Those that don't fly themselves have no idea what it is like. Greg S said "an experienced pilot should never have flown in those conditions"
Not quite correct... First off, you do not know what conditions were like from where they took off. With fog conditions, the situation changes by the minute, so what you have at a destination, or anywhere along the route, will be constantly changing on a foggy morning. One minute you can be clear at a location and a few minutes later you can be socked in. There are times when you can be on VFR and if you encounter some changing conditions, request SVFR and get assistance from ATC.
They will help guide you where you need to go, but... you need to know where you are if you suddenly encounter fog, while flying. When you are in a hilly area and this happens and you are below the tops, you need to be aware of what direction you can turn to get out of that area/situation, without flying into a hillside. You would be surprised how quickly foggy conditions can change all around you and in hilly conditions, this can happen much faster than you can image, with different temps on each side of hill depending on where the sun is.
As for obstacle avoidance systems, yes they are available but for helicopters, that presents a different issue, to a fix wing aircraft, due to the fact that they are often flying at a lower altitude and into areas that they can access, but a fixed wing aircraft could never get into. Therefore, when flying in a rotorcraft with obstacle avoidance on, there are many times when the bloody thing keeps going off, and causing you more hassle than with it on, due to where a pilot might be flying and the terrain around them, and I am speaking of a situation whereby you can clearly see around you. So, often the instrument is simply turned off, or not installed because it would be giving too many false positives during flight.
This may be why that helicopter did not have such an instrument installed. So to GregS, it is not an experienced pilot you should be speaking of, but a more safety conscious pilot, because even a less experienced pilot might decide not to fly on that morning, but an experienced pilot may feel fine flying in that area, but when conditions quickly change it might be that no amount of experience can get you out of the situation, if the pilot made a decision to do something that turned out to be not the best way out. It would be a very different thing if a pilot was socked in but chose to take off anyway and try and figure things out in the air. But to take off in acceptable conditions and then find things changing quickly while enroute, that presents a completely different situation.
Now, how this all came to be, that is best left up to the NTSB to work out. What I can tell you that in any aviation accident, there is 99% of the time a chain of events that have to take place to arrive at that accident and if just one of those links were removed, most often that chain would not lead to an accident, a close call maybe, but most times, not an accident. Therefore, we need to find out what all those links represented in that chain, in order to see what led up to the accident happening, We all learn, as pilots, from looking at all those links and remember them, in case we find ourselves flying into such a situation.