Pilot fatigue, bad judgment calls and a lack of oversight by aviation chiefs in Spain were among a string of failings which led to Ireland's worst plane disaster in 50 years.
Air accident inspectors identified nine significant issues which contributed to a twin engine turboprop aircraft crashing in dense fog at Cork Airport killing six people three years ago.
A final report on the accident said pilots - Spanish commander Jordi Gola Lopez, 31, and co-pilot Andrew Cantle, 27, from Sunderland - lost control of the plane as they aborted landing and attempted a third go-around too close to the ground.
A wing of the Fairchild Metroliner clipped the runway as the pilots poured on the power to gain height - the 18-seater plane flipped over and skidded for nearly 200m.
Six people survived, four of whom were seriously injured.
Isle of Man based virtual airline Manx2 sold the tickets for the service.
Ireland's Air Accident Investigation Unit (AAIU) said there was inadequate oversight of the remote service by operator Flightline and by the Agencia Estatal de Seguridad Aerea (AESA), the Spanish civil aviation authority.
"Systemic deficiencies at the operational, organisational and regulatory levels were also identified by the Investigation," it said.
"Such deficiencies included pilot training, scheduling of flight crews, maintenance and inadequate oversight of the operation by the operator (Flightline) and the state of registration (Spain)."
The AAIU said it was not about pointing the finger of blame but that the pilots' training was incomplete, they should not have been paired up and they were both tired.
Mr Lopex had taken his first flight as commander four days before the crash and Mr Cantle was only on the plane because he had swapped shifts with a colleague.
The inquiry found they gave inadequate consideration to the weather in Cork and two alternative airports should have been named in a back-up plan.
The AAIU said Mr Lopez did not get enough rest before taking command of the flight and Mr Cantle was in breach of flight and duty time limitations two days before the crash.
"It is likely that the Commander and particularly the Co-pilot, who had hand flown three raw data approaches, were suffering from fatigue and tiredness at the time of the accident," investigators said.
Manx2, which ceased trading in December 2012 and is in liquidation, said the crew bear responsibility for the crash.
"Unfortunately, the report is clear that the prime causes of the accident were decisions made by the Flightline crew in adverse weather conditions, compounded by inappropriate crew rostering by the operator and a significant lack of oversight by the Spanish air safety authority," a spokeswoman for the company said in a statement.
The AAIU said Manx2 was acting purely like a marketing agent even though it told pilots to wear its branding on uniforms and other livery and insisted it is not liable under aviation regulations.
Mr Lopez died alongside Mr Cantle in the cockpit.
Four passengers were killed - Brendan McAleese, 39, from Co Tyrone; Pat Cullinan, 45, a partner in accountancy firm KPMG in Belfast; Captain Michael Evans, 51, deputy harbour master in Belfast; and Richard Noble, a 49-year-old businessman who was originally from Yorkshire but lived in Northern Ireland.
Mr Cantle's family are taking legal action against Flightline, which was granted the Air Operator Certificate to run the service, and Airlada, which leased the crew and plane.
Claims against companies involved in the operation by some of the families of those who died and the survivors have been settled confidentially, lawyers said.
Legal action is being taken in Chicago over alleged defects in the aircraft and its components.
Investigators found uneven power distribution from the two engines. A defective sensor was found in engine no. 2 which could have caused abnormal fuel scheduling and power delivery or a torque split.
Law firm Stewarts Law, which represents the majority of families of the four dead passengers and six survivors, said the legality of the arrangements for the flight raised serious safety concerns.
James Healy-Pratt, head of aviation and travel at the firm, said the AAIU report had uncovered a "low cost, low safety" airline operation.
"The pilots ran three red stop lights in poor weather, with tragic results," he said.
"Needless lives were lost, and others seriously injured, in what was a preventable accident."
During the investigation Spanish aviation chiefs told the AAIU they did not know who owned the plane or the connection between Manx2 and the owners.
AAIU said it had considerable difficulty establishing pilot rosters in the days running up to the crash.
On the flight itself it said the approach continued in conditions of poor visibility, below required limits, that the descent continued below the decision height without adequate visual reference and that there was unco-ordinated operation of engine controls when a go-around was attempted.
Cockpit recorders showed Mr Lopez took the power levers seconds before the crash leading to a lack of co-ordination at a critical point.
Eleven safety recommendations have been made by the AAIU.
The European Commission has been asked to review rules on flight time limitations, the role of ticket sellers and the oversight of safety and operating licences.
Recommendations have been made to the European Aviation Safety Agency on the number of successive instrument approaches that can be made in certain weather, how pilots can be appointed commander and how Air Operator Certificate (AOC) variations are granted.
Flightline has been asked to review its operational policy and training and also its rules for pilots on diversions following a missed landing approach.
Spanish aviation authorities have been asked to review oversight of carriers.
The International Civil Aviation Organization has also been asked to look at regulations around the inclusion of the approach capability of aircraft/flight crew on flight plans.
In a statement investigators said: "The AAIU recognises that this is a difficult time for those families who lost loved ones and the surviving passengers who suffered injuries in this tragic accident. Our deepest sympathies to all concerned."