An investigation into a fatal helicopter crash off the Shetlands in 2013 revealed the deaths of all four victims.
Sarah Darnley, 45, of Elgin, Duncan Munro, 46, of Bishop Auckland, and George Allison, 57, of Winchester, drowned after the crash.
Gary McCrossan, 59, of Inverness, had climbed on a life raft but was killed by an enlarged heart.
The four passengers were among 18 people who were on board the Super Puma when it crashed.
On the first day of the investigation, it was also learned that the helicopter pilots only noticed their reduced speed when it was too late.
A Minute of Common Understanding at the start of the investigation outlined the sequence of events and loss of life.
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He said the helicopter had descended into Sumburgh, but with a reduction in speed.
When an alert sounded at 300 feet, the captain attempted recovery action, but it was “very likely unrecoverable” and the helicopter struck the water.
Steward at Sea Sarah Darnley and Safety Consultant George Allison were found in the water among the debris.
Post-mortem examinations revealed that their causes of death were drowning.
Production officer Duncan Munro, who also drowned, was found in the submerged fuselage still hitched to his seat.
Welder Gary McCrossan managed to escape to a life raft, but was later seen suffering from chest pain.
Resuscitation efforts were made and he was hoisted onto a helicopter to be brought back to earth, but he could not be saved.
A postmortem examination showed he was suffering from heart disease and the cause of death was an enlarged heart.
The stress caused by the accident was thought to have acted as a trigger for the fatal cardiac event.
The Air Accident Investigation Branch (AAIB) expects Philip Sleight, Deputy Chief Air Accident Inspector, to be the first witness.
He said: “The decreasing speed went unnoticed by the pilots until a very late stage, when the helicopter was in a critical low energy state.
“The captain’s attempt to recover from the situation failed and the helicopter struck the sea surface.
“It quickly filled with water and rolled over, but was kept afloat by the flotation bags that had deployed. “
No helicopter fault
The investigation revealed that the helicopter’s flight instruments were “not monitored effectively” during the final stages of the approach.
This allowed the helicopter to enter a critical low energy state, from which recovery was “not possible”.
There was no evidence of helicopter failure that caused or contributed to the accident.
The investigation had already been delayed due to measures against coronaviruses.
Derek Pyle, Senior Sheriff of Grampian, Highland and Islands, told the FAI’s opening that the investigation was of added importance because it was the first virtual investigative hearing of such a size and of such significance in Scotland, and possibly the UK.
Survivors are among those who should also testify.
The investigation is continuing.