Eli5: why is volcanic ash dangerous to aircraft, and yet they can fly through forest fire smoke?

Question

Thank you!

In: 32

Answer 1

There is a great video on the mentour pilot channel explaining this in more detail

In short, forest smoke are microscopic carbon particles, while volcanic ash are small pieces of stone, kinda like fine sand. When aircraft meets a cloud of volcanic ash, there are multiple dangers it presents. First, it starts sandblasting outside of the aircraft, including windshields, making it milky and foggy, affecting visibility, and external sensors (for example, pitot tubes, which affects air speed measurement). Also, it sandblasts engine blades, which may eventually weaken them, but main danger comes when ash gets into the combustion chamber, melts, and then sticks into engine parts after the combustion chamber solidifying into glass which stalls and damages the engine. When engine stalls, the combustion chamber cools down, and molten rock solidifies inside of it, which makes restarting the engine difficult if not impossible since all moving parts are glued by rock.