Originally Posted by
Machinbird
I think the sarcasm here is a bit harsh. The XL A320 got its stabilizer trim setting in Normal Law (with defective AOA operation). Then at the moment of stall, airflow assymetry caused an ADR problem that dropped them into Direct Law. The aircraft pitched up uncontrollably (without manually running trim down) and finally entered Abnormal Attitude Law when it was too late and the nose too high to recover in the altitude available.
Exactly - and that is why it has precisely nothing to do with a supposed design issue with C* in stall - they were not in C* in stall.
Nor is the trim up a C* or bus issue - it will happen exactly the same on a conventional, depending on AP mode, if speed is allowed to decay. I think XL is closer to G-THOF (a 737, thats how much C* has to do with it) than to AF447 - both crews had difficulty recovering due to being out of trim, both crews omitted to trim, G-THOF ended better only because they reduced thrust to get elevator authority back.
If XL (and G-THOF) illustrate any design flaw it is with underslung engines, not C* - but in my opinion every design decision has compromises, no design is perfect in every scenario, and what it really illustrates is the perils of trying to recover a pitch upset by adding thrust when your thrust line is below COG.