CNN
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A flight packed with vacationers had to be aborted in midair because a technical mistake meant the aircraft failed to pressurize.
An official report into the incident last year found that the 193 people on board the Tui Airways flight from Manchester Airport in the United Kingdom to Kos in Greece “were exposed to the risk of hypoxia.”
A cabin altitude warning was activated in the Boeing 737-8K5 on October 17, 2023 as the plane flew over Lincolnshire in eastern England.
The plane returned to Manchester and there were no injuries but the report from the Air Accidents Investigation Branch (AAIB) said that those on board were likely to have been at risk of dropping oxygen levels during the incident.
The investigation revealed that switches that regulate the air pressure inside the plane, known as bleed air switches, were turned off during maintenance work carried out on the air conditioning system before takeoff. This error was not picked up by the crew in their pre-flight safety measures.
One of the engineers who carried out the maintenance work on the plane told investigators that he believed the switches had been “returned to their original position” after checks on the jet’s air conditioning system. A second engineer failed to spot that they were, in fact, in the off position.
The oversight was also not detected by the pilots, either before takeoff or during “after takeoff checks,” the report found.
Once the error emerged, the pilots turned the switches back on but the report found that the crew failed to take other actions set out in the Quick Reaction Handbook (QRH) in response to the warning. These would have included donning oxygen masks.
The report suggested the pilots thought that turning the switches on was sufficient to correct the issue and that other measures would have been “disproportionate.”
“However, donning the oxygen masks as an immediate action would have given both pilots immediate protection from any hypoxia risk and allowed them to clarify the situation with the highest risk removed,” the report said.
Once the switches were turned back on the plane continued to climb, but the warning sign remained on for 43 minutes before action was taken to stop and consult with the Tui maintenance team at Manchester Airport, the report stated. The captain then made the decision to return to Manchester.
Cerebral hypoxia – which is when the brain is deprived of oxygen – can happen if a plane reaches too high an altitude or if there is a loss of cabin pressure. It can also be the result of carbon monoxide poisoning or breathing in too much smoke from a fire.
Every pilot’s reaction to hypoxia is different, according to the Federal Aviation Administration. But is extremely hard for a person to tell when it is happening to them because the onset of symptoms is subtle.
CNN reached out to Tui for comment.
CNN’s Jen Christensen contributed to this report.