Air Recommendations – 2001

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Reassessment of the Responses to Aviation Safety Recommendation A01–03

Material Flammability Test Requirements for Aircraft Wiring

Background

On 02 September 1998, Swissair Flight 111, a McDonnell Douglas MD–11 aircraft, departed John F. Kennedy Airport in New York, New York, en route to Geneva, Switzerland. Approximately one hour after take–off, the crew diverted the flight to Halifax, Nova Scotia, because of smoke in the cockpit. While the aircraft was manoeuvring in preparation for landing in Halifax, it struck the water near Peggy's Cove, Nova Scotia, fatally injuring all 229 occupants on board. The investigation revealed that the flight crew had lost control of the aircraft as a result of a fire in the aircraft's ceiling area, forward and aft of the cockpit bulkhead.

On 28 August 2001, the Board released interim safety recommendations as part of its investigation (A98H0003) into this occurrence.

Board Recommendation A01–03 (28 August 2001)

Irrespective of efforts to design, install and maintain an aircraft's wiring system to a high standard, deficiencies with wires will likely persist and present the potential for wire failures. While all wires will arc under certain circumstances, the dynamics of how a particular wire fails during an arcing event is highly dependant on the composition of the wire insulation. Understanding the dynamics of how a wire will fail under realistic conditions would be valuable, given the known consequences of the failure of an energized wire. While the Federal Aviation Administration (FAA) endorses several failure tests (for example, the dry arc tracking test procedure), it does not require any failure tests as a basis for wire certification.

The Board believes that, given the incidence of aircraft wire failures and their role as potential ignition sources, the absence of a certification requirement that measures a wire's failure characteristics, and that specifies performance standards under realistic operating conditions, constitutes a risk. Therefore, the Board recommended that:

A certification test regime be mandated that evaluates aircraft electrical wire failure characteristics under realistic operating conditions and against specified performance criteria, with the goal of mitigating the risk of ignition.

A01–03

Responses to A01–03 (08 November 2001)

In its response of 08 November 2001, Transport Canada (TC) states that it agrees that evaluation of aircraft wiring should be based on realistic operating conditions. The Canadian Airworthiness Manual 525.1357 specifies the protection required against aircraft wiring faults and 525.1351(b) (4) requires the electrical system to be tested to ensure that transients due to electrical faults will not create a fire hazard.

The FAA has advised TC that it concurs with this recommendation and that the FAA has initiated a project to revise the standards for wiring performance and test requirements. The FAA Wire Systems Harmonization Working Group will identify requirements for wire system safety and the assessment methodology will include common mode analysis, safety zonal analysis and specific risk analysis. The FAA is also evaluating the requirement for the installation of arc fault circuit breakers to reduce the chance of ignition from an electrical fault.

TC is also participating in a FAA Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) that has identified a wire system certification requirement as a task to be studied in cooperation with industry and other airworthiness authorities. TC will take action after ATSRAC recommendations are made and an approach is adopted by airworthiness authorities for current operating aircraft and future certification programs.

TC will continue to cooperate in these research activities associated with aircraft electrical wire failure characteristics and will introduce, in harmonization with other airworthiness authorities, the appropriate changes to certification test requirements and standards that are required.

Board Assessment of the Responses to A01–03 (20 March 2002)

In its response of 08 November 2001, TC states that it agrees that evaluation of aircraft wiring should be based on realistic operating conditions. However, TC falls short of endorsing the need for a certification test regime that evaluates aircraft electrical wire failure characteristics. In its response, TC references two sections of the Canadian Airworthiness Manual dealing with requirements for circuit protective devices and "transients" within electrical generating systems. As the recommendation deals with the adequacy of material flammability certification requirements for aircraft wire, it is uncertain why TC is referencing regulations that deal with overload protection.

According to TC, the FAA concurs with the recommendation and has initiated a project, under FAA's Wire Systems Harmonization Working Group, to revise the standards for wiring performance and test requirements. TC also advises that it is participating in the FAA's ATSRAC's task to study a wire system certification requirement. These preliminary actions are considered an appropriate "first step" and the response is considered as Satisfactory Intent.

