Only what's been shown on the news over the years - and people working on the oil rigs in the North Sea have to undergo helicopter escape training for just such an occurrence. Helicopters glide down 'relatively' slowly, air liners much faster - and the helicopter passengers are trained and dressed for the possibility.
Here's a list of helicopter crashes into the sea from Wikipedia.
1978 26 June – Sikorsky S-61 LN-OQS of Helikopter Service loses a rotor blade in flight and crashes into the North Sea off Bergen, Norway. All eighteen people on board are killed.
1981 13 August – Westland Wessex G-ASWI of Bristow Helicopters suffers an engine failure and ditches in the North Sea off the coast of Norfolk, United Kingdom. All thirteen people on board are killed.
1983 16 July – Sikorsky S-61 G-BEON of British Airways crashes into the Atlantic Ocean between the coast of Cornwall and the Isles of Scilly. Twenty of the 26 people on board are killed.
1986 6 November – Boeing 234LR Chinook G-BWFC of British International Helicopters suffers a mechanical failure. The aircraft ditches at sea off Sumburgh Airport, Shetland Islands, killing 45 of the 47 people on board.
1997 16 July – Sikorsky S-76A G-BJVX of Bristow Helicopters crashes into the North Sea off the coast of Norfolk following the loss of its rotor head in flight. All eleven people on board are killed
1995 19 January – Aérospatiale AS332 Super Puma G-TIGK, operating Bristow Flight 56C is struck by lightning and ditches in the North Sea off the coast of Aberdeenshire. All eighteen people on board survive.
1997 8 September – Eurocopter AS332L Super Puma LN-OPG operating Helikopter Service Flight 451 suffers a mechanical failure and crashed into the Norwegian Sea. All twelve people on board are killed.
2002 16 July – Sikorsky S-76A G-BJVX of Bristow Helicopters crashes into the North Sea off the coast of Norfolk following the loss of its rotor head in flight. All eleven people on board are killed.
2009 17 January – A Eurocopter AS 532 of the French Navy crashes shortly after take-off from the amphibious assault ship Foudre off the coast of Gabon. Eight of the ten people on board are killed.
2009 12 March – Sikorsky S-92 C-GZCH, operating Cougar Helicopters Flight 91, suffers a mechanical failure and ditches in the Atlantic Ocean off the coast of Newfoundland, Canada. Seventeen of the eighteen people on board are killed
2009 1 April – Eurocopter AS332L2 Super Puma Mk 2 G-REDL of Bond Offshore Helicopters suffers a mechanical failure and crashes into the North Sea off the coast of Aberdeenshire. All sixteen people on board are killed.
2013 23 August – A CHC Eurocopter AS332 Super Puma Mk 2 crashed into the sea 2 nm from Sumburgh in the Shetland Islands, Scotland while en route from Borgsten Dolphin oil platform. The accident killed four of the passengers; 12 other passengers and two crew were rescued.
2017 14 March – A Sikorsky S-92
crashed off
County Mayo on
Ireland′s west coast. All four crew members on board died.
In 13 helicopter in to the sea crashes spaning 400 years, 175 died, 43 lived. Not very good statistics.
