U.S. Department 

of Transportation 

Federal Aviation 

Administration

Advisory 

Circular

Subject: Development of Transport 

Category Airplane Electrical Wiring 

Interconnection Systems Instructions for 

Continued Airworthiness Using an 

Enhanced Zonal Analysis Procedure 

Date: 11/23/07 

Initiated By: 

ANM-100 

AC No: 25-27

1. PURPOSE. 

a. This advisory circular (AC) describes parts of the compliance process for the “Enhanced 

Airworthiness Program for Airplane Systems/Fuel Tank Safety (EAPAS/FTS)” rule. That 

rule requires design approval holders (DAH) and applicants to develop instructions for 

continued airworthiness (ICA) consisting of maintenance and inspection tasks, intervals, 

and procedures for the representative airplane’s electrical wiring interconnection systems 

(EWIS) for each affected type design. The DAH must also review any fuel tank system 

ICA it has developed in compliance with Special Federal Aviation Regulation (SFAR) 88 in 

order to ensure compatibility with the EWIS ICA, including minimizing redundant 

requirements. The DAH must then submit the EWIS ICA to the FAA Oversight Office for 

review and approval. 

b. This AC provides guidance for developing maintenance and inspection instructions for 

EWIS using an enhanced zonal analysis procedure (EZAP). For the purposes of this AC, 

the term “maintenance” encompasses both “maintenance” and “preventive maintenance” as 

those terms are defined in 14 CFR 1.1. For aircraft models whose maintenance programs 

already include a zonal inspection program, the logic described here provides guidance on 

improving those programs. For airplanes without a zonal inspection program, use of this 

logic will produce zonal inspections for wiring that can be added to the existing 

maintenance program. This AC contains information that can be used by operators to 

improve EWIS maintenance practices. It stresses the importance of inspecting EWIS and 

promotes a philosophy of “protect and clean as you go” when performing maintenance, 

repair, or alterations on aircraft. 

 
11/23/07 AC 25-27 

2 

2. Applicability and Explanation of Requirements. 

 a. Applicability. 

(1) The guidance in this document is directed towards design approval holders (DAH) 

(type certificate (TC) and supplemental type certificate (STC) holders and applicants). 

This guidance can also be used by air carriers and air operators, maintenance providers, 

and repair stations. 

(2) This AC provides the following information and guidance: 

(a) Development of EWIS ICA per part 25, appendix H, section H25.5(a)(1) as 

required by: 

• § 25.1729 (H25.5(a)(1) fulfills part of the requirements of § 25.1729). 

• § 26.11(b) and (c). 

(b) Development of the EWIS ICA source document per part 25, appendix H, 

section H25.5(b) as required by: 

• § 25.1729. 

• § 26.11(b) and (c). 

(c) Explanation of who is required to comply with § 26.11. 

 

NOTE: This AC only contains guidance for 

requirements of sections H25.5(a)(1) and (b). Advisory 

Circular 25.1701-1, Certification of Electrical Wiring 

Interconnection Systems on Transport Category 

Airplanes, contains guidance for H25.4(a)(3) 

(Airworthiness Limitations), and the remaining 

requirements of H25.5 — 

•H25.5 (a)(2) (standard wiring practices 

manual) 

•H25.5 (a)(3) (EWIS separation) 

•H25.5 (a)(4) (EWIS identification) 

•H25.5 (a)(5) (electrical load analysis) 
11/23/07 AC 25-27 

3 

NOTE: Guidance for air carriers 

and air operators on how to make 

changes to FAA-approved EWIS 

ICA will be contained in a separate 

AC titled Incorporation of 

Electrical Wiring Interconnection 

System (EWIS) Instructions for 

Continued Airworthiness into the 

Operators’ Maintenance 

Programs. 

(d) Explanation of the § 26.11(e)(4) requirement to make the design approval 

holder EWIS ICA available to affected persons. 

(e) Information on when air 

carriers and air operators must 

obtain FAA Oversight Office 

approval for changes to tasks 

based on FAA-approved EWIS 

ICA already incorporated into 

their maintenance program. 

(f) Good EWIS maintenance 

practices that can be helpful when 

identifying and developing EWIS 

maintenance tasks using an EZAP. 

(3) This material is neither mandatory nor regulatory in nature and does not constitute a 

regulation. It describes acceptable means, but not the only means, for showing 

compliance with the applicable regulations. We will consider other methods of showing 

compliance that an applicant may elect to present. While these guidelines are not 

mandatory, they are derived from extensive FAA and industry experience in determining 

compliance with the relevant regulations. On the other hand, if we become aware of 

circumstances that convince us that following this AC would not result in compliance 

with the applicable regulations, we will not be bound by the terms of this AC, and we 

may require additional substantiation or design changes as a basis for finding compliance. 

(4) This material does not change or create any additional regulatory requirements nor 

does it authorize changes in or permit deviations from existing regulatory requirements. 

(5) Except in the explanations of what the regulations require, terms such as “shall” or 

“must” are used in this AC only in the sense of ensuring applicability of this particular 

method of compliance when the acceptable method of compliance described here is used. 

b. Differing Requirements of §§ 25.1729 and 26.11. The requirements to develop 

EWIS ICA vary depending on whether the applicant is complying with part 25, subpart H, 

§ 25.1729, or with part 26, subpart B, § 26.11. 

 

(1) Airplane Models with § 25.1729 in their Type Certification Basis.

(a) For type, amended type, and supplemental type certificates with § 25.1729 in 

their certification basis, applicants must comply with requirements of part 25, 

Appendix H, sections H25.4(a)(3), and H25.5(a) and (b). These rules mandate that 

the applicant provide, as part of the ICA: 

 
11/23/07 AC 25-27 

4 

• Identification of any EWIS mandatory replacement times in the 

Airworthiness Limitations section of the ICA (H25.4(a)(3)). 

• EWIS maintenance and inspection requirements developed with an EZAP 

(H25.5(a)(1)). 

• EWIS maintenance practices in a standard format (H25.5(a)(2)). 

• EWIS separation requirements as determined under § 25.1707 

(H25.5(a)(3)). 

• EWIS identification methods and requirements for identifying any 

changes to EWIS under § 25.1711(H25.5(a)(4)). 

• Electrical load data and instructions for updating that data (H25.5(a)(5)). 

• A document that contains the EWIS maintenance inspection requirements 

or identifies their location in other ICA documents (H25.5(b)). This 

section also requires that the document be in a form appropriate for the 

information to be presented and that the EWIS ICA be easily recognizable 

as such. 

(b) Section 25.1729 applies to all transport category airplanes regardless of 

passenger- or cargo-carrying capacity. 

(c) Guidance for § 25.1729 and, as noted earlier, Appendix H sections 

H25.4(a)(3) and H25.5(a)(2) to (a)(5) is located in AC 25.1701-1, Certification of 

Electrical Wiring Interconnection Systems on Transport Category Airplanes. 

(2) Airplane Models Required to Comply with Part 26, Subpart B. 

(a) For airplane models that must comply with part 26, the requirement for 

preparing EWIS ICA is § 26.11(b) or (c), depending on whether the DAH holds, 

or is applying for, a type certificate (26.11(b)) or an amended or supplemental 

type certificate (§ 26.11(c)). Sections 26.11(b) and (c) state that EWIS ICA must 

be prepared per H25.5(a)(1) and (b). Therefore, DAHs complying with § 26.11 

must produce EWIS ICA developed with an EZAP (H25.5(a)(1)), and the ICA 

must be in an appropriate form and easily recognizable as EWIS ICA (H25.5(b)). 

The DAHs must make the ICA available to affected persons (operators and others 

required to comply with requirements of § 26.11, § 25.1729, § 121.1111, or 

§ 129.111). 

(b) Section 26.11 applies to transport category, turbine-powered airplanes with a 

type certificate issued after January 1, 1958, that, as a result of the original 

certification or later increase in capacity, have – 

• A maximum type-certificated passenger capacity of 30 or more, or 

• A maximum payload capacity of 7,500 pounds or more. 
11/23/07 AC 25-27 

5 

(3) Requirements for Supplemental Type Certificate and Amendments to 

Type Certificate Applicants—§ 26.11(c). 

Section 26.11(c) requires that applicants for supplemental type certificates (STC) 

or amendments to type certificates evaluate whether the design change for which 

approval is sought necessitates a revision to the EWIS ICA that have been 

previously developed and approved in compliance with § 26.11(b). Guidance for 

how an applicant can make this evaluation is contained in Appendix B of this AC. 

c. Representative Airplane and Special Federal Aviation Regulation (SFAR) 

88 Compatibility Requirements of § 26.11(b). 

(1) Representative Airplane. Section 26.11(b) requires that EWIS ICA be 

developed for the “representative airplane.” The representative airplane is the 

configuration of each model series airplane that incorporates all variations of EWIS 

used in production on that series airplane, and all TC-holder-designed modifications 

mandated by airworthiness directive as of the effective date of § 26.11(b). For example, 

a particular airplane model may be offered in both passenger and cargo versions. For 

that airplane model, the resultant EWIS ICA must account for any differences between 

the two versions. Another example would be the situation where the airplane 

manufacturer offered various interior configurations of a passenger model. The 

placement of galleys, lavatories, seats, and other interior furnishings may impact the 

type and frequency of inspections identified by the EZAP analysis. So the resultant 

EWIS ICA must reflect any such differences. Also, if any changes mandated by 

airworthiness directives have been incorporated, and those changes impact the EWIS 

ICA, then the EWIS ICA produced to comply with § 26.11(b) must reflect those 

changes. 

(2) EWIS ICA Compatibility with Fuel Tank System ICA. Section 26.11 

requires a review of any fuel tank system ICA developed to comply with SFAR 88. 

This is to ensure compatibility with the EZAP-generated EWIS ICA and to minimize 

duplication of requirements between them. It is likely that some of the EWIS on an 

aircraft will be part of the aircraft’s fuel tank system. In that case, the requirements for 

their maintenance and inspection might be more specific than those for wiring in 

general, and might contain additional requirements. For compatibility, it is important 

that the maintenance and inspections for these EWIS be carefully reviewed. If there are 

inspection or maintenance requirements for EWIS and for the fuel tank system within 

the same zone, there should be an effort to align the task interval. The two ICA should 

be reviewed to ensure that any maintenance tasks for EWIS do not compromise fuel 

tank system wire requirements, such as separation or configuration specifications. In 

addition, design holders’ existing documents containing EWIS and fuel tank system 

ICA should be reviewed to either remove or cross-reference redundant information. 

d. EWIS ICA Identification Requirements. Part 25, appendix H, section H25.5(b) 

requires that EZAP-derived EWIS ICA be uniquely identified so there is traceability during 
11/23/07 AC 25-27 

6 

future changes to maintenance programs that contain these EWIS ICA. This is intended to 

prevent inadvertent deletion, changes to the type of task, or escalation of EZAP-derived 

EWIS ICA without proper consideration of the reason for the task and its interval. Following 

approval of the EWIS ICA by the FAA Oversight Office, an operator may propose changes 

to maintenance or inspection program tasks that were based on the approved EWIS and fuel 

tank ICA. The AC titled Incorporation of Electrical Wiring Interconnection System (EWIS) 

Instructions for Continued Airworthiness into the Operators’ Maintenance Programs will 

contain guidance related to making changes to the approved-ICA-based maintenance and 

inspection program tasks. 

e. Requirements of §§ 121.1111 and 129.111. The EAPAS/FTS rule also requires 

part 121 certificate holders, part 129 operators, and part 129 air carriers operating U.S.-

registered airplanes to incorporate into their maintenance program tasks based on FAAapproved EWIS ICA. The AC titled Incorporation of Electrical Wiring Interconnection 

System (EWIS) Instructions for Continued Airworthiness into the Operators’ Maintenance 

Programs will contain guidance for these regulations. 

f. Explanation of Maximum Payload Capacity. For purposes of the requirements in 

§§ 26.11, payload capacity is defined by § 119.3. The current text of § 119.3 may be found 

in Appendix E of this AC. 

3. HOW THIS INFORMATION WAS DERIVED. The guidance in this AC is based on 

recommendations given to us by the Aging Transport Systems Rulemaking Advisory Committee 

(ATSRAC). It is drawn from maintenance, inspection, and alteration best practices identified 

through extensive research by ATSRAC and Federal government working groups. 

4. OBJECTIVE. 

a. The objective of this AC is to improve maintenance and inspection programs for all EWIS 

(as defined by § 25.1701) installed on transport category airplanes. Applying this 

information will improve the likelihood that EWIS degradation from many causes, including 

environmental, maintenance-related, and age-related problems, will be identified and 

corrected. In addition, this information has been reviewed to ensure that maintenance 

actions, such as inspection, repair, overhaul, replacement of parts, and preservation, do not— 

• Cause a loss of EWIS function. 

• Cause an increase in the potential for smoke and fire in the aircraft. 

• Inhibit the safe operation of the aircraft. 

This objective is met through the adoption of the following: 

(1) Enhanced Zonal Analysis Procedure (EZAP). The EZAP will allow the user 

to determine the appropriate general or detailed inspections and any cleaning tasks (also 

referred to as restoration tasks by some manufacturers) needed to minimize the presence 

of combustible material. An EZAP can be used to develop new wiring cleaning and 

inspection tasks for both zonal and non-zonal inspection programs. Using this 
11/23/07 AC 25-27 

7 

procedure to develop a maintenance program will help ensure that proper attention is 

given to wiring installations during maintenance. The EZAP provides a logical 

procedure for selecting inspections (either general or detailed) and other tasks to 

minimize combustibles. Examples could be cleaning (or restoration) procedures or the 

changing of an air filter. For aircraft without a structured zonal inspection program, an 

EZAP will identify new wiring inspection tasks. Appendix A of this AC provides stepby-step details of the EZAP process. 

(2) Guidance for a General Visual Inspection (GVI). This AC clarifies the 

definition of a general visual inspection and provides guidance on what is expected from 

such an inspection, whether performed as a stand-alone GVI or as part of a zonal 

inspection. 

(3) Protections and Cautions. This AC provides guidance for developing actions 

and cautionary statements to be added to maintenance instructions for the protection of 

wire and wire configurations. Maintenance personnel will use these enhanced 

procedures to minimize contamination and accidental damage to EWIS while working 

on aircraft. 

(4) “Protect and Clean As You Go” Philosophy. This philosophy is applied to 

aircraft wiring through inclusion in operators’ maintenance and training programs. This 

philosophy stresses the importance of protective measures when working on or around 

wire bundles and connectors. It stresses how important it is to protect EWIS during 

structural repairs, STC installations, or other alterations by making sure that metal 

shavings, debris, and contamination resulting from such work are removed. The protect 

and clean as you go philosophy is translated into specifics by the protection and caution 

recommendations described in section 11 of this AC. More information is contained in 

section 9 of this AC – “Causes of Wire Degradation.” 

 (5) Consolidation with Fuel Tank Requirements. The FAA has developed an 

extensive program to address safety problems associated with fuel tanks. Fuel tank 

systems contain EWIS that may be routed independently or may be integrated with other 

airplane systems’ EWIS. One part of the Fuel Tank Safety Rule, SFAR 88, requires 

development of maintenance and inspection instructions to ensure the safety of the fuel 

tank system. Other sections of the Fuel Tank Safety Rule require operators to include 

fuel tank safety maintenance and inspection instructions in their maintenance or 

inspection programs. An objective of this AC is to ensure that fuel tank system ICA 

developed to comply with SFAR 88 are compatible with the EWIS ICA, including 

minimizing redundant requirements. See section 2 of this AC for details. 

b. To fully realize the objectives of this AC, type certificate holders, STC holders, air 

carriers, air operators, maintenance providers, and repair stations will need to redefine their 

current approach to maintaining and altering aircraft wiring and systems. This redefinition 

must reach both overall philosophy and specific maintenance tasks. This may require more 

than simply updating maintenance manuals and work cards and improving training. 

Maintenance personnel need to be aware that aircraft EWIS must be maintained in an 
11/23/07 AC 25-27 

8 

airworthy condition. They also need to recognize that visual inspection of wiring has 

inherent limitations. Small defects such as breached or cracked insulation, especially in 

small-gage wire, may not always be apparent. Therefore, effective wiring maintenance 

combines good visual inspection techniques with improved wiring maintenance practices and 

training. 

5. ENHANCED ZONAL ANALYSIS PROCEDURE—GENERAL GUIDANCE. 

a. The enhanced zonal analysis procedure (EZAP) described in this AC was developed to 

identify tasks to: 

• minimize accumulation of combustible materials, 

• detect EWIS component defects, and 

• detect EWIS installation discrepancies that may not be reliably detected by 

inspections contained in existing maintenance programs. 

An EZAP logic diagram and an accompanying step-by-step explanation are contained in 

Appendix A. 

b. An EZAP will result in safety improvements for airplanes operated with a maintenance 

or inspection program that includes a zonal inspection program (ZIP). It is unlikely that 

ZIPs developed in the past considered wire or other EWIS components, except for the most 

obvious damage that could be detected by a GVI. 

c. For airplane models without a ZIP, the EZAP logic is likely to identify a large number of 

EWIS-related tasks that will need to be consolidated into the existing systems maintenance 

or inspection program. Design approval holders who have airplane models without a ZIP 

may find it worthwhile to develop a ZIP in accordance with an industry-accepted method in 

conjunction with an EZAP. 

d. When performing the EZAP, evaluate items such as plumbing, ducting, control cables, 

and other system installations located in the zone for possible contributions to wiring or 

other EWIS component degradation or failures. The results of the analysis will indicate 

whether a restoration task, a zonal GVI, a stand-alone GVI, or a DET inspection is required 

to inspect the EWIS in the zone. The way to determine the best type of inspection is 

graphically represented in Figure 2, Step 8 in Appendix A. The type of inspection is 

GENERAL COMPLIANCE INFORMATION 

Sections 5 to 8 of this AC provide general information regarding the performance 

of the enhanced zonal analysis procedure (EZAP). The EZAP process is 

described in detail in Appendix A of this AC. 
11/23/07 AC 25-27 

9 

determined by completing EZAP Worksheet 3A or EZAP Worksheet 3B in Appendix 

A. EZAP Worksheet 3A is used for airplanes with a ZIP. EZAP Worksheet 3B is 

used for airplanes without a ZIP. 

e. New tasks identified by the EZAP logic should be compared against existing tasks in the 

maintenance program to ensure that they are compatible with each other. Also, existing 

maintenance task type and frequency should not affect the outcome of the EZAP analysis. 

The analysis for a particular zone should be completed to identify appropriate EWIS tasks 

and their frequency. After the analysis is complete, these new EWIS tasks should be 

compared to existing maintenance program tasks to assess where the new tasks and the 

existing maintenance program tasks can be logically combined. The EZAP analysis should 

not be “tweaked” in order to make the tasks and intervals fit the existing maintenance 

program just for the sake of aligning tasks. Refer to the description of Figure 1, Step 9, in

Appendix A of this AC for a detailed discussion on task consolidation and alignment. 

f. Operators may want to use the EZAP logic to identify additional inspection and cleaning 

tasks for any design changes on their airplanes for which EZAP ICA are not available. 

EWIS ICA developed by a DAH may not have taken into account modifications made to the 

airplane by someone other than the DAH who developed the EWIS ICA. Also, when an 

STC is no longer supported by the STC holder, operators may want to perform an EZAP on 

the zone(s) affected by the modification. 

6. EWIS ICA Source Document as Required by Part 25, Appendix H, Section 

H25.5(b). Section H25.5(b) requires that the EWIS ICA be in the form of a document 

appropriate for the information to be provided, and be easily recognizable as EWIS ICA. The 

form the EWIS ICA data takes is at the discretion of the applicant. Different parts of it may 

appear separately in various stand-alone documents, or all the data may be contained in one 

document. Section H25.5(b) does not prescribe a specific data form. Whether contained in one 

document or several, however, the entire EWIS ICA must be referenced in one document. That 

document is referred to in this AC as the “source document.” If the entire EWIS ICA appear in 

one document, then that document is the source document. If the ICA are not contained in one 

document but several, there must be a single source document that provides references to all the 

other documents (e.g., the Maintenance Review Board (MRB) report, maintenance manuals, 

component maintenance manuals) that contain the required EZAP-derived EWIS ICA. The FAA 

Oversight Office will approve this source document. Its approval signifies approval of the actual 

EWIS ICA that is either contained in the source document itself or contained in other documents 

referenced in the source document. 

7. FAA and FAA Oversight Office Approval of EWIS ICA. 

a. The requirements for the FAA to approve EWIS ICA are contained in § 25.1729 and in 

§ 26.11(b) and (c). Section 25.1729 requires applicants to prepare EWIS ICA in accordance 

with part 25, appendix H, sections H25.4 and H25.5, and have them approved by the FAA. 

Sections 26.11(b) and (c) require that DAHs and applicants prepare EWIS ICA in 

accordance with sections H25.5(a)(1) and H25.5(b) of Appendix H. These also must be 
11/23/07 AC 25-27 

10 

approved by the FAA, in this case by the FAA Oversight Office. In summary, there are 

three different compliance scenarios that require FAA approval of EWIS ICA: 

(1) Part 26 DAH EWIS ICA requirements. 

(2) § 25.1729 EWIS ICA requirements for type certificate, amended type certificate, 

and supplemental type certificate applicants. 

