It's far too early to tell, but WX has to be the stand-out suspected cause of this tragic event. AF flights can be allocated 10-14 days ahead so it's too far out to assure WX will be suitable for VFR (and sometimes IFR). I've looked at forecasts the day prior to a planned AF flight and if it looked beyond the capacity of myself or my aircraft, it I've rung AF and cancelled. AF will then book them on RPT (providing the patient's origin is serviced by RPT) or reschedule the treatment where possible.