LIGHTNING Of course you should still be left with handhelds if they had been off and disconnected at the time but you would not have a 'system' left.

If you listen to accident investigators you will see that accidents nearly always occur after a series of problems which in themselves would not have caused the accident. They don't happen very often but they do happen.

How about a lightning strike that causes a fire in the section where all of your electronics toys (like handhelds) are kept? Suppose you'd discharged your (poxy useless dry powder) extinguishers and the fire was still smouldering so you start pouring water on it. The fire is out. You sift through the steaming mess and retrieve your handheld and find that it won't work. You're not going to get your toolkit out and try to fix it...it's kaput. What wasn't damaged by the fire has been damaged by the water.

I'm not saying that charts are any more immune to accidents but let's focus on your contention that multiple redundancy will make total failure almost impossible. It won't. You can put in three entirely separate systems and you will still have total outages. Murphy guarantees that you probably have rather more outages than anyone else - he does this to prove to you that you can't outsmart him!

The more complicated the systems, the more problems you will have. I guarantee it.