(3) Part 26 EWIS ICA requirements for STC and amended TC applicants.. 

b. The following guidance is related only to Sections H25.5(a)(1) and H25.5(b) of part 25, 

appendix H. Guidance for the other EWIS ICA requirements in Appendix H may be found 

in AC 25.1701-1, Certification of Electrical Wiring Interconnection Systems On Transport 

Category Airplanes. 

c. Each FAA office that issues approval of EWIS ICA will use its existing office 

procedures for indicating regulatory compliance findings, unless otherwise agreed to by the 

approving office and applicant. In other words, the FAA does not intend to develop new 

approval indication procedures for findings of compliance with the requirements of 

§§ 25.1729 and 26.11(b) and (c). Note that these procedures may differ between different 

FAA aircraft certification offices. 

d. The following are meant to represent the general types of activity that may occur when 

EWIS ICA are developed and approved. These sequences of events are presented as 

examples and may not necessarily represent the exact order in which these actions will 

occur every time or all the actions necessary for every situation. However, the actions listed 

are consistent with the Maintenance Review Board (MRB) procedures outlined in AC 121-

22A. 

(1) Following are typical actions for holders of, or applicants for, type certificates as 

they develop EWIS ICA to comply with requirements of part 25, Appendix H, sections 

H25.5(a)(1) and (b) (as required by § 25.1729 and § 26.11). 

The steps below are focused on the development, review, and 

approval of the EZAP-derived EWIS ICA. Other EWIS ICA and 

non-EWIS ICA may also be addressed during the review process, but, 

for clarity, they are purposely left out of the following sequence of 

events. 
11/23/07 AC 25-27 

11 

NOTE: The MRB Chairperson’s 

signature does not indicate approval 

of compliance with the requirements 

of §§ 26.11 and 25.1729. Those 

compliance findings must be issued 

by the FAA Oversight Office. 

(a) The DAH conducts preliminary EZAP analysis. 

(b) The DAH presents results of the EZAP analysis to the Industry Steering 

Committee (ISC) working group (WG) assigned to review the analysis. Typically 

this will be the Zonal WG. 

(c) The WG and the DAH agree on any necessary revisions to the analysis and the 

DAH updates the analysis based on these agreements 

(d) The DAH presents the revised EZAP analysis results to the ISC. 

(e) The ISC reviews the EZAP analysis results and identifies any necessary 

revisions. 

(f) The DAH updates the analysis based 

on ISC review and prepares the 

Maintenance Review Board (MRB) 

report, which includes EZAP-derived 

EWIS ICA. 

(g) The DAH transmits the MRB report 

to the applicable FAA Aircraft 

Evaluation Group (AEG) office for 

approval. 

(h) The AEG MRB Chairperson reviews and approves the MRB report and other 

relevant EWIS ICA documentation such as the airplane maintenance manual 

(AMM) and then transmits the approved report to the DAH. This could be an 

iterative process if the MRB Chairperson identifies any additional changes he or she 

believes are necessary. 

(i) The DAH prepares instructions for continued airworthiness which include 

EZAP-derived EWIS ICA based upon the content of the approved MRB report. 

(j) The DAH produces the source document (required by H25.5(b)), which either 

contains, or identifies the location of, the EWIS ICA. (The source document can 

either contain the EWIS ICA or reference its location in other documents – it’s the 

DAH’s choice). 

(k) The DAH submits the source document and any referenced ICA documents to 

the FAA Oversight Office for approval. 

(l) The FAA Oversight Office reviews and approves the source document, which 

indicates approval of the EWIS ICA referenced or contained in that document. 
11/23/07 AC 25-27 

12 

(2) Following are the typical steps that DAHs or applicants will need to go through in 

determining whether the modification for which they seek approval requires revisions to 

previously approved EWIS ICA. A modification (i.e., design change) can be 

accomplished through an amended TC (including service bulletins describing design 

changes), an STC, or changes to an existing STC. 

These actions apply to applicants who must comply with § 25.1729 (i.e., appendix H, 

section H25.5(a)(1)) and/or § 26.11(c) or both. 

(a) The applicant determines whether the proposed modification requires a revision 

to the existing EWIS ICA. Guidance on making this determination is contained in 

Appendix B of this AC. If required, the applicant develops a revised EWIS ICA. 

(b) If revised EWIS ICA are required, the applicant produces a source document 

(required by H25.5(b)) containing the EWIS ICA that were developed using an 

EZAP or identifying their location in other documents. (Whether the source 

document contains the EWIS ICA or references their location in other documents is 

the applicant’s choice). 

(c) The DAH submits the source document and any referenced ICA documents to 

the FAA Oversight Office for approval. 

(d) The FAA Oversight Office reviews and approves the source document, which 

indicates approval of the EWIS ICA referenced or contained in that document. 

8. MAKING EWIS ICA AVAILABLE TO OPERATORS AND OTHER PERSONS. 

Section 26.11(e)(4) requires that the compliance plan submitted by the DAH or applicant contain 

a proposal for how the approved EWIS ICA will be made available to affected persons. Section 

26.11(f) requires that the compliance plan be implemented in accordance with 26.11(e). The rule 

does not specify the manner in which the DAH must make the EWIS ICA available. It simply 

requires the DAH to make them available. The “affected persons” the rule refers to are operators 

and others required to comply with requirements of §§ 26.11, 25.1729, 121.1111, and 129.111. 

 

The steps below are focused on the development, review, and 

approval of the EZAP-derived EWIS ICA. Other EWIS ICA and 

non-EWIS ICA may also be addressed during the review process, but, 

for clarity, they are purposely left out of the following sequence of 

events. 
11/23/07 AC 25-27 

13 

9. CAUSES OF WIRE DEGRADATION. The following are considered principal causes of 

wiring degradation and should be used to help focus maintenance programs. 

VIBRATION. High vibration areas tend to accelerate degradation over time, resulting in 

“chattering” contacts and intermittent symptoms. High vibration of tie-wraps or string-ties can 

cause damage to insulation. In addition, high vibration will exacerbate any existing wire 

insulation cracking. 

MOISTURE. High moisture areas generally accelerate corrosion of terminals, pins, sockets, 

and conductors. It should be noted that wiring installed in clean, dry areas with moderate 

temperatures appears to hold up well.

MAINTENANCE. Scheduled and unscheduled maintenance activities, if done improperly, may 

contribute to long-term problems and degradation of wiring. Certain repairs may have limited 

durability and should be evaluated to ascertain if rework is necessary. Repairs that conform to 

manufacturers’ recommended maintenance practices are generally considered permanent and 

should not require rework. Care should be taken to prevent undue collateral damage to EWIS 

while performing maintenance on other systems. 

a. Metal shavings and debris have been discovered on wire bundles after maintenance, 

repairs, modifications, or STC work have been performed. Take care to protect wire 

bundles and connectors during modification work. Work areas should be cleaned while the 

work progresses to ensure that all shavings and debris are removed. The work area should 

be thoroughly cleaned after work is complete, and the area should be inspected after the 

final cleaning. 

b. Repairs should be performed using the most effective methods available. Since wire 

splices are more susceptible to degradation, arcing, and overheating, the recommended 

method of repairing a wire is with an environmentally sealed splice. 

EWIS DEGRADATION AND MAINTENANCE INFORMATION 

Sections 9 to 11 of this AC contain general information on: 

• Causes of wire degradation. 

• EWIS maintenance guidance, including the levels of inspection 

applicable to EWIS maintenance. 

• Protection and caution recommendations. 

The information in these sections can be used by manufacturers in developing EWIS 

maintenance guidance and by operators to improve EWIS maintenance practices. 
11/23/07 AC 25-27 

14 

INDIRECT DAMAGE. Events such as pneumatic duct ruptures or duct clamp leakage can 

cause damage that, while not initially evident, can later cause wiring problems. When events 

such as these occur, surrounding EWIS should be carefully inspected to ensure that there is no 

damage or potential for damage evident. Indirect damage caused by these types of events may 

be broken clamps or ties, broken wire insulation, or even broken conductor strands. In some 

cases the pressure of the duct rupture may cause wire separation from the connector or terminal 

strip. 

CONTAMINATION. Wire contamination refers to either of the following situations: 

• Presence of a foreign material that is likely to cause degradation of wiring. 

• Presence of a foreign material that is combustible, or capable of sustaining a fire after 

removal of ignition source. 

The contaminant may be in solid or liquid form. 

a. Solid Contaminants. Solid contaminants such as the following can accumulate on 

wiring and may degrade or penetrate wiring or electrical components. 

• metal shavings 

• swarf 

• debris 

• livestock waste 

• lint 

• dust 

b. Fluid Contaminants. Chemicals in fluids such as the following can contribute to 

degradation of wiring. 

• hydraulic fluid 

• battery electrolytes 

• fuel 

• corrosion inhibiting compounds 

• waste system chemicals 

• cleaning agents 

• deicing fluids 

• paint 

• soft drinks 

• coffee 

c. Contaminants Requiring Special Consideration. 

(1) Special consideration is required for − 

• hydraulic fluids 
11/23/07 AC 25-27 

15 

• deicing fluids 

• battery electrolyte 

These fluids, although essential for aircraft operation, can damage connector grommets, 

wire bundle clamps, wire ties, and wire lacing, causing chafing and arcing. Wiring 

exposed to these fluids should be given special attention during inspection. 

Contaminated wire insulation that has visible cracking or breaches to the core conductor 

can eventually arc and cause a fire. Wiring exposed to, or in close proximity to, any of 

the above chemicals may need to be inspected more frequently for damage or 

degradation. 

(2) When cleaning areas or zones of the aircraft that contain both wiring and chemical 

contaminants, special cleaning procedures and precautions may be needed. Such 

procedures may include wrapping wire and connectors with a protective covering prior 

to cleaning. This would be especially true if pressure washing equipment is used. In all 

cases the aircraft manufacturer recommended procedures should be followed. 

d. Waste System Contamination. Waste system spills also require special attention. 

Service history has shown that these spills can have detrimental effects on aircraft EWIS 

and have resulted in smoke and fire events. When this type of contamination is found, all 

affected components in the EWIS should be thoroughly cleaned, inspected, and repaired, or 

replaced if necessary. The source of the spill or leakage should be located and corrected. 

HEAT. Exposure to high heat can accelerate degradation of wiring by causing insulation 

dryness and cracking. Direct contact with a high heat source can quickly damage insulation. 

Burned, charred, or even melted insulation are the most likely indicators of this type of damage. 

Low levels of heat can also degrade wiring over a longer period of time. This type of 

degradation is sometimes seen on engines, in galley wiring such as in coffee makers and ovens, 

and behind fluorescent lights, especially ballasts. 

10. GENERAL EWIS MAINTENANCE GUIDANCE. Areas to be inspected should be clean 

enough to minimize the possibility that collected dirt, grease, or other contaminants might hide 

unsatisfactory conditions that would otherwise be detected during inspection. For any cleaning 

considered necessary, you should use the airplane manufacturer’s procedures or other methods, 

techniques, and practices acceptable to the FAA. The cleaning process itself should not 

compromise the integrity of EWIS. 

(a) Preventing Accumulation of Combustibles. Some applicants may set a 

numerical limit on the amount of contamination that may accumulate in a zone in order to 

avoid combustion of the contaminants. Other applicants may choose not to set a numerical 

limit, but rather give instructions that wires be cleaned to significantly remove the amount of 

combustible material. If an applicant has set a limit, wires should be cleaned at frequent 

enough intervals that the accumulation of combustibles never exceeds this limit. If no limit 

has been set, wires should be cleaned at frequent enough intervals that accumulation of 

combustibles never reaches unacceptable levels. Determining the interval would involve 

making an estimate of the rate at which combustible material will accumulate in that 
11/23/07 AC 25-27 

16 

particular zone and setting intervals to occur with enough frequency so that unacceptable 

levels are not reached. If at an inspection the contaminants in a zone have not yet 

accumulated to the level considered excessive, or to the set level which triggers the need for 

cleaning, a determination must be made about whether the contaminant accumulation will 

have exceeded the limit or reached excessive levels before the next inspection. If that is 

expected to be the case, then the wires should be cleaned during the current inspection even 

though the contaminants have not yet exceeded the accumulation limit or reached excessive 

levels. 

b. Levels of Inspection Applicable to EWIS. Though the term “detailed visual 

inspection” remains valid for detailed inspection using only eyesight, this may represent only 

part of the inspection called for in EWIS ICA used to establish an operator’s maintenance 

program. We recommend that the acronym “DVI” not be used because that term may 

exclude tactile examination, which is sometimes needed. Instead, we provide the following 

definitions. 

(1) Refer to Figures 1 and 2 for examples of EWIS that are contaminated. Such 

contamination could cause EWIS component degradation and also prevent an effective 

GVI or DET inspection if it were not cleaned. Additionally, depending on the type and 

amount present, contaminants may also be combustible and sustain a fire should 

electrical arcing occur. 

Figure 1: EWIS Contaminated with Dust and Dirt 
11/23/07 AC 25-27 

17 

Figure 2: EWIS Contaminated with Grease 

(2) Detailed Inspection (DET)—An intensive examination of a specific item, 

installation, or assembly to detect damage, failure, or irregularity. Available lighting is 

normally supplemented with a direct source of good lighting at an intensity deemed 

appropriate. Inspection aids such as mirrors, magnifying lenses, or other means may be 

necessary. Surface cleaning and elaborate access procedures may be required. A DET 

can be more than just a visual inspection, since it may include tactile assessment in 

which a component or assembly is checked for tightness/security. It may require the 

removal of items such as access panels and drip shields, or the moving of components. 

(3) General Visual Inspection (GVI)—A visual examination of an interior or 

exterior area, installation, or assembly to detect obvious damage, failure, or 

irregularity. This level of inspection is made from within touching distance unless 

otherwise specified. A mirror may be necessary to enhance visual access to all exposed 

surfaces in the inspection area. This level of inspection is made under normally 

available lighting conditions such as daylight, hangar lighting, flashlight, or droplight 

and may require removal or opening of access panels or doors. Stands, ladders, or 

platforms may be required to gain proximity to the area being checked. 

(a) Recent changes to this definition have added proximity guidance (within 

touching distance) and the allowance of a mirror and flashlight to improve visual 

access to exposed surfaces when performing a GVI. These changes should result in 

more consistent application of the GVI. They also support expectations of the 

types of EWIS discrepancies that should be detected by a GVI.
11/23/07 AC 25-27 

18 

(b) When performing a GVI, there is usually no need to remove equipment or 

displace wire unless the access instructions specifically call for it. 

(c) The area to be inspected should be clean enough to minimize the possibility 

that collected dirt or grease, or other contaminants, might hide unsatisfactory 

conditions that would otherwise be obvious. For any cleaning considered 

necessary, you should use the airplane manufacturer’s procedures or other methods, 

techniques, and practices acceptable to the FAA. The cleaning process itself should 

not compromise the integrity of EWIS. Avoid using high pressure cleaning and 

abrasive materials that could damage wire insulation and other EWIS components. 

(d) In general, the person performing a GVI is expected to identify degradation 

from wear, vibration, moisture, contamination, excessive heat, aging, etc., and 

assess what actions are appropriate to address the discrepancy. This assessment 

should consider potential effects on adjacent system installations, particularly if 

those systems include wiring. You should address any observed discrepancies, 

such as chafing, broken clamps, sagging, interference, contamination, etc. 

(4) Zonal Inspection—A collective term comprising selected general visual 

inspections and visual checks that are applied to each zone of the airplane, defined by 

access and area, to check system and powerplant installations and structure for security 

and general condition. A zonal inspection is essentially a GVI of an area or zone to 

detect obvious unsatisfactory conditions and discrepancies. Unlike a stand-alone GVI, it 

is not directed to any specified component or assembly. 

c. EWIS-Related Guidance for Zonal Inspections. The following EWIS 

degradation conditions are typical of what should be detectable and addressed as a result of 

a zonal inspection (as well as a stand-alone GVI). Maintenance and training documentation 

should include these items. This list is not intended to be all-inclusive and may be expanded 

as considered appropriate. 

(1) Wire/Wire Harnesses. 

• Wire bundle/wire bundle or wire bundle/structure contact/chafing 

• Wire bundles sagging or improperly secured 

• Wires damaged (obvious damage because of mechanical impact, overheat, 

localized chafing, etc.) 

• Lacing tape and/or ties missing/incorrectly installed 

• Wiring protection sheath/conduit deformed or incorrectly installed 

• End of sheath rubbing on end attachment device 

• Grommet missing or damaged 

• Dust and lint accumulation 

• Surface contamination by metal shavings/swarf 

• Contamination by liquids 

• Deterioration of previous repairs (splices, for example) 

• Deterioration of production splices 
11/23/07 AC 25-27 

19 

• Inappropriate repairs (for example an incorrect splice) 

• Inappropriate attachments to or separation from fluid lines 

(2) Connectors. 

• External corrosion on receptacles 

• Backshell tail broken 

• Rubber pad or packing on backshell missing 

• No backshell wire securing device 

• Foolproofing chain broken 

• Safety wire missing or broken 

• Discoloration/evidence of overheat on terminal lugs/blocks 

• Torque stripe misaligned 

(3) Switches. 

• Rear protection cap damaged 

• Missing hardware (screws, washers, etc.) 

• Loose hardware 

• Improper hardware 

(4) Ground Points. 

• Corrosion 

• Loose hardware 

(5) Bonding Braid/Bonding Jumper. 

• Braid broken or disconnected 

• Multiple strands corroded 

• Multiple strands broken 

(6) Wiring Clamps or Brackets. 

• Corroded 

• Broken/missing 

• Bent or twisted 

• Unstuck/detached 

• Attachment faulty (bad attachment or fastener missing) 

• Protection/cushion damaged 
11/23/07 AC 25-27 

20 

(7) Supports (Rails or Tubes/Conduit). 

• Broken 

• Deformed 

• Fastener missing 

• Edge protection on rims of feed-through holes missing 

• Racetrack cushion damaged 

• Drainage holes (in conduits) obstructed 

(8) Circuit Breakers, Contactors, or Relays. 

• Signs of overheating 

• Signs of arcing 

• Missing hardware (screws, washers, etc.) 

• Loose hardware 

• Improper hardware 

d. Wiring Installations and Areas of Concern. Maintenance material should address 

the following installations and areas. 

(1) Wiring Installations. 

• Clamping points—Damaged clamps, migration of clamp cushions, or 

improper clamp installations aggravate wire chafing. Aircraft manufacturers 

specify clamp type and part number for EWIS throughout the aircraft. When 

replacing clamps, use those specified by the aircraft manufacturer. Tie wraps 

provide a rapid method of clamping, especially during line maintenance 

operations. But improperly installed tie wraps can have a detrimental effect on 

wire insulation. When new wiring is installed as part of an STC or other 

modification, the drawings will provide wire routing, clamp type and size, and 

proper location. Examples of significant wiring alterations are the installation 

of new avionics systems, new galley equipment, and new instrumentation. 

Wire routing, type of clamp, and clamping location should conform to the 

approved drawings. Adding new wire to existing wire bundles may overload 

clamps, causing wire bundles to sag and wires to chafe. Raceway clamp foam 

cushions may deteriorate with age, fall apart, and thus fail to provide proper 

clamping. 

• Connectors—Worn environmental seals, loose connectors, missing seal 

plugs, missing dummy contacts, or lack of strain relief on connector grommets 

can compromise connector integrity and allow contamination to enter the 

connector, leading to corrosion or grommet degradation. Connector pin 

corrosion can cause overheating, arcing, and pin-to-pin shorting. Drip loops 

should be maintained when connectors are below the level of the harness and 

tight bends at connectors should be avoided or corrected. 
11/23/07 AC 25-27 

21 

• Terminations—Terminations, such as terminal lugs and terminal blocks, are 

susceptible to mechanical damage, corrosion, heat damage, and contamination 

from chemicals, dust, and dirt. Over time, vibration can cause high-currentcarrying feeder cable terminal lugs to lose their original torque value, resulting 

in arcing. One sign of this is heat discoloration at the terminal end. Proper 

build-up and nut torque is especially critical on high-current-carrying feeder 

cable lugs. Corrosion on terminal lugs and blocks can cause high resistance 

and overheating. Dust, dirt, and other debris are combustible and could 

sustain a fire if ignited from an overheated or arcing terminal lug. Terminal 

blocks and terminal strips located in equipment power centers (EPC), avionics 

compartments, and throughout the aircraft need to be kept clean and free of 

combustibles. 

• Backshells—Wires may break at backshells from excessive flexing, lack of 

strain relief, or improper build-up. Loss of backshell bonding may also occur 

because of these and other factors. 

• Sleeving and conduits—Damage to sleeving and conduits, if not 

corrected, may lead to wire damage. So damage such as cuts, dents, and 

creases on conduits may require further investigation for condition of wiring 

within. 

• Grounding points—You should check grounding points for security (i.e., 

finger tightness), condition of the termination, presence of corrosion, and 

cleanliness. Grounding points that are corroded or have lost their protective 

coating should be repaired. 

• Splices—Both sealed and non-sealed splices are susceptible to vibration, 

mechanical damage, corrosion, heat damage, chemical contamination, and 

environmental deterioration. Power feeder cables normally carry high current 

levels and are very susceptible to installation error and splice degradation. All 

splices should conform to the TC or STC holder’s published 

recommendations. In the absence of published recommendations, we 

recommend use of environmentally sealed splices. 

(2) Areas of Concern. 

• Wire raceways and bundles—Adding wires to existing wire raceways 

may cause undue wear and chafing of the wire installation and inability to 

maintain the wire in the raceway. Adding wire to existing bundles may cause 

wire to sag against the structure, which can cause chafing. 

• Wings—Wing leading and trailing edges are difficult environments for 

wiring installations. On some aircraft models, wing leading and trailing edge 

wiring is exposed whenever the flaps or slats are extended. Slat torque shafts 

and bleed air ducts in these areas are other potential damage sources. 
11/23/07 AC 25-27 

22 

• Engine, pylon, and nacelle area—These areas experience high vibration, 

heat, and frequent maintenance, and are susceptible to chemical 

contamination. 

• Accessory compartment and equipment bays—These areas typically 

contain items such as electrical components, pneumatic components and 

ducting, and hydraulic components and plumbing. They may be susceptible to 

vibration, heat, and liquid contamination. 

