G-REDL
See the interim AAIB report is out - reports findings of a "catastrophic main gearbox failure" resulting in the detachment of the main rotor, striking the aircraft resulting as I understand it in the tailrotor also breaking away. I take it (if I interpret it rightly) that means one of the strikes resulted in the rotor slicing through the tailboom.
Truly awful - no wonder they didn't stand a chance.