Woof etc;
Can anyone explain to me why it is not feasible for Airbus to build some sort of gross error check for take-off acceleration into the FMS?
You answered the question yourself, with:
for the entered TOW.
GIGO. If the weight(s) are out by a digit, ('2' instead of a '3' in a 375,000kg GTOW), the FMC will rationalize incorrect data as correct. It's already occurred as you know.
Some suggest that the aircraft have a weight/balance system installed using oleo deflection etc - such a system is available (from Airbus, I recall) and, we have read here, was "not reliable".
Also, airlines may not be too keen to have such a system which would be independant of their own load control departments and programs. Keep in mind that most airlines do not weigh baggage and they
never weight passengers, just to avoid the inevitable harrassment/embarrassment lawsuits from passengers if nothing else.
So on any one takeoff, an installed aircraft w/b system would rarely agree with the "official" numbers as transmitted to the aircraft by the airline's load control department.
The question would be, how does one rationalize the discrepancies and which figures "trump" the other figures? In an accident investigation, which data is correct? Why?
Also, for those companies that choose to overload their aircraft, such a system would not be installed or, if mandated, would at least be heavily lobbied against. The business of aviation is about "max lift-min cost", first.
As has been pointed out earlier (Radio altimeter thread), how do you resolve differences between only two systems' data? Would a third data calculation provide a sufficiently robust voting system?