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.
