Footballer Emiliano Sala and the pilot flying the plane he was in when it crashed into the Channel were probably exposed to “potentially fatal” levels of carbon monoxide, investigators have announced.

Toxicology tests on the Cardiff City footballer found levels of carboxyhaemoglobin – formed in the blood when exposed to carbon monoxide (CO) – above the point doctors consider to be fatal.

Inspectors at the Air Accident Investigations Board (AAIB) said that as the cockpit of the Piper Malibu light aircraft was not separated from the cabin when it crashed in January, it was likely that the pilot, David Ibbotson, would also have been affected.

The report reveals that Sala had CO saturation levels of 58% in his blood. Levels in excess of 50% are “generally considered to be potentially fatal”, doctors said.

The AAIB said the gas can “reduce or inhibit a pilot’s ability to fly an aircraft depending on the level of that exposure”. The body of Ibbotson, from Lincolnshire, has still not been found.

Dave Ibbotson. Photograph: Alan Thompson/Facebook

Lawyers for the Sala family called for the plane to be recovered from the sea for further investigation, saying the carbon monoxide levels “raised many questions”.

Daniel Machover, of Hickman & Rose solicitors, said: “The family believe that detailed technical examination of the plane is necessary. Future air safety rests on knowing as much as possible.”

The symptoms of poisoning by carbon monoxide range from impaired judgment and drowsiness to confusion, blurred vision and loss of coordination, with seizures, unconsciousness and heart attacks likely at the level of exposure recorded in Sala’s blood.

The colourless, odourless gas is produced in high concentrations in piston engine planes, but should be extracted by the exhaust system. Leaks into the heating and ventilation system could bring the gas into the plane cabin.

Although investigators have not published conclusions, the special bulletin issued by the AAIB could explain why the plane carrying Sala fell thousands of feet in seconds after making a 180-degree turn. The pilot had requested a descent minutes earlier after encountering bad weather on the journey from Nantes to Cardiff on 21 January. Previous reports said unconfirmed radar readings showed the plane may have also climbed rapidly before its final descent.

Questions remain around the legal status of the flight and the pilot’s licence to carry Sala.

The Argentinian footballer signed for Cardiff City from French club Nantes for a record £15m on 18 January. The plane crashed 22 miles off Guernsey on 21 January while travelling from Nantes to Cardiff. Sala’s body was found in the wreckage 220ft down on the seabed near the Channel’s most perilous underwater valley, known as Hurd’s Deep.

A Cardiff City spokesperson said: “CCFC is concerned at the AAIB’s latest report, which once again highlights that the aircraft used for Emiliano Sala was not appropriate. We continue to believe that those who were instrumental in arranging its usage are held to account for this tragedy.”

Football agent Willie McKay arranged the flight but said previously he was not involved in choosing the plane or selecting the pilot, and claimed the club had left Sala to organise his own travel. Cardiff City “strongly rejected” the allegation and said they had offered to book a commercial flight for the footballer.

The rear left side of the fuselage found on the seabed of the Channel. Photograph: AAIB/AFP/Getty Images

The body of the 28-year-old Argentinian was recovered in February but that of Ibbotson, 59, has not been found. The wreckage of the fuselage was found on the seabed off Guernsey in the Channel Islands but the aircraft remains underwater after an attempt to recover it was hampered by adverse weather conditions.

Nora Ibbotson, the pilot’s widow, said recovering the aircraft from the seabed could help investigators. But she added: “It’s not going to change my situation, I’ve lost a husband, a father, a grandfather,” she told Sky News. “Nothing can repay that, and change it.”

Sala’s family called for the plane to be salvaged “without delay”, but the AAIB said it would “not add significantly to the investigation” and that it was continuing to investigate operational, technical, organisational and human factors that may have contributed to the accident.

“The reasons for our decision not to recover the aircraft wreckage have been explained in detail to both families concerned,” a spokesperson for the AAIB said. “In February our underwater search operation successfully located the wreckage, recovered the passenger’s body and captured substantial video evidence from the scene using a remotely operated vehicle.

“It was not possible at the time to recover the wreckage. We have carefully considered the feasibility and merits of returning to attempt to recover the wreckage. In this case, we consider that it will not add significantly to the investigation and we will identify the correct safety issues through other means.

“In making our decision, we took into account the high cost of underwater recovery, the evidence we collected in February and the risk that, after a violent impact with the sea, the wreckage would not yield definitive evidence.”

Investigators issued the special bulletin to warn other pilots and operators of small aircraft of the possibility of CO poisoning. Although alarms are not mandatory, the AAIB said pilots should consider buying CO indicators that could alert them to a potentially deadly threat.

A full accident report is not expected to be published until early 2020, and the investigation is ongoing.