The most likely cause for deadly levels of carbon monoxide inside the cabin of the plane carrying footballer Emiliano Sala was the faulty exhaust system, an inquest heard.

Brian McDermid, an inspector with the Air Accidents Investigation Branch (AAIB), said there were only two plausible explanations for the build-up of carbon monoxide in the Piper Malibu plan – fire or a damaged exhaust.

He told Dorset Coroner’s Court there was no evidence of a fire in the cabin of the single-engine aircraft prior to the crash and therefore the exhaust system was the likely cause.

Sala, 28, died alongside 59-year-old pilot David Ibbotson when the aircraft crashed into the sea near Guernsey during from a flight from Frances to Wales in January 2019.

The Argentinian striker had just signed for Premier League club Cardiff City in a £15 million transfer from French Ligue One side Nantes.

Mr McDermid said carbon monoxide was odourless and tasteless and piston engine exhaust fumes contained between 5% to 7% carbon monoxide, which can result in death in between one and three minutes.

“We first became aware of carbon monoxide being an issue when we received the toxicology report,” he said.

“At that point we had been looking at a loss of control in flight and flight break up.”

The jury has previously heard toxicological tests on samples of Sala’s blood showed a carbon monoxide blood saturation level of 58%, which a pathologist described as “severe poisoning”.

Explaining how the carbon monoxide could have entered the cabin, Mr McDermind said the Piper Malibu was fitted with an onboard heating system, which drew cold air in from outside.

The air passes through a sealed chamber and is heated by the exhaust gasses as they flow through the system.

Mr McDermid said the most likely cause of the carbon monoxide was from exhaust gasses leaking into the heater muff and into the cabin.

“There is no evidence of a fire, so we believe the carbon monoxide must have come from the engine into the cabin,” he said.

“Our analysis, taking everything into consideration, for the exhaust fumes to get into the fuselage, which leads us to conclude that the most probable way is through the cabin air system.

“It took us a while to get there because we couldn’t find a way of getting the carbon monoxide in.

“I went through the summaries of 190 accident reports, and I could not find anything there referring to problems with carbon monoxide – there was no history for it.

“Since 1984 we have not been able to identity something similar.

“When we looked at all the possibilities this one was the most probable explanation and there must have been significant disruption (to the exhaust system).

“It was on the balance of probabilities we reached the conclusion it was the exhaust muffler.”

He added: “The exhaust system will deteriorate and therefore it is important regular maintenance is carried out to ensure its integrity and to ensure the aircraft remains safe.”

The inquest in Bournemouth heard light aircraft pilots were encouraged to carry carbon monoxide detectors on flights but this was not mandatory.

“One of the problems of carbon monoxide is its odourless and in the cabin you may not be aware of its presence,” Mr McDermid said.

“Which is why we think the use of carbon monoxide detectors in light aircraft should be mandatory – at the moment they are not. Pilots are advised to carry them but it’s not mandatory.”

Later, Mr McDermid told the inquest there was no record of a pressure testing being carried out on the plane’s exhaust system, although there was no legal requirement to do so.

“When the aircraft left that last maintenance check there was no evidence to suggest that the aircraft was not serviceable or fit to do that flight,” he said.

“Something on the way to Nantes – that bang. We tried and talked to a lot of people. What could it possibly be and was it a release of energy that weakened something?

“I would have had an engineer look at the aircraft to find out what the bang was – things just don’t happen for no reason.”