The Padstow speedboat crash which claimed two lives earlier this month could have been averted had the boat's driver used a "kill cord", say investigators.
Nick Milligan, 51, and his daughter Emily, eight, were killed after the entire family of six were thrown from the vessel near Padstow in Cornwall.
The engine continued running and "as the boat circled, it ran over the family in the water a number of times", the initial report by the Marine Accident Investigation Branch concluded.
Milligan's wife Victoria, 39, survived after having her leg amputated below the knee, while their four-year-old son Kit suffered "life-changing" injuries inflicted by the boat's propeller. Two other daughters Amber, 12, and Olivia, 10, escaped with minor injuries after witness Charlie Toogood, 32, jumped onto the boat and cut the engine.
The MAIB said the unnamed driver was not using the vessel's kill cord, which would have cut the engine when they fell. It remains uncertain what caused the boat to flip over on May 5, during the bank holiday weekend.
Victoria Milligan, a yoga teacher, and Kit remain in hospital in London, having been transferred from Derriford Hospital in Plymouth.
Police said the toll would have been "far worse" but for the bravery of watersports instructor Toogood, who risked his life to leap into the runaway boat from his own vessel.
Witnesses watched in horror as the empty craft veered round in circles, turning the water "red with blood".
Simon Lewins, from Wadebridge, said: "We saw a boat coming up the estuary and it seemed to take a right turn. As it took the turn it flopped and the people in the boat went out in the water and then the boat went round in circles and it seemed to come back into the group on three or four occasions.
"We heard screaming and saw seagulls coming into the water. It wasn't good.
"As this happens the boat was taking ever-decreasing circles with nobody in it because they were all in the water and it was slowing and it kept going for ten, 15 minutes."
An interim report highlighted photographs showing the cord still in place, unused, as the boat was being taken away by coastguards.
It should have been attached to the driver's leg as a "dead man's handle" to cut the throttle if the driver was thrown overboard.
Boat owners are not legally required to use the cord, but investigators hope the case will lead to increased use.
Padstow harbourmaster Rob Atkinson suggested the disaster could have been averted if the device had been used.
"Please, please, please, when you have a boat fitted with a kill cord, make sure the kill cord is operating correctly and make sure it is attached to you because if you go out of the boat, it will stop the engine and it will prevent tragedies like this happening," said Atkinson.
Police said the kill cord was a "key focus" of their investigation.
Meanwhile Nick Milligan's brother Max has paid tribute to "an extremely loving father and husband, son and brother, who doted on his family".
Nick Milligan, a co-founder of Channel 5 who went on to become a managing director at Sky TV, had built a beach house at Daymer Bay in Trebetherick, across the estuary from Padstow, several years ago, said his brother.
A statement from the family, from Wandsworth in south London, said: "We are grateful for the continued support of our family and friends and the good wishes we have received from the public."