A preliminary report from the NTSB reveals the helicopter lost power moments after it took off from UC Davis Medical Center.
The surviving flight paramedic told investigators that she noticed the power cut out at just 500 feet above the ground. That's when the chopper's "auto-rotation system" kicked in.
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The report says the helicopter fell for 11 seconds before crashing onto Highway 50.
NTSB investigators found a piece of the rotor embedded in the garage of a home nearby.
The pilot and paramedic survived the crash, but with serious injuries. A nurse, who was also on board, died four days later from her injuries.