What happened
On 20 May 2019, a Boeing 737-89P, registration SP-LWA, departed London Heathrow Airport for Warsaw Chopin Airport as a commercial passenger flight. During the takeoff roll, the flight crew operated the aircraft based on a load sheet that underestimated the actual weight. While cruising at FL350, the crew received an updated load sheet via ACARS, revealing that the aircraft's zero fuel weight was 953 kg higher than previously indicated, with a corresponding 3% forward shift in the center of gravity. The crew updated the flight management computer, and the flight continued to its destination without further incident.
The investigation
The investigation established that a consignment of mail, weighing 953 kg, had been loaded into hold 2 but was missing from the final load sheet. The error originated in the operator's load management system, where the mail had initially been recorded twice. The dispatcher, noticing the duplication, manually deleted one entry to produce a Loading Instruction Report (LIR). However, shortly after this manual correction, an automated electronic message from the cargo company was processed by the system. This message resulted in the removal of both the manual entry and the original duplicate entry, effectively deleting the mail consignment from the digital records entirely.
When the dispatcher attempted to print the final load sheet, the system displayed an "external input accept/reject" message. Unfamiliar with this specific notification, the dispatcher treated it as a system error and proceeded. Consequently, the dispatcher did not realize the mail weight had been stripped from the final documentation.
Findings
- The aircraft was 953 kg heavier than the load sheet indicated because a mail consignment was omitted from the final calculations.
- The error was caused by a dual removal of cargo data; a manual correction by the dispatcher was followed by an automated electronic update from the cargo company that deleted the remaining entry.
- The dispatcher failed to identify the omission because they did not recognize the significance of the system's warning message regarding external inputs.
- The initial duplicate entry of the mail in the load management system was not the cause of the final omission, though its presence triggered the sequence of corrections.