A light aircraft crash near Canons Ashby House was due to engine failure after the pilot performed a steep left turn.
The Air Accidents Investigation Branch (AAIB) has released a report about the crash involving a 1930 Gipsy Moth aircraft, on August 12 this year.
The pilot of the plane was Giles English, the owner of Bremont Watch Company, an award-winning British luxury watch manufacturer whose watches are worn by Tom Cruise, Orlando Bloom and Hugh Laurie.
Mr English and his passenger, an 11-year-old boy later named as Oliver Nuttall, were left with “serious injuries” as a result of the crash.
A report published by the AAIB, following an interview with Mr English, states the engine had been “consistently reliable” and there was no identified reason for it failing.
The report states: “The aircraft was performing a steep turn to the left when the engine stopped.
“It entered a spin and, whilst the pilot was able to recover from the spin, during the subsequent forced landing the aircraft struck a grass bank and was extensively damaged.
The pilot told collision investigators that he believed he avoided a serious head injury because he was wearing a protective helmet.
“He also said he had become involved in discussions with others in the historic aircraft community regarding energy absorbing foam in seat pans to help reduce the level of back injuries in crashes.”
Mr English said he had carried out two medium banked turns and a “gentle” wingover manoeuvre before performing the steep left turn.
A member of the public witnessed the accident and called emergency services who recovered the pair from the wreckage.
Clive Goodwin, who took photographs of the De Havilland-built aircraft before it crashed, said: “We went to Canons Ashby to have a look around and while we were there the plane came across and it came back about 10 minutes’ later and I started to take some photos.
“It went over my head and I turned around and we heard the engine cut out.
“All of a sudden we heard this spluttering noise and it just started to spiral down and it went behind the trees.”
Oliver was taken to Birmingham Children’s Hospital, while Mr English was taken to Walsgrave Hospital, in Coventry.