(Note: Non-777 Dino comments follow. If these upset you, kindly skip down to the next post.)
Nothing's worse than a compartment fire since you can never be sure just how bad it is. We used to get them all the time (cargo fire lights) loading 747 holds on the ground due to dust being stirred up, condensation in the tropics etc. A few times they would recur on the taxi out and we would act very deliberately and slowly, prepare for the possibility that it was real but not evacuate until it went on for some time. As I remember, the door seal height was over 30 feet up in the air for the upper deck and it was common for those using that wicked steep slide to be seriously injured. If the wind was blowing hard like it was with Pan Am in SFO, the slides flip sideways and up into the air, and some of the pax could wind up falling to the ground as in that accident. So evac was not something you rushed into. Ask the cabin crew first if they smell smoke. Ask flights next to you and ATC if they see anything unusual like smoke. (Although this is extremely unlikely to help unless flames are already shooting out somewhere, it eats up the clock (allowing the optical light device to clear), and lets the rest of the airport know you may need assistance.) Call a fire truck first to CYA. At least they can heard the wanderers if it's a false alarm and tape up the broken ankles which are sure to occur if you evac.
On most jets I've operated,
on the ground and pressurized, the Lower holds are part of the "pressure vessel" and exchange some air with the main cabin until you or the aircraft deliberately arm them into a fire/smoke mode which shuts off air flow into or out of these compartments. Now in climb, some gradually squeeze off air flow, as the aircraft differential rises in the climb, but on the ground, doesn't the 777 feed air into the lower compartments and discharge it out the ships main outflow valves? Most jets I've flown do that.
Doesn't this mean that the cabin crew might indeed smell lower hold smoke if a fire is really present downstairs? Some jets, like the 74 and the A300 a crewmember can even access the forward lower hold through the hellhole and you will know for sure (except if it's mid/aft.). So I think, Stay cool; don't rush.
Cargo fire really means particles obscuring the light beam in the detector.
Right?
Livestock charters were particular susceptible to these false alarms because of the breath and commotion of the animals. As I remember, a trick we used was to go to manual and cycle the outflow valves full open to change the airflow around, and if the cargo fire lights went out, and did not re-illuminate once the cabin pressure re-stabilized in auto, we would press on.
This was not part of a checklist. This was technique and systems knowledge.
In flight fires like Saudia are different altogether and mean get the thing on the ground and evac asap. After the Air Canada MD80 lav fire disaster and Halifax, it's clear you can't guess how bad an
inflight fire is, or even rely on the cabin crew's opinion, you must assume it's roaring through the overhead or lower holds unknown to the cabin crew.
At least that's what I think.
CC
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