A TUI flight carrying 187 passengers was forced to abort its journey and return to Manchester after a series of errors left those onboard at risk of passing out due to a lack of oxygen.
The near-disaster occurred last October, but the findings of the Air Accidents Investigation Branch (AAIB) have only just been revealed.
The issue began when engineers left vital safety systems—responsible for pressurising the Boeing 737’s cabin—switched off during routine maintenance. These systems were not reactivated before takeoff, leaving the plane unpressurised.
The AAIB report stated: "Both engine bleed air systems had been inadvertently left off for the departure, so the aircraft failed to pressurise."
Although the crew switched the systems back on during the flight’s ascent, a "master caution" warning was triggered due to a fault with the air conditioning pack. The pilot, working with air traffic control, decided to return to Manchester.
However, the aircraft was overweight, requiring it to remain in a holding pattern over London to burn fuel before landing.
During this period, the crew missed an oxygen mask warning light for 43 minutes, which the AAIB said exposed passengers and crew to "the risk of hypoxia"—a dangerous condition where oxygen levels in the body drop, potentially impairing cognitive functions and decision-making.
The report added: "In this altitude window, the hypoxic exposure can be sufficient to affect cognitive performance and decision-making."
Compounding the issue, the captain had only three hours of sleep after being on-call the night before. The AAIB suggested fatigue may have been a contributing factor, stating: "Fatigue, particularly chronic fatigue, can be insidious such that an individual may not recognise the symptoms in themselves."
Fortunately, the plane landed safely at 8:10am, and no medical issues were reported among passengers or crew.
