Originally Posted by
DaveReidUK
That sounds like a description of a random failure, rather than something that would manifest itself over several consecutive flights, as was the case with Lion Air.
Depends on what causes the holes to line up. On a new system it is more likely to be random occurrence as it is just a case of a very low probability of event(s) that eventually just happens. On an old system that has had an additional piece of software bolted on (MCAS) it is more likely to be the new software that has now introduced a significant hole in the cheese. Obviously as a system starts up, if all of the external factors are the same, the processing sequence will be exactly the same, including which bit of code is interrupted by a specific interrupt. However, if something happened on both of the Lion Air flights just prior to take-off (purely as an example, such as detection of an IAS Disagree), the change to the processing sequence would be the same on both flights, which caused the software frailty and the colliding interrupt to create a corruption. All other flights without the special trigger would get away with it, perhaps forever, perhaps not.