So what evidence does the coroner work with to provide their verdict.
TBH don't know. If the coroner's verdict is so important (and I accept it will be for many people) and it hinges on the AAIB report then surely the simple answer is the coroner waits until the AAIB report is out (or, genuine question: are there reasons in law that cannot be done) ?
I've been around the block enough (amongst other things a witness at two miltary BoIs, one sadly a multiple fatal) to know that despite sentiment accident investigations are rightly things that cannot be rushed if you want the investigation team to reach a considered and objective conclusion. Even in the civvie world for major accidents you rarely see an AAIB report within twelve months, more like 18 months at least for a major accident, so I don't think the AAIB are being particulary slow with this one.