Deano
If I remember correctly the FMS will calculate a ZFW, and will know what fuel you have on board, but it won’t know the Traffic Load, this will be entered in manually. So it was pretty obvious this was loaded in and not crosschecked somehow.
Deano, can I question this in a manner that is made understandable to those on this forum not familiar with aircraft weight and balance, and which is no way meant to question or undermine your professional standing.
My confusion lies in not knowing the onboard system used to calculate the desired weights and I stand to be corrected on my assumptions. This incident does however appear to highlight a failure of automated cross checking.
Unless I am very much mistaken, the three main weights used for aircraft operations are Zero Fuel Weight (ZFW) , Take-Off Weight (TOW) and Landing Weight (LW)
During the manual calculation of loadsheets, the ZFW is derived by taking the Aircraft Prepared for Service Weight (APS – Basically, the weight of the a/c as it stands including catering and any spares carried, but without fuel, passengers, baggage or cargo) and adding to it the Traffic / Payload (passengers, baggage or cargo).
To this you add the fuel weight minus the weight of fuel used for taxying to give you your Take-Off weight.
From this figure you then subtract the Burn-Off (Fuel used during flight) to give the Landing weight
In an automated system, the variables that need to be manually imputed as the weights vary are APS, Traffic/Payload, Fuel and Burn-Off. From these inputs the required three weights can be calculated and displayed
During the incident in question we are told that “The investigation has determined that the pre-flight take-off performance calculations were based on an incorrect take-off weight (262.9 tonnes, instead of 362.9 tonnes) that was inadvertently entered into the take-off performance software on a laptop computer used by the flight crew”. It was the Take-Off weight and not the Traffic Load tnat was a hundred tons less than it should have been, but why was the need to manually input this figure and even more so, how is it possible to do so? Doesn’t the system calculate this figure based on the explanation above.
OK, it was a human error that caused this incident but surely it is a fundamental error that the FMS did not pick it up.
Am I being too simplistic and missing something?
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