What happened
On 20 May 2019, a Boeing 737-89P, registration SP-LWA, departed London Heathrow Airport for Warsaw Chopin Airport. During the takeoff phase, the flight crew utilized a load sheet that failed to account for a 953 kg consignment of mail located in hold 2. While the initial takeoff was completed without incident, the crew received an updated load sheet via ACARS while cruising at FL3000. This new data revealed that the aircraft's zero fuel weight was 953 kg higher than previously calculated, and the center of gravity had shifted 3% forward. The crew updated the flight management computer, and the flight continued to its destination without further issues.
The investigation
The AAIB investigation focused on how the weight discrepancy occurred. It was established that a consignment of mail had been recorded twice in the operator's load management system. The dispatcher, noticing the duplication, manually deleted one entry to create the 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 duplicate entry and the original entry, effectively deleting the 953 kg of mail from the digital records.
When the dispatcher attempted to print the final load sheet, the system displayed an 'external input accept/reject' notification. Unfamiliar with this specific error message, the dispatcher treated it as a routine system glitch and proceeded. Consequently, the dispatcher did not realize the mail consignment had been omitted from the final documentation, even though the physical cargo had been loaded onto the aircraft.
Findings
- The aircraft was 953 kg heavier than the load sheet indicated.
- A duplicate entry for a mail consignment caused the dispatcher to manually delete one record.
- An automated update from a cargo company subsequently deleted the remaining record for that same mail.
- The dispatcher failed to notice the omission of the mail weight due to an unfamiliar system notification.
- The handling agent's dispatcher was working with a system error message they did not fully understand.