• Auxiliary power unit (APU)—Like the engine/nacelle area, the APU is 

susceptible to high vibration, heat, frequent maintenance, and chemical 

contamination. 

• Landing gear and wheel wells—This area is exposed to severe external 

environmental conditions in addition to vibration and chemical contamination. 

• Electrical panels and line replaceable units (LRUs)—Electrical panel 

wiring is particularly prone to broken wires and damaged insulation when 

these high density areas are disturbed during troubleshooting activities, 

alterations, and refurbishments. Tying wiring to wooden dowels to reduce its 

disturbance during modification can minimize wire damage. For some 

configurations, use of connector support brackets would be more desirable and 

cause less wire disturbance than removal of individual connectors from the 

supports. 

• Batteries—Wires in the vicinity of all aircraft batteries are susceptible to 

corrosion and discoloration and should be inspected for those problems. You 

should inspect discolored wires for serviceability. 

• Power feeders— High-current wiring and associated connections have the 

potential to generate intense heat. Vibration may cause degradation or 

loosening of power feeder cables, terminals, and splices. If signs of 

overheating are seen, splices or termination should be replaced. For both 

galley and engine/APU generator power feeders, depending on the design, 

service experience may indicate a need for periodic checks of proper torque on 

power feeder cable terminal ends, especially in high vibration areas. 

• Under galleys, lavatories, and cockpit—Areas under the galleys, 

lavatories, and cockpit are particularly susceptible to contamination from such 

things as coffee, food, water, soft drinks, lavatory fluids, dust, and lint. Proper 

floor panel sealing procedures can minimize such contamination in these 

areas. 

• Fluid drain plumbing—Leaks from fluid drain plumbing may lead to liquid 

contamination of wiring. Service experience may show a need for periodic 
11/23/07 AC 25-27 

23 

leak checks or cleaning, in addition to routine visual inspections. 

• Fuselage drain provisions—Some installations include plumbing features 

designed to catch leakage and drain it to an appropriate exit. Blockage of the 

drain path can result in liquid contamination of wiring. In addition to routine 

visual inspections, service experience may signal a need to check these 

installations and associated plumbing periodically to ensure the drain path is 

free of obstructions. 

• Cargo bay underfloor— Damage to wiring in the cargo bay underfloor can 

occur from maintenance activities in the area. 

• Wiring subject to movement—Wiring that is subject to movement or 

bending during normal operation or maintenance access, at locations such as 

doors, actuators, landing gear mechanisms, and electrical access panels, should 

be inspected at those areas where movement occurs. 

• Access panels—Wiring near access panels may be accidentally damaged 

from repetitive maintenance access and may warrant special attention. 

• Under doors—Areas under cargo, passenger, and service entry doors are 

susceptible to fluid entering from rain, snow, and liquid spills. Fluid drain 

provisions and floor panel sealing in these areas should be periodically 

inspected and repaired as necessary. 

• Under cockpit sliding windows—Areas under cockpit sliding windows 

are susceptible to water entering from rain and snow. Fluid drain provisions in 

these areas should be periodically inspected and repaired as necessary. 

• Areas where wiring is difficult to access—Areas difficult to access, 

such as flight deck instrument panels and the cockpit pedestal area, may 

accumulate excessive dust and other contaminants because of infrequent 

cleaning. In these areas it may be necessary to remove components and 

disassemble other systems to facilitate access to the area. 

11. PROTECTION AND CAUTION RECOMMENDATIONS. 

Section 43.13(b) requires anyone performing maintenance or alteration to do the work— 

in such a manner and use materials of such a quality that the condition of the aircraft, 

airframe, aircraft engine, propeller, or appliance worked on will be at least equal to its 

original or properly altered condition (with regard to aerodynamic function, structural 

strength, resistance to vibration and deterioration, and other qualities affecting 

airworthiness). 
11/23/07 AC 25-27 

24 

Anyone performing maintenance must use methods, techniques, and practices prescribed in the 

manufacturer’s current maintenance manual or in ICA prepared by the manufacturer, or methods, 

techniques, and practices referred to in § 43.13(a) as acceptable to the Administrator. Protection 

and caution recommendations, while not required as part of the EZAP process discussed in this 

AC, are required by H25.5 (a)(1)(vi) of part 25. They are an important part of the “protect and 

clean as you go” philosophy, which contributes to preserving the integrity of EWIS. Some 

practices in use today may actually compromise the integrity of EWIS, albeit inadvertently. 

Therefore, we have identified some specific maintenance and servicing tasks and recommend 

that air carriers and air operators adopt these more robust practices. Such information may be 

provided in training, on job cards or task cards, or in handout information for maintenance 

personnel. These maintenance practices will help prevent inadvertent contamination of EWIS 

with harmful solids (such as metal shavings) or fluids during maintenance, alteration, and repair 

of airplane structures and components. Training of maintenance and servicing personnel should 

address potential consequences of their actions to wiring in the work area. FAA advisory 

circular AC 120-94, Aircraft Electrical Wiring Interconnection Systems Training Program, 

provides details of EWIS training that could be adopted by air carriers and air operators. 

a. Installation, Repair, or Modification of Wiring. Wiring and other EWIS 

components (e.g., protective coverings, connectors, clamping provisions, and conduits) 

often comprise the most vulnerable and maintenance-sensitive portions of an installation or 

system. Extreme care and proper procedures should be used during installation, repair, or 

modification of EWIS components to ensure safe and reliable performance of the wire 

function. 

(1) Proper EWIS component selection, routing/separation, clamping configurations, use 

of splices, repair or replacement of protective coverings, pinning/de-pinning of 

connections, etc., should be performed in accordance with the applicable sections of the 

aircraft maintenance manual (AMM), standard wiring practices manual (SWPM), or 

other manufacturer’s maintenance documents or in accordance with the operator’s 

approved maintenance program. 

(2) You should take special care to minimize disturbance of existing adjacent wiring 

during maintenance activities. When wiring is displaced during a maintenance activity, 

special attention should be given to returning it to its normal configuration in 

accordance with the applicable maintenance instructions. 

b. Structural Repairs and STCs. Structural repairs and STC installations inevitably 

introduce tooling and residual debris that is harmful to aircraft wiring and other EWIS 

components. They often require displacement or removal of wiring to provide access to the 

work area. Even minor displacement of wiring, especially while clamped, can damage its 

insulation and result in degraded performance, leading to subsequent arcing or circuit 

failure. 

(1) Use extreme care to protect wiring from mechanical damage by tools or other 

equipment during structural repairs, installation of STCs, and repairs or alterations. 

Avoid drilling blindly into the aircraft structure. Damage to the wire installation could 
11/23/07 AC 25-27 

25 

cause arcing, fire, and smoke. Carefully cover or displace wiring located adjacent to 

drilling or riveting operations to reduce the possibility of mechanical damage. 

(2) Do not allow debris such as drill shavings, liberated fastener pieces, broken drill 

bits, etc., to contaminate or penetrate wiring or electrical components. This can cause 

damage to insulation and potential arcing by providing a conductive path to ground or a 

conductive path between 2 or more wires of different loads. Once wire bundles are 

contaminated with this type of debris, it is extremely difficult to remove it. So take 

precautions to prevent contamination of any kind from entering the wire bundle. 

(3) Before beginning structural repair work and STC installation, survey the work area 

carefully to identify all EWIS and electrical components that may be subject to 

contamination. EWIS and electrical components in the debris field should be covered or 

removed. Drills equipped with vacuum aspiration can be used to minimize risk of 

metallic debris contaminating wire bundles or other EWIS components. When work is 

complete, clean electrical components, wiring, and other EWIS components per 

applicable maintenance instructions. 

c. Aircraft De-Icing or Anti-Icing. Exercise care when spraying de/anti-icing fluids to 

prevent damage to exposed electrical components and wiring in areas such as wing leading 

and trailing edges, wheel wells, and landing gear. Direct pressure spray onto electrical and 

EWIS components can lead to contamination or degradation and should be avoided. 

d. Inclement Weather. EWIS in areas below doorways, floors, access panels, and 

servicing bays are prone to corrosion or contamination from exposure to the elements. 

Snow, slush, or excessive moisture should be removed from these areas before closing doors 

or panels. Before loading items into the aircraft (cargo containers, for example) remove 

deposits of snow or slush. Keep doors/panels closed as much as possible during inclement 

weather to prevent ingress of snow, slush, or excessive moisture. 

e. Component Removal/Installation (relating to attached wiring). 

(1) Excessive component handling and movement during installation and removal may 

harm EWIS. Use appropriate connector pliers (e.g., soft jawed) to loosen coupling rings 

that are too tight to be loosened by hand. Alternately pull on the plug body and unscrew 

the coupling ring until the connector is separated. Do not use excessive force and do not 

pull on attached wires. When reconnecting, take special care to ensure the connector 

body is fully seated, the jam nut is fully secured, and no tension is on the wires. 

(2) When equipment is disconnected, use protective caps on all connectors (plug or 

receptacle) to prevent contamination or damage of the contacts. Sleeves or plastic bags 

may be used if protective caps are not available. Use of sleeves or plastic bags should 

be temporary because of the risk of condensation. Use of a humidity absorber is 

recommended with sleeves or plastic bags. 
11/23/07 AC 25-27 

26 

f. Pressure Washing. Exercise care when spraying water or cleaning fluids to prevent 

damage to exposed electrical components and EWIS in areas such as wing leading and 

trailing edges, wheel wells, and landing gear. Avoid direct high-pressure spray onto 

electrical components and wiring. It can lead to contamination or degradation. When 

practical, protect EWIS components (e.g., wiring and connectors) before pressure washing. 

Use water rinse to remove cleaning solution residue after washing. Breakdown of wire 

insulation or material used in other EWIS components may occur with long-term exposure 

of EWIS components to cleaning solutions. Although these recommendations are good 

practice and technique, consult the airplane maintenance manual or STC holder’s 

instructions for additional detailed instructions about pressure washing. 

g. Cleaning of EWIS (in situ). Exercise extreme care and use proper procedures when 

cleaning to ensure safe and reliable performance of the function supplied by EWIS. 

Although these recommendations for cleaning of EWIS are considered good practice and 

technique, consult the airplane maintenance manual or STC holder’s instructions for 

additional detailed instructions. 

(1) Avoid displacing or disturbing wiring during cleaning of non-aggressive 

contamination, such as dust, dirt, or swarf. Displacement may be necessary for 

aggressive contaminants (livestock waste, salt water, battery electrolyte, for example). 

In those cases, release wiring from its installation in a way that avoids placing undue 

stress on the wiring connectors and wire bundle support devices. If liquid 

contamination enters the bundle, remove ties before separating wires. 

(2) Clean only contaminated areas and items. Before cleaning, make sure that the 

cleaning materials and methods will not cause more contamination. Make sure cloths 

used are clean, dry, and lint-free. Connectors should be completely dry before mating. 

Fluids left on connectors can have a deteriorating effect on the connector or the system 

or both. 

h. Servicing or Repairing Waste/Water Systems. EWIS in areas adjacent to 

waste/water systems are prone to contamination from those systems. Use care to prevent 

fluids from reaching EWIS components while servicing or repairing waste/water systems, 

and cover exposed EWIS components while working. Operator practice may call for a 

weak acid solution to be periodically flushed through lavatory systems to improve reliability 

and efficiency of operation. Because of the effect of acid contamination on systems and 

structure, confirm that the system is free of leaks before using such solutions. 

i. Servicing or Repairing Oil Systems. EWIS in areas adjacent to oil systems are 

prone to contamination from those systems. Oil and debris in combination with damaged 

wiring can present a fire hazard. To minimize the attraction and adhesion of foreign 

material, use care to prevent fluids from reaching EWIS components while servicing or 

repairing oil systems. 

j. Servicing or Repairing Hydraulic Systems. EWIS in areas adjacent to hydraulic 

systems are prone to contamination from those systems. To minimize the attraction and 
11/23/07 AC 25-27 

27 

adhesion of foreign material, use care to prevent fluids from reaching EWIS components 

while servicing or repairing hydraulic systems. 

k. Gaining Access (entering zones). When entering the aircraft or working on it, use 

care to prevent damage to adjacent EWIS components, including wiring or other EWIS 

components that may be hidden from view (covered by insulation blankets, for example). 

Use protective boards or platforms for adequate support and protection. Avoid using wire 

bundles as handholds, steps, and supports. Don’t use wiring to hang or support work lights. 

If wiring must be displaced or removed for work area access, it should be adequately 

released from its clamping or other restraining provisions to allow movement without 

damage, and returned to position after work is completed. 

l. Applying Corrosion Prevention Compounds (CPC). When applying CPC in 

airplane zones containing EWIS, use care to prevent CPC from contacting it. Dust and lint 

are more likely to collect on wire that has CPC on it. Apply CPCs according to the aircraft 

manufacturer’s maintenance instructions. 

/s/Ali Bahrami 

Ali Bahrami 

Manager 

Transport Airplane Directorate 

Aircraft Certification Service 

11/23/07 AC 25-27 

 Appendix A 

A-1 

APPENDICES 

APPENDIX A 

EZAP—THE ENHANCED ZONAL ANALYSIS PROCEDURE 

APPENDIX B 

EVALUATING WHETHER A DESIGN CHANGE IMPACTS 

PREVIOUSLY APPROVED EWIS ICA AND DEVELOPING ANY 

NECESSARY REVISED EWIS ICA AS REQUIRED BY § 26.11(C) 

and 

GUIDANCE FOR THE COMPLIANCE PLAN REQUIREMENTS OF 

§ 26.11(E) IF NO CHANGES TO EXISTING EWIS ICA ARE 

NECESSARY 

APPENDIX C

DEFINITIONS 

APPENDIX D 

FAA OVERSIGHT OFFICES FOR THE PURPOSES OF PART 26 

APPENDIX E 

APPLICABLE REGULATIONS AND RELEVANT PREAMBLE 

DISCUSSION 

APPENDIX F 

 BACKGROUND 
11/23/07 AC 25-27 

 Appendix A 

A-2 

APPENDIX G 

RELATED REGULATIONS AND DOCUMENTS 

APPENDIX H 

EZAP WORKSHEETS FOR USE BY APPLICANTS 
11/23/07 AC 25-27 

 Appendix A 

A-3 

APPENDIX A 

EZAP—THE ENHANCED ZONAL ANALYSIS PROCEDURE

The figures and explanations on the following pages describe the EZAP process. 

Before you begin using this logic, you should be thoroughly familiar with the contents 

and philosophy of this AC and the results the AC and the EZAP seek to achieve. 
11/23/07 AC 25-27 

 Appendix A 

A-4 

No further action is required

Select wiring inspection 

level and interval

See Figure 2

Assign task to EWIS ICA

Maintenance program systems and 

powerplant section

Recommend inclusion in ATA 20

Aircraft with ZIPs

Assign task to EWIS ICA

Maintenance program zonal section

YES

NO

YES

YES

YES

INSPECTION TASK(S)

NO

8

Does the zone contain wiring?

3

List details of zone, for example:

Access

Installed equipment

Lightning / HIRF protection features

Wire bundle installations

Possible combustible materials

2

Is wiring close (2 in/50 mm) 

to both primary and backup 

hydraulic, mechanical, or 

electrical flight controls?

7

Is there an effective task to 

significantly reduce the likelihood of 

accumulation of combustible 

materials?

5

Define the task and 

assign an interval for 

performing it.

6

Consider consolidation with existing 

inspection tasks in systems and 

powerplant and/or zonal programs *

9

NO

CONTINUE THE 

ANALYSIS

STAND-ALONE GVI 

CONSOLIDATED IN 

ZONAL INSPECTION

Identify aircraft zones, including boundaries

1

NO

Figure 1

Enhanced Zonal Analysis 

Procedure

STAND-ALONE GVI

DET

Cleaning (Restoration)

Other Task(s)

* Section 26.11(b) requires 

EWIS ICA and fuel tank 

system ICA developed to 

comply with SFAR 88 be 

compatible and any 

redundancies between 

them minimized

Are there, or are there

likely to be, combustible 

materials in the zone?

4
A-5 

Figure 

Step 8 

Select Wiring 

Level and 

Using rating tables, assess likelihood of damage to w

zone to determine an appropriate interval for each i

task identified (example provided later in this app

Define spec

zone for whic

Define spec

zone for wh

frequent int

List zone d

boundarie

wiring 

Zonal GVI must be augmented 

with stand-alone GVI and/or 

DET inspection

Using rating tables, assess zone attributes to determine 

appropriate level of inspection 

(examples provided later in this appendix)

Is GVI of all wiring in the 

zone at same interval effective 

for all wiring in the zone?

Is zonal GVI alone effective 

for all wiring in the zone?

Define specific wiring in the 

zone for which stand-alone 

GVI is justified

Define specific wiring in the 

zone for which DET is justified

Some wiring requires GVI at 

more frequent interval and/or 

DET inspection

YES

NO NO

YES

PROGRAMS WITH ZONAL 

INSPECTION PROGRAM 

PROGRAMS WITHOUT ZONAL 

INSPECTION PROGRAM 

List zone description and 

boundaries for zonal GVI

A-5 
11/23/07 AC 25-27 

 Appendix A

A-6-6 

EXPLANATION FOR STEPS IN ENHANCED ZONAL ANALYSIS PROCEDURE 

LOGIC DIAGRAMS 

The following paragraphs provide further explanation of each step in the enhanced 

zonal analysis procedure (EZAP) logic (Figures 1 and 2). Applicants performing the 

EZAP analysis should use the “representative airplane” (see paragraph 2.c. of this AC) 

and, where possible, verify the analysis using an actual aircraft (typical airplane that has 

not been cleaned) to ensure that they fully understand the zones being analyzed. Using 

an actual airplane will help in determining density, size, environmental issues, and 

accidental damage issues for each zone.

STEP 1: Identify aircraft zones, including boundaries

If the design approval holder or operator has not already established aircraft zones, we 

recommend that this be done. Wherever possible, the definition of zones should follow 

a consistent method such as Air Transport Association (ATA) iSpec 2200 (formerly ATA 

Spec 100), varied only to accommodate particular design constructional differences. 

Define the zones, wherever possible, by actual physical boundaries such as wing spars, 

major bulkheads, cabin floor, control surface boundaries, skin, etc., and include access 

provisions for each zone. 

STEP 2: List details of zone

Within the zone, identify system installations, significant components, lightning and high 

intensity radiated field (L/HIRF) protection features, typical power levels in any installed 

wiring bundles, combustible materials (present or with the potential for accumulation) 

and any other features that may affect wiring integrity or accumulation of combustibles. 

With respect to power levels, the person performing the EZAP analysis should know 

whether the wire bundle consists primarily of main generator feeder cables, low voltage 

instrumentation wiring, or standard bus wiring. This information will be used in 

determining potential effects of deterioration. 

Identify any locations where both primary and back-up flight controls are routed within 2 

inches/50 mm of a wiring harness. This information is required to answer the question 

in STEP 7.

STEP 3: Does zone contain wiring? This question eliminates from the EZAP those 

zones that do not contain wiring. 

STEP 4: Are there, or are there likely to be, combustible materials in zone? This 

question requires evaluating whether the zone might contain combustible material that 

could cause a fire to be sustained in the event of an ignition source arising in adjacent 

wiring. Examples include the presence of fuel vapors, dust/lint accumulation, and 

contaminated insulation blankets. 
11/23/07 AC 25-27 

 Appendix A

A-7-7 

• With respect to commonly used liquids (oils, hydraulic fluids, corrosion prevention 

compounds, for example) refer to the product specification to assess potential for 

combustibility. The product may be readily combustible only in vapor mist form. If 

so, an assessment is required to determine if conditions might exist in the zone for 

the product to be in this state. 

• Liquid contamination of wiring by most synthetic oil and hydraulic fluids (e.g., 

skydrol) may not be considered combustible. It is a concern, however, if it occurs in 

a zone where dust and lint are present, because wet or oily surfaces attract dust 

and lint. 

Assess what sources of combustible products may contaminate the zone following any 

single failure considered likely from in-service experience. For example, consider 

unshrouded pipes with connections within the zone to be potential contamination 

sources. Forced air ventilation in a zone tends to blow dust and lint through the air, 

causing it to lodge on wiring surfaces. Wet or oily surfaces attract more dust and lint. 

This needs to be considered when you are assessing the possibility of a buildup of 

combustibles in the zone. 

• Avionics and instruments located in the flight compartment and equipment bays 

tend to attract dust, dirt, and other contamination. Because of the heat generated 

by these components and their relatively tightly packed installations, you should 

consider that these zones have the potential for accumulating combustible material. 

Forced air ventilation is often used in these areas, causing lint and dust to be blown 

about the area and often resulting in a buildup of dust and lint on wire surfaces. 

Always use the EZAP logic for these zones. For flight compartment and equipment 

bays, the answer to the question in STEP 4 should be “yes.” 

Although moisture (whether clean water or otherwise) is not combustible, its presence 

on wiring increases the probability of arcing from small breaches in the insulation. This 

could cause a localized fire in the wire bundle. The fire could spread if there are 

combustibles in close proximity. The risk of a sustained fire caused by moistureinduced arcing is mitigated in STEP 5 by identifying a task to reduce the likelihood of 

accumulation of combustible material on or adjacent to the wiring. 

STEP 5: Is there an effective task to significantly reduce the likelihood of 

accumulation of combustible materials? Most operator maintenance programs have 

not included tasks directed towards removing combustible materials from wiring or 

adjacent areas or preventing their accumulation. Evaluate whether accumulation on or 

adjacent to wiring can be significantly reduced. 

Though restoration tasks such as cleaning are the most likely applicable tasks, the 

possibility of identifying other tasks is not eliminated. For example, a detailed inspection 

of a hydraulic pipe might be appropriate if high-pressure mist from pinhole corrosion 
11/23/07 AC 25-27 

 Appendix A

A-8-8 

could impinge a wire bundle and the inherent zone ventilation is low. Task 

effectiveness criteria should include considering the potential for damaging the wiring. 

