Even though this was a diffuse ash cloud, the exposure was long enough and engine temperatureswere high enough that engine hot section blades and vanes were coated and cooling air passages werepartially or completely blocked. The uncooled blades still performed aerodynamically but necessitatedexpensive overhauls. The insidious nature of this encounter and the resulting damage was such thatengine trending did not reveal a problem, yet hot section parts may have begun to fail (through bladeerosion) if flown another 100 hr.
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