An initial report by the Marine Accident Investigation Branch has said a kill cord, designed to stop the boat if the driver went overboard, was not being worn at the time of the accident that killed a father and daughter in Padstow.
Sky television executive Nick Milligan and his eight-year-old daughter Emily died in the incident on May 5, while while his wife, Victoria, and their four-year-old son, Kit, suffered "life-changing" leg injuries.
The initial report said: "At this early stage in the investigation, the mechanism that led to the family being ejected from the RHIB into the water, is not clear.
"The RHIB was fitted with a kill cord but this was not attached to the driver at the time of the accident. Consequently, when the driver was ejected from the boat, the kill cord did not operate to stop the engine and the RHIB continued to circle out of control, and at speed.
"As the RHIB circled, it ran over the family in the water a number of times, leading to the deaths and injuries. A few minutes later a local boatman was able to board the RHIB and bring it under control before further people were hurt."
The MAIB is carrying out an investigation into the ejection of the family of six from a RHIB and will publish a full report on completion of the investigation.
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