Given the importance of all-up weight, why does it continue to be estimated?
In most cases an estimated weight will be within 1/2 tonne the actual (assuming they operate in a similar fashion to other parts of QLink), and for practicalities sake would have minimal difference on an aircraft of that size.
Ampan's point is that if a self-weighing system existed, it would have challenged the weight that the crew inserted into the FMC. Numerous other very close calls (inc SIA NZ, Emirates MEL) would indicate that such a system would be very helpful in preventing these types of events.