Who cares who's fault it is ? The blame game is really unproductive and rarely anything good comes from it.
Here is a different approach to handling mistakes.
If you are never making a mistake, you are not doing it right.
Doing things better, different or innovative involves risk. Occasionally you will fall on your face. That's normal and to be expected. If that never happens you are just playing it overly safe and defensively. Mistakes are also one of best ways of learning. If you never make any you are probably not growing.
Communication is key
If you make a mistake, fess up immediately. Explain exactly what happened, what the immediate impact is, what the potential options are and a recommendation of what to do next. There is no need to beat yourself, it's all about "the car is in the ditch, how do we get it out of there". If you are about to take a calculated risk communicate upfront about this: "We are going to build another 100 units next week, there is risk that they will fail radiated emissions tests. However, if we don't, the schedule is guaranteed to slip by two weeks. If this goes wrong we have to toss 100 units and the schedule will still slip. Let me know if you want me to do anything differently".
Even if your very first thought and reaction is "How the heck did that happen?", don't say it. It just makes people defensive and doesn't help at the moment. Again, the car is in the ditch and you need to get it out there as quickly as possible with as little damage as possible. Right away it's not so important how it got in there. Of course there needs to be a follow up but it should be later and in private when the immediate emergency has been resolved and tempers are cooler.
Don't make the same mistake twice
Mistakes are one of the best ways of learning new things. Typically the lessons sticks. Having an open and blame-free environment helps enormously with this. All mistakes are out in the open which means other people are a lot less likely to repeat them and can freely analyze them. For example you can easily approach a senior person and ask them: "Hey I screwed up on the release of project XYZ, what do you think I could do differently next time?"