What's this then:
The helicopter manufacturer was provided with a copy
of the recorded flight data for analysis. They concluded
from their analysis that, in the last 30 minutes of flight
prior to impact with the sea, the helicopter had behaved
as expected based on the recorded control inputs, and no
pre-impact malfunction was evident.
This initial analysis also showed that the combination of
the nose-high attitude, low airspeed, high rate of descent
and high power placed the helicopter in a vortex -ring state entry condition (VRS) during the final stages of the flight. The manufacturer’s modelling indicated that, in this condition, the reduced helicopter performance,
together with the limited height available, meant that the
impact with the sea was unavoidable
AAIB Special Bulletin: S7/2013
G-WNSB
EW/C2013/08/03