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maintenance of airplane electrical systems and associated documentation and training.

As part of its effort to ensure the continued airworthiness of aging airplanes (i.e., airplanes built to type designs that are more than 20 years old), the U.S. Federal Aviation Administration (FAA) formed a fact-finding committee in 1998 to evaluate the airplane systems of the aging fleet and propose enhancements to current procedures. The Aging Transport Systems Rulemaking Advisory Committee (ATSRAC), which is composed of representatives from various segments of the aviation industry, is focusing its investigation on airplane wiring. (See “Aging Airplane Systems Investigation,” Aero no. 7, July 1999.) The committee completed its initial tasks in January 2001 and is continuing with plans to implement its recommendations. This article discusses

  1. ATSRAC findings and recommendations.
  2. Implementation of ATSRAC recommendations.
  3. FAA actions.
  4. Enhanced Airworthiness Program for Airplane Systems.
  5. Boeing support.


The initial ATSRAC investigation of aging airplane wiring studied five factors: fleet condition, fleet service history, maintenance criteria, standard practices for wiring, and inspection and repair training. A team of ATSRAC members and industry representatives was assigned to evaluate each parameter. The teams conducted analyses, made conclusions, and recommended follow-up actions, which the ATSRAC then reviewed, approved, and provided to the FAA.

Although none of the teams identified any issue related to the immediate safety of the aging fleet, they did suggest enhancements to existing design, maintenance, and operational procedures for the continued airworthiness of all airplanes.

Fleet condition.
One team reviewed the condition of the aging fleet by conducting a nonintrusive evaluation of the wiring on 81 in-service airplanes and a detailed, intrusive inspection of the wiring removed from six recently retired airline airplanes.

The team found that wiring degradation primarily is not related to the age of the airplane (i.e., the time since manufacture), the environment in which the airplane operates, or the type of wiring. Rather, wiring degradation is influenced significantly by the maintenance and modification performed throughout the life of the airplane. The team also determined that a general visual inspection of the wiring installed on airplanes, which typically is conducted from a distance of a few feet, cannot adequately assess the condition of the wiring. Specific recommendations included an increased emphasis on the periodic removal of accumulated contaminants and clarification of the requirements regarding the spatial separation of wiring for critical airplane systems.

Fleet service history.
A second team reviewed all existing service information applicable to the older airplanes under study. Of the thousands of wiring-related service documents (e.g., service bulletins, service letters, all-operator letters, in-service activity reports) reviewed, 29 service bulletins contained airplane modifications important enough to justify upgrading the service bulletins to alert status. (Boeing releases alert service bulletins to address issues of safety over the life of the fleet.) The FAA has released 26 airworthiness directives (AD) and proposed one AD that mandate incorporation of the modifications (table 1).







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Maintenance criteria.
A third team evaluated the recommended scheduled maintenance activities for older airplanes. Most modern commercial airplanes are delivered with a recommended maintenance plan based on an airplane zonal analysis using the Maintenance Steering Group Level 3 (MSG-3) evaluation process. However, the MSG-3 and previous evaluation processes did not consider the airplane wiring as a specific system. The typical result was that airplane wiring was examined visually when a maintenance technician was in the general area for other reasons.

The team concluded that an enhanced maintenance analysis process was needed to specifically evaluate airplane wiring. This enhanced zonal analysis procedure (EZAP) can be accomplished on all airplanes regardless of whether they have been evaluated previously using the MSG-3 process. (See “Enhanced Zonal Analysis Procedure”)

Standard practices for wiring.
Another team evaluated the documentation concerning wiring repair and maintenance and determined that the information used to inspect, repair, and replace airplane wiring could be improved and made easier to use. The team recommended that all airplane manufacturers adopt a common document format and include the same types of information in new documents so that technicians and engineers can easily use documents from different manufacturers. The team also recommended that existing documents be updated to reflect the revised format and content.

Inspection and repair training.
The fifth team reviewed available programs for training personnel with access to wiring and electrical systems. The team found a need for a training program specific to wiring to ensure that all aviation personnel who are in contact with the airplane are aware of the importance of airplane wiring. The team recommended a training curriculum that is standardized, with content customized to operators’ specific airplane models.







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The teams recommended enhancements to maintenance programs, training programs, airplane documentation, and future airplane design. However, the level of detail and the methods of implementing these enhancements needed further development.

In January 2001, the FAA rechartered the ATSRAC to provide more details on the recommendations and develop implementation plans. Specifically, the FAA asked the ATSRAC to accomplish four tasks by January 2003:

  • Review and consolidate the federal regulations used to certify airplane wiring systems.
  • Standardize the format and content of wiring standard-practices documents.
  • Develop the content and implementation plan for an industrywide common training program.
  • Develop an enhanced zonal maintenance plan.

To accomplish these tasks, the ATSRAC formed four new teams, each cochaired by industry representatives under the authority of the FAA and the European Joint Aviation Authorities. In addition to completing its specified task, each team was asked to produce guidance material in the form of draft advisory circulars (AC) and recommend specific terminology for use in future regulatory mandates.

