A TUI plane with 193 people on board failed to pressurise because crew members did not realise a switch had been left off by maintenance workers, forcing the pilots to abort the flight, an investigation has found.
The Boeing 737-8K5 took off from Manchester Airport for Kos, Greece, on 17 October last year, but only got as far as northern Lincolnshire before having to return.
The 193 people on board, six crew and 187 passengers, were at risk of oxygen deprivation after a major error was made by both pilots.
The Air Accidents Investigation Branch found the pilots had failed to spot that switches that controlled the engine air bleed systems had been left off by maintenance workers. The aircraft failed to pressurise and a cabin altitude warning sign turned on.
The warning sign was on for 43 minutes, the report found. The jet returned to Manchester, with no injuries reported, but investigators said that the crew and passengers “were exposed to the risk of hypoxia”.
Hypoxia is low levels of oxygen in the body, which can lead to confusion, difficulty breathing, and eventually people passing out.
While the risk of loss of consciousness was small for the altitude the plane was at when the fault was discovered, it would have been higher if the plane continued to climb.
The lack of oxygen could have contributed to bad decision-making by the crew, investigators found.
According to the report, both pilots had thought that the bleed switch was on before take off, but when the plane passed around 15,000 feet the altitude warning sign came on.
The commander said “it was quickly noticed that both engine bleeds were off, these were placed straight back on and the problem was resolved”. The crew did not don oxygen masks and continued as normal until a fault was noticed with the right air conditioning unit.
The commander then stopped the climb and sought advice from bosses on the ground, with the decision being made to return to Manchester Airport.
The report found that the crew did not complete prescribed drills from a Quick Reaction Handbook in response to the cabin altitude warning.
Neither of the pilots had been originally scheduled to operate the flight, and were both on standby duty starting at 3am that day. The commander was woken up by his phone at 1am with the news that he had been assigned the Manchester to Kos flight.
The co-pilot received a call at 2.30am and they were both told to turn up for work at 4.30am.
