The aviation industry, because there seems to have been so little prior investigation of the physical effects of this phenomenon. How can airframe and engine manufacturers have issued documents stating that should be no flight through ash-contaminated airspace with a straight face? Surely that was a prohibition honoured more in the breach than the observance, since a zero concentration of ash is clearly never possible, mathematically or practically, in the atmosphere of a planet whose geology is driven by plate tectonics.
Question above ..... How could XXX have issued documents ....
Be careful of using a lay persons intreprrtation of what these documents for the pilots are intended to convey.
Lets get back to the traffic light anology of
red light clouds,
yellow light clouds ad
green light clouds.
It was postulated based on routine everyday maintenance findings that volcanic ash in clouds exists everyday someplace in the world and that some planes fly through it without impact on the flight. Thus the
Green-light cloud concept.
Then there are the rash of events following a major eruption like Pinatuba where the cloud being unseen and untracked produces any symptoms described in detail in the OEM warnings that should be reacted to by the flight crews and the ground engineers This at least defines the
Yellow clouds that were either not identified and tracked or that there was no intended avoidance. The OEMs thus have a duty to warn that abnormalities may occur in this situation.
And finally the
Red Light cloud that represents the worst of the combinations of either not being tracked or not being avoided and at the same time producing major symptoms in combination of smell, sight, windshield effects, Pitot effects, engine symptoms and an immediate need to throttle back engine descend and turn away.
I believe that what is being dealt with today is the realization that all clouds are not bad and that traffic control and alert pilots can still lead to safe flights.