The Boeing 737-8K5 was flying above North Lincolnshire when the incident occurred in October last year
A TUI passenger aircraft flying from Manchester Airport experienced a “serious incident” mid-flight, just three days prior to suffering an unrelated “catastrophic failure” on landing at Leeds Bradford Airport. Investigation results from the Air Accidents Investigation Branch (AAIB) about the event have been made public.
The Boeing 737-8K5, bearing the registration G-TAWD, had departed from Manchester Airport at 6:06am on October 17 last year, carrying six crew members and 187 passengers bound for Kos Airport in Greece. Just six minutes after takeoff, as the aircraft was over North Lincolnshire, it triggered a cabin altitude warning of a “serious incident” due to a lack of pressurisation. According to the AAIB report, both engine bleed air systems weren’t activated following maintenance, an oversight not caught during pre-flight checks.
Once the issue was identified, the flight crew quickly turned both systems on and continued their ascent, believing the matter resolved. However, new alarms signalled a fault in the right-hand-side air conditioning pack, prompting the captain to reach out to maintenance control and decide on a return to Manchester Airport.
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With the aircraft still overweight for landing, it needed to circle to burn off fuel and lighten the load. 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, reports Hull Live.
The report highlighted the dangers of hypoxia, noting: “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.”
It also mentioned the challenges at certain altitudes: “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.”
The complexity of determining the effects was underlined: “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 interruption in the aircraft’s climb by the air conditioning caution prevented a situation where, had the plane continued to ascend, “the aircraft’s passenger oxygen system would have deployed automatically when the cabin altitude reached 14,000 ft”. At an altitude of 15,800 ft, the pilots would face additional challenges, as the report stated: “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 initially slated to operate the service and both were scheduled for a standby duty starting at 3am, according to the report.
The commander was woken up by a notification on his smartphone roster app at 1am indicating he had been assigned the Manchester to Kos duty. The co-pilot was alerted by a phone call from crewing at 2.30am.
Both pilots were given a report time of 4.30am. The report stated that the commander only managed three hours of sleep the previous night as a result, and “had carried out a significant number of overtime duties” over the past eight weeks. Although they weren’t necessarily individually tiring, the cumulative disruption may have played a part, the report suggested.
It said: “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.”
Analysis also revealed 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 reported injuries. However, on October 20, the same plane, registered G-TAWD, veered off the runway while landing in stormy conditions at Leeds Bradford Airport. An investigation by the AAIB revealed that one of the aircraft’s nosewheel bearings had “suffered a catastrophic failure” during Storm Babet, resulting in minor damage to the plane but no injuries.
TUI was approached for comment by Hull Live.