Aviation Investigation Report A98H0003

2.7.2  Emergency Electrical Load-Shedding

The pilots initially assessed that the smoke was originating from an air conditioning source. Having made this determination, there is no indication that they immediately initiated any checklists. Even if they began immediately with the Smoke/Fumes of Unknown Origin Checklist, it would not likely have affected the fire scenario, as the fire is believed to have been self-propagating by the time the smoke appeared in the cockpit. However, there are circumstances where a rapid de-powering of electrical systems might prevent a fire by removing the ignition source before any combustible materials ignite.

No regulatory requirement exists for transport category aircraft to be designed to allow for a checklist procedure that de-powers all but essential electrical equipment for the purpose of eliminating a potential ignition source. Checklists that are used for electrical load-shedding, such as the MD-11 Smoke/Fumes of Unknown Origin, are intended to isolate a malfunctioning component that is generating smoke or fumes. The associated checklist actions could take up to 30 minutes or more, depending on how early in the checklist procedure the malfunctioning component is deactivated.

No regulatory requirement exists to govern the length of time that checklists designed to deal with odour or smoke events could take to complete. The 20 to 30 minutes typically required to complete the Smoke/Fumes of Unknown Origin Checklist in the MD-11 could allow an electrical malfunction that is generating smoke and increasing heat energy to develop into an ignition source. To be effective in helping prevent the initiation of a fire, a checklist procedure must quickly eliminate the ignition source before a fire has become self-sustaining.

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Date modified :
2012-07-27