Transportation Safety Board of Canada / Bureau de la sécurité des transports du Canada
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SR 111 Investigation Report

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4.1.1  MD-11 Wiring Transportation Safety Board of Canada United States National Transportation Safety Board United States Federal Aviation Administration The Boeing Company Swissair Swiss Federal Office for Civil Aviation

Back to the top  Transportation Safety Board of Canada

Aircraft wiring was of immediate and ongoing interest to the investigation team. The team inspected several MD-11 aircraft in order to identify potential areas of arcing or sources of heat generation. These inspections yielded wiring discrepancies that included chafed, cut, and cracked wires. Inconsistencies in wire and wire bundle routing were also discovered, which raised concern about the overall integrity of the MD-11's wiring system. While the investigation team could not establish a direct relationship between the in-service wiring discrepancies and the wires recovered in the Swissair Flight 111 (SR 111) wreckage, the team felt that the data warranted a wider review to better define the risk to the MD-11 fleet. Therefore, on 22 December 1998, the TSB sent an ASA (980031-1) (STI4-1) to the NTSB concerning the MD-11 wiring issues.

Back to the top  United States National Transportation Safety Board

Shortly after receiving the TSB's ASA (980031-1), on 11 January 1999, the NTSB recommended that the FAA require an inspection of all MD-11 aircraft for wiring discrepancies (NTSB Recommendation A-99-3 available at The NTSB recommended that the inspection concentrate in and around the cockpit overhead circuit breaker (CB) panel and the avionics CB panel. The inspection should also include examinations for loose wire connections, inconsistent wire routing, broken bonding wires, small-wire bend radii, and chafed or cracked wire insulation.

Back to the top  United States Federal Aviation Administration

In early 1999, the FAA responded to the NTSB's recommendation by issuing an MD-11 Airworthiness Directive (AD) requiring inspections to determine whether wiring discrepancies exist that could cause electrical arcing. Such arcing could cause a fire or smoke or both in the cockpit or cabin. Based on the results of these inspections, the FAA launched a two-phase MD-11 Wiring Corrective Action Plan. The first phase consisted of three ADs that focused on the areas of concern highlighted in the TSB's safety advisory. Subsequently, the FAA, working closely with Boeing, launched the second phase, which consisted of five Corrective Action Packages, each comprising a series of ADs. Each AD was based on a Boeing-generated MD-11 Service Bulletin (SB). As of 10 May 2002, the MD-11 Wiring Corrective Action Plan had yielded 41 related ADs with additional SBs undergoing Notice of Proposed Rulemaking (NPRM) review.

In a parallel initiative, the FAA used lessons learned from the SR 111 investigation to shape its "Aircraft Wiring Practices" interactive training program for FAA certification engineers, designated engineering representatives, and aviation safety inspectors. In addition, the FAA has produced an Internet-based training aid entitled, "Aircraft Wiring Practices (Job Aid)" (available at

In August 2001, the FAA launched the Enhanced Airworthiness Program for Airplane Systems (EAPAS), designed to address the realities of an aging transport aeroplane fleet. Presently, EAPAS is focused on aging wiring systems. Short-term objectives are those that raise awareness of aging wiring systems, and that implement basic changes to maintenance and training programs. Long-term objectives will concentrate on institutionalizing the management of aging wiring systems.

During the course of this investigation, the FAA requested that the Air Transport Association introduce a new reporting code (sub-chapter 97) to facilitate more accurate tracking of specific wire-related problems and anomalies.

Back to the top  The Boeing Company

In addition to its integral support for the FAA's MD-11 Wiring Corrective Action Plan, Boeing responded to the need for additional technical training with respect to wiring by developing a wiring inspection course for airline and government agencies. Furthermore, these initiatives have resulted in enhancements to Boeing's Standard Wiring Practices Manual.

Back to the top  Swissair

The need to enhance technical training with respect to wiring was also recognized by Swissair. Subsequently, SR Technics revised its technician training syllabus to include such topics as wire cleanliness, handling, protection, and grounding. They have also developed a series of engineering orders to comply with all applicable ADs called for in the FAA's MD-11 Wiring Corrective Action Plan, and have mandated several special inspections related to wiring issues.

Back to the top  Swiss Federal Office for Civil Aviation

As is the practice of the Swiss Federal Office for Civil Aviation (FOCA), all ADs issued by the FAA in relation to the MD-11 wiring issue have been reviewed and reissued as Swiss ADs.

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Updated: 2003-03-27

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