JohnBurke

No, you might as well do quickly. It's about you retaining consciousness every bit as much as about the fire. The fire is irrelevant if you lose consciousness, and your ability to remain conscious is irrelevant if you don't get pointed toward a diversion location.

Have you ever intentionally shut off all the bleeds or packs at altitude, above FL350 before in a widebody aircraft? It can take a long time to depressurize, even running the outflow valve open. If it remains closed, it can take a longer time.

If you descend to a low altitude and have some distance to go, bearing in mind that in some diversion scenarios you may arrive with previous little time remaining in fuel or survivability, you're going to burn what fuel you've got, reduce your true airspeed, and increase your time to your divert point. There is no value descending to the water immediately if you're going to spend time trouble shooting, analyzing, running checklists, and taking selfies. Either stay at altitude where it can benefit you, or get to the water and ditch. No point going down there "just in case."

Procedure exists for a reason. If it's a "false warning" then it needs to be treated the same as a fire. Dont' guess as to what you've got. Follow the procedure. You have a choice to make; you're going to attempt to extinguish or slow the fire. High or low, you're not going to extinguish a self-oxidizing fire, other than you may be able to cool it or reduce it depending on what's fueling or reacting with the fire. Remember that fire has four points; the fire tetrahedron (often incorrectly taught as the "fire triangle"). Fuel, heat, oxygen, and a chemical reaction. Interrupt or change any of those four, you control the fire, or change its behavior.

The only thing you can do by descending, so far as the fire is concerned, is increase fire behavior; make it more aggressive. Remember that the ignition source may not be what's burning or causing the fire to burn. You may have had a lithium battery start it, but it may be burning in conventional materials; the more it grows the harder it will be to control and the more "exposures" (other matererial and fuels) it will ignite. Second by second, minute by minute. You may or may not be able to terminate the ignition source (which could be en electrical short, hot bleed, or any other number of sources), but you may be able to limit fire spread or reduce fire behavior by depressurizing, remaining in a lower-pressure environment, altering airflow or ventilation, discharging available extinguishing agents, etc.

Your progress toward a diversion field will be much faster at altitude, all things equal, minus a given wind, so long as your true airspeed remains higher, and if fuel is an issue diverting, you're going to burn a lot less of it at FL250 than 050. Correct?

You're going to wait for smoke? You're going to wait until you've sorted all this out before diverting?

At the first indication of fire you need to be diverting. UPS 6 might have been able to make straight for Doha, instead of attempting a return to Dubai. Might have made it. If you've studied the incident, it's horriffic in every respect, but you must know that by descending, you're going to increase fire behavior. You must also know that if you intend to ditch, you're not going to be flying around leisurely at 1,000' looking for a good line to make your run into the water, and certainly not to be running checklists. If you're going to ditch, you're going to be going straight down and getting it in the water quickly, with all checklists completed, everyone briefed on the way down. You might wish to minimize fire spread and behavior until you're committed to that point.

You're certainly not going to descend to 1,000 above the waves, where your fire behavior and growth will be the most aggressive, think about it, trouble shoot it, prepare to ditch, then climb back up to altitude and decide to divert. The decision to divert needed to be on the heels of the fire warning. I don't know if you've ever been on fire in flight. I have, several times, and you have an emergency on your hands, whether it's a light, a failed sensor or detector, or a birthday candle. If you're over the ocean and you've got distance to go to get to a diversion point, you don't have the fuel to be descending to the water, screwing with your four scenarios, picking one, then deciding it was all a misunderstanding before climbing back to altitude...or attempting to divert. Too little, too late. It's a one-shot deal; divert, sort it out on the way, and if you need to ditch, make your rapid emergency descent and do it.

That said, no one can account for every possible scenario or situation, and in your finest hour when there is no one to make the call for you, as a crew you have a decision to make. Fortunately or not, you have the rest of your life to do it.

If you go zipping down to the water to troubleshoot, run checklists, and screw around, you may be the one that just made the clock expire by promoting fire behavior in an unfavorable manner. You may have just cancelled your own check.

Freelance procedures at your peril. Guess and risk guessing wrong. That's a big gamble. Does everyone else on board agree?