A passenger jet carrying more than 270 people was forced into a 30,000-feet emergency descent after a failure in cabin pressure, a report has found.
As the chartered flight was travelling from London Stansted to Rzeszow in Poland, it issued a mayday call after alarms went off and emergency oxygen masks dropped into the cabin.
The Titan Air Boeing 767 flight was diverted to land at Amsterdam Schiphol Airport on 19 March 2017. It was established that a faulty positive pressure relief valve (PPRV) was the cause of the problem.
Both the plane's PPRVs had been replaced during maintenance before the flight, but tests found no issues with the new parts. A later examination found "no obvious reason for the malfunction".
The plane's flight recorder found that the seatbeat signs had automatically illuminated around 20 minutes after takeoff from Stansted.
The report by the Air Accidents Investigation Branch into the incident concluded: "The maintenance checks of the replacement valves did not identify the defect with the faulty PPRV.
"The event was a failure to pressurise correctly, rather than a sudden depressurisation and the crew's timely actions in identifying the problem and carrying out the appropriate emergency procedures ensured a safe outcome."
Titan Airways is a British charter airline founded in 1988 and based at Stansted Airport.
The year 2017 was the safest in aviation history, with no deaths from large passenger airliner accidents. There were only 10 fatal air accidents, resulting in the deaths of 44 passengers and 35 people on the ground.