Ash happens. How it happens often depends on the type of cooker you're using, how, and the environment around it.
The PBC will "spit" ash up into the barrel when meats that are extremely fatty are cooked and I've had only one problem with a Turkey, one time, easily fixed. Make sure you trim all the big, "flappy" extra skin off the bird. That skin is mostly fat and will do enough sizzling over the coals to cause embers and ash. I trim off everything that isn't actually touching meat. No ash. Great tasting skin.
Stick burners and charcoal smokers will ash up the groceries occasionally in a very windy environment. A "whoosh" in just the place around and into a vent or stack will puff a poof of ash into some place it shouldn't go. Only cure is to either don't cook in the wind or put something up to block it. My old Yoder stick burner hated the wind and would reward me with lots of temperature problems and ash if I didn't shield it some way or another.
Pellet cookers will ash up more often than not when the fire pot is getting full but the cook has been too lazy to clean it out before firing it up. My Memphis doesn't even like to light with any ash already in the pot so it sort of takes care of the problem itself. My Traeger will blow soot at around 300 degrees (roasting temperature) if I haven't scooped it lately.
Barring some motivation (breezes, sizzling grease, or a dirty fire pot) ash will give in to gravity
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