a single failure. This would normally require a combination
of qualitative and quantitative analyses to demonstrate compliance.
    The requirements of Sec.  25.1707 do not preclude use of valid
component failure rates if the applicant chooses to use a probability
argument in addition to the design assessment to demonstrate
compliance. It also does not preclude the FAA from requiring such an
analysis if the applicant cannot adequately demonstrate that hazardous
conditions will be prevented solely by using the qualitative design
assessment. However, we did not include the words ``unless shown to be
extremely remote'' in Sec.  25.1707 because we did not want to imply
that a numerical probability assessment was required to comply with
this rule.
    The engine nacelles and APU enclosures are designated as fire zones
and this is taken into account in the design and installation of EWIS
in those areas. But we do not agree with GE and Honeywell that a fire
in the engine nacelle or APU enclosure could never create a hazardous
condition. There is always the possibility that the fire could not be
suppressed and could result in a safety hazard. We made no changes
because of these comments.
    The National Air Carrier Association (NACA) commented that the
proposed EWIS system separation requirements in Sec.  25.1709 (now
Sec.  25.1707) are necessary for new aircraft. However, it said that
imposing these requirements and those of Sec.  25.1711 on existing
airplanes would be a significant economic burden.
    The separation and identification requirements of Sec. Sec.
25.1707 and 25.1711 are applicable to new designs and do not apply to
previously certified products.
    In a comment relating to proposed Sec.  25.1709 (now Sec.
25.1707), IASA requested that specific mention be made of wiring that
is required to regularly flex in position (such as that in doors and
hatches).
    We agree that designers and installers should address the
additional stresses placed on wires and cables that are required to
regularly flex, such as those in doors and hatches. We have revised the
advisory material for Sec. Sec.  25.1703 and 25.1709 to reflect this.
However we do not concur that a change to Sec.  25.1707 is necessary.
As stated, these requirements are performance based. Applicants would
have to demonstrate that any wiring required to regularly flex in
operation would be able to maintain its designed separation distance
from other EWIS, components, or airplane structure as applicable.
    Boeing and GE requested that we clarify Sec.  25.1709(d) (now Sec.
25.1707(d)). They asked whether an ``independent airplane power
source'' is considered to be an airplane level power source as is
related to an APU, battery, etc., or whether it is any power source
that transmits power. If it is the latter, they recommended that there
be some differentiation in the associated guidance material for the
differences between ground blocks and ground studs, and for the
differences between static grounds terminating at ground blocks and
ground studs. The commenters did not consider ground blocks ``a common
terminating location'' for non-redundant grounds.
    As used in Sec.  25.1707(d), ``independent airplane power sources''
means a general source of power for the whole of the airplane or for
major subsystems (such as the permanent magnet generators that provide
power for fly-by-wire systems ). Examples include engine-or APU-driven
generators, batteries, and ram air turbines. We have revised the AC to
reflect this.
    GE requested that the word ``physical'' be deleted from the text of
Sec.  25.1709(d) (now Sec.  25.1707(d)). It stated that adequate
separation should be all that is required and that using physical
separation is only one means of achieving this.
    The FAA believes that the word ``physical'' is necessary, as
recommended by ATSRAC, to ensure that necessary separation is not
achieved solely by electrical isolation and use of control logic via
hardware or software implementation. We made no changes due to this
comment.
    Airbus requested that the phrase ``will not create a hazardous
condition'' be replaced by the phrase ``will not create a hazard'' in
proposed Sec.  25.1709 (e), (f), (g), (h), (i), and (j) (proposed Sec.
25.1709 is now Sec.  25.1707). Airbus commented that this would
eliminate ambiguous interpretation from inappropriate use of what is a
system safety classification term used in Sec.  25.1309(b).
    We believe the word ``hazard'' is ambiguous and could cause
confusion in the context of the requirement. We believe that the
preamble discussion in the NPRM (which refers to this rule as Sec.
25.1709), the additional clarification given in this final rule, and
the advisory material for final Sec.  25.1707 clearly articulate what
is meant by the term ``hazardous condition.''
6. System Safety: EWIS (Sec.  25.1709)
    This rule requires applicants to perform a system safety assessment
of the EWIS on their airplane. The current regulation requiring system
safety assessment for certification is Sec.  25.1309. But current Sec.
25.1309 only covers systems and equipment that are ``required by this
subchapter,'' and wiring for non-required systems is sometimes ignored.
The objective of new Sec.  25.1709 is to apply the concepts of Sec.
25.1309 to all wiring.
    The safety assessment required by Sec.  25.1709 must consider
effects that both physical and functional failures of EWIS would have
on the airplane's safety. Based on that safety assessment, the
applicant must show that each EWIS failure considered to be hazardous
is extremely remote. Each EWIS failure considered to be catastrophic
must be shown to be extremely improbable and may not result from a
single failure.
    This rule was proposed as Sec.  25.1705. That number has been
changed to Sec.  25.1709, to harmonize with foreign airworthiness
authorities. With the exception of that number change, this rule
remains unchanged from the form in which it was proposed.
    Airbus suggested that use of the words ``extremely remote'' and
``extremely improbable'' should be avoided. It pointed out that the
preamble discussion for Sec.  25.1705 (now Sec.  25.1709) is based on a
qualitative approach and this was the basis of ATSRAC's recommendation.
Airbus said that no calculated number should be necessary for
compliance with this rule. It also said, with reference to the NPRM
preamble discussion, that ``jamming'' cannot be a justification for
creating Sec.  25.1705 because an EWIS cannot cause flight control
surface or pilot controls jamming.
    The analysis required by Sec.  25.1709 is not purely a qualitative
assessment of the effects of EWIS failures. Nor was this the basis of
the ATSRAC recommendation. The analysis required by Sec.  25.1709 is
based on a qualitative and quantitative approach to assessing EWIS
safety, as opposed to a purely numerical, probability-based
quantitative analysis. This is consistent with existing Sec.  25.1309
assessments, where a qualitative analysis is always necessary, and the
quantitative