Next TSB Action (20 March 2002)

TSB Air Branch staff will monitor these deliberations to assess the extent to which their work addresses the safety deficiencies raised in the recommendation.

Response to A01–03 (14 December 2005)

In its update of active recommendations dated 14 December 2005, TC indicated that an update to Recommendation A01–03 was not available due to scheduling conflicts for some Swissair recommendation team members. Furthermore, TC indicated that an update will follow as soon as team members can meet and draft updates.

Board Reassessment of the Response to A01–03 (12 July 2006)

Actions taken by the FAA have focused on re–organizing wiring–related Federal Aviation Regulations (FARs), on 05 February 2002, issuing a "wiring" policy letter, and conducting research and development on material flammability standards for wire insulation. Although TC's activity update of 14 December 2005 did not include any information regarding Recommendation A01–03, it is the Board's understanding that TC remains committed to its 08 November 01 response, which, if fully implemented, will reduce the safety deficiency described in Recommendation A01–03.

Therefore, the assessment remains at Satisfactory Intent.

Next TSB Action (12 July 2006)

TSB staff will liaise with TC to solicit an activity update with respect to the deficiency described in Recommendation A01–03.

Response to A01–03 (07 February 2007)

TC's response advises that it has initiated Canadian–specific rulemaking activities which will disposition into the Canadian regulatory framework the findings of FAA's Aging Transport Systems Rulemaking Advisory Committee. TC states that its rulemaking will include new Design Approval Holder requirements, specifically for type certificate and supplemental type certificate holders. These requirements would reference technical standards to ensure that an acceptable level of safety is maintained for the affected aeroplanes. TC's response does not make reference to any initiative that would mandate a certification test regime for electrical wire as suggested in Recommendation A01–03.

Board Reassessment of the Response to A01–03 (24 July 2007)

Although TC's response outlines its initiative with respect to the Aging Transport Systems Rulemaking Advisory Committee findings; however, the risks remain with respect to the lack a certification test regime for aircraft electrical wire failure characteristics as identified in Recommendation A01–03. The planned action will reduce but not substantially reduce or eliminate the deficiency.

Therefore, the assessment is changed to Satisfactory in Part.

Next TSB Action (24 July 2007)

TSB staff will liaise with TC to seek clarification as to how its rulemaking addresses the deficiency described in Recommendation A01–03.

Response to A01–03 (06 March 2008)

In its response of 6 March 2008, TC reviews the various initiatives undertaken to ensure that aircraft wiring systems are designed, maintained and modified for continuing operational safety. The results of these activities are now being considered for inclusion into the CARs to parallel the FAA's Aging Airplane Program.

Board Reassessment of the Response to A01–03 (13 August 2008)

TC's response outlines its initiative with respect to the CARAC's Ageing Aeroplane Transport Systems Rulemaking Advisory Committee findings; however, the risks remain with respect to the lack of a certification test regime for aircraft electrical wire failure characteristics as identified in Recommendation A01–03. The planned action will reduce but not substantially reduce or eliminate the deficiency.

Therefore, the assessment is changed to Satisfactory in Part.

Next TSB Action (13 August 2008)

TSB Air Branch staff will continue to monitor occurrences reflecting similar type deficiencies upon which this recommendation was based, and to monitor TC's activities to determine whether the proposed regulatory change addresses the deficiency associated with Recommendation A01–03.

Response to A01–03 (15 February 2010)

In its latest response TC states that a Notice of Proposed Amendment 2008–013 effective 11 May 2009 amends Part V – Airworthiness Manual Chapter 525 for transport category aeroplanes. Specifically, these amendments establish a new sub–chapter H – Electrical Wiring Interconnection Systems (EWIS) which provides comprehensive certification requirements including assessment of EWIS failure scenarios and consequential effects to other systems.

