It's not uncommon for a new engine to have problems like this during a teething period. There are always going to be issues that need to be fixed, but the last Airworthiness Directive issued on the Trent 900 required immediate compliance. An Airworthiness Directive is an order to fix aircraft issues that comes from regulatory agencies. In this case, it started with the European regulator, EASA, and then was adopted by the FAA here in the US. Once that happens, most other agencies around the world will adopt as well.
What was the problem? Here's the raw read, and then I'll translate into actual English:
Wear, beyond Engine Manual limits, has been identified on the abutment faces of the splines on the Trent 900 Intermediate Pressure (IP) shaft rigid coupling on several engines during strip. The shaft to coupling spline interface provides the means of controlling the turbine axial setting and wear through of the splines would permit the IP turbine to move rearwards.Ok, got that? That's what I thought. Below is a diagram of the Trent 800, a different engine but it does show the basic makeup of how an engine is put together.
Rearward movement of the IP turbine would enable contact with static turbine components and would result in loss of engine performance with potential for in-flight shut down, oil migration and oil fire below the LP turbine discs prior to sufficient indication resulting in loss of LP turbine disc
integrity. Some of these conditions present a potential unsafe condition to the aeroplane.
The focus here is on the intermediate-pressure turbine. Apparently, inspections had turned up abnormal wear on parts in that part of the engine. Enough wear, and the intermediate pressure turbine would have been able to move backwards. When that moving part backs up into a non-moving part, bad stuff can happen. The engine might need shutting down, and the problem could also cause an oil leak or even an oil fire.
So, the Airworthiness Directive was issued to make sure that operators inspected their airplanes for this specific problem. It's unclear whether Qantas has complied with this Airworthiness Directive or not, but I would assume the airline has done so. This A380 was the first new aircraft to use the Trent 900 engine, so it's safe to assume that it would be most likely to exhibit wear before other airframes.
We also know that the Trent 1000, the newest engine that will be going on to the Boeing 787, suffered an uncontained failure in testing thanks to an oil fire related to the intermediate pressure turbine. Hmm.
Engines are incredibly complicated, and it's possible that a lot of things could have gone wrong here. But until more details come out, all we can do is start looking at every possibility. My guess is that initial investigations will be looking at the intermediate pressure turbine to see if that was the issue here. If so, then the question becomes, how long until these airplanes can be fixed and put back into service?
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