Bear: you probably know most of this, but I am in part thinking aloud in response to your thoughts.
The specificity of the AD's and the focus on Spline wear underscore something I see too in Turbine D's post relative to failChain.
Stub Pipe 6/7 is vulnerable to fracture due poor machining or wear (caused by vibration?).
bear, as I understand it, the proposed defect on that is off center manufacture of what ought to be a concentric counterbore, which means wall thicknes min dimensions are not met for that particular piece. If that is what you mean by poor machining, concur. I find it easy to support your estimation that vibration contributes to premature fatigue failure/ (strain/creep) for that element of the engine's problems. It fits with other acft type I've see have odd problems (nsv causing things elsewhere to break) that beigin with a vibe initiated weakening of a part. Its relationship to the spline's problems will or won't be confirmed, by the time this is all over, if I understand RR's reporting requirements to the FAA/CAA/EASA etcetera.
The engine's are "identical" in design and construction throughout the inventory (900), one assumes the Oiling is consistent?
I don't recall seeing non similar lube on those "family" engines I worked with in the fleet, but that doesn't mean that RR may not have a few tweaks here and therebetween various mods of a given base configuration..
Vibration, assumedly, is not present on Install or early service life, but develops.
Vibration is a part of the flight environment. In my very humble opinion, the state of the art currently allows some predictable or estimatable fatigue (and thus safety factor) calculations to be made by those taking advantage of the decades of work and improvement in vibe analysis and failure analysis. I have no idea what sort of HMS (with vibe sensors in critical points) is built into A380, or if the rotary wing world's lessons on that have fully crossed over into fixed wing. I'd guess that the data would go to something like the ACARS/telemetry system right to the maintenance crews at various bases, so that a change in trend, spike, would trigger at least an inspection, and possibly further maintenance action when the hull arrives on a given sector's terminus. If X line is slightly mismounted or slightly misrouted (used to happen quite a bit in helicopters, which led to some innovative and cheap mitigation) it may pick up a vibe at a freq it isn't designed for.
How RR might, in the wake of this incident, back track that particular vibe/mounting for the tube in question is unclear to me, but I suspect it's in the realm of the possible.
The AD directs inspections of Spline Wear "At the Abutment Face".
Is Spline Wear due lack of Lubrication? Does it make a difference, at this point?
Good question.
People do guess at the cause of important problems, especially when involved in the Industry displaying same. Rolls serves no one, least of all themselves, by being so coy.
They serve themselves in not speaking prematurely, since they cannot ignore the reality of the litigous nature of modern society (global sense) and have to use sound survival skills to remain RR, maker of fine jet engines.
Cross-Type Modularity is a boon ... . , but carries some important pitfalls. snip the rest of that thought.
Concur
Early on, I figured this problem would cost about a Billion dollars. Exclusive of Marque Tarnish. Rolls needs "Marqued" improvement in Disclosure.
bear, I'll take a bit of RR's side on this, and advocate patience for us on the receiving end. They need to be very careful that whatever they say publicly and officially is dead right. They cannot afford to be the least bit careless about official utterances on this very important matter: the health and soundness of their amazing products.
I flew a WW II era designed trainer (T-28) some years ago (Wright Cyclone engine) that had a man-satisfying amount of horsepower at the sea level stop. When you put that throttle full forward, the engine roared that deep throaty bellow of power, and you leapt forward ... you'd better not be miserly with the right rudder application when you did so!
I think of 72,000 lbs of thrust in a Trent 972 and it makes me feel all tingly inside.
Four of them? Tingly squared.