just as an aside to design, wouldnt it be sensible to have a contained area around the engine where fuel bays must have some form of Fuel tank inerting, in my case with the aircraft type I fly, this is foam.
For those that dont know, military aircraft have been lost due to FVE - Fuel vapour explosion - when large, hot pieces of metal have hit the fuel ullage where vapour naturally forms. The effects typically are catastrophic.
Other point to note is Hydrodynamic Ram effect. With the advent of modern high speed computing and CFD, isnt it time the regulators introduced mandatory protection in the form of baffles to protect from this in the engine area:
Hydrodynamic Ram - BAE Systems
ScienceDirect - International Journal of Impact Engineering : Numerical modelling of the hydrodynamic ram phenomenon
Hell, seeing as this pprune, I will do what all knobheads do and speculate up the jing yang. My uni dissertation background is vibrational analysis of high cycle fatigue components in hot sections of gas turbines. I now fly transport aircraft of the non civilian variety.
It looks like a hot section failure with subsequent disruption to flow causing surging (and the blackening round the cowling).
Its highly unlikely a catastrophic turbine blade failure would cause rupture like that of an entire disk.
Without looking at the cross-section of the disk under a microscope, the exact cause of the disk failure cannot be determined. but, going of previous examples, its not a design issue. Its could be a manufacturing issue, or it could have been something (damage causing propagation) that has been missed on an inspection major. These cracks propagate pretty quickly to pretty slowly. If you know anything about high cycle fatigue, you know it takes millions, potentially hundreds of millions of cycles to generate failure. Unfortunately, gas turbines operate under conditions where they are recieving vaying loading at the rotational frequency and multiples of the rotational frequency also. Then you get harmonics in the components. all you need is harmonic to adjust slightly due to an imbalance, or damage, and the 2 frequenencies interact. You get forcing every time a blade passes through an injector flow, or every time the disk rotates, or every time a blade passes a stator. Its hugely complex and is why gas turbine design often gets delayed. Despite all the CFD, FEA and computational design elements, you can have everything perfect, put the turbine together and then find something else is causing a vibration that requires a complete redesign of a component or a section. Then again, this is all complete speculation and will probably be proved to complete and utter horsesh!t.
How the engine vib sensors didnt get advance warning of this though is beyond me. If there was any single lesson I learned from my dissertation is this: Vibration is one of the best indications of impending engine failure I know.