Essentially the issue is a matter of increasing complexity in an already complex system.
The FLEX/RTOW take offs are a means of safely borrowing from safety to increase system efficiency by saving fuel and engine life by only using as much as you need.
This is an effect of added technology, and it introduces a level of coupling such that the outputs in terms of V speeds and flex temperature are not necessarily obviously wrong, as the variables involved make it intractable to get a simple rule of thumb.
I was dismayed by the AAIB suggestion to use EVEN MORE automation and technology.
Ironically some airlines use a simple error trap in the RTOW calculations so that it will spit back an error message on ACARS if the TOW from the pilot is less than the MZFW. In this case it would have worked, as would the previous case in MEL.
As was the case of the BA B744 in JNB, the coupling is very tight on takeoff, so I admire and respect any pilot that can get the aircraft safely off the ground in these conditions.
If is easy to point the finger of blame to the unfortunate pilot who may have contributed the proximal failure in the 'chain of events', but this is a systems accident that has manifested itself repeatedly, and is a function of the system and the relentless trade off of throroughness for efficiency.
Discuss