TUI Boeing 737 carrying 187 passengers in 'serious incident' over Humber area, report finds

A TUI passenger plane was in a "serious incident" above the Humber area three days before it had an unrelated "catastrophic failure" while landing at Leeds Bradford Airport, a report has found.

Air Accidents Investigation Branch has now released a report into the North Lincolnshire incident, in which nobody was injured. The Boeing 737-8K5, registered G-TAWD, had taken off from Manchester Airport at 6:06am on October 17 last year carrying six crew and 187 passengers.

Barely six minutes later, there was a cabin altitude warning as the plane flew over North Lincolnshire en route to Kos Airport in Greece. The 'serious incident' report said: "Both engine bleed air systems had been inadvertently left off for the departure, so the aircraft failed to pressurise." They had been left off by engineers following earlier maintenance and not turned on during pre-flight checks.

The crew selected both systems on, continued the climb, and believed the problem was solved. During the climb, the master caution lit up, indicating a fault in the right air conditioning pack. The commander consulted the operator’s maintenance control and agreed the aircraft should return to Manchester Airport.

Because the plane was too heavy for landing, it had to enter a hold to burn fuel and reduce weight. The crew did not complete the prescribed drills specific to them in response to a cabin altitude warning - such as donning oxygen masks - which remained illuminated for 43 minutes.

Describing the risk of hypoxia, the report said: "As the aircraft did not pressurise, the crew and passengers were exposed to the risk of hypoxia. At cabin altitudes above 10,000 ft but below 14,000 ft, without the pre-existence of significant medical issues, the likelihood of loss of consciousness is very small.

"However, in this altitude window, the hypoxic exposure can be sufficient to affect cognitive performance and decision-making to the point where the decline would be observable in cognitive tests. In this range of altitudes there are many variables that affect the severity and impact of hypoxia, including duration of exposure, rate of hypoxia onset (eg rate of climb if no pressurisation), physical workload, fatigue, individual responses and type of task being performed.

"In this range of altitudes it is also difficult to separate the relative contribution of hypoxia versus other performance degraders such as fatigue, distraction or other human performance issues."

The aircraft's climb was interrupted by the air conditioning caution. The report said that, had the aircraft continued to climb, "the aircraft’s passenger oxygen system would have deployed automatically when the cabin altitude reached 14,000 ft".

At 15,800 ft cabin altitude, the pressurisation auto fail master caution would have been triggered. The report added: "As progressive exposure to hypoxia increased, the likelihood of the crew taking correct recovery actions would have decreased."

Neither of the pilots were originally scheduled to operate the service and both were rostered for a standby duty commencing at 3am, according to the report. The commander was awoken by a notification on his smartphone roster app at 1am indicating he had been assigned the Manchester to Kos duty. The co-pilot was notified by a phone call from crewing at 2.30am. Both pilots were given a report time of 4.30am.

The report said the commander only had three hours of sleep the previous night as a result, and "had carried out a significant number of overtime duties" over the previous eight weeks. Although they were not necessarily individually fatiguing, the cumulative disruption may have been a factor, the report stated.

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"Though the commander did not believe fatigue was a factor in this event, the analysis of his roster over the eight weeks preceding the event and the rest period immediately before it suggest that fatigue could still have been a contributory factor. It should be noted that fatigue, particularly chronic fatigue, can be insidious such that an individual may not recognise the symptoms in themselves," it said.

Analysis also showed that the commander’s exposure to 'fatiguing duties' was among the highest across the operator’s B737 fleet and joint highest amongst its commanders at Manchester.

The plane landed safely at Manchester Airport at 8:10am and nobody was injured. Three days later, on October 20, the same aircraft registered G-TAWD left the runway while landing in stormy weather at Leeds Bradford Airport.

An investigation by AAIB found that one of the aircraft’s nosewheel bearings had "suffered a catastrophic failure" during Storm Babet. The aircraft sustained minor damage in that incident and there were no injuries.

TUI was approached for comment.