@Sunfish:
I should have known, that you would be coming back with that NASA DC8 case. You obviously haven't read the thread thoroughly and certainly not my own post
#2486.
Allow me to post this information again.
Read page 11 of
the report you linked to:
The flight crew noted no change in cockpit readings, no St. Elmo’s fire, no odor or smoke, and no change in engine instruments. They did notice that no stars were visible, but this is typical of flight through high cirrus clouds. After seven minutes the crew noticed that the stars had reappeared, and at about this time the scientists reported that the research instrument readings had returned to normal. There was still no change in engine or airplane instrument readings.
The ash cloud they flew through was so thick that it was able to obscure the stars. I can assure you that such a cloud would have been easily visible, if they had been flying by daylight VMC!!
When the stars reappeared, the readings returned to normal. This would suggest to me that no visible ashes, also means that no significant ash concentrations are likely to be present or even measurable.
So what would I suggest? Restrict flying into the black areas of
the ash concentrations charts to daylight VMC conditions. By "flying VMC" I mean that you can fly through a thin layer of low level stratus or a typical nice-weather cumulus or a thin layer of nicely white cirrus or cirrostratus. Flight through thick layers of nimbostratus would
NOT be wise, as it would be able to obscure otherwise visible ash clouds. And of course any layer of visible ash -so even a slightly discoloured layer- would be an absolute NO-NO!
Furthermore research A/C AND military A/C (with post flight inspections!) should be out there
NOW over the ocean flying in the black areas, to collect
VALID scientific data on flying through measurable ash concentrations. Why? Because, looking at these ash concentration charts it's clear that it's only a matter of time until the whole UK and Western-Europe gets covered again by such a black area. So collect data NOW on flying through these areas. And then if these test flights show evidence of damage, well then so be it. We will then KNOW that there is a risk.
Until proven otherwise I will continue to believe that flying in clear blue skies in invisible ash concentrations will not cause any direct danger to the flight or any severe damage to the airframe and engines.
Conclusion: the challenge is still on: Give us ONE example of an aircraft that had extremely costly damage to the engine, after flying through an ash cloud so thin that it wasn't noticeable to the eye! Just ONE example! PLEASE...!!!
Best regards,
Sabenaboy