probability analysis is a means of compliance for the hazardous and
catastrophic failure conditions.
    Section 25.1709 is based on the recommendation from ATSRAC. The
Sec.  25.1709 safety assessment must consider effects that both
physical and functional failures of EWIS would have on airplane safety.
The physical analysis is meant to be a qualitative assessment and its
results are to be integrated into the analysis required by Sec.
25.1309 (or other required assessments such as Sec.  25.671 as
applicable), which is both a qualitative and quantitative assessment.
    In response to Airbus's comment that creation of EWIS requirements
should not be predicated on flight control surface or pilot controls
jamming, the NPRM preamble reference is in the context of explaining
that certain airplane systems are exempt from Sec.  25.1309. EWIS
associated with those exempt systems are thus also excluded, even
though those EWIS could create hazardous conditions in the same way as
any other EWIS. As a result, there is a need for a requirement to
address all the EWIS on an airplane. We made no changes based on these
comments.
    While acknowledging that the aim of proposed Sec.  25.1705 (now
Sec.  25.1709) is to make the requirements of Sec.  25.1309 more
explicitly applicable to EWIS, Airbus requested that the text of this
rule be revised to read as follows:

    Each EWIS must be designed and installed so it does not lead to
a catastrophic failure condition as a consequence of a single EWIS
failure. EWIS failure should be understood as failure affecting from
one to all EWIS components within a single bundle.

