OK, so based on the articles it looks to me that this issue was discovered through some kind of regression testing (for non-software folks, this is essentially a form of testing which continually runs scenarios against the software throughout the life of the product, in particular checking that fixes and updates don't break existing code). The reason this is important is because testing of this kind is and always has been mandatory for aviation/safety-critical systems - in fact many of the methods were invented and perfected by the aviation software pioneers. It doesn't matter that a real-world occurrence of this scenario is very unlikely, for this software specialty that's not good enough. By the sound of things, it seems this scenario was encountered in testing by Boeing's software team/contractors, and the FAA was immediately notified. In short, this is what's supposed to happen and - if anything - only serves to prove that the system for finding and resolving this kind of issue is working as it should.
@Gertrude the Wombat - As a more mundane software engineer myself, I can only repeat that your hypothetical management dismissal simply won't fly in the aviation software world.
@ion_berkley - Your analysis sounds about right, but from what I've been told real-time aviation software isn't usually hand-coded in the manner most other software is. I know that Airbus's development environment is essentially a graphical system with discrete blocks of tested and approved code underpinning the graphical logic structure. That said, I don't have any info on how this specific system on the B787 was put together.
[EDIT : As far as finding the issue now goes - one aspect of this kind of testing in terms of scientific software reliability is that the engineers will continue adding scenarios to the suite of tests, and if the scenario is considered unlikely in the field it is usually called an "edge case" in software terminology. I suspect that this particular edge case was added to the suite fairly recently.]
Last edited by DozyWannabe; 2nd May 2015 at 01:42.