Whilst the causes of this have yet to be established, there is an interesting article in Flyer this month from Brian Lecomber in which he also talks about single engine IFR operation.
I probably wont be popular in this forum saying this but I do worry about single engine IFR operation - it doesnt matter in my book whether you have an expensive turbine or piston they do go wrong and normally at the most inappropriate times (I have had failures with both) and in my view some the weather in europe just isnt good enough for long term safe single engine operation particularly with aircraft that can take a considerable number of PAX like the PC-12 (not in this case but in Montana a PC-12 crash killed 14 - half children).
I know that I am also going to upset the Cirrus, Meridian etc etc guys but I personally do have serious concerns over this even if it may be unfashionable to mention it.
My sympathies to the families