STEP 6: Define the task and assign an interval for performing it 

This step will define an applicable EWIS ICA task to reduce accumulation of 

combustible materials and an effective interval for performing that task. The defined 

task should be included as a dedicated task in the systems & powerplant section of the 

maintenance program. Within MRB (maintenance review board) reports, it may be 

introduced under the standard practices section (ATA (Air Transport Association) 

chapter 20 of the MRB report) with no failure effect category assigned. 

Restoration tasks should not be so aggressive that they damage wiring, but should be 

performed at a level that significantly reduces the likelihood of combustion. 

STEP 7: Is wiring close to both primary and backup hydraulic, mechanical, or 

electrical flight controls? This question is asked to ensure that STEP 8 logic is 

applied where wiring is close (i.e., within 2 inches/50 mm) to both primary and backup 

hydraulic, mechanical, or electrical flight controls, even in the absence of combustible 

materials in the zone. 

For zones where combustible materials are present (as determined in STEP 4), 

proximity is addressed in the inspection level definition portion of STEP 8, and this 

question need not be asked. 

This step addresses the concern that segregation between primary and back-up flight 

controls may not have been consistently achieved. Even in the absence of combustible 

material, a localized wire arcing could prevent continued safe flight and landing if 

hydraulic pipes, mechanical cables, or wiring for fly-by-wire controls are routed in close 

proximity (within 2 inches/50 mm) to a wiring harness. In consideration of the 

redundancy in flight control systems, this question should be answered ‘Yes’ if both the 

primary and back-up system might be affected by wire arcing. 

 

On all aircraft type designs, regardless of TC date, alterations performed by an STC 

holder or a field-approved repair or alteration may not have taken into account the TC 

holder’s design criteria. We recommend that STC holders assess whether their design 

changes route wires within 2 in. or 50 mm of both primary and back-up hydraulic, 

mechanical, or electrical flight control cables and lines. Similarly, air carriers and air 

operators should assess any field-approved repairs or alterations or other modifications 

that have been made to their aircraft to identify any added or altered wiring that may be 

close to flight control cable and lines. 
11/23/07 AC 25-27 

 Appendix A

A-9-9 

STEP 8: Select wiring inspection level and interval (Figure 2)

a. Inspection level. At this point in the analysis, it is already confirmed that wiring 

is installed in a zone where the presence of combustible materials is possible 

and/or the wiring is in close proximity to primary and backup hydraulic or 

mechanical flight controls. Therefore, some level of inspection of the wiring in the 

zone is required. This step details how to select the proper level of inspection and 

interval. 

We recommend selecting the proper inspection level and interval by using ratings 

tables which rate characteristics of the zone and how the wiring is affected by, or 

can affect, those attributes. The analyst will determine the precise format of such a 

rating table, but example rating tables appear later in this appendix. 

The inspection level characteristics that may be included in the rating system are 

the following. 

• Zone identification – According to ATA Specification iSpec 2200, 

“Manufacturer’s Technical Data,” zones are identified by the airplane 

manufacturer “to facilitate maintenance, planning, preparation of job 

instructions, location of work areas and components, and a common basis 

for various maintenance tasks.” iSpec 2200 contains guidelines for 

determining airplane zones and their numbering. The EZAP process uses 

these manufacturer-identified zones. The zones are not created uniquely 

for EZAP. 

• Zone size − Zone size determination is based on comparing all the zones 

in a given airplane model and assessing them in relation to each other. For 

the purposes of the EZAP analysis, zone sizes are identified as small, 

medium, or large. For example, the aft cargo bay on a large transport 

category airplane would be considered a large zone, but the radome on the 

same airplane would be considered a small zone. The smaller the zone 

and the less congested it is, the more likely it is that wiring degradation will 

be identified by GVI. 

• Zone density – The density of installed equipment, including wiring and 

other EWIS components, within the zone is assessed in relation to the size 

of the zone. For the purposes of the EZAP analysis, zone density is 

identified as low, medium or high. Typical factors to consider are the 

number of components, their relative closeness to one another, and the 

complexity of these components (e.g., multiple electrical, mechanical, or 

hydraulic connections). For example, the electrical and electronics 

compartment located in the forward nose section, below the flight deck of 

most large transport category airplanes, could be considered a high density 

zone. This is because the relatively small physical area is crowded with 

avionics equipment and a large number of wires and other EWIS 
11/23/07 AC 25-27 

 Appendix A

A-10-10 

components. An example of a low density zone on some airplanes is the 

cargo compartment (as defined by the cargo compartment walls and 

forward and rear bulkheads). Although this is a large zone relative to other 

zones on the airplane, it has relatively few systems or EWIS components 

installed in it. 

• Potential effects of fire on adjacent wiring or systems − This question 

should be answered from the point of view that a fire has occurred. So the 

question to be answered is what is the effect on the safe operation of the 

airplane should a fire occur. This assessment should include consideration 

of the potential for loss of multiple functions and the resulting effect on 

continued safe operation of the airplane. The presence of flammable fluids 

should also be considered, although design features such as shrouds over 

the fuel line can be considered to mitigate the likelihood that the fuel will be 

a source of fuel for a fire. Base the determination of potential effects of a 

fire on adjacent wiring and systems on knowledge of what airplane systems 

are in the area under analysis (i.e., what’s in the zone) and how loss or 

degradation of these systems could affect safe operation. The rating 

system developed should take these potential effects into account.

If a zone does not have mitigating design features that would reduce the 

adverse effects of a fire, then the potential effects of a fire should be rated 

higher (e.g., medium or high). Credit for fire mitigation capability can be 

given to zones that contain a fire detection and suppression system, or a 

zone that is designated a “fire zone.” Potential effects of a fire in such 

zones could then possibly be rated at a lower level. Consideration can also 

be given to whether the fire could be easily detected by crewmembers or 

passengers, and to whether, if there was a fire, it could be extinguished or 

controlled by available means. Fire can result in severe outcomes, such as 

wire-to-structure or wire-to-wire shorting and arcing, in areas such as the 

cockpit, electrical power centers, and those that contain power feeder 

cables, which are subject to chafing, if they have flammable materials close 

by. A fire in these areas could present a high risk to continued safe flight 

and landing, 

Potential effects of fire must also be considered when wiring is in close 

proximity (within 2 inches/50 mm) to both primary and backup flight 

controls. A GVI alone may not be adequate if a fire caused by failure of the 

wiring poses a risk to aircraft controllability. 

At minimum, all wiring in the zone will require a GVI at a common interval. 

For operators with a zonal inspection program, this may be defined as a zonal GVI. 

For operators without a zonal inspection program, it’s a GVI of all wiring in the zone. 

The logic in Figure 2 begins by asking a question. 
11/23/07 AC 25-27 

 Appendix A

A-11-11 

• For airplane models with a ZIP, the logic asks: "Is zonal GVI alone 

effective for all wiring in the zone?” 

• For airplane models without a ZIP, the logic asks: “Is a GVI of all wiring 

in the zone at the same interval effective for all wiring in the zone?” 

This step calls for consideration of whether there are specific items or areas in the 

zone that are more vulnerable to damage or contamination than others and thus 

may warrant a closer or more frequent inspection. 

Such a determination could result in selection of a more frequent GVI, a standalone GVI (for operators with a zonal inspection program), or even a DET. The 

intent is to select a DET of wiring only when it is determined that a GVI will not be 

adequate. The person performing the EZAP should avoid unnecessarily selecting 

DET where a GVI is adequate. Over-use of DET dilutes the effectiveness of the 

inspection. 

The level of inspection required may be influenced by tasks identified in STEP 5 

and STEP 6. For example, if you have selected a cleaning task in STEP 5 and

STEP 6 that will minimize accumulation of combustible materials in the zone, this 

may justify selecting a GVI instead of a DET for the wiring in the zone. 

b. Selecting an inspection interval. You can select an effective inspection 

interval by using a rating system. The characteristics for wiring to be rated should 

include— 

• Likelihood of accidental damage. 

• Environmental factors. 

Rating tables should be designed to define increasing inspection frequency based 

on increasing risk of accidental damage and increasing severity of the local 

environment within the zone. Examples are provided in EZAP Worksheet 4 in this 

appendix. 

The sample “Interval Determination” table on EZAP Worksheet 4 provides a range 

of intervals you can choose from. Your choice of interval should be based on the 

reasons for assigning specific rating values for hostility of environment and 

likelihood of accidental damage. You should also use your knowledge of the types 

of EWIS components to be inspected. 

As an example, for a hostility of environment rating of 3 and a likelihood of 

accidental damage rating of 3, the table gives a range of inspection intervals. It 

says that the inspection should occur as frequently as every A check but the 

interval could be as long as once every 1C check. You should base your choice on 

the reasons that a 3 rating was assigned. 
11/23/07 AC 25-27 

 Appendix A

A-12-12 

• The importance of assessing likelihood of accidental damage is that the 

higher the likelihood of accidental damage from multiple sources, the more 

frequent the inspection task should be. If, on the other hand, all of the 

factors except one have been rated as a 1, then the inspection interval 

could be somewhat longer. 

• The choice of the inspection interval should also be based on what type of 

environment the EWIS is located in. Just as with the ratings for likelihood of 

accidental damage, the more the EWIS is exposed to various harsh 

environmental conditions, the more frequent the inspection interval should 

be. You should consider the assigned ratings from both of these tables—

“Hostility of Environment” and “Likelihood of Accidental Damage”— and use 

sound maintenance judgment to assign the inspection task interval. 

The selection of inspection tasks possible in this step is specific to whether the 

maintenance program includes a zonal inspection program (ZIP) or not. 

For ZIP programs, the possible inspection tasks are: 

● Zonal GVI 

● Stand-alone GVI 

● DET 

For non-ZIP programs, the possible inspection tasks are: 

● GVI 

● DET 

At the conclusion of this step you will have determined the required inspection level and 

interval for wiring in the zone. Task consolidation in STEP 9 allows consideration of 

whether an inspection selected as a result of this analysis can be considered 

accomplished as part of the existing maintenance program. 

STEP 9: Consider consolidation with existing inspection tasks in systems and 

powerplant and/or zonal programs 

This step in the procedure examines the potential for consolidation between the tasks 

derived from the EZAP and inspections that already exist in the maintenance program. 

Consolidation would require that the inspections in the existing maintenance program 

are performed in accordance with the inspection definitions provided in this AC. 

Consolidation with the fuel tank ICA where possible is required by § 26.11(b). 

Compare new tasks identified by the EZAP logic against existing tasks in the 

maintenance program to ensure that: 
11/23/07 AC 25-27 

 Appendix A

A-13-13 

1) Tasks are compatible with each other. Existing maintenance tasks and EZAPgenerated inspection or maintenance tasks (such as a restoration task) should not 

compromise or negate each other. For example, an EZAP-generated task should not 

compromise existing fuel tank system wire maintenance requirements (e.g., those 

generated by SFAR 88) such as separation or configuration specifications. 

2) Task intervals are aligned to the maximum extent possible so undue disturbance of 

EWIS and other systems located within the zone does not occur. However, the 

inspection interval you choose must ensure that the intent and reason for the EWIS 

inspection is not compromised. The EZAP-generated task interval is determined by 

completing EZAP Worksheet 4, found later in this appendix. 

3) Redundant (or duplicate) tasks are consolidated into a single task. 

For inspection programs that include a zonal inspection program (ZIP):

• The EZAP may identify some stand-alone GVIs for a zone that are adequately 

covered by existing zonal GVIs. In those cases no change or addition to the 

existing zonal GVI would be required. This should reduce the number of new 

GVIs that must be introduced into a program that already includes a ZIP. In 

other words, a stand-alone GVI identified by EZAP may in certain circumstances 

be combined with an existing zonal GVI. The analyst should fully consider 

whether performing the existing zonal GVI would accomplish the same level of 

inspection, would provide the same level of safety benefits, and could be 

performed at least at the same interval (or less) as the interval identified by the 

EZAP for the stand-alone GVI. For instance, if the inspection interval named in 

Step 8 is 1C – 4C and the existing zonal inspection requires the same level of 

inspect ion at 4C; then 4C can be selected for the inspection frequency. 

However, a stand-alone GVI of the wiring would be justified if the zonal GVIs of 

Example 

Results of the EZAP for a particular zone indicate that using an existing zonal GVI is an 

effective inspection task for all of the EWIS in the zone. The analysis must be continued to 

determine the appropriate inspection interval (EZAP Worksheet 4). If the results of the 

analysis contained on EZAP Worksheet 4 indicate that the EWIS inspection interval is 

greater than the interval for the existing zonal GVI, the existing zonal GVI interval should be 

used for the EZAP-identified inspection task. The existing zonal GVI interval cannot be 

escalated solely based on results of the EZAP analysis. The EZAP only analyzes the need 

for inspection type and frequency for EWIS within a zone. It does not analyze all of the 

systems in the zone. Therefore its results cannot be used as the sole reason to escalate an 

existing zonal inspection task. 
11/23/07 AC 25-27 

 Appendix A

A-14-14 

A stand-alone GVI identified 

by EZAP may in certain 

circumstances be combined 

with an existing zonal GVI. 

The safety objective must 

always be met and the 

analyses must provide 

detailed reasoning why the 

inspection that would have 

been performed by the standalone GVI can be 

accomplished with the existing 

zonal GVI. This reasoning 

should be documented on 

EZAP Worksheet 5. The 

existing zonal GVI must now 

be identified as an EZAPrelated task. This is to prevent 

the possibility that it could be 

deleted or inappropriately 

escalated. 

the other systems within the same zone do not need to be carried out as 

frequently. In this case the stand-alone GVI should not be consolidated into the 

existing zonal GVI. If the analyst proposes to combine a new stand-alone GVI 

with an existing zonal GVI, detailed reasoning for doing so should be provided 

as part of the analysis. 

• You should not adjust the interval of the stand-alone inspection to match the 

interval of the existing zonal inspection solely for the purposes of aligning the 

separate task intervals. Task intervals should only be aligned if the interval will 

ensure that the safety objectives of identifying the stand-alone GVI in the first 

place can be met. One of the criteria for 

considering task interval alignment is access 

requirements for the zone. Task intervals 

should be aligned to the maximum extent 

possible so undue disturbance of EWIS and 

other systems located within the zone does 

not occur. If a task is aligned with an 

existing zonal inspection, it must be 

identified as an EZAP-related task to prevent 

the possibility that it could be deleted or 

inappropriately escalated. 

• Stand-alone GVIs and DETs identified by 

the EZAP should not be consolidated into 

the zonal inspection program. They must be 

introduced and retained as dedicated tasks 

in the scheduled maintenance program 

under ATA 20 (the Air Transport Association 

category for electrical wiring). These tasks, 

along with tasks identified to reduce 

accumulation of combustible materials 

(known as cleaning or restoration tasks), 

should be uniquely identified to ensure they 

are not consolidated into the zonal program 

or deleted during future program 

development. Within MSG (Maintenance Steering Group)-3-based MRB 

reports, these may be introduced under ATA 20 with no failure effect category 

assigned. While a stand-alone GVI and a DET cannot be combined with 

existing zonal inspections, the intervals for performing them should be aligned 

with other maintenance tasks in the zone, such as zonal GVIs, to the extent 

possible. 

For programs without a ZIP: 

Although some non-zonal inspection programs may already include some dedicated 

inspections of wiring that may be equivalent to new tasks identified by an EZAP, it is 
11/23/07 AC 25-27 

 Appendix A

A-15-15 

expected that a significant number of new wiring inspections will be identified for 

introduction as dedicated tasks in the system & powerplant program. All new tasks 

identified by an EZAP should be uniquely identified to ensure they are not deleted 

during future program development. 

For programs with or without a ZIP:

The following guide can be used for programs with or without a ZIP to determine proper 

consolidation between EZAP-derived inspections and existing inspections of the same 

item or area. When an EZAP task is selected for consolidation, the documentation 

should include a record identifying it for traceability purposes. 

• If the EZAP inspection interval and existing inspection interval are equal, but the 

inspection levels are different, the more detailed inspection takes precedence 

(for example a 1C DET takes precedence over a 1C GVI). 

• If the EZAP inspection interval and existing inspection interval are different, but 

the inspection levels are equal, the more frequent inspection interval takes 

precedence (a 1C GVI takes 

precedent over a 2C GVI). 

• If the EZAP inspection interval 

and level are different than the 

existing inspection interval and 

level, these tasks may be 

consolidated using the more 

frequent inspection and at the 

more detailed (a 1C DET takes 

precedent over a 2C GVI, for 

example). When the more 

frequent inspection is less detailed, the tasks should not be consolidated. 

For EZAP-developed STC tasks, it may not be possible for the STC holder to determine 

whether a ZIP exists on specific aircraft that will utilize the STC. If a ZIP exists, 

consolidation of EZAP-derived STC tasks into an operator’s ZIP will be the responsibility 

of the operator and should be approved by the operator’s FAA principal inspector or 

cognizant Flight Standards District Office (FSDO). The AC titled Incorporation of 

Electrical Wiring Interconnection System (EWIS) Instructions for Continued 

Airworthiness into the Operator’s Maintenance Program will contain guidance related to 

this. 

In cases where the STC holder determines a requirement for a GVI that should not be 

consolidated into a ZIP, this stand-alone GVI should be specifically identified as such in 

the EZAP-derived ICA for the STC. 

NOTE: The more frequent 

inspection at the more detailed level 

should be used unless it is judged 

that performing the more detailed 

inspection too frequently can result 

in stressing/disturbance of EWIS 

components. 
11/23/07 AC 25-27 

 Appendix A

A-16-16 

EXAMPLES OF TYPICAL EZAP WORKSHEETS 

For Anyone Required to Conduct an EZAP Evaluation — 

The following pages contain worksheets you can use to conduct an EZAP. The first 6 

worksheets contain notes to assist you in proper use of the worksheet. There are blank 

worksheets in Appendix H of this AC that you can copy and use to conduct the analysis. 

 

• EZAP Worksheet 1 Details of Zone 

• EZAP Worksheet 2 Assessment of Zone Attributes 

• EZAP Worksheet 3A Inspection Level Determination Based on Zone Size, 

Density, and Potential Impact of Fire (For Programs with a Dedicated Zonal 

Inspection Program (ZIP)) 

• EZAP Worksheet 3B Inspection Level Determination based on Zone Size, 

Density, and Potential Impact of Fire (For Programs without a Dedicated Zonal 

Inspection Program (ZIP)) 

• EZAP Worksheet 4 Interval Determination Based on Hostility of Environment 

and Likelihood of Accidental Damage 

• EZAP Worksheet 5 Task Summary 
A-17-17 

A-17 

A-17 
A-18-18 

A-18 A-18 
A-19-19 

A-19 A-19
A-20-20 

A-20 
A-21-21 

A-21 
A-22-22 

A-22 
11/23/07 AC 25-27 

 Appendix B

B-1 

APPENDIX B 

EVALUATING WHETHER A DESIGN CHANGE IMPACTS 

PREVIOUSLY APPROVED EWIS ICA AND DEVELOPING ANY 

NECESSARY REVISED EWIS ICA AS REQUIRED BY § 26.11(C) 

and 

GUIDANCE FOR THE COMPLIANCE PLAN REQUIREMENTS OF 

§ 26.11(E) IF NO CHANGES TO EXISTING EWIS ICA ARE 

NECESSARY 

Section 26.11(c) requires that applicants for amendments to type certificates (TC), 

supplemental type certificates (STC), and changes to STCs evaluate whether the 

design changes for which approval is sought require revisions to previously approved 

EWIS ICA. 

Section 26.11(c) applies to all projects (provided the project is related to an affected 

airplane model as determined by § 26.11(a)), not just those that include EWIS 

modifications. For example, if an applicant proposes to modify stow bin latches, it 

should be relatively easy for the applicant to make a statement that the EWIS ICA are 

not impacted. On the other hand, if an applicant introduces a new hydraulic line, or 

creates a hole in a zone that previously did not have one, some of the previously 

developed EWIS ICA may be impacted (e.g., the modification may introduce new 

sources of contamination that were not previously addressed by the EWIS ICA). 

This appendix provides guidance to help the applicant determine whether the proposed 

modification impacts previously approved EWIS ICA. It also provides guidance to help 

applicants meet the compliance plan requirements of § 26.11(e) if no EWIS ICA 

additions or revisions are necessary. Section 26.11(e) requires applicants for amended 

TCs, STCs, and changes to existing STCs to submit a compliance plan to the FAA for 

approval if the date of application for the modification was prior to the effective date of 

§ 26.11 and the certificate was issued on or after the effective date. If following the 

logic in Flowchart 1 results in a determination that the previously approved EWIS ICA 

must be revised because of the modification, guidance for developing and submitting a 

compliance plan to the FAA Oversight Office may be found in AC 26-1 Part 26, 

Continued Airworthiness and Safety Improvements. 
11/23/07 AC 25-27 

 Appendix B

B-2 

NOTE: Each person (applicant) identified in § 26.11(d)(1), 

(d)2), and (d)(4) must comply with the requirements of 

§ 26.11(e) no matter what the nature of the modification for 

which they are seeking approval – even if the modification 

does not require a revision to previously approved EWIS ICA. 

A. Determining Whether an Amended TC, STC, or Changes to an Existing STC 

Require Changes to Previously Approved EWIS ICA

You can determine whether an amended TC, STC, or changes to an existing STC 

(referred to in this appendix as a “modification”) requires revision to previously approved 

EWIS ICA by following the process outlined in Flowchart 1 of this appendix. 

