David Ibbotson, the pilot in the plane crash that killed footballer Emiliano Sala, did not have the required licence or permissions to fly commercially.
The Air Accidents Investigation Branch (AAIB) on Friday published its report into the loss of the Piper Malibu aircraft, which crashed over the English Channel on January 21 last year, two days after Sala's move from Nantes to Cardiff City was confirmed.
It found Ibbotson's previous licence for flying that plane had become invalidated in November 2018.
In addition, the aircraft did not have the correct license or permissions to operate.
The body of Sala, who was 28 at the time, was recovered on February 7, 2019. Ibbotson's body has not been found.
A report released in August said Sala had clearly been exposed to carbon monoxide.
And in publishing their final findings, the AAIB wrote: "At 20:16 hrs (local time), probably while manoeuvring to avoid poor weather, the aircraft was lost from radar and struck the sea 22 nautical miles north-north-west of Guernsey.
"Neither the pilot nor aircraft had the required licences or permissions to operate commercially."
The investigation found that Ibbotson lost control during a manually-flown turn, likely initiated to remain in or regain Visual Meteorological Conditions, and that the aircraft subsequently broke up "while manoeuvring at an airspeed significantly in excess of its design manoeuvring speed".
Additionally, the investigation determined that Ibbotson was probably affected by carbon monoxide poisoning.
Furthermore, the report revealed there was no carbon monoxide detector with an active warning to alert Ibbotson to the presence of carbon monoxide in time for him to take mitigating action.
The report also found that: "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 in instrument flying."
