A passenger was dragged more than 60ft along a station platform after her hand got stuck between the train doors at Hayes and Harlington.
A Rail Accident Investigation Branch report found that the woman deliberately put her hand between the closing doors believing they would automatically reopen.
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She suffered head, back and hand injuries after being pulled along the platform at the station in West London.
According to the report, the train driver did not identify that the passenger was trapped and the train moved off. After being dragged for about 19 metres, the passenger lost her footing and fell onto the platform.
RAIB concluded that after closing the doors of the train, the driver either did not make a final check that it was safe to depart, or that the check was insufficiently detailed to allow him to identify the trapped passenger.
The driver may have been misled into thinking that it was safe to depart because a door interlock light in his cab had illuminated, indicating that the doors were closed and locked and he was able to take power.