And, SM, how do you make a safety case based on last year's eruption when this one has a completely different "make up" with different size of ash particles, different concentrations, different weather conditions affecting the spread of the "plume", a specific height limit, etc, etc, etc.
If you are "management" of any kind then you will understand how a "risk assessment" works, how it can only apply to ONE SPECIFIC SET OF CIRCUMSTANCES, and how no airline can manage to get a PROPER "safety case" sorted out in the space of two days when you consider that the input from the engine manufacturers will need longer due to the lack of knowledge they had 24 hours after the volcano farted it's guts out.
NO airline can possibly have a VIABLE "safety case" drafted in 48 hours of an event like this, every eruption is different. To try and say that any airline has a "state of the art safety toolkit" to allow them to "fly safe" in these circumstances (when they didn't actually go anywhere near the ash cloud) is absolute malebovinefaeces.