Why close isolation valve and APU bleed air for engine fire?
Closing the isolation &amp; APU bleed valves keeps hot bleed air away from areas near the engine that may have damaged bleed air ducting. Closing the Pack valve causes the other pack to switch to high flow, making up for some of the lost output of the affected-side's pack. The steps are together in the checklist because it's all on the same overhead panel, even though the reasons differ.