A TUI passenger plane encountered a “serious incident” over North Lincolnshire, just three days before it experienced an unrelated “catastrophic failure” at Leeds Bradford Airport. The Air Accidents Investigation Branch disclosed their findings on the first incident, confirming that there were no injuries.
The Boeing 737-8K5, carrying registration G-TAWD, departed from Manchester Airport at 6:06am on October 17 last year with six crew members and 187 passengers bound for Kos Airport in Greece. Merely six minutes into the flight, as the aircraft was travelling above North Lincolnshire, the cabin gave an altitude warning.
According to the ‘serious incident’ report, this eventuated because “Both engine bleed air systems had been inadvertently left off for the departure, so the aircraft failed to pressurise.” Maintenance personnel had neglected to re-engage these systems after previous maintenance work, and they were overlooked during the pre-flight procedures.
The flight crew promptly switched both systems on, continued their ascent, and believed they had rectified the issue. Yet, as the aircraft climbed, the master caution alarm signaled a problem with the right-hand side air conditioning pack, reports Grimsby Live.
After conferring with the operator’s maintenance control, the decision was made to head back to Manchester Airport. Due to the plane’s weight at the time, which was too high for an immediate landing, it had to hold in the air until enough fuel was consumed to lower its weight.
The AAIB report indicated that the crew did not perform all the customary emergency drills in response to a cabin altitude alert—for example, putting on oxygen masks—which remained on for a total of 43 minutes.
The report highlighted the risk of hypoxia, stating: “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 ascent was interrupted by an air conditioning caution. The report indicated that if the aircraft had continued to ascend, “the aircraft’s passenger oxygen system would have deployed automatically when the cabin altitude reached 14,000 ft”. At a cabin altitude of 15,800 ft, the pressurisation auto fail master caution would have been activated.
The report concluded: “As progressive exposure to hypoxia increased, the likelihood of the crew taking correct recovery actions would have decreased.”
Neither of the pilots were initially slated to operate the service, with both rostered for a standby duty starting at 3am, as per the report. The commander was roused by an alert on his smartphone roster app at 1am, indicating he had been assigned the Manchester to Kos duty.
The co-pilot was informed via a phone call from crewing at 2.30am. Both pilots were given a report time of 4.30am.
The report revealed that the commander only managed three hours of sleep the previous night and had undertaken “had carried out a significant number of overtime duties” over the past eight weeks. While these may not have been individually exhausting, the cumulative disruption could have played a part, the report suggested.
“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 stated. Analysis also indicated 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 aircraft touched down safely at Manchester Airport at 8:10am, with no injuries reported. However, three days later, on October 20, the same plane, registered as G-TAWD, veered off the runway while landing in turbulent weather at Leeds Bradford Airport.
An AAIB investigation revealed that one of the aircraft’s nosewheel bearings had “suffered a catastrophic failure” during Storm Babet. The incident resulted in minor damage to the aircraft, but thankfully, no injuries were reported.
TUI was contacted for a statement.