Originally Posted by
kiwi grey
I found this rather significant
This reads to me that the fundamental design of an element that is subject to certification testing was changed, but the new design was not subjected to certification testing.
How can such a thing happen? Was the FAA aware of the design change or was it signed off by a Boeing "FAA Representative"?
Disclaimer - I had no knowledge or involvement in the nacelle change in question.
That being said, there definitely would have been testing done on the new CFRP nacelle components in order to certify the change. However, they are NOT going to do a full-blown repeat of the fan blade out test - such a test is terrifically expensive (at least $50 million) to demonstrate a nacelle material change. Rather, testing and analysis would have been performed to show that the new CFRP could handle the same loads as were measured in the original FBO tests. However FBO test are highly dynamic and the loads that are measured may or may not be fully representative of what the structure will actually see, and the associated analyses are something of an art rather than an exact science. Apparently in this case they got it wrong.