 
11/23/07 AC 25-27 

 Appendix B

B-3 

No further analysis is required

No further analysis is required 

because the existing EWIS ICA 

tasks do not require revsion

Does the modification*:

Affect or modify wiring or its environment, or

Install or result in wiring being located within 2in/50mm of 

both primary and backup hydraulic, mechanical, 

or electrical flight controls, or

Change the density of the zone, or

Change the potential effects of fire in the zone?

1

Determine whether existing EWIS ICA 

tasks for the zones affected by the 

modification require revision **

3

Perform an EZAP analysis on the 

airplane zones affected by the 

modification

Flowchart 1

Determining Whether a Modification* Requires Revision to Previously 

Approved EWIS ICA and Development of Revised EWIS ICA as Necessary

2

3A

1A

YES

NO

NO

* Modification means any 

change to an existing type 

design accomplished through 

any of the following:

An amended type certificate 

(including service bulletin 

design changes),

A supplemental type 

certificate (STC)

Changes to an existing STC

Submit compliance statement 

for:

§ 26.11(c)

§ 26.11(e) (if applicable)

1B

Develop appropriate EWIS ICA*** in 

accordance with requirements of 

Part 25, Appendix H, sections 

H25.5(a)(1) and (b)

4

*** Ensure that revised EWIS ICA 

remain compatible with ICA 

developed to comply with SFAR 

88 and any redundant 

requirements between them are 

minimized (as required by 

§ 26.11(c)(2)).

Submit EWIS ICA to FAA Oversight 

Office for Review & Approval** as 

required by § 26.11(c)(1)

5

YES
11/23/07 AC 25-27 

 Appendix B

B-4 

NOTE: The following persons must submit to the FAA Oversight 

Office, by March 10, 2008, a compliance plan describing how they plan 

to meet the requirements of § 26.11. 

• TC holders 

• Applicants for TCs and amendments to TCs if the date of 

application was before December 10, 2007, and the certificate 

was issued on or after that date 

• Applicants for STCs, including changes to existing STCs, if the 

date of application was before December 10, 2007, and the 

certificate was issued on or after that date 

Any or all steps described in this appendix may be completed before 

submitting the required compliance plan. Guidance for developing and 

submitting a compliance plan may be found in AC No. 26-1 Part 26, 

Continued Airworthiness and Safety Improvements. 

DETERMINING WHETHER A MODIFICATION REQUIRES REVISION TO 

PREVIOUSLY APPROVED EWIS ICA

Explanation of Steps in Flowchart 1

STEP 1: Does the modification affect or modify EWIS or its environment? 

Does it— 

• Install wiring or result in wiring being located within 2 inches (50mm) of both 

primary and back-up hydraulic, mechanical, or electric flight controls? 

• Change potential effects of fire in the zone? 

• Affect zone density? 

• Introduce other systems into the area such as hot air ducting, hydraulic tubing, 

water tubing, etc.? 

• Introduce new sources of contamination?

This step asks whether the modification affects or modifies EWIS. Modifications to 

wiring or other EWIS components include, but are not limited to, removal, addition, and 

relocation. 

The additional questions in STEP 1 serve as examples for consideration of ways the 

modification may have affected or modified EWIS or its environment. 
11/23/07 AC 25-27 

 Appendix B

B-5 

• Consideration of potential effects of the modification must include whether wiring 

is in close proximity (i.e. within 2 inches/50 mm) to both primary and back-up 

flight controls. 

• If the modification includes the addition or removal of numerous components in a 

small area, the density of the zone could be changed even if wire bundles are 

untouched. A significant change in the zone density should warrant reanalysis 

(i.e., EZAP) of the zone. 

• Potential effects of fire on adjacent EWIS components and systems must be 

assessed, and this requires the analyst to consider potential for loss of multiple 

functions to the extent that a hazard could be introduced. 

• Addition of other systems into the area, such as hot air ducting, hydraulic tubing, 

water tubing, etc., could introduce potential sources for contaminants. The 

possibility of wire arcing could pose a safety threat to the added systems. 

• Additionally, STEP 1 requires an evaluation of whether the zone might contain 

combustible material that could cause a fire to be sustained in the event of an 

ignition source arising in adjacent wiring. Examples include the possible 

presence of fuel vapors, dust/lint accumulation, and contaminated insulation 

blankets. 

When considering the presence or possible presence of commonly used liquids 

(e.g., oils, hydraulic fluids, and corrosion prevention compounds), the analyst 

should refer to the product specifications in order to assess the potential for 

combustibility. The product may be readily combustible only in vapor/mist form 

and thus an assessment is required to determine if conditions might exist in the 

zone for the product to be in this state. 

Although liquid contamination of wiring by most synthetic oil and hydraulic fluids 

(e.g., skydrol) may not be considered combustible, it is a cause for concern if it 

occurs in a zone where significant dust and lint occur. Contamination of wires or 

other EWIS components with oils and other fluids increases adherence of 

airborne dust and lint to those wires. 

Here are some examples that illustrate the questions asked in STEP 1: 

• Example 1 The modification installs a “T” fitting in a fuel pressure line to 

support a new fuel pressure indication system. Prior to the alteration, the 

fuel line passed through the zone with no connections or couplings in the 

zone that could be potential leak sources, and the zone had no other 

potential sources of combustible materials. In this example, the answer to 

the question would be 'YES’ – the newly installed T fitting introduces a 

potential source of combustible materials in the zone for the first time. 
11/23/07 AC 25-27 

 Appendix B

B-6 

• Example 2 The modification installs a “T” fitting in a fuel pressure line to 

support a new fuel pressure indication system. The “T” is installed at an 

existing coupling in the line. In this example, the answer to the question 

would be 'NO,’ because the potential for a fuel leak already existed at the 

fuel line connection in the zone. 

• Example 3 The modification installs new terrain awareness warning 

system (TAWS) wiring adjacent to existing wiring associated with primary 

flight instrumentation. This alteration could increase the potential effect of a 

fire in the zone by the adding TAWS to the multiple systems contained in a 

single wire bundle that could be lost as a result of a localized arc or fire. 

The answer to the question is ‘YES.’ 

• Example 4 The modification replaces existing analog flight instrumentation 

with new digital displays that include replacement of a single, large, multifunction wire bundle with separately routed wire bundles for the pilot and 

co-pilot flight displays. This alteration reduces the potential effect of a fire in 

the zone by providing greater separation of wiring for primary flight 

instruments. In this example, the answer is “YES,” with the possibility that 

re-application of EZAP to the entire zone may determine that a GVI, rather 

than a DET, is adequate for the wiring in the zone after alteration. 
11/23/07 AC 25-27 

 Appendix B

B-7 

Compliance Statement for § 26.11(c) and (e) if the Modification Does Not 

Require Revisions to Previously Approved EWIS ICA

If the applicant determines that no revisions to previously approved EWIS ICA are 

necessary, the applicant can submit the following statement AND provide a detailed 

rationale of the reasons why it is true. This rationale should include the data 

developed as a result of performing the applicable steps from Flowchart 1 of this 

appendix that were necessary to come to the conclusion that no revision to 

previously approved EWIS ICA is needed. 

 “The modification has been reviewed per the guidance provided 

in FAA AC 25-27. It has been determined that the modification 

does not necessitate a revision to the EWIS ICA that were 

required to be developed by § 26.11(b).” 

STEP 1A: If the answers to the questions in STEP 1 are 

“NO,” then no further analysis is required. The final step 

(STEP 1B) you need to perform is to submit a compliance 

statement for § 26.11(c) and, if applicable, 26.11(e). Refer 

to the box following STEP 1B, below, for guidance on 

submitting an acceptable compliance statement for these 

two requirements when your modification does not 

necessitate a change to previously approved EWIS ICA. 

STEP 1B: Submit compliance statement for: 

• § 26.11(c)

• § 26.11(e) (if applicable)

If the existing EWIS ICA are found to be adequate, then 

no further analysis is required. The final step you need to 

perform is to submit a compliance statement for 

§ 26.11(c) and, if applicable, § 26.11(e). 
11/23/07 AC 25-27 

 Appendix B

B-8 

STEP 2: Perform an EZAP analysis on the airplane zones affected by the 

modification

If the answer to any of the questions in STEP 1 is “YES,” then the only way to determine 

if existing EWIS ICA are sufficient is to perform the EZAP (as explained in the main 

body of this AC and in Appendix A) for the modification and compare the results with the 

existing EWIS ICA (see STEP 3). 

STEP 3: Determine whether existing EWIS ICA tasks for the zones affected by the 

modification require revision

Once the modification’s EZAP has been accomplished, a comparison of these EWIS 

ICA can be made with the existing EWIS ICA. If the existing task is adequate, then no 

further action regarding EWIS maintenance actions for the STC is necessary. An 

existing EWIS ICA task is adequate if it is the same task, performed at the same 

interval, as the EWIS ICA task identified as a result of the EZAP performed in STEP 2. 

STEP 3A: If the existing EWIS ICA tasks for the zones 

affected by the modification are adequate and do not 

require revision, then no further analysis is required. The 

final step (STEP 1B) you need to perform is to submit a 

compliance statement for § 26.11(c) and, if applicable, 

26.11(e). Refer to the box following STEP 1B for guidance 

on submitting an acceptable compliance statement for 

these two requirements when your modification does not 

necessitate a change to previously approved EWIS ICA. 

STEP 4: Develop appropriate EWIS ICA in accordance with requirements of part 

25, Appendix H, sections H25.5(a)(1) and (b)

If new EWIS ICA tasks are found to be necessary, you must develop appropriate ICA 

for the modified airplane. Follow the guidance in Appendix A of this document for 

choosing appropriate tasks. If a compliance plan was required, adhere to the 

compliance plan approved by the FAA Oversight Office. 
11/23/07 AC 25-27 

 Appendix B

B-9 

NOTE: Section 26.11(c) requires 

evaluation by the modifier of whether or 

not the modification necessitates a 

“revision” to previously approved EWIS 

ICA (those required by § 26.11(b)). It 

does not require the DAH who originally 

developed them for compliance with 

§ 26.11(b) to make changes to those 

original EWIS ICA unless that DAH is 

seeking approval of the design change. 

STEP 5: Submit EWIS ICA to FAA Oversight Office for Review & Approval as 

required by § 26.11(c)(1) Remember that § 26.11(c) also requires that these new 

EWIS ICA remain compatible with ICA developed to comply with SFAR 88 and that any 

redundant requirements between them are minimized. 

11/23/07 AC 25-27

 Appendix C 

C-1 

APPENDIX C 

DEFINITIONS 

Arc tracking—A phenomenon in which a conductive carbon path forms across 

an insulating surface. This carbon provides a short circuit path through which 

current can flow. Arc tracking is normally a result of electrical arcing. Also 

referred to as "carbon arc tracking," "wet arc tracking," or "dry arc tracking."

Aircraft Evaluation Group (AEG)—Flight Standards Service (AFS) 

representatives who know the operational and maintenance aspects of a 

certification project and are responsible for helping to determine their operational 

suitability. This role includes providing support to the cognizant ACO in the 

review and approval of the initial ICA and later changes to it related to the safety 

initiatives referenced in this AC. 

Aircraft Maintenance Manual—A manual developed by the manufacturer of a 

particular airplane that contains information necessary for the continued 

airworthiness of that airplane. 

Auxiliary Tanks—Fuel tanks installed in an airplane which make additional fuel 

available for increasing the flight range of that airplane. The term “auxiliary” 

means that the tank is secondary to the airplane’s main fuel tanks. Auxiliary 

tanks have been installed in various locations, including center wing structure, 

horizontal stabilizers, wings, and cargo compartments. 

Combustible—For the purposes of this AC, the term combustible refers to the 

ability of any solid, liquid, or gaseous material to cause a fire to be sustained 

after removal of the ignition source. The term is used in place of 

inflammable/flammable. It should not be interpreted as identifying material that 

will burn when subjected to a continuous source of heat as occurs when a fire 

develops. 

Contamination—For the purposes of this AC, wiring contamination refers to 

either of the following: 

• Presence of a foreign material likely to cause degradation of 

wiring. 

• Presence of a foreign material that is combustible, or capable of 

sustaining a fire after removal of ignition source. 

Detailed Inspection (DET)—An intensive examination of a specific item, 

installation, or assembly to detect damage, failure, or irregularity. DET is 

discussed in greater detail in paragraph 10b(2) of this AC. 
11/23/07 AC 25-27

 Appendix C 

C-2 

Effective Task/Task Interval—An “effective” task is an inspection or 

maintenance task, performed at defined intervals, that will ensure that the 

desired outcome of the task is achieved. To be effective the task must reduce 

the risk of wire failure, to ensure safe operation. For example, a cleaning task to 

remove contaminants that have accumulated on a wire bundle would be 

considered effective if it cleaned the bundle sufficiently to minimize the potential 

of contaminant-induced failure of the bundle, and allow an inspection for wire 

defects to be performed. The methods and intervals for performing an effective 

task are developed using a combination of standard industry practices, expert 

opinion, and engineering judgment from operators, manufacturers, and 

regulatory authorities. The criteria for the effectiveness of a task should include 

safety and operational, as well as economic, considerations. Tasks should, at a 

minimum, be such that they will effectively accomplish all of the following: 

• Make identification of failures possible. 

• Detect wire degradation with frequent and consistent inspection intervals. 

• Reduce the risk of failures. 

Electrical Wire Interconnection Systems (EWIS)—An EWIS is defined by 14 

CFR section 25.1701. As defined by that section, EWIS means any wire, wiring 

device, or combination of these, including termination devices, installed in any 

area of the airplane for the purpose of transmitting electrical energy between two 

or more intended termination points. The complete regulatory definition appears 

in Appendix E to this AC. 

Environmentally Sealed Splice—A wire splice that ensures that moisture or 

fluid will not penetrate the spliced area. 

Enhanced Zonal Analysis Procedure (EZAP)—A logical process for 

developing maintenance and inspection instructions for Electrical Wiring 

Interconnection System (EWIS). 

FAA Oversight Office—The FAA Oversight Office is defined by 14 CFR section 

26.3 as “the aircraft certification office or office of the Transport Airplane 

Directorate with oversight responsibility for the relevant type certificate, 

supplemental type certificate, or manufacturer, as determined by the 

Administrator.” 

Flammable fluid leakage zone—Any area where flammable liquids or vapors 

are not intended to be present, but where they might exist due to leakage from 

flammable-fluid-carrying components (e.g. leakage from tanks, lines). These 

zones are typically identified by the airplane manufacturer. 
11/23/07 AC 25-27

 Appendix C 

C-3 

Examples of such areas include: 

• The wing leading and trailing edges (including any adjacent compartment 

such as the strut) 

• Farings located below the fuel tanks 

• Wheel wells 

• Fuel pump enclosures 

• Unpressurized areas of the fuselage surrounding fuel tanks 

• Areas containing flammable fluid lines or tanks 

Flight Standards Service (AFS) Offices—Offices located in FAA headquarters 

(for transport category airplanes, AFS-200/-300) responsible for developing 

guidance and policy for AEG personnel who may assist cognizant Aircraft 

Certification Offices (ACO) and AFS field personnel (aviation safety inspectors) in 

the conduct of their responsibilities. 

Functional Failure—Failure of an item to perform its intended function within 

specified limits. 

General Visual Inspection (GVI)—A visual examination of an interior or exterior 

area, installation, or assembly to detect obvious damage, failure, or irregularity. 

This level of inspection is made from within touching distance unless otherwise 

specified. A mirror may be necessary to enhance visual access to all exposed 

surfaces in the inspection area. This level of inspection is made under normally 

available lighting conditions such as daylight, hangar lighting, flashlight, or 

droplight and may require removal or opening of access panels or doors. 

Stands, ladders, or platforms may be required to gain proximity to the area being 

checked. 

Instructions for Continued Airworthiness (ICA)—The information 

documented in accordance with 14 CFR 25.1529 that includes the applicable 

methods, inspections, processes, procedures, and airworthiness limitations 

required to keep the airplane airworthy throughout its operational life. 

Lightning/High Intensity Radiated Field (L/HIRF) Protection—The protection 

of airplane electrical systems and structure from induced voltages or currents by 

means of shielded wires, raceways, bonding jumpers, connectors, composite 

fairings with conductive mesh, static dischargers, and the inherent conductivity of 

the structure; may include aircraft specific devices, e.g., RF (radio frequency) 

gaskets. 

Maintenance—As defined in 14 CFR 1.1, “maintenance means inspection, 

overhaul, repair, preservation, and the replacement of parts, but excludes 

preventive maintenance.” For the purposes of this advisory circular, 

maintenance also includes preventive maintenance, as described in both § 1.1 
11/23/07 AC 25-27

 Appendix C 

C-4 

and 14 CFR part 43, Appendix A(c). Section 1.1 of 14 CFR provides the 

following definition: “Preventive maintenance means simple or minor 

preservation operations and the replacement of small standard parts not 

involving complex assembly operations.” Appendix A(c) of 14 CFR part 43 lists 

the tasks that are considered preventive maintenance. 

Maintenance Instructions—Information that provides recommended periods for 

cleaning, inspection, adjustment, testing, lubrication, degree of inspection, 

applicable wear tolerances, and recommended work necessary for each part of 

the airplane and its engine auxiliary power units, propellers, accessories, 

instruments, and equipment to provide for continued airworthiness of the 

airplane. Recommended overhaul periods and necessary cross-references to 

the Airworthiness Limitations section of the maintenance manual are also 

included. 

Maintenance Significant Item (MSI)—Items (system or component) identified 

by the manufacturer whose failure could have one or more of the following 

results or characteristics – 

• Could affect safety (on ground or in flight). 

• Is undetectable during operations (on ground or in flight). 

• Could have significant operational impact. 

• Could have significant economic impact. 

MRB Report—Maintenance Review Board (MRB) Report (Transport Category 

Aircraft). A report intended for use by air carriers that contains the initial 

minimum scheduled maintenance and inspection requirements for a particular 

transport category aircraft maintenance program. Air carriers use the MRB 

report and its associated requirements to develop maintenance programs. See 

AC 121-22A Maintenance Review Board Procedures for more information. 

Needling— The puncturing of a wire’s insulation to make contact with the core to 

test the continuity and presence of voltage in the wire segment. 

Stand-Alone GVI—A general visual inspection which is not performed as part of 

a zonal inspection. Even in cases where the interval coincides with the zonal 

inspection, the stand-alone GVI remains an independent step on the work card. 

Structural Significant Item (SSI)—Any detail, element, or assembly that 

contributes significantly to carrying flight, ground, pressure, or control loads and 

whose failure could affect the structural integrity necessary for the safety of the 

aircraft. 
11/23/07 AC 25-27

 Appendix C 

C-5 

Swarf—British term used to describe the metal particles generated from drilling 

and machining operations. Such particles may accumulate on and between wires 

within a wire bundle. 

Zonal Inspection—A collective term comprising selected general visual 

inspections and visual checks that are applied to each airplane zone, defined by 

access and area, to check system and power plant installations and structure for 

security and general condition. Zonal inspections are discussed in greater detail 

in section 10 of this AC. 

11/23/07 AC 25-27

 Appendix D 

D-1 

APPENDIX D 

FAA OVERSIGHT OFFICES FOR THE PURPOSES OF PART 26 

The following table lists the FAA Oversight Offices, as currently determined by 

the Administrator, that oversee issuance of type certificates and amended type 

certificates for manufacturers of transport category airplanes with a passenger capacity 

of 30 passengers or a payload capacity of 7500 pounds or greater. 

Airplane Manufacturer FAA Oversight Office 

Aerospatiale Transport Airplane Directorate, 

International Branch, ANM-116 

Airbus Transport Airplane Directorate, 

International Branch, ANM-116 

BAE Transport Airplane Directorate, 

International Branch, ANM-116 

Boeing Seattle Aircraft Certification Office 

Bombardier New York Aircraft Certification Office 

CASA Transport Airplane Directorate, 

International Branch, ANM-116 

deHavilland New York Aircraft Certification Office 

Dornier Transport Airplane Directorate, 

International Branch, ANM-116 

Embraer Transport Airplane Directorate, 

International Branch, ANM-116 

Fokker Transport Airplane Directorate, 

International Branch, ANM-116 

Lockheed Atlanta Aircraft Certification Office 

McDonnell-Douglas Los Angeles Certification Office 

SAAB Transport Airplane Directorate, 

International Branch, ANM-116 

11/23/07 AC 25-27

 Appendix E

E-1 

APPENDIX E 

APPLICABLE REGULATIONS AND RELEVANT PREAMBLE 

DISCUSSION 

The text of the regulations referred to in this AC are reproduced here for easy reference. 

This information is provided as reference only. If any deviation exists between the 

reference material provided here and the regulations contained in the Code of Federal 

Regulations (CFR), it is the regulations in the CFR that must be complied with. We 

have also included here the applicable preamble discussions from the EAPAS/FTS 

Notice of Proposed Rulemaking (NPRM) issued on October 5, 2005 (70 FR 58508). 

The preamble discussion for a particular regulation follows the text of that regulation. 

You should refer to the NPRM and the Final Rule for a complete discussion of the 

requirements. Only the most relevant text from those discussions have been 

reproduced here. 

The preamble discussions reprinted here refer to proposed AC 120-XX. That proposed 

AC was posted for public comment with the above-referenced NPRM. We have since 

reorganized the information presented in that proposed AC into three different guidance 

documents. Most of the information that was included in proposed AC 120-XX is now 

presented in this final AC. Two additional ACs, directed towards operators, are 

forthcoming. Guidance for operators on incorporating EWIS ICA will be contained in a 

120-series AC entitled Incorporation of Electrical Wiring Interconnection System (EWIS) 

Instructions for Continued Airworthiness into the Operators’ Maintenance Program. 

Another AC will present guidance for operators on incorporating fuel tank ICA. That AC 

will be titled Incorporation of Fuel Tank System Instructions for Continued Airworthiness 

into Operator Maintenance or Inspection Programs. Since the preamble for the NPRM 

referenced the originally proposed AC, however, we have left those references 

unchanged. 

