What happened
On 21 July 2020, a Boeing 737-8K5, registration G-TAWG, departed Birmingham International Airport for Palma de Mallorca as part of a scheduled passenger service. During the pre-departure phase, the flight crew noted a discrepancy between the flight plan and the load sheet, specifically observing a higher number of children than anticipated. However, the crew proceeded with the flight using the data provided on the load sheet.
Subsequent analysis revealed that the aircraft's actual takeoff mass was 1,244 kg higher than the weight stated on the load sheet. This error meant that the takeoff performance calculations, including required airspeeds and thrust settings, were based on inaccurate data. While the actual thrust required for the flight was marginally lower than the setting used, the discrepancy exceeded the airline's internal limit for last-minute changes without requiring a new load sheet.
The investigation
The investigation focused on the airline's integrated check-in system, which had recently undergone an upgrade. It was discovered that a programming error occurred because the system interpreted the passenger title 'Miss' as denoting a child rather than an adult female. This was due to different linguistic conventions used in the country where the software was developed.
Because the system assigned a standard weight of 35 kg to anyone identified as a child instead of the 69 kg allocated to adult females, the cumulative effect of 38 passengers being misidentified led to the significant mass error. Although the operator had identified the issue on previous flights and implemented manual corrections, a combination of weekend staffing gaps and a software 'fix' being applied to the system on the day before the flight allowed the incorrect weights to persist for the G-TAWG departure.
Findings
- A flaw in the IT system's programming caused the title 'Miss' to be incorrectly categorized as a child.
- The error resulted in the aircraft departing with a takeoff mass 1,244 kg above the weight documented on the load sheet.
- The software upgrade's User Acceptance Testing failed to identify the relationship between passenger titles and weight allocations.
- The weight discrepancy exceeded the 500 kg threshold that should have triggered the production of a new load sheet.