Pilot and Aprentice:
" and the relevance is?"
The relevance is that the double engine failure rate in twins is not as low as the 'theory' predicts - it's bogus - the rarity needs to be as great as predicted for the other downside points to be out weighed.
There are many cases of double engine failure on this site - one of which, shortly followed by another near one, is here:
When checking out in the BO, we were told of a tall pilot who left his transfer pumps off and subsequently had a dual engine failure because the glare shield of that particular ship blocked his view of the "FUEL LOW" caption. We were told that you might have approx. 20 minutes to flameout in such a case. (I might add here that I remember thinking the requisite "Oh, that'll never happen to ME!") As a hedge against such a brain fart, I got into the habit of always without fail leaving the transfer pump switches on and NEVER shutting them off.
One day, I was shut down, showing another pilot the avionics suite in my ship. To save battery power I had turned the transfer pumps off. You guessed it, I forgot to turn them on at startup next time. I had been airborne for fifteen or twenty minutes, cruising along........
Someone said the fuel system was simple -
read the 135 thread - particularly from post 83 to 114. (great post Giovanni - btw) And tell me honestly if that mess is not an accident waiting to happen - you can't have that many permutations without atracting human error.
This pilot was not a 135 pilot when this pprune post (83) was published - unlikely to have read it and it is most conceivable that his (recent) type rating would not have assured a knowledge as displayed by Giovanni or indeed Mighty Gem (who has conducted numerous experiments to establish the workings thereof - as one does in the real world).
Quick: Which pump failure gives you big unuseable in the hover and which gives you big unuseable in the cruise ? Quick Aft for Hover ? right? quick! Sure? What should you do for a transfer pump failure? Disable it? both? pull the wrong circuit breaker (another (of the many) opportunity for error).
It's all just fine in theory...