Boeing engine fire on ground and evacuation
 

In the event of an engine fire on the ground, Boeing procedures call for using one fire extinguisher bottle, as this is likely will be more effective than discharging the 2 bottles (though there may be other reasons I'm not aware of). However, the last step in the evacuation checklist states, 'if an engine or APU fire is observed or indicated: rotate the related fire switch to the stop and hold for 1 second.' I interpret this as meaning that if the engine fire is still burning when pax are evacuating, I should discharge the second bottle. But what's the purpose of this step?

I guess it’s a back up to the Boeing procedure which is fire Btl 1, if still burning after 30sec fire Btl 2, if still burning after 20 sec stop the fire drill and initiate the evacuation ck list. Reminder that the APU has its own extinguisher so you now know that everything that can be done has been done.

Discharging the second fire extinguisher bottle is literally the final step in the evacuation checklist, after the evacuation has already been ordered. So again I don’t see whats the point.

You're just trying to save what's left of the aircraft with the 2nd bottle.

Engine fire = engine replacement
Unable to extinguish engine fire = hull loss

Financial difference of a factor 10-15.

Yes, but that goes against what Boeing recommended in Engine fire checklist, which is that discharging two bottles might not be effective and could even reduce the effectiveness of the first one. I mean if the second bottle had a real chance of putting out the fire and prevent an evacuation, why didn’t they include it in the engine fire checklist?

Listen, you’re not stopping an evacuation once it’s started.
Youre using the second bottle as a Hail Mary to save the hull from burning to the ground.
The fire might be dying out already, just residual oil burning or it may still be a raging pit of hell.

Thanks for the respond, but that didn't answer the question. I also didn’t mean “stopping” the evacuation at all. My whole point was about the effectiveness of the second bottle. If Boeing believed that discharging a second bottle would be useful (after the evacuation had already started), then why didn’t they include this step in the engine fire on ground checklist?

I think they mean firing the second bottle immediately after the first is not appropriate.

If the first one hasn't worked then fire the second one.

If evacuation is already in progress, it surely makes more sense to have the step to fire the second bottle in the Evacuation NNC rather than having to go back to the Engine Fire on Ground NNC for that step?

Discharging of the second bottle used to be the memory item (on the 737 at least), but that usually delayed the decision to evacuate the aircraft, while waiting 30 seconds, then discharging the second bottle, then waiting if it had any effect. That is why NTSB recommended that Boeing develops the new checklist, which now redirects you to Evacuation NNC before firing the second bottle, and you fire the second bottle only while people are already jumping down the slides.

Thanks, this makes a lot more sense. The thing is, I read in another thread that Boeing removed the second bottle discharge because it was found to be ineffective and could even interfere with the first bottle, making it less effective. I didn’t realize it was removed due to the delay in the evacuation process. So, Boeing calls for evacuation immediately if the first bottle doesn't put out the fire, even though the second bottle could still do the job. But yeah, I understand we need to expect the worst-case scenario here.