IRONCHEFFLAY, Thanks for the information. I undertsand all of that. What my post refers to specifically is the NASA DC-8 incident (occurred druing a 7 minute flight through an unseen volcanic ash cloud of minute particles North of Iceland in 2000.
The result was as you describe, melting of the particles onto the turbine blades and partial blocking of the air holes that maintain the temperatures of the blades wihtin their design profile.
This incident was highly specific and the results were belived to have been caused by the particles being coated in ice, allowing them to get all the way through the engine withoun deterioration until they hit the hot turbine blades. NASA speculated that the specifics of the incidnet added greatly to the very rapid deterioration of the blades.
The engine manufacturer stripped all four engines. They
state in the report that the blades were less than 100 hours from failure.
The most important issue here is that the flight crew and the afterflight did not pick up the contamination in the normal inspection phase. It was only the presence of highly sensitve volcano sniffing kit in the back (as it was a valcano monitoring flight) that alerted them to the fact they had an encounter with ash.
My point on this post, is that believing we can regularly operate in significant ashclouds, and simply expect a redcution in Turbine TBO is naive when considered against the NASA incident.
I have had a turbine jammed (on AS355 - Allsion 250 engine) found during an after flight. The strip report concluded that a manufacturing error had occurred allowing the trubine baldes to creep and contact the shroud. The turbine was 8 hours old. I was lucky that the turbine diod not let go in flight. Tha same result will occur if massive overtemp of the turbine blades is effected in flight.
I think you will agree that if you found a jammed turbine during after flight the conclusion would have to be that the crew were very lucky to complete the last flight without a major problem.
I am not concerned at all flying in the current conditions that the CAA and Governmet have decided are acceptable buit it is not by accident we can only do so provided an increase in monitoring is implemented.