Aviation Investigation Report A98H0003
2.4 Aircraft Fire Detection and Suppression
Large transport aircraft are designed according to a standard that requires built-in fire detection and suppression systems only in designated fire zones, such as engines and auxiliary power units, and in potential fire zones, such as lavatories and cargo compartments. That is, only in these areas are risks from the combination of potential ignition sources and flammable materials recognized to co-exist to the extent that detection and suppression systems are required by regulation. Other areas, such as in the hidden areas above the cockpit ceiling and cabin attic space in the MD-11, have been shown to be at risk from fire because they also contain flammable materials and potential ignition sources. The FAA was aware of the existence of flammable materials and potential ignition sources in these areas; however, it assessed the risk of fire as minimal. Current standards do not require these areas to have built-in smoke/fire detection and suppression features. Therefore, detection of smoke or fire in other than designated fire zone and potential fire zone areas is totally reliant on human sensory perception. In areas such as the attic space, normal airflow patterns and highly effective air filtering systems can isolate odours or smoke, and significantly delay their detection.
The MD-11 was not required to have built-in fire suppression features in areas other than the designated fire zones and potential fire zones. Nor was the aircraft required to have access panels or other alternative methods to allow for firefighting in hidden areas. Without built-in fire suppression, or access to currently inaccessible areas by crews to use fire extinguishing equipment, the opportunities to control fires in those areas are limited. Even if the SR 111 crew had known the source of the smoke early in the event, it would have been a significant challenge for them to gain access to the attic area where the fire was underway. By the time the general location of the fire became known in the last few minutes of the flight, it would have been unlikely that they could have accessed the attic area and been able to control or extinguish the fire using the hand-held fire extinguishers. It is unknown whether such an attempt was made.
Initially, the crew was unaware that smoke was present in the hidden areas above the cockpit ceiling and cabin attic space. After the smoke was detected in the cockpit, communications took place between the pilots and the cabin crew. However, there was no recorded mention of smoke having been detected in the cabin at any time before the CVR stopped recording. If smoke had been detected in the cabin area, it is expected that the cabin crew would have relayed this information to the pilots.
Reliance on human detection was inadequate, as the location and extent of the smoke and fire was not discerned by the aircraft crew until the fire was uncontrollable using available firefighting means. The crew members were significantly hampered in their ability to deal with the fire situation owing to the lack of built-in detection and suppression equipment in the area of the fire.
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