Comments received about the NPRM are summarized and discussed in the Final Rule. 

You can download a copy of the Final Rule from the Internet at 

http://www.gpoaccess.gov/cfr/. Mail, telephone, and fax request information is given in 

APPENDIX G. 

Part 25 

§ 25.1701 Definition. 

 (a) As used in this chapter, electrical wiring interconnection system (EWIS) means 

any wire, wiring device, or combination of these, including termination devices, 

installed in any area of the airplane for the purpose of transmitting electrical 
11/23/07 AC 25-27

 Appendix E

E-2 

energy, including data and signals, between two or more intended termination 

points. This includes: 

 (1) Wires and cables. 

 (2) Bus bars. 

(3) The termination point on electrical devices, including those on relays, 

interrupters, switches, contactors, terminal blocks and circuit breakers, 

and other circuit protection devices. 

 (4) Connectors, including feed-through connectors. 

 (5) Connector accessories. 

(6) Electrical grounding and bonding devices and their associated 

connections. 

 (7) Electrical splices. 

(8) Materials used to provide additional protection for wires, including wire 

insulation, wire sleeving, and conduits that have electrical termination 

for the purpose of bonding. 

 (9) Shields or braids. 

 (10) Clamps and other devices used to route and support the wire bundle. 

 (11) Cable tie devices. 

 (12) Labels or other means of identification. 

 (13) Pressure seals. 

(14) EWIS components inside shelves, panels, racks, junction boxes, 

distribution panels, and back-planes of equipment racks, including, but 

not limited to, circuit board back-planes, wire integration units, and 

external wiring of equipment. 

(b) Except for the equipment indicated in paragraph (a)(14) of this section, EWIS 

components inside the following equipment, and the external connectors that 

are part of that equipment, are excluded from the definition in paragraph (a) of 

this section: 
11/23/07 AC 25-27

 Appendix E

E-3 

(1) Electrical equipment or avionics that are qualified to environmental 

conditions and testing procedures when those conditions and 

procedures are— 

(i) Appropriate for the intended function and operating environment, 

and 

(ii) Acceptable to the FAA. 

(2) Portable electrical devices that are not part of the type design of the 

airplane. This includes personal entertainment devices and laptop 

computers. 

(3) Fiber optics. 
11/23/07 AC 25-27

 Appendix E

E-4 

§ 25.1729 Instructions for Continued Airworthiness: EWIS. 

The applicant must prepare Instructions for Continued Airworthiness applicable to EWIS 

in accordance with Appendix H sections H25.4 and H25.5 to this part that are approved 

by the FAA 

NPRM Preamble Discussion (§ 25.1729 was proposed as § 25.1739). 

FR 70 58526 

Section 25.1739 Instructions for Continued Airworthiness: 

EWIS. 

 Proposed § 25.1739 would require that applicants prepare 

EWIS ICA in accordance with the requirements of Appendix H to 

part 25. The proposed EWIS ICA requirements are discussed in the 

next section of this document. 

Part 25, Appendix H 

Section H25.5 

H25.5 Electrical Wiring Interconnection System (EWIS) Instructions for Continued 

Airworthiness. 

(a) The applicant must prepare Instructions for Continued Airworthiness (ICA) 

applicable to EWIS as defined by § 25.1701 that are approved by the FAA and 

include the following: 

(1) Maintenance and inspection requirements for the EWIS developed with 

the use of an enhanced zonal analysis procedure that includes: 

(i) Identification of each zone of the airplane. 

(ii) Identification of each zone that contains EWIS. 

(iii) Identification of each zone containing EWIS that also contains 

combustible materials. 

(iv) Identification of each zone in which EWIS is in close proximity 

to both primary and back-up hydraulic, mechanical, or 

electrical flight controls and lines. 
11/23/07 AC 25-27

 Appendix E

E-5 

 (v) Identification of −

(A) tasks, and the intervals for performing those tasks, that 

will reduce the likelihood of ignition sources and 

accumulation of combustible material, and 

 

(B) procedures, and the intervals for performing those 

procedures, that will effectively clean the EWIS 

components of combustible material if there is not an 

effective task to reduce the likelihood of combustible 

material accumulation. 

 

(vi) Instructions for protections and caution information that will 

minimize contamination and accidental damage to EWIS, as 

applicable, during performance of maintenance, alteration, or 

repairs. 

 (2) Acceptable EWIS maintenance practices in a standard format. 

 (3) Wire separation requirements as determined under § 25.1707. 

 (4) Information explaining the EWIS identification method and 

requirements for identifying any changes to EWIS under § 25.1711. 

 (5) Electrical load data and instructions for updating that data. 

(b) The EWIS ICA developed in accordance with the requirements of H25.5(a)(1) 

must be in the form of a document appropriate for the information to be 

provided, and they must be easily recognizable as EWIS ICA. This document 

must either contain the required EWIS ICA or specifically reference other 

portions of the ICA that contain this information. 
11/23/07 AC 25-27

 Appendix E

E-6 

NPRM Preamble Discussion for H25.5 

70 FR 58532

Appendix H to Part 25 – Instructions for Continued Airworthiness 

As previously noted, improper maintenance, repair, and 

modifications often hasten the “aging” of EWIS. To properly maintain, 

repair, and modify airplane EWIS, certain information must be available 

to the designer, modifier, and installer. This information should be part 

of the ICA as required by current § 25.1529 and the proposed § 25.1739. 

This proposal would amend Appendix H by adding a new section, 

H25.5, to require TC applicants to develop maintenance information for 

EWIS as part of the ICA as a requirement for getting a design approval. 

The proposed rule would also apply to applicants for design change 

approvals (supplemental TCs and amended TCs). 

The proposal would require applicants for TCs to prepare ICA for 

EWIS that are approved by the FAA Oversight Office, in the form of a 

document that is easily recognizable as an EWIS ICA. To prepare these 

instructions, they must use an EZAP such as the one described in AC120-

XX, “Program to Enhance Aircraft Electrical Wiring Interconnection 

System Maintenance” to perform a review of their representative airplane 

covering all areas, including the flightdeck (also known as the cockpit), 

electrical power center, fuel tank wiring and powerfeeder cables, as well 

as the engine. Applicants for design change approvals would have to 

perform a similar review for their proposed design changes. 

A zonal analysis procedure is an assessment of the structures and 

systems within each physical zone of the airplane. It is used to develop 

an inspection program to assess the general condition and security of 

attachment of all system components and structures items contained in 

the zone, using general visual inspections (GVI). An enhanced zonal 

analysis procedure (EZAP) is an enhanced version of the zonal analysis 

procedure. It focuses on EWIS components. An EZAP-generated 

inspection program might call for the use of stand-alone GVI and detailed 

inspections (DET). A stand-alone GVI is one that is performed 

separately from the regularly scheduled GVI (typically more frequently) 

and is focused on a particular area or component. In this case, the focus 

would be wiring. So while the zonal analysis procedure would result in a 

regularly scheduled GVI for the entire zone, in which each of its systems 

and structures are inspected at the same time, the EZAP could result in 

additional GVIs or DETs for the EWIS in that zone, which occur more 

frequently. These inspection techniques are discussed later in this 

section. 
11/23/07 AC 25-27

 Appendix E

E-7 

An EZAP identifies the physical and environmental conditions 

contained in each zone of an airplane, analyzes their effects on electrical 

wiring, and assesses the possibilities for smoke and fire. From such an 

analysis, maintenance tasks can be developed to prevent ignition sources 

and to minimize the possibilities for combustion by minimizing the 

accumulation of combustible materials. Such a procedure would involve 

dividing the airplane into physical areas, or zones, including actual 

physical boundaries such as wing spars, bulkheads, and cabin floor, and 

access provisions for the zone, and identifying which of those zones 

contain EWIS components. For those zones with EWIS components, 

characteristics and components of all systems installed in the zone would 

be listed. The EWIS in the zone would be described, including 

information on the full range of power levels carried in the zone. And the 

presence or possibilities for ignition sources or accumulation of 

combustibles would be noted. 

Combustibles are any materials that could cause a fire to be 

sustained in the event of an ignition source. Examples of combustible 

materials would be dust or lint accumulation, contaminated insulation 

blankets, and fuel or other combustible liquids or vapors. Wire 

contaminants are foreign materials that are likely to cause degradation of 

wiring. Wire contaminants can also be combustibles. Some commonly 

used airplane liquids, like engine oils, hydraulic fluids, and corrosion 

prevention compounds, might be readily combustible, but only in vapor 

or mist form. In that case, an assessment must be made of conditions that 

could exist within the zone that would convert the liquid to that form. 

Combustibles appearing as a result of any single failure must be 

considered. An example would be leaks from connection sites of 

unshrouded pipes. For the purposes of this new requirement, the term 

combustible does not refer to material that will burn when subjected to a 

continuous source of heat as occurs when a fire develops. Combustibles, 

as used here, will sustain a fire without a continuous ignition source. 

An EZAP must address: 

• Ventilation conditions in the zone and the density of the 

installations that would affect the presence and build-up of 

combustibles and the possibilities for combustion. Avionics and 

instruments located in the flightdeck and equipment bays, which 

generate heat and have relatively tightly packed installations, require 

cooling air flow. The air blown into the area for that cooling tends 

to deposit dust and lint on the equipment and EWIS components. 

 

• Liquid contamination on wiring. Most synthetic oils and hydraulic 

fluids, while they might not be combustibles by themselves, could be 
11/23/07 AC 25-27

 Appendix E

E-8 

an aggravating factor for accumulation of dust or lint. This 

accumulation could then present fuel for fire. Moisture on wiring 

may increase the probability of arcing from small breaches in the 

insulation, which could cause a fire. Moisture on wires that contain 

insulation breaches can also lead to “arc tracking.” As discussed 

previously, arc tracking is a phenomenon in which an electrical arc 

forms a conductive carbon path across an insulating surface. The 

carbon path then provides a short circuit path through which current 

can flow. Short circuit current flow from arc tracking can lead to 

loss of multiple airplane systems, structural damage, and fire. 

• EWIS in close proximity to both primary and back-up hydraulic, 

mechanical, or electrical flight controls. 

• The type of wiring discrepancies that must be addressed if they are 

identified by general visual or detailed inspections. A listing of 

typical wiring discrepancies that should be detectable during EZAPderived EWIS inspections is given in AC120-XXX, Section B 

“Guidance for Zonal Inspections.” 

• Proper cleaning methods for EWIS components. 

Once information about such contaminants and combustibles 

within an airplane zone is collected, each identified possibility for 

combustion would then be addressed to determine whether a specific task 

could be performed to reduce that possibility. An example of a specific 

task to reduce build-up of combustibles on EWIS components is the use 

of temporary protective covers (such as plastic sheeting) over EWIS 

components in a zone where corrosion prevention fluids are being used. 

This would minimize the amount of fluid contamination of the EWIS 

components. Preventing fluid contamination reduces the probability of 

other contaminants, like dust and dirt, accumulating on the EWIS 

components. If no task can be developed to prevent accumulation of 

combustibles in a zone, such as the dust blown through the air by cooler 

fans, then tasks must be developed to minimize their buildup, such as 

scheduled cleaning. 

Developing an ICA to define such tasks would include assessing 

whether particular methods of cleaning would actually damage the EWIS 

components. Although regular cleaning to prevent potential combustible 

build-up would be the most obvious task for an EWIS ICA, other 

procedures might also be called for. A detailed inspection of a hydraulic 

pipe might be appropriate, for instance, if high-pressure mist from a 

pinhole caused by corrosion could accumulate on a wire bundle in a low 

ventilation area, creating a possibility for electrical arcing. 

 
11/23/07 AC 25-27

 Appendix E

E-9 

Proximity of EWIS to both primary and back-up hydraulic, 

mechanical, or electrical flight controls within a zone would affect the 

criticality of inspections needed, their level of detail, and their frequency. 

Even in the absence of combustible material, wire arcing could adversely 

affect continued safe flight and landing if hydraulic pipes, mechanical 

cables, or wiring for fly-by-wire controls are routed close to other wiring. 

The EZAP-generated ICA must be produced in the form of a 

single document, easily recognizable as EWIS ICA for that specific 

airplane model. The single document is relevant to the maintenance and 

inspection aspects of the ICA, and not the standard wiring practices 

manual or electrical load analysis, etc. 

The ICA must define applicable and effective tasks, and the 

intervals for performing them, to: 

• Minimize accumulation of combustible materials. 

• Detect wire contaminants 

• Detect wiring discrepancies that may not otherwise be reliably 

detected by inspections contained in existing maintenance programs. 

As noted earlier, among the types of tasks to be developed from 

an EZAP are general visual inspections (GVI) and detailed inspections 

(DET). A GVI is defined as a visual examination of an interior or 

exterior area, installation, or assembly to detect obvious damage, failure, 

or irregularity. This level of inspection is made from within touching 

distance of the inspected object unless otherwise specified. It is made 

under normally available lighting conditions such as daylight, hangar 

lighting, flashlight, or droplight and may require removal or opening of 

access panels or doors. It may be necessary to use a mirror to improve 

visual access to all exposed surfaces in the inspection area. Stands, 

ladders, or platforms may be required to gain proximity to the area being 

checked. It is expected that the area to be inspected is clean enough to 

minimize the possibility that accumulated dirt, grease, or other 

contaminants might hide unsatisfactory conditions that would otherwise 

be obvious. It is also expected, as an outcome of the EZAP applied to 

EWIS, that any cleaning considered necessary would be performed in 

accordance with procedures that minimize the possibility of the cleaning 

process itself introducing anomalies. The EZAP must identify guidelines 

to assist personnel performing a GVI in identifying wiring discrepancies 

and in assessing what effect such discrepancies, if found, could have on 

adjacent systems, particularly if these include wiring. As discussed 

previously, a list of typical wiring discrepancies that should be addressed 

is contained in proposed AC120-XX, Section B, “Guidance for Zonal 

Inspections.” 
11/23/07 AC 25-27

 Appendix E

E-10 

A DET is an intensive examination of a specific item, installation, 

or assembly to detect damage, failure, or irregularity. Available lighting 

is normally supplemented with a direct source of good lighting at an 

intensity considered appropriate. Inspection aids, such as mirrors, 

magnifying lenses, or other means, may be necessary. Surface cleaning 

and elaborate access procedures may be required. A DET can be more 

than just a visual inspection. It may include tactile assessment to check a 

component or assembly for tightness and security. Such an inspection 

may be needed to ensure the continued integrity of installations such as 

bonding jumpers, terminal connectors, etc. 

A DET would be required when the developer of the EZAP 

determines that a GVI is inadequate to reliably detect anomalies or 

degradation of EWIS components. Any detected discrepancies must be 

corrected according to the operator’s approved maintenance procedures. 

It is not intended that the EZAP ICA identify how to correct detected 

discrepancies. 

 

 To prevent improper modification and repair of existing EWIS or the 

improper installation of a new EWIS, modification designers and 

modification personnel must know the applicable standard wiring 

practices, EWIS identification requirements, and electrical load data for 

the airplane undergoing modification. The proposed Appendix H 25.5 

would also require that the following information be included in ICA 

applicable to EWIS: 

• Standard wiring practices data. 

• Wire separation design guidelines. 

• Information to explain the airplane’s EWIS identification method 

required by the proposed § 25.1711. 

• Electrical load data and instructions for updating that data. Such 

information will help ensure that those modifying, repairing, or 

installing new EWIS will not perform any action that will adversely 

affect previously certified systems and unintentionally introduce 

potential hazards. 

 Standard wiring practices are defined as standards developed by the 

specific airplane manufacturer or industry-wide standards for the repair 

and maintenance of EWIS. They include procedures and practices for the 

installation, repair, and removal of EWIS components, including 

information about wire splices, methods of bundle attachment, connectors 

and electrical terminal connections, bonding, and grounding. Although a 
11/23/07 AC 25-27

 Appendix E

E-11 

standard wiring practices manual is not a design manual, and those 

designing a new EWIS modification for a specific model airplane should 

not use it as such, it does provide the designer with insight into the types 

of EWIS components used by the TC holder and the procedures 

recommended by the manufacturer for maintenance or repair that 

supports continued airworthiness of the components. 

 EWIS separation guidelines are important for maintaining the safe 

operation of the airplane. Maintenance and repair personnel need to be 

aware of the type certificate holders’ separation requirements so they do 

not compromise separation in previously certified systems. In fuel tank 

systems, the separation of certain wires may be critical design 

configuration control items and therefore qualify as an airworthiness 

limitation. Maintenance personnel need to be aware of these guidelines 

and limitations because many times wire bundles must be moved or 

removed to perform necessary maintenance. They must be able to readily 

identify EWIS associated with systems essential to the safe operation of 

the airplane. 

 Similarly, those who design and install new EWIS need to be aware 

of separation requirements so they can use the same methods to develop 

the required separation for the EWIS they are adding to the airplane. 

This would help to ensure both that newly added EWIS is adequately 

separated from other EWIS, airplane system components, and structure 

so they do not damage the added EWIS, and that the addition of the new 

EWIS does not invalidate separation for previously certified EWIS. 

 Electrical load data and the instructions for updating that data are 

necessary to help ensure that future modifications or additions of 

equipment that consume electrical power do not exceed the generating 

capacity of the onboard electrical generation and distribution system. 

The existing § 25.1351(a)(1) mandates that the required generating 

capacity, and the number and kinds of power sources, must be 

determined by an electrical load analysis. Typically, after an airplane is 

delivered and enters service, it is modified numerous times throughout its 

service life. Each addition or deletion of an electrical-power-consuming 

system changes the electrical load requirements. The only way to ensure 

that the capacity of the overall generating and distribution system, as well 

as individual electrical buses, is not exceeded is to have an up-to-date 

electrical load analysis. The best way to ensure that an up-to-date 

electrical load analysis is maintained is for the type certificate holder to 

include such data in the ICA provided with the airplane when it is first 

delivered to a customer, along with recommended practices for keeping it 

updated as electrical loads are deleted and added. 
11/23/07 AC 25-27

 Appendix E

E-12 

Part 26 

§ 26.3 Definitions 

FAA Oversight Office is the aircraft certification office or office of the Transport Airplane 

Directorate with oversight responsibility for the relevant type certificate, supplemental 

type certificate, or manufacturer, as determined by the Administrator. 

§ 26.11 Electrical wiring interconnection systems (EWIS) maintenance program 

(a) Except as provided in paragraph (g) of this section, this section applies to 

transport category, turbine-powered airplanes with a type certificate issued 

after January 1, 1958, that, as a result of the original certification, or later 

increase in capacity, have - 

 

(1) A maximum type-certificated passenger capacity of 30 or more or 

(2) A maximum payload capacity of 7,500 pounds or more. 

(b) Holders of, and applicants for, type certificates, as identified in paragraph (d) of 

this section must develop Instructions for Continued Airworthiness (ICA) for the 

representative airplane’s EWIS in accordance with part 25, Appendix H 

paragraphs H25.5(a)(1) and (b) of this subchapter in effect on [effective date of 

this final rule] for each affected type design, and submit those ICA for review 

and approval by the FAA Oversight Office. For purposes of this section, the 

“representative airplane” is the configuration of each model series airplane that 

incorporates all variations of EWIS used in production on that series airplane, 

and all TC-holder-designed modifications mandated by airworthiness directive 

as of the effective date of this rule. Each person specified in paragraph (d) of 

this section must also review any fuel tank system ICA developed by that 

person to comply with SFAR 88 to ensure compatibility with the EWIS ICA, 

including minimizing redundant requirements. 

(c) Applicants for amendments to type certificates and supplemental type 

certificates, as identified in paragraph (d) of this section, must: 

(1) Evaluate whether the design change for which approval is sought 

necessitates a revision to the ICA required by paragraph (b) of this 

section to comply with the requirements of Appendix H, paragraphs 

H25.5(a)(1) and (b). If so, the applicant must develop and submit the 

necessary revisions for review and approval by the FAA Oversight 

Office. 
11/23/07 AC 25-27

 Appendix E

E-13 

(2) Ensure that any revised EWIS ICA remain compatible with any fuel tank 

system ICA previously developed to comply with SFAR 88 and any 

redundant requirements between them are minimized. 

(d) The following persons must comply with the requirements of paragraph (b) or 

(c) of this section, as applicable, before the dates specified. 

(1) Holders of type certificates (TC): [insert date 24 months after effective 

date] 

(2) Applicants for TCs, and amendments to TCs (including service bulletins 

describing design changes), if the date of application was before 

[effective date of final rule] and the certificate was issued on or after 

[effective date of final rule]: [insert date 24 months after effective date], 

or the date the certificate is issued, whichever occurs later. 

(3) Unless compliance with § 25.1729 of this subchapter is required or 

elected, applicants for amendments to TCs, if the application was filed 

on or after [effective date of final rule]: [insert date 24 months after 

effective date], or the date of approval of the certificate, whichever 

occurs later. 

(4) Applicants for supplemental type certificates (STC), including changes 

to existing STCs, if the date of application was before [effective date of 

final rule] and the certificate was issued on or after [effective date of 

final rule]: [insert date 30 months after effective date], or the date of 

approval of the certificate, whichever occurs later. 

(5) Unless compliance with § 25.1729 of this subchapter is required or 

elected, applicants for STCs, including changes to existing STCs, if the 

application was filed on or after [effective date of final rule], [insert date 

30 months after effective date], or the date of approval of the 

certificate, whichever occurs later. 

(e) Each person identified in paragraphs (d)(1), (d)(2), and (d)(4) of this section 

must submit to the FAA Oversight Office for approval a compliance plan by 

[insert date 90 days after effective date of final rule]. The compliance plan 

must include the following information: 

(1) A proposed project schedule, identifying all major milestones, for 

meeting the compliance dates specified in paragraph (d) of this 

section. 

