The KL test flight can only give some partial indications and further prolonged tests will have to be done before any conclusion is reached.
Flying in volcanic ash for 30 mins or 1.5 hour can have opposite effects and results.
The invisble ash is 100% real over our sky: a clear blue sky does not mean anything in volcanic ash terms, you can check your car and you can clearly see the layer of golden dust if you live under the cloud. Up in the air there is a lot more of that fine abrasive invisible material. High atmospheric pressure means the cloud is not moving much, weather did not help at all.
The main worry now remains the duration of this eruption and the neighbour Katla.
The present activity could last several months and, even if winds will change direction and ash emissions will reduce, European air traffic might be intermittently disrupted again for long periods. Frightening.
We must hope that this volcano calms down asap, the biggest danger remains Katla which could activate within 2 years if it follows the historical pattern.
At this stage nobody really knows what is going to happen
Nature is in full charge.