An Easyjet flight from Manchester to Tel Aviv made an emergency landing in Berlin following a suspected carbon monoxide leak which saw members of the crew feeling unwell.
Four passengers were taken to hospital for tests and all 175 passengers and crew were assessed by paramedics at Schonefeld Airport in Germany.
Manchester Evening News reports that an airport spokesman said 20 passengers were placed under "medical supervision" when the plane landed.
The spokesman said: "The Airbus A320 was en route from Manchester to Tel Aviv with 175 passengers and six members of crew on board. A suspicion of carbon monoxide poisoning was not confirmed."
An Easyjet spokesperson told the Daily Mail: "Paramedics who met the aircraft on arrival into Berlin took the decision, as a precaution only, to administer medical checks to everyone on-board. Four passengers received medical checks at the hospital and subsequently returned to the airport."
The spokesman added that the passengers continued their journey to Tel Aviv on another aircraft.
The Federal Flight Accident Investigation Authority is investigating the incident.
Professor Chris van Netten said the monitors could easily detect leaks of carbon monoxide, which is odourless, colourless and highly toxic.
He explained: "Carbon monoxide is a relatively rare event but it's an acute one that can bring an aircraft down.
"When it happens you want to know what is going on because it is incapacitating and you want to be able to flush it out.
"If you can put detectors in the home, why not put them in the aircraft?"
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