(2) A proposed means of compliance with this section, identifying all 

required submissions, including all compliance items as mandated in 

part 25, Appendix H paragraphs H25.5(a)(1) and (b) of this subchapter 
11/23/07 AC 25-27

 Appendix E

E-14 

in effect on [effective date of this final rule], and all data to be 

developed to substantiate compliance. 

(3) A proposal for submitting a draft of all compliance items required by 

paragraph (e)(2) of this section for review by the FAA Oversight Office 

not less than 60 days before the compliance time specified in 

paragraph (d) of this section. 

(4) A proposal for how the approved ICA will be made available to affected 

persons. 

(f) Each affected person must implement the compliance plan, or later approved 

revisions, as approved in compliance with paragraph (e) of this section. 

 (g) This section does 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 
11/23/07 AC 25-27

 Appendix E

E-15 

NPRM Preamble Discussion 

Part 26 was proposed as a new Subpart I to Part 25. The placement of these 

requirements was changed in the final rule. 

70 FR 58526 

B. Part 25 Subpart I – Continued Airworthiness and Related Part 25 

Changes 

 As discussed below, the following proposals are applicable to 

holders of existing TCs for transport category airplanes and applicants for 

approval of design changes to those certificates. On July 12, 2005, we 

issued policy statement PS-ANM110-7-12-2005, “Safety – A Shared 

Responsibility – New Direction for Addressing Airworthiness Issues for 

Transport Airplanes” (70 FR 40166). The policy states, in part, “Based 

on our evaluation of more effective regulatory approaches for certain 

types of safety initiatives and the comments received from the Aging 

Airplane Program Update (July 30, 2004), the FAA has concluded that 

we need to adopt a regulatory approach recognizing the shared 

responsibility between design approval holders (DAH) and operators. 

When we decide that general rulemaking is needed to address an 

airworthiness issue, and believe the safety objective can only be fully 

achieved if the DAHs provide operators with the necessary information in 

a timely manner, we will propose requirements for the affected DAHs to 

provide that information by a certain date.” 

 We believe that the safety objectives contained in this proposal can 

only be reliably achieved and acceptable to the FAA if the DAHs provide 

the operators with the EWIS- and fuel-tank-system-related maintenance 

information required by the proposed operational rules for Parts 91, 121, 

125, and 129. Our determination that DAH requirements are necessary to 

support the initiatives contained in this proposal is based on several 

factors:

• Developing EWIS and fuel tank system ICA is complex. Only the 

airplane manufacturer, or DAH, has access to all the necessary type 

design data needed for the timely and efficient development of the 

required EWIS and fuel tank system maintenance tasks. 

• FAA-approved EWIS and fuel tank system ICA need to be available 

in a timely manner. Due to the complexity of these ICA, we need to 

ensure that the DAHs submit them for approval on schedule. This 

will allow the FAA Oversight Office having approval authority to 

ensure that the ICA are acceptable, are available on time, and can be 
11/23/07 AC 25-27

 Appendix E

E-16 

readily implemented by the affected operators. Additionally, accurate 

and timely information is necessary to ensure alignment with the 

requirements of the Fuel Tank Safety Rule (FTSR). The compliance 

deadline for the operational requirements of the FTSR was extended 

to facilitate this alignment, as stated in the Federal Register notice “ 

Fuel Tank Safety Compliance Extension (Final Rule) and Aging 

Airplane Program Update (Request for Comments)” (69 FR 45936). 

• The proposals in this NPRM affect a large number of different types 

of transport airplanes. Because the safety issues addressed by this 

proposal are common to many airplanes, we need to ensure that 

technical requirements are met consistently and the processes of 

compliance are consistent. This will ensure that the proposed safety 

enhancements are implemented in a standardized manner. 

• The safety objectives of this proposal need to be maintained for the 

operational life of the airplane. We need to ensure that future design 

changes to the type design of the airplane do not degrade the safety 

enhancements achieved by the initial incorporation of EWIS and fuel 

tank system ICA. We need to be aware of future changes to the type 

designs to ensure that these changes do not invalidate the 

maintenance tasks assigned to a particular type design when the ICA 

are first developed under the requirements of this proposal. 

Based on the above reasons and the stated safety objectives of FAA 

policy PS-ANM110-7-12-2005, we are proposing to implement DAH 

requirements applicable to EWIS and fuel tank system ICA. 

 In the past, we have issued a similar requirement in the form of a 

special federal aviation regulation (SFAR). But SFARs appear in various 

places in the CFR and are difficult to reference as a whole. The FAA 

believes that placing these types of requirements in a new subpart of part 

25, which contains the airworthiness standards for transport category 

airplanes, would provide a single, readily accessible location for this type 

of requirement. Therefore, we are proposing new subpart I to part 25 to 

contain these requirements. 

 In preliminary discussions with foreign airworthiness authorities of 

the concept of this new subpart, they have expressed concerns that their 

regulatory systems may not be able to accommodate these types of 

requirements in their counterparts to part 25. While agreeing on the need 

for these types of requirements, they have suggested that it may be more 

appropriate to place them in part 21 or another location. As discussed 

below, because we expect these new subpart I requirements to be similar 

to new part 25 airworthiness standards, we have tentatively decided to 

place them in part 25. However, we specifically request comments on the 

appropriate location of these requirements, particularly from the foreign 
11/23/07 AC 25-27

 Appendix E

E-17 

authorities. If, based on comments received, we conclude that another 

location is more appropriate, we may move them in the final rule. 

Because such a move would not affect the substance of the requirements 

themselves, we would not consider this to be an expansion of the scope of 

this rulemaking that would require additional notice and comment 

procedures. 

Section 25.1 Applicability. 

 As stated in § 25.1, part 25 currently prescribes airworthiness 

standards for issuance of TCs, and changes to those certificates, for 

transport category airplanes. As discussed in more detail above, with this 

NPRM the FAA is proposing to expand the coverage of part 25 to include 

a new subpart I containing requirements that must be complied with by 

current holders of these certificates. Therefore, we are proposing to 

amend § 25.1, “Applicability,” to state that part 25 also includes 

requirements for holders of these design certificates. As discussed in the 

FAA’s final rule, “Fuel Tank Safety Compliance Extension and Aging 

Airplane Program Update” (69 FR 45936), this NPRM is one of several 

proposals for adoption of these kinds of requirements for current holders 

of type certificates. 

 A theme common to this and other possible subpart I proposed rules 

is that the rulemaking projects include proposals for changes to 

operational rules to require operators to implement programs or take 

other actions that the FAA has determined are necessary for safety. In 

several recent rules we have adopted operational requirements without a 

corresponding requirement for design approval holders to develop and 

provide the necessary data and documents to support the operators’ 

compliance. The difficulty encountered by operators in complying with 

these rules has convinced us that the corresponding design approval 

holder requirements are necessary to enable operators to comply by the 

regulatory deadlines. 

Section 25.2 Special retroactive requirements. 

 Section 25.2 currently contains “special retroactive requirements.” 

These requirements are “retroactive” in the sense that they require 

applicants for changes to TCs to comply with requirements that were not 

applicable to the original TC. As discussed below, proposed subpart I 

would have a similar effect, in that it would impose new requirements on 

both existing design certificate holders and applicants for changes to 

those certificates. Therefore, we are proposing to amend § 25.2 to make 

reference to proposed subpart I. 
11/23/07 AC 25-27

 Appendix E

E-18 

Section 25.1801 Purpose and definition. 

Paragraph (a) of this section states that this subpart would 

establish requirements for holders of TCs to take actions necessary to 

address particular safety concerns or to support the continued 

airworthiness of transport category airplanes. Such actions may include, 

but are not limited to, performing assessments, making design changes, 

developing revisions to ICA, and making necessary documentation 

available to affected persons. 

The specific applicability of each subpart I rule will be established 

as part of the rulemaking adopting each rule. Generally this subpart 

would also apply to applicants for type certificates and changes that are 

pending as of the effective date of this rule. It would also apply to future 

applicants for changes to existing type certificates. Under § 21.101, the 

FAA may determine that it is not appropriate to require such applicants to 

comply with new airworthiness standards, such as proposed new subpart 

H. However, it is appropriate for them to comply with the same 

requirements as existing certificate holders. Otherwise, the safety 

improvements that result from type certificate holder compliance with 

these requirements could be undone by later modifications. 

For example, in the case of this proposed rule, as discussed below, 

operators would be required to revise their maintenance programs based 

on EWIS ICA developed by the type certificate holder. Unless future 

STC applicants are required to provide similar ICA for their 

modifications, the TC holder’s ICA could become obsolete or, in some 

cases, even provide incorrect and potentially unsafe information as 

applied to the STC holder’s modification. In other cases, because subpart 

I rules accompany corresponding operating requirements, failure of an 

STC applicant to comply with a subpart I rule could make it impossible 

for an operator to comply with the corresponding operating requirement. 

Subpart I does not apply to future applicants for TCs, because those 

applicants will be covered by other proposed changes to part 25, 

including Appendix H. 

Therefore, adoption of a new subpart I rule would also necessitate 

new requirements for certification of changes to TCs that are in addition 

to the requirements that are specified under § 21.101. Under that section, 

if a change is “significant” and certain other criteria are met, the applicant 

would have to show compliance with the latest airworthiness 

requirements. For example, an applicant applying for such a change after 

this final rule becomes effective would have to comply with the proposed 

EWIS requirements in subpart H. Even if we determine that these 

broader regulations do not apply, the applicant for a change must still 

comply with the subpart I rule. 
11/23/07 AC 25-27

 Appendix E

E-19 

 Paragraph (b) of this section provides a definition of the term “FAA 

Oversight Office.” The FAA Oversight Office is the aircraft certification 

office or office of the Transport Airplane Directorate with oversight 

responsibility for the relevant TC or STC, as determined by the 

Administrator. As stated later in the discussion of the proposed operating 

rules, the primary means for operators to comply with those requirements 

would be by implementing programs or taking other actions developed 

by the TC and STC holders under this proposed subpart. In each case, to 

ensure compliance with the relevant subpart I rule, the TC and STC 

holder’s compliance documentation (for example, in this case, EWIS 

ICA) must be submitted to the FAA Oversight Office. Because we 

expect this will be a standard approach to compliance with the 

requirements of this subpart, we are including this definition in this 

section to avoid having to repeat it in each section within this subpart. 

25.1805 — Electrical wiring interconnection systems (EWIS) 

maintenance program. 

This proposal would apply to holders of TCs and to applicants for new 

TCs, amended TCs, and supplemental TCs if the application was filed 

before the effective date of this rule and the certificate was issued on or 

after the effective date of this rule. It would also apply to future 

applicants for approval of changes to existing TCs. 

Paragraph (a) states that this rule would apply, with some 

exceptions, to transport category turbine-powered airplanes with a 

maximum type-certificated capacity of 30 or more passengers, or a 

maximum payload capacity of 7500 pounds or more resulting from the 

original certification of the airplane or later increase in capacity. This 

would result in the coverage of airplanes where the safety benefits and 

the public interest are the greatest. 

The reference to the originally certificated capacity, or later increase 

in capacity, is intended to address two situations: 

• In the past, some designers and operators have tried to avoid applying 

requirements mandated only for airplanes over specified capacities by 

getting a design change approval for a slightly lower capacity. By 

referencing the capacity resulting from original certification, this 

proposal would remove this possible means of avoiding compliance. 

• It is also possible that an airplane design could be originally certified 

with a capacity slightly lower than the minimum specified in this 

section, but through later design changes, the capacity could be 

increased above this minimum. The reference to later increases in 
11/23/07 AC 25-27

 Appendix E

E-20 

capacity would ensure that, if this occurs, the design would have to 

meet the requirements of this section. 

Compliance is not proposed for airplanes with a certificated 

passenger capacity of fewer than 30 passengers, or having a maximum 

capacity of less than 7500 pounds payload resulting from original 

certification, because it is not clear at this time that the possible benefits 

for those airplanes would be proportionate to the cost involved. The 

FAA intends to evaluate the merits of applying these requirements to 

those airplanes. We are currently working with ATSRAC to assess how 

these issues might be addressed in those transport category airplanes. 

We request comments on the feasibility and benefits of requiring holders 

of TCs for those airplanes to comply with these requirements. 

This proposed rule, as it applies to EWIS, is not applicable to 

holders of existing (already issued) STCs. Often, the wire design for 

STC installations of EWIS was based on operator or repair station 

standard practices and therefore details of the installation are not 

available. In the cases where such information is available, it would 

usually indicate that the wiring for the modification follows the same 

path, or is in the same airplane zone, as the wiring in the original type 

design. We anticipate that operators would inspect those areas while 

performing the TC holder’s EZAP program. We also expect that any 

possible discrepancies will be further mitigated by operators 

incorporating applicable EWIS maintenance tasks into the maintenance 

program for that zone. Accordingly, the FAA has decided not to require 

compliance with this section for existing STCs. However, if an existing 

STC is amended, this section would apply to the amendment. 

TC holders, who design EWIS on airplanes, are the technical 

experts who possess information about those systems. This proposal 

would apply to the following: 

• TC holders. 

• Applicants for TCs and for approval of design changes to existing 

TCs whose applications are pending when this rule becomes 

effective. 

• Future applicants for approval of design changes to existing TCs. 

Section 25.1805(b) would require TC holders to complete a 

comprehensive assessment of the EWIS of each “representative” airplane 

for which they hold a TC, develop inspection and maintenance 

instructions for them, and incorporate those instructions into the 

airplane’s ICA. 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-
11/23/07 AC 25-27

 Appendix E

E-21 

designed modifications mandated by AD, as of the effective date of this 

rule. 

For example, for the Boeing Model 737, the representative 

airplane would be the configuration of each of the airplane series, 737-

100 through 737-900 that incorporates all the variations of EWIS used in 

producing each airplane series. The purpose of this definition is to ensure 

that the TC holder considers the full range of EWIS configurations that 

may affect the results of the EZAP. Further, AD 99-03-04 applies to all 

Boeing Model 737-100, -200, -300, -400, and -500 series airplanes. It 

requires installation of components to provide shielding and separation of 

the fuel system wiring from adjacent wiring. It also requires installation 

of flame arrestors and pressure relief valves in the fuel vent system. 

Boeing would be required to develop ICA for each of those series 

airplanes as modified by installation of these components and all other 

modifications mandated by ADs. 

The purpose of including these mandated design changes is to 

ensure that the TC holder’s EZAP addresses the existing configuration of 

airplanes in the operating fleet, rather than just the configuration 

produced and delivered by the manufacturer. 

Applicants for approval of design changes would be required to 

evaluate the effect of their proposed change on the EWIS ICA developed 

by the TC holder for the representative airplane and to develop EWIS 

ICA to address those effects. For TC holders, this requirement would 

apply to any design changes that may affect the ICA for the 

representative airplane. This includes service bulletins describing such 

design changes. Under § 21.113, these design changes are amendments 

to the TC. 

A description of what must be included in those ICA, and the 

EZAP that must be used to develop them, is contained in the section of 

this preamble discussing the proposed revision to Appendix H, part 25. 

 The requirement for ICA was effective on January 28, 1981. 

TC holders whose application was dated before that date are not subject 

to that requirement. This proposal would require TC holders who do not 

have ICA for specific airplane models to create EWIS ICA for them. As 

discussed below, air carriers and operators of those airplanes would then 

be required to revise their maintenance or inspection programs based on 

the new ICA for EWIS and fuel tank systems. 

As discussed earlier, SFAR 88 requires TC holders to develop 

maintenance and inspection instructions to assure the safety of the fuel 

tank system. Proposed § 25.1805(b) would require that TC holders align 
11/23/07 AC 25-27

 Appendix E

E-22 

the fuel tank system instructions with the results of the EZAP applied to 

EWIS to ensure compatibility and minimize redundancies. All EWIS 

would be subject to review in developing the EWIS ICA, and the 

appropriate instructions for their maintenance and inspection would be 

required. But some EWIS are also part of the fuel tank system. The 

requirements for their maintenance and inspection might be more specific 

than those for wiring in general, and might contain additional 

requirements. That is why the two must be reviewed for compatibility. 

As discussed later in this section, the ICA for fuel tank system 

electrical wiring required by SFAR 88 will be determined in accordance 

with guidance provided by Policy Statement ANM100-2004-1129, 

“Process for Developing Instructions for Maintenance and Inspection of 

Fuel Tank Systems Required by SFAR 88” (a copy of which may be 

found in the docket), or other acceptable process. Compliance with 

Subpart I will require ICA for the same wire to be determined using an 

EZAP. While these processes have similarities, they may result in 

identification of different tasks and intervals. The ICA maintenance tasks 

and intervals that result from these determinations are expected to be 

additive. If there is a conflict in the task or interval, for purposes of this 

section, the FAA Oversight Office will resolve the conflict. 

 The ICA should be reviewed to ensure that any maintenance tasks 

for EWIS do not compromise fuel tank system wire requirements, such as 

separation or configuration specifications. If there is an inspection or 

maintenance requirement for EWIS and the fuel tank system within the 

same zone, there must be an effort to align the task interval. In addition, 

design certificate holder’s existing documents containing EWIS and fuel 

tank system ICA should be reviewed to either remove or cross-reference 

redundant information. 

The compliance plan required by this proposal must include 

identification of those common locations in the airplane where EWIS and 

fuel tank ICA apply. The considerations for compatibility and 

minimization of redundancy for the two systems will be reviewed and 

approved by the FAA Oversight Office. The plan for documenting the 

required ICA for EWIS and fuel tank system will also be reviewed as part 

of the compliance plan. These documents are critical to the effort that 

will be required of operators to show compliance with the operational 

rules contained in this proposal. We intend that the ICA information, 

both in content and format, will be readily usable by the affected 

operators for developing proposed changes to their maintenance or 

inspection programs. Generally, the information contained in the ICA for 

the fuel tank system required by SFAR 88 would include: 

• The location of the fuel tank system components to be maintained or 

inspected and any access requirements. 
11/23/07 AC 25-27

 Appendix E

E-23 

• Any unique procedures required, such as special, detailed inspections 

or dual sign-off of maintenance records. 

• Specific task information, such as inspections defined by pictures or 

schematics. 

• Intervals for any repetitive tasks. 

• Methods, techniques, and practices required to perform the task. 

• Criteria for passing inspections. 

• Any special equipment or test apparatus required. 

• Critical Design Configuration Control Limitations — for example, 

wire separation or pump impeller material specifications — that 

cannot be altered, except in accordance with the applicable limitation. 

The information for EWIS ICA would generally include: 

• Identification of each zone of the airplane. 

• Identification of each zone that contains EWIS. 

• Identification of each zone containing EWIS that also contains 

combustible material. 

• Identification of each zone in which EWIS is in close proximity to 

both primary and back-up hydraulic, mechanical, or electrical flight 

controls and lines. 

• The location of the EWIS components to be maintained or inspected 

and any access requirements. 

• Any unique procedures required, such as special, detailed inspections, 

or a dual sign-off of maintenance records. 

• Specific task information, such as inspections defined by pictures or 

schematics. 
11/23/07 AC 25-27

 Appendix E

E-24 

• Intervals for any repetitive tasks. 

• Methods, techniques and practices required to perform the task. 

• Criteria for passing inspections. 

• Any special equipment or test apparatus required. 

• Instructions for protection and caution information that will minimize 

contamination and accidental damage to EWIS during performance of 

maintenance, alterations, or repairs. 

• Guidelines for identifying wiring discrepancies and assessing what 

effect such discrepancies, if found, could have on adjacent systems, 

particularly if these include wiring. 

•

• Critical Design Configuration Control Limitations — for example, 

wire separation specifications — that cannot be altered, except in 

accordance with the applicable limitation. 

 Policy Statement No. PS-ANM100-2004-10029 provides guidance 

on acceptable processes for developing fuel tank system ICA as required 

by SFAR 88. The FAA expects that engineers from aircraft certification 

offices or from the Transport Airplane Directorate will review and 

approve the results of the EZAP. 

 The three groups whose compliance with this proposal would 

be required, and their required compliance dates, indicated in paragraph 

(c), are as follows: 

• Existing TC holders: No later than December 16, 2007. 

• Current applicants for TCs and amendments to TCs (including 

service bulletins describing design changes) whose applications are 

pending and future applicants for TC amendments: No later than 

December 16, 2007, or the date of approval of their application, 

whichever is later. 
11/23/07 AC 25-27

 Appendix E

E-25 

• Pending and future applicants for STCs: No later than June 16, 

2008, or the date of the approval of their application, whichever is 

later. 

Future applicants for changes to TCs that comply with proposed § 

25.1739 would not be required to comply with this section. As discussed 

previously, under § 21.101, applicants for “significant” changes that meet 

certain criteria must comply with the latest airworthiness requirements. 

If this NPRM is adopted as a final rule, such a future applicant would 

have to comply with § 25.1739. Because the proposed requirements of 

that section are more extensive than the proposed requirements of § 

25.1805, requiring compliance with this section would be redundant. 

In determining the compliance schedules for the requirements 

covered in this proposal, the FAA balanced the safety-related reasons for 

the rule against the need to give industry enough time to comply with it. 

Therefore, before setting the proposed compliance times for the TC 

holders to complete their analysis of their representative type design, the 

FAA considered the following: 

• Input from industry. 

• Current or planned compliance periods of several aging-related 

rulemakings, such as the pending Aging Airplane Safety proposed 

rule, Fuel Tank System safety initiatives (69 FR 45936, 66 FR 

23086), and the pending Widespread Fatigue Damage proposal. 

• Safety improvements that will result from compliance with this 

rule. 

• Industry’s current efforts to incorporate some of these safety 

initiatives. 

