While there seems to be much conversation the cause of "bangs" heard.
How about HP/IP bearing fire, bearing seizure and IP turbine wheel on end of said shaft shearing off could be BANG #1
Bang #2 is when IP turbine disc of huge mass bursts its way out of the turbine case travels upwards and hits the nacelles thankfully overdesigned "firewall" and shatters sending disc segments blades thru the wing, wing to body fairings thru air-conditioning bays, fuselage, fin leading edge etc.
That is the Bangs covered. Much of the gas path theory being discussed with a giant slit in the turbine section to describe the bangs heard is beyond the scope of my experience.
( Please see the above comments with tongue firmly in cheek.)
IP coupling failure. ?? There is an inspection of the IP shaft coupling for wear (trent 900). It is a laborious and tedious task and was being scheduled as per requirements but it is unrelated to this failure.
As regulators they do no more than RUBBER STAMP what the manufacturers tell them. THE DOCUMENTS THEY PRODUCE ARE IMPENETRABLE AND INCORRECT.
They are not independent.
This does look to be the case but who else is qualified with large engine and metallurgical technology, GE or P&W ? I don't think that will happen.
To look at the root cause of this incident, if it were as simple as quality control issue and poor manufacturing of an oil pipe. RR would have said check your engines and if no fault found fly on. But this did not happen.
RR said fly on but don't use (no de-rate) high thrust even thou "high" thrust was NOT being used at time of the incident SIN - SYD.
The Trent 900 was developed for A380 when there was a perfectly acceptable Trent 800 with 110 inch fan producing more thrust than was required of the new T900 116 inch fan.
What was changed in the core engine? Why was it changed? The T900 is heavier, larger and produces less thrust.
IMHO I think I will be seeing a modification program mandated by RR to replace the turbine bearing section with a module that will look incredibly like the same fixture fitted to a T800 to take the stresses of the engine at the top end of the design thrusts.
As someone has already said “As regulators they do no more than RUBBER STAMP what the manufacturers tell them”
A setback or design flaw, I guess it depends if you are an accountant or an engineer.
2 cents