Originally Posted by
Redredrobin
The experienced rate of fan cowl opening (Report 1.18.2, page 84) is 1 in 1.28 million flight cycles pre EASA AD F-2001-381 (hold open device) and 1 in 2.42 million after that AD. I don't know the average hours per A319/320/321 cycle but say it is about 2 hours, then the occurrence of fan cowls opening is about 200 times over the acceptable limit of a 'system' and it would be more of an issue.
Again, that's not what happened, nor is it what the AAIB said. The occurrence rates you quote are for loss in flight of cowl doors that are effectively already open, not the rate at which fully closed cowl doors open themselves in flight (which I suspect is zero).
The difference being that certification requirements can't possibly mitigate against the effects of departing with unsecured cowls any more than they could against, say, an unsecured cabin door (albeit that the latter, of course, have warning systems).