Triplebravo
There is such thing as an "acceptable accident rate". Airplanes are built to have an incident probability of better than ten to the 9th. Boeings and Airbusses alike, since this is a certification requirement. It does not prevent to improve though.
methinks some confusion here and some old wifes tale.
There is
no acceptable accident rate within published aviation standards
Allow me to remove the undefined word above
incident probability and stick to the definition of catastrophic accident (not survivable). Catastrophes in commercial service happen at the rate of E-7 and someday we may even get this lowered by a factor of 2 but no way will we acchieve E-8 let alone E-9
Tis true however that for a very specific area of design requirements, that is multiple system failures etc. (Far/JAR 25.1309) that there is a target of achieving E-9 against the occurence of a catastrophe.
So we are then left with things like a single system failure (not specifically regulated by design) coupled with inappropriate crew response as one of the biggest contributors to our catastrophic accident rate among all aircraft