A programming error in the software used by UK airline TUI to check-in passengers led to miscalculated flight loads on three flights last July, a potentially serious safety issue.
The error occurred, according to a report [PDF] released on Thursday by the UK Air Accidents Investigation Branch (AAIB), because the check-in software treated travelers identified as "Miss" in the passenger list as children, and assigned them a weight of 35 kg (~77 lbs) instead of 69 kg (~152 lbs) for an adult.
The AAIB report attributes the error to cultural differences in how the term Miss is understood.
"The system programming was not carried out in the UK, and in the country where it was performed the title Miss was used for a child, and Ms for an adult female, hence the error," the report says.
The Register asked TUI where the system programming was done, but the company ignored that question in its response to our inquiry.
"The health and safety of our customers and crew is always our primary concern," a TUI spokesperson said in an emailed statement. "Following this isolated incident, we corrected a fault identified in our IT system. As stated in the report, the safe operation of the flight was not compromised."
Potentially fatal math
Flight load miscalculations have the potential to affect aircraft handling and to create serious safety issues: the figures are used for figuring out fuel levels, altitude, takeoff thrust, and so on. The 2018 fatal crash of Cubana de Aviación Flight 972, for example, has been attributed to excessive load, as has the 1997 crash of Fine Air Douglas DC-8 cargo flight.
According to the AAIB, the software issue was first spotted on July 10, 2020, when three adult passengers identified as Miss were checked in as children. Airline personnel caught the discrepancy and proceeded to make adjustments manually.
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On July 17, the developer(s) working on the check-in application "adapted a piece of software, which changed the title of any adult female from Miss to Ms automatically."
Alas, the revised code could only convert honorifics for passengers prior to check-in. Bookings made with the title Miss that had already checked in, including those checking in online 24 hours prior to departure, could not be changed.
"On 20 July, 2020, the programmer was making enhancements to the program to improve its performance," the report says. "This should not have stopped the program from working, but as this was a 'fix,' it could not be known for sure. A combination of the [TUI] teams not working over the weekend [to make manual corrections] and the 'online' check-in being open early on Monday 20 July, 24 hours ahead of the flight, meant the incorrectly allocated passenger weights were not corrected."
On 21 July, 2020, three TUI Airways flights departed from the UK with inaccurate load sheets as a result of the software issue, which would not be fixed until July 24, 2020.
The first of these, and the only one detailed in the report, was TUI Airways flight BY-7226, a Boeing 737-800 with the registration G-TAWG. The plane travelled from Birmingham International Airport in the UK to Palma de Mallorca in Spain, carrying 167 passengers and 6 crew.
The 737-800 departed with a takeoff weight that exceeded the load sheet (the projected weight) by 1,244 kg (~2743 lbs) because the load sheet listed 65 children on board, compared to the 29 children expected from the flight plan – which includes the actual weight. The load sheet also varied from the flight plan due to errant baggage weight calculations.
The result of all this was that the plane used less thrust to take off than it should have – 88.3 per cent instead of 88.9 per cent given its actual takeoff weight and environmental conditions. Fortunately, this was "marginally" more than the minimal regulatory requirements – 88.2 per cent – and the flight made it to its destination safely.
It's suggested this won't happen again: "An upgrade of the system producing load sheets was carried out to prevent reoccurrence," the report concludes. ®