A report into the death of footballer Emiliano Sala has found that neither the pilot nor plane had the required licence to operate commercial flights.
Sala died on January 21 last year, when the plane he was travelling in from Nantes in France to Cardiff came down in the English Channel. The body of the pilot, David Ibbotson, has never been found.
At £15m, Sala was Cardiff City's record signing. He had played for Nantes for four years and was the club's star striker, having scored 42 goals in 120 games.
Shortly before the fatal crash, he sent WhatsApp messages to friends, saying he thought the Piper Malibu aircraft was going to fall apart.
Friday's report by the Air Accidents Investigation Branch has found that the pilot, Ibbotson, lost control of the plane during a manually-flown turn, which was more likely to have happened because the flight was "not conducted in accordance with safety standards applicable to commercial operation".
Ibbotson, who was colour blind, had no previous training to fly at night and his SEP rating, which allowed him to fly a single-engine piston aeroplane, had expired three months before the accident.
He was paid for the flight, even though his licence didn't permit it.
Ibbotson had flown the Piper Malibu over to Nantes from Cardiff and had reported various issues, including an oil leak, as well as problems with the brakes and the stall warning system. While those couldn't have contributed to the accident, it is not known whether a reported 'bang' and mist in the cabin on the previous flight may have done.
It is likely that Ibbotson had felt pressure to complete the return leg of the journey at night and in poor weather conditions. But the plane was only allowed for private use and no permission had been sought or granted for it to be used commercially.
After the initial search operation was called off on January 24, Sala's family fundraised, in order to recover his body. A post-mortem examination found harmful levels of carbon monoxide in his system and it was therefore likely that the pilot had also come into contact with the toxic gas too. That would have impacted his ability to control the plane during the later stages of the flight.
While the plane's aircraft maintenance checks were complete, there were no carbon monoxide detectors on board. Friday's report found that the most likely reason the gas entered the cabin was a failure in part of the exhaust's tailpipe.
Before the plane came down, there was a period of erratic flying. As the aircraft made contact with the sea, the tail section broke away, forcing the left wing to come away. It wouldn't have been possible to survive the impact.
Still questions left unanswered for Sala family
While the Sala family were pleased that the report finally came to light, they feel there are still many questions that remain unanswered.
"The Sala family are grateful that the AAIB has finally published their report which contains a large amount of important technical detail about how Emiliano's plane crashed," a statement from Javier Canosa, on behalf of Emiliano Sala's family, read.
"But the report leaves many questions for the inquest to address. It is crucial that the information held by the police and which went into compiling this report now be made available to the coroner and in turn to the family.
"Over a year has passed since Emiliano Sala died. His family remain distraught by their loss but determined to find the full truth of how and why he died, which requires the inquest to be held without delay."
Principal Inspector Brian McDermid said: "The aircraft was extensively damaged and the wreckage was in three parts, held together by electrical and flying control cables. The engine had disconnected from the cockpit area, and the rear section of the fuselage had broken away from the forward section.
"The cockpit area and instrument panel were badly disrupted, such that it would not have been possible with any confidence to determine the position of controls and switches before the crash."
There has been criticism of the Air Accidents Investigation Branch for failing to recover the plane wreckage when it had the opportunity last year. It has since been broken up by fishing trawlers, which means there is a lack of physical evidence to explore.
Cardiff City told Sky Sports News: "We welcome the publication of the AAIB report, an important step in understanding the full facts surrounding this tragedy.
"It is a detailed and technical piece of work which, whilst apportioning no blame or liability, raises a number of questions which we hope will be addressed during the inquest recommencing next week.
"We are determined to read that the CAA is determined to tackle illegal activities by pursuing those involved, it is a practice which must be stopped and we hope the industry will be supported in order to prevent this tragedy happening again."