The crew of the Boeing 747 received a provisional load sheet for the flight while they were carrying out their pre-flight checks. The information on the load sheet was close to the crew's expectations. However, when the final load sheet was subsequently delivered to the crew the computed centre of gravity (CoG) had moved forward significantly, from 25% mean aerodynamic chord (MAC) to 16% MAC.
The captain immediately queried the change. The load controller reported that the load computer program was corrupted, and that he had completed the computations using a manual backup method. He added that he was confident the information was correct.
While the aircraft was taxiing, air traffic control advised the crew to contact their company, who reported that the CoG figure stated on the final load sheet was incorrect, and provided a revised CoG figure that was closer to that shown on the provisional load sheet. However, when the crew entered that figure into the flight management computer (FMC) they received a "> STAB GREENBAND" warning from the engine indicating and crew alerting system (EICAS). The warning indicated that the stabiliser trim setting was incorrect for the CoG position, as sensed by the nose landing gear pressure switch, and that the aircraft was therefore "out of trim". The crew discussed the problem with the load controller, without resolution. The captain decided to return the aircraft to the terminal.
The crew requested company engineers to investigate the problem. In addition, they asked the load controller to investigate the distribution of passengers, baggage and freight. Engineers fitted a new nose landing gear pressure switch, and the load controller assured the crew that the computed figures were correct.
The crew again received a "> STAB GREENBAND" message from the EICAS when the aircraft commenced to taxi. After further discussions with company engineers, the aircraft returned to the terminal. The load controller subsequently informed the crew that further investigation had revealed that 50 passengers in "B Zone" had not been considered in the load calculations. The aircraft had therefore been "out of trim".
The operator reported that no fault was found in the load control computer system, and that the error had resulted from the load controller incorrectly interpreting computer generated information.
Local safety action
The operator completed a full audit of its load control operations at each port to identify and rectify any deficiencies.
|Date:||28 April 1999||Investigation status:||Completed|
|Time:||0805 hours EST|
|State:||New South Wales||Occurrence type:||Loading related|
|Release date:||01 November 1999||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Sydney, NSW|