Airbus's rationale for this change is based on the originally estimated
32.8 accidents that adoption of the proposed rules will prevent over
the next 25 years. When combined with the number of airplanes projected
to be in service and their combined operating hours, the probability of
an EWIS causing a hazardous or catastrophic failure condition will be
less than is required to demonstrate compliance with Sec.  25.1709. The
commenter contended that if this rationale is accepted by the FAA, then
all an applicant should have to do is show in a qualitative manner that
an airplane's EWIS will not be the cause of a catastrophic event.
    The purpose of Sec.  25.1709 is to ensure that the same analytical
rigor applied to other systems for compliance with Sec.  25.1309 is
applied to EWIS. That is why the proposal specified the same criteria
as Sec.  25.1309(b). Airbus's request would impose lesser criteria for
analysis of EWIS, even though the consequences of EWIS failures may be
just as severe as any other system failures. Airbus's justification for
its request relies on the estimated numbers of incidents in the initial
regulatory evaluation and an apparent assumption that this number would
meet the computed risk threshold required by Sec.  25.1309. This is not
the case. The analytical methods used for an economic evaluation are
very different from methods required for risk assessment by Sec.
25.1309 (or Sec.  25.1709). The regulatory evaluation is a projected
incident rate based on historical data. Estimating possible failures
for compliance requires a detailed evaluation of the modes and effects
of potential failures in a specific system design. We made no change
because of this comment.
    Boeing requested that proposed Sec.  25.1705 (now Sec.  25.1709) be
included as a reference within Sec.  25.1309(b) as previously proposed
by industry. Boeing stated that duplicating the regulations leaves open
the possibility of deviations in application. GE commented that
proposed Sec.  25.1705 is not acceptable. It said the discussion of
this proposal, and the accompanying AC, contain several misstatements
regarding current use and means of compliance with Sec.  25.1309.
According to GE, this misunderstanding of Sec.  25.1309 has led to a
perception by the FAA that a new rule is needed, when in fact, Sec.
25.1309 already addresses the area of concern. The NPRM preamble states
that Sec.  25.1309 does not address single wire chafing or arcing as a
cause of failure: ``the physical portion has been neglected in past
system safety analyses.'' GE contended this is not true, because Sec.
25.1309 safety assessments have addressed wiring failures as sources of
fire. GE recommended that proposed Sec.  25.1705 be removed. It
suggested that the AC material for proposed Sec.  25.1705 be provided
to ARAC for incorporation into the Sec.  25.1309 AC.
    As stated in the preamble discussion of the NPRM, and in its
related draft advisory material, the Sec.  25.1709 analysis may be
accomplished in conjunction with Sec.  25.1309 assessments. Having a
separate requirement for EWIS safety assessments will ensure that all
airplane EWIS are assessed for potential impact on safe operation. This
cannot be accomplished if Sec.  25.1709 is simply included as a
reference in Sec.  25.1309. Nor can we delete Sec.  25.1709 and
incorporate its means of compliance into future versions of advisory
material for Sec.  25.1309, as GE suggests. As discussed in the NPRM,
the requirements of Sec.  25.1709 are necessary. Current safety
analysis practice has been proven--by accidents and service history--to
be insufficient with respect to safety assessments of wire designs and
installations, including wire failures that can cause fires. The
requirements of Sec.  25.1709 are such that they complement those of
Sec.  25.1309 and address its shortcomings when it comes to safety
assessments of EWIS. Section 25.1309 does not allow any single failure
to result in catastrophic consequences, regardless of the failure
probability. The requirements of Sec.  25.1709 are consistent with
those of Sec.  25.1309. We made no changes due to these comments.
    Federal Express referred to this statement in the preamble
discussion of proposed Sec.  25.1705 (now Sec.  25.1709):

    If this information [what systems and functions the other wires
in the same and surrounding bundles support] is not available to the
modifier, then the EWIS system must be designed to accommodate this
lack of knowledge * * *.

FedEx said this would typically mean that wire being added for the
modification would need to be routed separately from existing airplane
wiring. It requested that, prior to adoption of this concept into any
advisory material or design standard, detailed guidance on separation
in confined areas such as equipment racks or breaker panels be
developed.
    We believe that the advisory material for post-TC modifications
provides clear guidance for the case cited by Federal Express. When
separation cannot be maintained because of physical constraints (in
terminal strips and connectors, for instance), the applicant should
conduct the appropriate analysis to show that no adverse failure
conditions result from sharing the common device. This analysis
requires knowledge of the systems or system functions sharing that
device (again, the example would be terminal strips and connectors). If
a modifier cannot identify the systems or system functions in the
congested area, then the new EWIS would have to be routed through a
different area if an acceptable alternative method of providing
adequate separation is not provided. We made no changes to the final
rule because of this comment. However, we have expanded the final
advisory material for this requirement to provide clear guidance on the
specific scenario contained in FedEx's comment.
    Boeing commented on the part of the Sec.  25.1705 (now Sec.
25.1709) discussion in the NPRM that states that an in-flight
entertainment (IFE) system installed on an airplane with subpart H as
part of its type certification basis would be subjected to a more
rigorous safety

assessment. Boeing noted its understanding that subpart H is applied to
applicants for type certificates, amended type certificates, and
supplemental type certificates. It asked whether it is correct that
``an application for that or another IFE system to be installed on any