alt Hacker NewsHigh reliability of airliners is achieved by having redundancy of all critical parts. The idea is no single failure can cause a crash.
For example, if system A has a failure probability of 10%, if A is redundant with another A', the combined failure probability is 1%.
That of course presumes that A and A' are not connected.
Yes for systems, not always for structure. A failed wing spar means everybody dies. For real-world examples, there were two 747 crashes caused by improper repairs to a rear pressure bulkhead or aircraft skin. When the repairs eventually failed, the explosive decompression caused catastrophic damage to the tail in one instance, and total structural failure resulting in a mid-air breakup in the other.
The response to this was to make sure repairs are carried out correctly so the structure doesn’t fail, not to somehow make two redundant bulkheads or two skins.