In its final report into the incident, the National Transportation Safety Board (NTSB) in the US concluded tailwinds, potential downdrafts and turbulence were the probable cause of the loss of control of the aircraft.The "most significant factor" affecting survival of those on board the helicopter was the post-crash fire, according to the findings.
The aircraft was "not equipped, nor was it required to be equipped, with a crash-resistant fuel system".
After the crash, the helicopter company announced that it would fit crash-resistant tanks to its fleet.
https://www.bbc.com/news/uk-england-sussex-55674015