Shell M,
As part of a safety case the Airline will have to provide evidence that the engines are allowed (by the engine manufacturer) to operate in airspace contaminated by ash in the relevent quantities.
The engines being those currently attached to their aircraft.
Further requirements are needed but that is the most relevant to your question and statements.
TO DATE
NO engine manufacturer has given the aproval needed to operate in the red zone - therefore
NO airline can present the case to operate in the red zone.
A safety case requires there to be SAFETY not just words from the oil industry - itself a fine example of safety management
.