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The aircraft type has been the subject of recurring fume incidents throughout its operating life as commented on by the PIC. It has been subject to intense investigations by both operators and the manufacturer. These investigations have resulted in the promulgation of several service information letters, bulletins, airworthiness directives and NOTOP troubleshooting requirements.

Because of this history, the fume events may have become `routine' in the thinking of some operating crew and awareness of the possible risks may have diminished as a result. This familiarity was a concern to the manufacturer as evidenced by the wording in the AOM to the operator. Familiarity may have led the PIC to delay the donning of his oxygen mask. The imperative to ascertain the source of contamination as soon as practicable in accordance with the operator's NOTOP directive may have also influenced the PIC's decision making.

Although the PIC felt that there was no need for him to don his oxygen mask, this action was contrary to the operator's emergency procedures. The completion of the NOTOP diagnostic action should be accomplished after any emergency checklist actions. By choosing to remain exposed to potentially contaminated air, the PIC might have risked degradation of his faculties, which then may have reduced his ability to correctly determine if there was a flight hazard and respond appropriately. This increased exposure may also have long term or cumulative effects that are not yet understood.

If the emergency checklist had been performed first, both pilots should have donned oxygen masks and the subsequent occasional removal of an oxygen mask by one pilot for air sampling would have likely had minimal safety consequences. This is further reinforced by the fact that both pilots experienced some after-effects that required stand down from flight duties even though one, the copilot, had donned an oxygen mask early in the event.

The PIC's request to the FAs and their subsequent actions in opening the flight deck door were contrary to procedures. The smoke/fumes procedures in both cockpit and cabin are safety of flight defences designed to minimise the potential for flight crew incapacitation by isolating the flight deck from cabin hazards. Again the possible perception that fume events are a `routine' part of the environment in which the crews operate may have led both flight and cabin crew to believe that the action was appropriate under the circumstances.

The oxygen bottle used by the cabin crew was fitted with a diluter or therapeutic type mask. This design does not provide protection from smoke or fumes as most of the air mixture provided is ambient air. Under certain circumstances involving heavy contamination by fumes, the use of this type of mask might mislead the user into a false sense of protection and lead to the possibility of being overcome by the fumes. The limited protection afforded by this type of mask should be brought to the attention of cabin crew.

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