I'm not certain if you're making reference to a LI battery fire specifically or any in-flight fire warning.
Originally Posted by
decrabbitz
All good points. But if you are going to roll the dice/bet your life on the low O2 suppression route, wouldn't it be better to climb as high as you can go (MAX ALT) rather than FL250?
I'm not sure about this. I would suggest getting more information on the system and logic behind it's design. The 777 still maintains some measure of positive differential with a main deck smoke warning and depressurization scenario (25K altitude w/ 23K cabin altitude). I'm not sure if those altitudes were selected ONLY to deal with potential physiological issues with the crew in a depressurized situation or if there are other factors at play. There may be some unintended consequences by attempting to deviate from the QRC procedure. The pack configurations during a main deck smoke event attempt to keep positive pressure to the flight deck and hopefully minimize smoke aft of the flight deck flowing forward. With one pack off and the other in low flow to accomplish this, climbing above what is recommended by the checklist may defeat what the system and checklist have been designed to accomplish. Though, as I said, I'm not certain of that.
To your other points:
Not sure if you're advocating the descent plan with any fire warning or something specifically tied to LI batteries known to be involved. If I am hours away from a suitable field, an off airport landing or ditch decision isn't going to be my starting plan. I would advocate an attempt to gather as much information as possible about the situation before considering those options. The lower cargo compartments are designed to buy some time and have the best chance (IMO) of successfully suppressing a fire while we get to a suitable field. Perhaps the main deck FSS in combination with the "factory" system using depressurizing/airflow control is working as advertised. Maybe the position involved has the fire retardant bags (make a point of asking if you don't - they're used regularly).
Because of the nature of the LI battery threat specifically, I will probably be less likely to rely on our current suppression methods if I'm certain they're involved. Either way, if we can determine the situation is deteriorating or already out of control, I think your plan to head for the deck and prepare for more bad stuff makes some sense.
One other tidbit I recently learned. UPS is fielding ceramic cans that can contain a LI battery fire for 4 hours. As an added bonus, they are significantly lighter than the metal ones we currently use. Next time I come out of SIN with the typical load of 6K+ lbs of LI batteries, I'd sure feel better if they were in those UPS cans.