Or an invisible ash cloud, for that matter.
I kept on flying through the last 'crisis' because I (correctly, as it turned out) believed that on the evidence available there was no ash cloud along our planned route. Otherwise my machine would have remained in the hangar with the doors firmly shut.
Plenty of pictures available on the internet to show what ash does to a jet engine.
Volcanic Ash Gives Jet Engine a Turbocharge : Discovery News