I have flown in Nigeria for many years, and for 6 months of the year, up to about FL100 there is constant Harmattan dust in the air. Sometimes so thick that the visibility can be reduced to 400 M. Yet everyone keeps flying in this dust/sand from the Sahara. Yes, over time it erodes the turbine blades and things, but engines do not stop.
I understand that the BA Aircraft that had all engines stop flew through the thick plume created by the volcano near Indonesia.
So why is invisible ash deemed to be so dangerous?
Volcanic ash is very different from sand:
- Sand usually has a much higher melt point (1300C and up) than volcanic ash (600C). This means that sand goes through a turbine with abrasive effects only, volcanis ash melt and adheres, causing other issues.
- Sand is usually far more "rounded" and worn down grains of material than volcanic ash, which is usually very sharp shards of a glass like substance. Inhaling this can quickly cause respiratory issues.
-A