De Villota lost an eye at Duxford Airfield while testing for Marussia and died a year later, aged 33.
A Health and Safety Executive (HSE) report says De Villota's helmet hit a tail-lift, despite the driver thinking she would miss the lorry.
Last month, the HSE chose not to prosecute Marussia for the crash.
De Villota died from neurological injuries sustained in the crash. Her family said it was considering claiming compensation.
Part of the investigation report was released to the BBC through the Freedom of Information Act after the HSE came to its conclusions.
It said on 3 July 2012 De Villota, daughter of F1 driver Emilio, was carrying out her first straight line test for Marussia at the Cambridgeshire airfield.
After reaching speeds of up to 149mph (240 km/h), the Spaniard's car collided with a support lorry, which had its tail-lift positioned at eye-level, when she was stopping.
The report said it was a standard lorry, which had an "unusual" and "larger" tail-lift than on a normal race trailer.