 ATSRAC recommended a compliance time of 24 months for TC 

holders to develop these ICA. To align this proposal with other rules in 

the aging airplane program, the FAA has adjusted the time frame to that 

of other rules discussed earlier, so that operators can more efficiently 

comply with requirements to revise their maintenance programs. To 

support this realignment, compliance dates that allow an 18-month time 

frame for TC holders to develop the EWIS ICA and 12 months for 

operators to implement them were determined to be appropriate and were 

included in this proposal. We believe these time frames are supported by 

the experience gained from the EZAPs already performed. Since 

ATSRAC made its recommendation, several manufacturers have applied 

an EZAP to their type design airplanes and have completed those 

reviews. 
11/23/07 AC 25-27

 Appendix E

E-26 

When we initially drafted this proposal, we assumed the final rule 

would be adopted by mid-2006. As a result, we set the compliance dates 

in the proposal using the mid-2006 time frame as the baseline. However, 

the proposed rulemaking process took longer than we had anticipated. 

Consequently, we expect that the time frame for adoption of the final rule 

will be sometime after mid-2006. We recognize that this delay will 

adversely impact the compliance dates we propose for TC holders and 

operators and we may need to adjust them. Therefore, we request and 

will consider your comments on revising the proposed compliance dates. 

Once the ICA are approved by the FAA Oversight Office, the submitter 

must make the ICA available to affected persons as required by § 21.50. 

Because this proposal sets a precedent in introducing part 25 

requirements for holders of existing TCs, it is the FAA’s expectation that 

they will work closely with the FAA Oversight Office in putting together 

a compliance plan for developing the required ICA. Proposed section 

25.1805(d) would require that the compliance plan be approved by the 

FAA Oversight Office as sufficient basis for showing compliance with 

the proposed § 25.1805. 

Development of a compliance plan is necessary to ensure that TC 

holders thoroughly understand the requirements of this proposal and 

produce on time appropriate ICA that are acceptable in content and 

format in addressing the maintenance and inspection tasks for EWIS and 

the fuel tank system. Integral to the compliance plan will be the inclusion 

of procedures to allow the FAA to monitor progress towards compliance. 

These aspects of the plan will help ensure that the expected outcomes will 

be acceptable and on time for incorporation by the affected operators in 

accordance with the operational rules contained in this proposal. 

To help ensure that TC holders are fully informed of what is 

necessary to show compliance with these requirements, as previously 

discussed, we are issuing AC 120.XX, and have issued a policy statement 

that describes an acceptable means, but not the only means, of complying 

with these requirements for developing EWIS ICA and the fuel tank 

system ICA required by SFAR 88. AC 120-XX, “Program to Enhance 

Transport Category Airplane Electrical Wiring Interconnection System 

Maintenance,” provides an enhanced zonal analysis procedure (EZAP) 

for completing a review of the representative airplane covering all areas, 

including the flight deck (or cockpit), electrical power center, fuel tank 

wiring, and powerfeeder cables. Policy Statement ANM100-2004-10029, 

“Process for Developing Instructions for Maintenance and Inspection of 

Fuel Tank Systems Required by SFAR 88,” provides guidance for 

identifying ICA, including any airworthiness limitations, as a result of the 
11/23/07 AC 25-27

 Appendix E

E-27 

fuel tank system review required by SFAR 88 and compliance with 

Amendment 102 to part 25 Appendix H and § 25.981. 

Proposed § 25.1805(d) is intended to provide TC holders, 

applicants with pending TC-amendment or STC applications, and the 

FAA with assurance that they understand what means of compliance are 

acceptable and have taken necessary actions, including assigning 

sufficient resources, to achieve compliance with this section. This 

paragraph is based substantially on “The FAA and Industry Guide to 

Product Certification,” which describes a process for developing projectspecific certification plans for type certification programs. A copy of this 

guide may be found in the docket. This planning requirement would not 

apply to future applicants for TC amendments or STCs because, as 

described in the guide, this type of planning routinely occurs at the 

beginning of the certification process. 

The guide recognizes the importance of ongoing communication 

and cooperation between applicants and the FAA. Section 25.1805, 

while regulatory in nature, is intended to encourage establishment of the 

same type of relationship in the process of complying with this section. 

In particular, in addition to other necessary information, paragraph (d)(3) 

makes it clear that, to the extent that they intend to use means of 

compliance different from those already identified as acceptable by the 

FAA, it is imperative that they identify those differences at the earliest 

possible stage so any compliance issues can be resolved without risk of 

unnecessary expenditure of resources or, ultimately, noncompliance. 

Proposed § 25.1805(d) would require TC holders and applicants 

to submit to the FAA Oversight Office the following within 90 days after 

the effective date of the rule: 

 

• A proposed project schedule, identifying all major milestones, for 

meeting the compliance dates of this rule. 

• A proposed means of compliance with this section, identifying all 

required deliverables, including all compliance items and all data to 

be developed to substantiate compliance. If any affected person has 

already initiated compliance, the FAA Oversight Office will review 

the results of those efforts to ensure that the results are acceptable. 

• A detailed explanation of how the proposed means will be shown to 

comply with this section if the affected person proposes a means of 

compliance that differs from that described in FAA advisory 

material. 
11/23/07 AC 25-27

 Appendix E

E-28 

• A proposal for how the approved ICA will be made available to 

affected persons.

 It should be noted that this section applies not only to domestic TC 

holders and applicants, but also to foreign TC holders and applicants. In 

this sense, this section is different from most type certification programs, 

where foreign applicants typically work with their responsible 

certification authority, and the FAA relies on that authority’s findings of 

compliance under bilateral airworthiness agreements. Since this 

rulemaking is not harmonized in all cases, the FAA will make all the 

necessary compliance determinations, and where appropriate we may 

accept findings of compliance made by the appropriate foreign authorities 

using procedures developed under the bilateral agreements. The 

compliance planning provisions of this section are equally important for 

domestic and foreign TC holders and applicants, and we will work with 

the foreign authorities to ensure that their TC holders and applicants 

perform the planning necessary to comply with the requirements of this 

section. 

 One of the items required in the plan is, "If the proposed means of 

compliance differs from that described in FAA advisory material, a 

detailed explanation of how the proposed means will comply with this 

section." FAA advisory material is never mandatory because it describes 

one means, but not the only means of compliance. In the area of type 

certification, applicants frequently propose acceptable alternatives to the 

means described in advisory circulars. But when an applicant chooses to 

comply by an alternative means, it is important to identify this as early as 

possible in the certification process to provide an opportunity to resolve 

any issues that may arise that could lead to delays in the certification 

schedule. 

 The same is true for this requirement. As discussed earlier, TC 

holder compliance with this section on time is necessary to enable 

operators to comply with the operational requirements of this NPRM. 

Therefore, this item in the plan would enable the FAA Oversight Office 

to identify and resolve any issues that may arise with the TC holder's 

proposal without jeopardizing the TC holder's ability to comply with this 

section by the compliance time. 

As of the date of this proposal, certain TC holders have 

voluntarily started to develop the EWIS EZAP that would be required by 

proposed § 25.1805. An EZAP has been completed on certain transport 

category airplanes. Although the EZAP used by those TC holders may 

not be the version outlined in AC120-XX, it is similar. The FAA would 

expect that after issuance of the final rule, these TC holders would either 

submit a plan proposing revisions to the EZAP for those model airplanes 
11/23/07 AC 25-27

 Appendix E

E-29 

to be consistent with the guidance given in AC120-XX, or use the 

planning process to show that their EZAP complies with this section. 

The FAA Oversight Office will then review the results of those efforts to 

ensure that the results are acceptable for compliance with this section. 

Section 25.1805(e) requires that TC holders and applicants correct 

a deficient plan, or deficiencies in implementing the plan, in a manner 

identified by the FAA Oversight Office. Before the FAA formally 

notifies a TC holder or applicant of deficiencies, however, we will have 

communicated with them to try to achieve a complete mutual 

understanding of the deficiencies and means of correcting them. 

Therefore, the notification referred to in this paragraph should document 

the agreed corrections. 

Because operators’ ability to comply with the applicable 

operational rules will be dependent on TC holders’ and applicants’ 

compliance with § 25.1805, the FAA will carefully monitor their 

compliance and take appropriate action if they fail to achieve compliance. 

Failure to comply within the specified time would constitute a violation 

of the requirements and may subject the violator to certificate action to 

amend, suspend, or revoke the affected certificate in accordance with 49 

U.S.C. § 44709. In accordance with 49 U.S.C. § 46301, it may also 

subject the violator to a civil penalty of not more than $25,000 per day 

per TC until § 25.1805 is complied with.
11/23/07 AC 25-27

 Appendix E

E-30 

OPERATING REQUIREMENTS 

Part 119 

§ 119.3 Definitions

Maximum payload capacity means: 

(1) For an aircraft for which a maximum zero fuel weight is prescribed in FAA 

technical specifications, the maximum zero fuel weight, less empty weight, less 

all justifiable aircraft equipment, and less the operating load (consisting of 

minimum flightcrew, foods and beverages, and supplies and equipment related 

to foods and beverages, but not including disposable fuel or oil). 

(2) For all other aircraft, the maximum certificated takeoff weight of an aircraft, less 

the empty weight, less all justifiable aircraft equipment, and less the operating 

load (consisting of minimum fuel load, oil, and flightcrew). The allowance for 

the weight of the crew, oil, and fuel is as follows: 

(i) Crew – for each crewmember required by Federal Aviation Regulations – 

(A) For male flight crewmembers – 180 pounds. 

(B) For female flight crewmembers – 140 pounds. 

(C) For male flight attendants – 180 pounds. 

(D) For female flight attendants – 130 pounds 

. 

(E) For flight attendants not identified by gender – 140 pounds. 

(ii) Oil – 350 pounds or the oil capacity as specified on the Type 

Certificate Data Sheet. 

(iii) Fuel – the minimum weight of fuel required by the applicable 

Federal Aviation Regulations for a flight between domestic points 

174 nautical miles apart under VFR weather conditions that does 

not involve extended overwater operations. 
11/23/07 AC 25-27

 Appendix F 

F-1 

APPENDIX F 

BACKGROUND 

Over the years there have been a number of in-flight smoke and fire events where 

contaminants ignited by electrical faults allowed the fire to be sustained and spread. 

The FAA and the National Transportation Safety Board (NTSB) have conducted 

aircraft inspections and found wiring contaminated with items such as dust, dirt, 

metal shavings, lavatory waste water, coffee, soft drinks, and napkins. Sometimes 

wire bundles and surrounding areas have been found to be completely covered with 

dust. 

In recent years Federal government and industry groups have realized that current 

maintenance practices may not be enough to address aging non-structural 

systems. Over time, insulation can crack or breach, thus exposing the conductor. 

While age is not the sole cause of wire degradation, the likelihood of EWIS damage 

from inadequate maintenance, contamination, improper repair, or mechanical 

damage increases over time. Examples include the practice of needling wires to 

test the continuity or voltage, and using a metal wire or rod as a guide to feed new 

wires into an existing bundle. These practices could cause a breach in the wiring 

insulation that can contribute to arcing. 

Research has shown that maintenance work on other aircraft systems can cause 

collateral damage to nearby wiring. Normal maintenance actions, even using 

acceptable methods, techniques, and practices, can, over time, contribute to wire 

degradation. A person inspecting an electrical power center or avionics 

compartment, for example, may inadvertently cause damage to wiring in a nearby 

area. Zones of an airplane subject to a high level of maintenance activity display 

more deterioration of wiring insulation. Undisturbed wiring will have less 

degradation than wiring that is disturbed during maintenance. 

Typical analytical methods used for developing maintenance programs have not 

provided a focus on wiring. As a result, most operators have not adequately 

addressed EWIS deterioration in their programs. We have reviewed current 

inspection philosophies to identify improvements that could lead to a more 

consistent application of inspection requirements, whether for zonal, stand-alone 

GVI, or DET inspections, as they relate to airplane wiring.

We believe it would be valuable to provide guidance on the type of deterioration a 

person performing a GVI, DET, or zonal inspection could expect to discover. 

Though it may be assumed that all operators provide such guidance to their 

affected personnel, it is evident that significant variations exist, and a significant 

enhancement to wiring inspection could be obtained if standardized guidance 

material existed. Achievement of the objectives of this AC is dependent on each 

operator conducting GVI and DET inspections as defined in this document. These 
11/23/07 AC 25-27

 Appendix F 

F-2 

definitions should be incorporated in operators’ training material and in the 

introductory section of maintenance planning documentation. 
11/23/07 AC 25-27

 Appendix G 

G-1 

APPENDIX G 

RELATED REGULATIONS AND DOCUMENTS 

Title 14 Code of Federal Regulations (CFR) parts and specific regulations.

You can download an electronic copy of 14 CFR from the Internet at 

http://www.gpoaccess.gov/cfr/. A paper copy can be ordered by sending a request to 

the U.S. Superintendent of Documents, U.S. Government Printing Office, Washington, 

D.C. 20402-0001, or by calling telephone number (202) 512-1800; or by sending a 

request by facsimile to (202) 512-2250. 

Part 21, Certification Procedures for Products and Parts. 

Special Federal Aviation Regulation No. 88 – Fuel Tank System Fault Tolerance 

Evaluation Requirements 

Part 25, Airworthiness Standards: Transport Category Airplanes. 

Subpart H – Electrical Wiring Interconnection Systems (EWIS) 

Appendix H – Instructions for Continued Airworthiness 

Part 43, Maintenance, Preventive Maintenance, Rebuilding, and Alteration. 

 

§ 43.13 Performance rules (general). 

Part 119, Certification: Air Carriers and Commercial Operators. 

Advisory Circulars (ACs). The following advisory circulars also provide information 

that may support the method of compliance established by this AC. They are stored on 

the Internet in the FAA’s Regulatory & Guidance Library (RGL), a set of searchable 

databases containing regulatory, guidance, and aviation product information. The RGL 

contains certain Federal Aviation Regulations and Special Federal Aviation Regulations 

(SFAR) from 14 CFR in their current versions as well as historical versions. 

You can download an electronic copy of the latest version of the following ACs and 

policy from the FAA Internet at http://rgl.faa.gov. 

• 25-8 Auxiliary Fuel System Installation 

• 25-16 Electrical Fault and Fire Prevention and Protection 

• 25.981-1B Fuel Tank Ignition Source Prevention Guidelines 
11/23/07 AC 25-27

 Appendix G 

G-2 

• 25.1701-1 Certification of Electrical Wiring Interconnection Systems on 

 Transport Category Airplanes 

• 26-1 Part 26, Continued Airworthiness and Safety Improvements. 

• 43-12A Preventive Maintenance 

• 43.13-1B Acceptable Methods, Techniques and Practices— Aircraft 

 Inspection and Repair 

• 43-204 Visual Inspection For Aircraft 

• 43-206 Inspection, Prevention, Control, and Repair of Corrosion on 

 Avionics Equipment 

• 65-15A Airframe & Powerplant Mechanics Airframe Handbook, 

 Chapter 11, Aircraft Electrical Systems 

• 120-XX Incorporation of Electrical Wiring Interconnection System (EWIS) 

 Instructions for Continued Airworthiness into the Operators’ 

 Maintenance Program (AC 120-XX was not yet final at the time this 

 AC was issued. A final AC number for AC 120-XX will be assigned 

 upon issuance.) 

• 120-94 Aircraft Electrical Wiring Systems Training Program 

• 120-16D Air Carrier Maintenance Programs 

• 121.22A Maintenance Review Board Procedures 

Policy and Orders.

• FAA Policy Statement No. ANM112-05-001, “Process for Developing SFAR 

88-related Instructions for Maintenance and Inspection of Fuel Tank 

Systems”(69 FR 60170) 

• FAA Order No. 8110.104, “Responsibilities and Requirements for 

Implementing Part 26 Safety Initiatives” 

Reports.

• “Transport Aircraft Intrusive Inspection Project, (An Analysis Of The Wire 

Installations Of Six Decommissioned Aircraft), Final Report,” The Intrusive 

Inspection Working Group, Aging Transport Systems Rulemaking Advisory 
11/23/07 AC 25-27

 Appendix G 

G-3 

Committee, December 29, 2000. 

http://www.mitrecaasd.org/atsrac/intrusive_inspection.html

• FAA Aging Transport Non-Structural Systems Plan, July 1998. 

(http://www.faa.gov/aircraft/air_cert/design_approvals/transport/Aging_Aircr

aft/media/aging_transport_plan.pdf) 

• National Transportation Safety Board Safety Recommendations A-00-105 

through –108, September 19, 2000. 

(http://www.ntsb.gov/recs/letters/2000/A00_105_108.pdf) 

• Wire System Safety Interagency Working Group, National Science and 

Technology Council Committee on Technology, “Review of Federal 

Programs for Wire System Safety, Final Report” (2000). 

 (http://www.ostp.gov/html/wire_rpt.pdf) 

• Aging Systems Task Force Aging Transport Systems Task 1 & 2 Final 

Report. 

(http://www.mitrecaasd.org/atsrac/final_reports/Task_1&2_Final%20_Augus

t_2000.pdf) 

• Aging Transport Systems Rulemaking Advisory Committee Task 3 Final 

Report. (http://www.mitrecaasd.org/atsrac/final_reports/Task_3_Final.pdf) 

• Aging Transport Systems Rulemaking Advisory Committee Group 4 Final 

Report, Standard Wiring Practices. 

(http://www.mitrecaasd.org/atsrac/final_reports/Task_4_Final_Report_Sept

_2000.pdf) 

• Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) Task 

5 Final Report, Aircraft Wiring Systems Training Curriculum and Lesson 

Plans. 

(http://www.mitrecaasd.org/atsrac/final_reports/Task_5_Final_March_2001

%20.pdf) 

• ATA Specification 117 (Wiring Maintenance Practices/Guidelines). 

(http://www.iasa.com.au/folders/Safety_Issues/Aircraft_Wire/ATAonwiring.h

tml) 

Other Documents. 

• Operator/Manufacturer Scheduled Maintenance Development, Revision 

2001, ATA Maintenance Steering Group (MSG-3). (May be obtained from 

the Air Transport Association of America; Suite 1100, 1301 Pennsylvania 

Ave, NW, Washington, DC 20004-1707.) 

11/23/07 AC 25-27

 Appendix H 

H-1

APPENDIX H 

 EZAP WORKSHEETS FOR USE BY APPLICANTS 
H-1

H-2 

EZAP WORKSHEET 1

Enhanced Zonal Analysis – Details of Zone 

(steps 1 & 2 of Figure 1)

Zone Number: Zone Description:

Comments Hydraulic plumbing

Hydraulic component (valves, actuators, pumps)Pneumatic plumbingPneumatic components (valves, actuators)Electrical wiring – power feeder (high voltage, high amperage)Electrical wiring – motor driven devicesElectrical wiring – instrumentation and monitoringElectrical wiring – data busElectrical componentsPrimary flight control mechanismsSecondary flight control mechanismsEngine control mechanismsFuel system componentsInsulationOxygen system componentsPotable water system componentsWaste water system components

H-2
H-1

H-3 

EZAP WORKSHEET 2 Enhanced Zonal Analysis – Assessment of Zone Attributes (steps 3 – 7 of Figure 1) Zone Number: Zone Description: 6. Define task and interval. List on worksheet 5, Task 

Summary area

NO

YES

4. Are there, or are there likely to be, combustibles in the zone?

NO

YES

5. Is there an effective task to significantly reduce the likelihood of accumulation of combustible materials?

NO

YES

7. Is wiring close to both primary AND back-up hydraulic, mechanical, or electrical flight controls?

NO

YES

3. Does the zonecontain wiring?

No further action is 

necessary

8. Wiring inspection tasks determination.See worksheets 3A and 3B

Continue the analysis

Answers and Explanations

(Notes: Steps 1 & 2 Completed on wo

3.4.5.6.7.
H-1

H-4 
H-1

H-5 

EZAP WORKSHEET 3B – For Programs without Dedicated Zonal Inspection Program (ZIP)

Enhanced Zonal Analysis – Inspection Level Determination Based on zone Size, Density, & Potential Impact of F

(step 8 of Figure 1, refer to Figure 2)

Zone Number: Zone Description:

Size / Density Factor

Potential 

Effects of 

Fire in the 

Zone

Lo

Med

GVI of all wiri

same i

GVI of all wi

at same inte

some wirin

frequent 

GVI of all wiring in zone at 

same interval

GVI of all wiring in zone at 

same interval + GVI of some 

wiring at more frequent 

interval and/or DET of some 

wiring

GVI of all wiring in zone at 

same interval + GVI of some 

wiring at more frequent 

interval

Low

High

Medium

1 2 3

GVI of all wiring in zone at 

same interval

GVI of all wiring in zone at 

same interval + GVI of 

some wiring at more 

frequent interval

GVI of all wiring in zone at 

same interval

Circle appropriate result and answer questions in the boxes below

Inspection Level Determination Based on Potential Effect of Fire in the Zone Density / Zone Size

 Assessment

Zone Size

Density

Low

High

Medium

333

232

Low

High

Medium

Small Medium Large

122

Circle appropriate result & insert below

RESULT

GVI of all wiri

same interval 

wiring at mo

interval and/o

wir

* If answer to Box 1 is “YES,” answer box 2 only and then continue the analysis on Worksheet 4 in order to determine the task interval.If answer to Box 1 is “NO,” answer Boxes 2, 3, & 4

and then continue the analysis on Worksheet 4 in order to determine the task interval.

Answers and Explanations

1243

Some wiring requires GVI at more frequent interval and/or DET inspection

8. Wiring inspection tasks determination.See worksheets 3A and 3B2. List zone description and boundaries for GVI of all EWIS in the zone3. Define specific items/areas in the zone for which GVI at more frequent interval is justified4. Define specific items/areas in the zone for which a DET is justified

YES

NO

1. Is a GVI alone effective for all EWIS in the zone at the same interval?*
H-1

H-6 
H-1

H-7