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The FAA already has taken regulatory action to increase the margin of safety of older airplane models. These actions include issuing ADs regarding airplane modifications (table 1), developing a training program about airplane wiring systems, forming a policy statement on the certification of wiring systems, releasing bulletins on operation specifications and the principal maintenance inspector handbook, and improving rules and communication with worldwide regulatory authorities on service difficulty reports.

The FAA’s long-term plans are to

  • Implement the remaining four ATSRAC tasks.
  • Change maintenance and training requirements under Part 121 of the Federal Aviation Regulations (FAR).
  • Release related ACs and operation specifications.
  • Enhance airplane design requirements as appropriate.
  • Issue requirements and guidelines for the installation of arc-fault circuit breakers that are under development.
  • Establish wire performance requirements.
  • Develop an automated system for reporting service difficulties.
  • Conduct ongoing research and development of maintenance equipment used in the assessment
    of airplane wiring.

Institutionalizing the ATSRAC results and recommendations will require all holders of type certificates and supplemental type certificates to change existing instructions for continued airworthiness. These requirements are expected to apply to all FAR Part 91, 121, 125, 129, and possibly 135 operators. In addition, changes to Part 25 will combine existing wiring design and certification requirements and include any new requirements identified by the ATSRAC. These changes will apply to all new type certificate and supplemental type certificate applications.

The FAA plans to release a special federal aviation regulation (SFAR), based on ATSRAC recommendations, which will mandate the incorporation of an EZAP to enhance airplane maintenance programs. In addition, the FAA plans to update sections of the FARs for private, charter, and domestic commercial operators and foreign commercial operators operating in the United States. These operators will be required to update their maintenance and training documentation to include the noted enhancements. In addition to the SFAR and changes to FAR Parts 91, 121, 125, and 129, related ACs will provide guidance on an acceptable means of compliance.

The FAA expects to begin developing the SFAR changes, the FAR changes, and the accompanying ACs and other guidance material during fourth-quarter 2002. The ATSRAC will review these materials before they are placed on the public docket to help ensure that mandated actions are readily implemented in the fleet. All changes are subject to public review under the Notice of Proposed Rulemaking procedures. Regulation changes, AC releases, and the issuance of operations specifications are expected to continue through 2004.

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The ATSRAC efforts are part of an overarching plan developed by the FAA known as the Enhanced Airworthiness Program for Airplane Systems (EAPAS). The EAPAS outlines the results and recommendations of the ATSRAC and other fact-finding groups and explains how this knowledge will be applied throughout the aviation industry. Although the program has been designed to encourage voluntary compliance, the FAA’s objective of institutionalizing an enhanced and acceptable level of safety requires the use of mandatory requirements. The EAPAS organizes this information and initiates both short-term and long-term implementation actions to enhance the safety of the entire domestic fleet. For this reason, the EAPAS omits specific reference to older airplanes. The program is intended to focus on all airplane systems, with mechanical systems to undergo detailed evaluation after wiring.


Boeing supports the ATSRAC and EAPAS through active participation and the development of both guidance material and programs to comply with expected regulatory mandates.

  • Boeing has developed the EZAP based on the MSG-3 process for older Boeing airplane models. Boeing has applied the EZAP to the 727 and plans to apply it to all in- and out-of-production airplanes.
  • FlightSafety Boeing Training International has developed a wiring training course to meet the expected FAR requirements. The program enables the operator or repair station to tailor the curriculum to the technical expertise of the student and to the specific airplane model. (See “Airplane Wiring Systems Training”)
  • Boeing is revising the Boeing Standard Wiring Practices Manual to add new procedures for cleaning installed wiring, performing a detailed wiring inspection, and protecting wiring during related and unrelated maintenance.
  • In addition to the requirements outlined in the regulatory mandate and the guidance provided by the ACs, Boeing will be available to assist operators in the development and implementation of their enhanced continued airworthiness programs. For example, Boeing will release supplemental guidance material that, although not expected to be regulatory agency approved, will provide information on existing maintenance, training, and inspection programs that are known to have complied with the SFAR. This guidance material also will describe regulatory programs or material not typically distributed worldwide. Operators can use this information to develop their programs.





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The FAA asked industry representatives to review the systems installed on the aging airplane fleet and determine whether changes to existing processes and designs were needed to offset the effects of aging. Investigation of airplane wiring systems indicated that, although no endemic issues related to the immediate safety of the airplanes were identified, safety enhancements could be implemented. These enhancements relate to the design and maintenance of airplane electrical systems and associated documentation and training.

The FAA has developed a program, the EAPAS, to promote voluntary incorporation of these enhancements, charter related reporting and research projects, and provide guidance on the expedited incorporation of the anticipated changes to related federal regulations.

Boeing is actively participating in the EAPAS and is providing the industry with information and entire programs that are expected to comply with the forthcoming changes. In addition, Boeing will assist operators in their efforts to incorporate these changes into their current maintenance and training programs.




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