> ...with a computer system you could have 3 or more systems all getting a vote before action is taken and each of those 3 could be written by 3 separate compan

> ...with a computer system you could have 3 or more systems all getting a vote before action is taken and each of those 3 could be written by 3 separate companies using unique security and code. You could have this. But what are the chances that this will happen in practice, instead of a general reduction in this kind of measure in the interests of cost-cutting? Humans are notoriously bad in assessing risk for unlikely events. If an accident hasn't happened, then this tends to become a justification to compromise and cut costs even when the sample size is too small.