Originally Posted by
verticallimit
What if a new error occurs and this becomes much more serious because it already has a flaw in the system.
The systems on the aircraft depend on each other and multiple defects may well provide an unintended and unknown effects.
That's why the guiding document, the Master MEL, is produced by the OEM, and is dependent upon safety analyses which mirror that for basic certification. "Next significant failure" is a key part of that assessment, and that's why some items can't go on the MEL - not because they are unsafe per se, but because they leave no redundancy for the next failure.
Originally Posted by
verticallimit
The systems on the aircraft has been designed for optimum safety, every time a system is flawed, its removes a part of safty.
Actually, not true. "Optimum" safety is unattainable. You could just keep adding system redundancy until the aircraft weighed a million tons.
Aircraft are designed and certified for safety goals, expressed in the likelihood of a failure per flight hour, compared to the hazard of that failure. A "catastrophic" failure can occur no more than once per billion flight hours. But once you meet that standard, you're done.
So if I do my MMEl analysis, and I *still* meet the 1 in a billion rule - I'm good.
Originally Posted by
verticallimit
I can not imagine that they will put many additional systems into the cockpit, just because you have to be able to fly for longer time without repair.
Actually, intentionally adding redundancy to improve dispatch reliability is not that uncommon. It all depends on the cost of a missed dispatch versus the cost of carrying the extra redundancy around. Sometimes it will make sense to add it, sometimes not.
Originally Posted by
verticallimit
And it should be possible for both mechanic and pilot to ground the plane
Actually, neither can, they can only release it or not. If some other pilot is willing to fly, or some other engineer to sign it off ... well, ultimately there's an element of engineering judgement involved.