Board Reassessment of the Response to A01–03 (28 July 2010)

The proposed amendments to Airworthiness Manual Chapter 525 do not specifically address the lack of a certification test regime for the evaluation of electrical wire failure characteristics as identified in Recommendation A01–03. Additionally, the response contains no definitive indication as to whether or not TC intends any future regulatory change that would require such a test regime. Therefore, the risks remain with respect to the lack of a certification test regime for aircraft electrical wire failure characteristics. The action as stated in the response will reduce but not substantially reduce or eliminate the deficiency.

Therefore, the assessment remains as Satisfactory in Part.

Next TSB Action (28 July 2010)

TSB staff will solicit a definitive statement from TC as to whether or not it plans any further action to address the deficiency identified in Recommendation A01–03.

Transport Canada Response to A01–03 (21 January 2011)

TC's latest update indicates that the completion of rulemaking on EWIS for Design Approval Document Holders is the number two priority on its Aircraft Certification Standards Domestic Regulation agenda. This activity would complete the rulemaking that amended Part V – Airworthiness Manual Chapter 525 for transport category aeroplanes in May 2009 which provided "flammability test requirements for wiring". An NPA is to be presented at the Canadian Aviation Regulation Advisory Council (CARAC) Technical Committee meeting in spring 2012.

Board Reassessment of the Response to A01–03 (09 Mar 2011)

The flammability test requirements in TC's May 2009 amendments to Part V – Airworthiness Manual Chapter 525 appear to refer to flammability standards related to the EWIS itself rather than a certification test regime for the wires. These amendments do not establish a certification requirement that measures a wire's failure characteristics, and specifies performance standards under realistic operating conditions as stated in the preamble to Recommendation A01–03.

Other than to state that its next rulemaking activity will address EWIS requirements for Design Approval Document Holders, no information was provided about the content of the future NPA activity. Consequently, it is impossible to assess whether or not the NPA will mitigate the risks identified in Recommendation A01–03.

The risks remain with respect to the lack of a certification test regime for aircraft electrical wire failure characteristics. The action as stated in the response will reduce but not substantially reduce or eliminate the deficiency.

Therefore, the assessment remains as Satisfactory in Part.

Next TSB Action (09 March 2011)

TSB staff will follow–up with TC to clarify its statement regarding the existence of "flammability test requirements for wiring" in Part V – Airworthiness Manual Chapter 525 for transport category aeroplanes and solicit details regarding its upcoming NPA activity.

Transport Canada's Response to A01–03 (30 September 2011)

"May 2011 Input:
Transport Canada is continuing to pursue completion of the Aging Airplane Program – Continued Airworthiness and Safety Improvement (CASI) which includes completing rulemaking on Electrical Wiring Interconnection Systems (EWIS) for Design Approval Document Holders. Transport Canada plans to present an NPA to the CARAC Technical Committee in 2012.

September 2011 update:
TC to provide clarification to the TSB in regards to the existence of flammability tests TC requires for wiring."

On 28 March 2012, TC submitted an update stating the following:

Continued work is planned for the fiscal year 2012/2013 in order to investigate possibilities to establish a certification test regime that evaluates aircraft electrical wire failure characteristics under realistic operating conditions and against specified performance criteria, with the goal of mitigating the risk of ignition.

Board Assessment of the Response to A01–03 (31 March 2012)

TC has indicated that continued work is planned for the fiscal year 2012/2013 in order to investigate possibilities to establish a certification test regime that evaluates aircraft electrical wire failure characteristics under realistic operating conditions and against specified performance criteria, with the goal of mitigating the risk of ignition.

Therefore, the risks remain with respect to the lack of a certification test regime for aircraft electrical wire failure characteristics. The action as stated in the response will reduce but not substantially reduce or eliminate the deficiency.

The response is considered Satisfactory in Part.

Next TSB Action (31 March 2012)

The TSB will continue to liaise with TC staff to arrange a briefing at the earliest opportunity.

The deficiency file is assigned an Active status.