Very, very simple. Erosion and overheat damage to turbine blades and nozzle guide vanes associated with glass clogged cooling holes. Very simple really.
Sunfish
Sorry cannot agree with you that its simple really
You could quite easely have an area marked as below the accepted limits in Ash and have one cloud which is unique and solitary but of a much denser level than the remaining area.
Nothing is constant sadly in our atmosphere.
I can well remember flying a twin to Malaga single pilot with only the owner on board airways at FL120 Near Madrid. Radar gave me help with storm cloud avoidance as did my on board radar. I picked a way between two cells in VMC. The ground temperature was 42 deg C.
As I passed well clear and between the cells I experienced something I had never done in 20+ plus years. The IAS shot from 160 kts IAS to 65 kts IAS in seconds and the aircraft felt as it had flown into a vacuum. No control response, No Pitch response, No increase of speed with power.
The aircraft sank vertically like a towerblock lift for 2000 feet as if in a vacuum and then came alive again.
You simply cannot prove anything in the atmosphere as being constant! ash density or otherwise especially with computer predicted movement. One area may be ok while a few hundred metres and its not.
The best indicator with storms or otherwise is to use your eyes and your instincts and knowledge as relying on aids only whether aircraft based or land based will give you a shock you dont want.
That is why I dont hold with the science but do with pilots and good old see and avoid.The SCIENCE is an aid to the captain not the CAPTAIN and for me thats the whole basis of my arguement with this thread. Listen to the airlines and the pilots and thankfully that message seems to be proving correct.
The same goes with ASH which to date has not harmed anyone in I repeat over 50 years when there were no fancy gizmos to mislead anyone which sadly also now seems proved to be a costly mistake.
Pace