Blame it on the Salesman!
Where does the ‘mentality’ come from? I reckon it comes from the manufacturers and the salesmen active between 1960 and 1990; and I was one of them.
We would tell any potential buyer that would listen that two engines were safer than one; and I think that we were correct in presenting that argument. Of course it also helped to increase the value of our order book.
The argument stemmed from the statistics of the previous 20 to 30 years that supported the argument. In piston engine times big engines were less reliable, hence it was safer to propose two smaller engines than one big one. Whether this argument should have been translated across to turbine helicopters is of course another topic.
It is only in living memory that bigger engines have established the reliability figures that gave travelers and operators the confidence to accept a fleet of twin engine aircraft flying across the Atlantic and the Pacific.
How long will it take the modern helicopter engines to establish an improved failure rate giving a probability of better than 1:100,000 and get us out of the ‘reasonably probable’ definition? Probably never!
When it comes to being a passenger I will choose a multi over a single every time because you have to factor in the pilot. I have been taken on some horrendous rides by pilots of single engine helicopters who would almost certainly have killed everyone on board if the only engine on their light helicopter was to stop. Those of you who have been on a scenic flight in Rio or the high mountains of Nepal or India will know what I mean.