A report has found that David Ibbotson was not licensed to fly the aircraft which crashed into the sea, killing both himself and Emiliano Sala.
Sala, 28, was flying from Nantes in France to Cardiff after signing for Cardiff City, when the Piper Malibu aircraft crashed near Guernsey on January 21 2019.
The report from the Air Accident Investigation Branch (AAIB) said David Ibbotson attempted a manoeuvre at high speed and lost control of the Piper Malibu aircraft, which broke up mid-flight.
It is thought he did so to avoid poor weather conditions which would have affected visibility, and it is likely he had been affected by carbon monoxide (CO) poisoning during the flight.
The report also found Ibbotson was wrongly authorised to fly aircraft at night but there was no evidence found of completing night flying training.
It was also revealed the Yorkshireman was paid a fee for the flight despite only having a private pilot licence which did not permit him to be paid.
The Argentinian striker's body was recovered but Ibbotson has not been found.
A previous toxicology report found Sala had been exposed to harmful levels of carbon monoxide in the cockpit when the plane crashed.
The final report from the AAIB found there was no CO detector on the aircraft and that inspection of the exhaust systems could not rule out the risk of poisoning.
The AAIB investigation identified the following as causal factors that led to the plane crash:
The pilot lost control of the aircraft during a manually-flown turn, which was probably initiated to remain in or regain Visual Meteorological Conditions.
The Aircraft subsequently suffered an in-flight break-up while manoeuvring at an airspeed significantly in excess of its designs manoeuvring speed.
The pilot was probably affected by carbon monoxide (CO) poisoning.
The also identified the several contributory factors:
A loss of control was made more likely because the flight was not conducted in accordance with safety standards applicable to commercial operations. This manifested itself in the flight being operated under Visual Flight rules (VFR) at night in poor weather conditions despite the pilot having no training in night flying and a lack of recent practice instrument training.
In service inspections of exhaust systems do not eliminate the risk of CO poisoning.
There was no CO detector with an active warning in the aircraft which might have alerted the pilot to the presence of CO in time for him to take mitigating action.
The Air Accidents Investigation Branch (AAIB) have released the findings after a 14-month inquiry.