Oct 3

Why do we need to close Pack switch (affected side), Isolation Valve and APU Bleed Air switch in case of Engine Fire?


Having a look at the system, what I'd say is :

Closing the isolation valve prevents possible smokes or fumes from the affected engine (fire) "getting" into the working one and into pack that, then goes into the cabin and the flight deck as well.

Regarding the APU valve my thought would be the same. Since

I am simple FO so don't take my comment as an answer.