Originally Posted by FrequentSLF
Based on your statement crash investigations are not necessary, the thousand of hours spent in improving flight safety are not needed.
If TOTAL is not the target, what is acceptable 80%, 90% 95%?
There is no total safety. And indeed, a decision needs to be made as to what the acceptable level is. However, your numbers are way off. We are talking about a current safety of 99.99999% (this is the percentage of flights without fatal accidents). There is a certain cost to increase this safety. To bring it to, say, 99.999995% might increase costs by 20%. Apparently, most passengers are not willing to pay this premium, otherwise such investments would be incurred. This is for example the reason why there is often only triple redundancy and not quadruple redundancy (according to your logic, we should aim for 100+ x redundancy).
Now, your suggestion regarding grounding a/c with inoperable T/R, this is the same issue. If the airline knows that more of their a/c will be on the ground because of inoperable T/R, it will have to buy more a/c to be on standby. This costs money. And passengers are not prepared to pay for it.
Ask yourself: When you bought a car, why did you go for the Golf, and not the high-security S-class Mercedes? Shouldn't you have if you aim for total security?
In a nutshell, the risk of flying is tiny, and a lot less than driving, cycling or just walking in a city.
So why are there accident investigations? To find about the causes of accidents. If there is a cheap way of making flying more secure, you can bet that it will be implemented. If it is expensive, it will only be implemented if the costs outweigh the benefits.