You can look this one up. See FY 09 budget request, justification materials, US Air Force, Aircraft procurement-Vol. 2, page 71.
You'll find on that page a detailed description for not one, but two potential mechanical problems that could cause a B-2A to crash.
Here's a sampling (read highlighted text):
The problem is caused by the B-2A's distorted engine inlets.
The distortion causes excessive wear on the stage 1 fan blades for the F118-GE-100 engines. Take that and an unplanned "foreign object damage event", and, voila, your $1.1 billion bomber may experience a "catastrophic in-flight emergency".
But there's another problem. A loose fan blade also can spark an "uncontained titanium fire". According to the same document, the titanium fire -- whatever that is -- may cause a "Class A event", or what normal people call a "crash".
The problem is listed in the budget justification documents because the USAF is buying repair blades this year to fix the problem. I'm sure it will be interesting for the investigators to find out whether the "Spirit of Kansas" had received the repairs before the crash, among other items of interest, of course.
it is amazing how sometimes lack of testing brings proof the hard way that there was a problem with the CONCEPT of the airplane from the start.
engines and enginehousing should have been tested during the pre-production periode by the aircraftfactory !
Maybe it is because I am the son of an 'Engine Man' who had been tutored in gas turbine theory by the time I was 12, but I find this information is neither alarming nor atypical of many aircraft.
Asymmetrical airflow occurs in any asymmetrical engine inlet/nacelle, and under certain circumstances even in 'perfectly' round inlets. By way of example, Rohr, Boeing and CFM had a particularly tough time putting the CFM-56s on the 737-300s because the installation required rotating the engines such that the accessory pack/generators were canted AND the lower wing of the 737 (vis-à-vis a 707 et al) required distorting the engine inlets into a sort of tri-oval design. That installation design was prone to some VERY interesting first stage fan blade bang/stall events until they got it worked out for the regime it would be operating in. All engines run the risk of shedding blades, and engine fires...and they do occur.
As this seems to be a durability issue, obviously the 119 is not as robust in the first stage as the AF now desires, because you can bet your bottom dollar that this engine was tested on a stand WITH a representative inlet installed.
Any assertion there wasn't 'enough testing' done earlier based upon this post indicates a naiveté concerning the purpose and scope of 'test' (not to mention R&M). Deducing some deficiency of concept from the improvement effort planned screams a surfeit of knowledge on aircraft design and optimization.
Good on the AF for keeping the edge on sharpest, longest knife in the drawer.