Progress. I think about it a lot. Like the transmission in the Sikorsky S-92 with the dual oil pumps that can not independently supply sufficient pressure to preclude an emergency situation if one fails. Now there's some great design progress, eh?
My experience is not with the EC-135. I flew the old, antique Bo-105. It has a similar fuel tank/supply setup as the EC-135 apparently. You had to turn transfer pumps on to move fuel forward from the main tank to the little supply tanks in which were the "real" fuel pumps that sent it up to the engines. The transfer pumps did not have caution/advisory lights to tell you when they were off. PHI (knowing that we dumb pilots would sooner or later forget them) added white "Transfer Pump OFF" lights to the dash. Turning the pumps on extinguished the lights. The system was not foolproof. The lights were white. On a bright, sunny day they could "disappear" under the glare shield. Ask me how I know. Wait- don't ask.
As SASless says, no self-respecting Bo105 pilot would *ever* deliberately turn the transfer pumps off in flight. If you did, you'd run out of fuel in about twenty minutes (on a good day) when the supply tanks ran dry. Or maybe it was eleven minutes - I don't remember. What I *do* remember is that we never shut the transfers off.
The fuel quantity indicator system in the Bo-105 was stone-simple.
You had a fuel gauge with two needles. One was for the main tank and the other, the supply. Because of where the fuel quantity sensor was located, in forward flight (about 10 degrees nose down) the main tank fuel indicator would show empty even when there was plenty of fuel in it. You did not use the gauge for the main tank in cruise; you used your watch. (For aviation-savvy but non-pilot passengers who were new to the Bolkow, it was kind of scary on a long flight to see the fuel gauge go to zero.) But if you ever saw your supply tank needle coming down, your LZ better be in sight.
I cannot believe that Eurocopter made the EC-135 "better" by requiring the pilot to periodically switch the transfer pumps off and on. That's ridiculous. That's not progress, is it.
Now then... We all know good pilots who've inexplicably come to grief in helicopters. It's hard for us to wrap our heads around it: How someone we know and admire could make such a dumb, fatal mistake? We arrogantly think that *we* ourselves would never do such a thing - so how/why did someone as good as "X" do it? Would a CVR have told us? Not necessarily. Would more training in full-down night EOL's have helped? I doubt it, but YMMV. Once that first engine quit I'll bet it was fair pandemonium in that cockpit, or at least a lot of, "What the hell is going on??" and a lot of cuss words. Things were surely happening fast.
I've said before and I'll say again: Helicopters are very easy to crash. The helicopter does not care how much experience you've got or how good a pilot you are or what your friends think of you. And neither you nor I are immune to making the same kind of fatal mistakes as the ones who've sadly, tragically gone before us. I know how close I've come over the years and I get shivers up and down my spine when I recall them. Grace of God and all that.
Look at those two guys who crashed the AW-139 taking-off in the fog from that rich guy's estate a couple of years ago. Should have been a "simple" vertical take-off through the fog layer. Set the hover attitude and then straight up: easy-peasy. But no, as he pulled pitch the PF started (inadvertently?) pushing forward on the cyclic. Did neither of the *two* pilots onboard see that the nose was going down, down, down? Did neither of them notice that the rate-of-climb indicator wasn't showing a climb? Apparently not. We think they had plenty of time to recognize what was going on, but I'll bet things happened pretty fast for them as well. Two qualified and experienced professional pilots killed everybody onboard that night.
We all make mistakes. Why the pilot of the EC-135 continued to fly beyond 1:30 makes no sense especially when he'd already received low-fuel warnings. "Everybody" knows the -135 doesn't have all that much endurance. He *had* to know he was about empty. And why he was messing around with the transfer pump switches with so little fuel left is extremely puzzling. That the engines ran dry with fuel onboard is simply inconceivable. What was he thinking?? Even a CVR cannot tell us.
There are a lot of unanswered and unanswerable questions. Some accidents are like that. Sometimes you never know. Sometimes all you can do is shake your head, accept that the pilot screwed up and move on with the knowledge that in our world sometimes things just don't make sense.