(See update below.) The first reaction to news of the crash yesterday over I-287 in New Jersey, in which a married couple in their 40s, their two children, and a friend in his 30s all died (plus a dog), is the overwhelming tragedy of it all. I am so sorry for everyone affected by this loss. Anyone who has been touched by such events knows that their effects fade but never really go away.
The second is of course to wonder how it could have happened -- in a Socata TBM 700 that, while it may sound small because it is referred to as "single-engine," is in fact a very robust and capable turbo-prop airplane. As always, it will take a while to know. But it will be very surprising if the answer does not involve in-flight icing. As a reminder, icing also played a crucial part in the Colgan commuter-plane crash in Buffalo nearly three years ago, and in the Air France 447 crash over the Atlantic a few months after that. (About which, yes, I have a ton of material to update and share.)
For now, an explanation and some resources.
Explanation: Why can icing conditions be so dangerous? There are two different but mutually worsening problems. The first is icing's aerodynamic effect. When ice covers the plane's wings and tail surfaces, they provide less and less lift (because their shape is changed -- see below). Eventually they provide none at all, and the plane simply falls out of the air. Ice over the plane's body makes it "draggier" too. Thus a vicious cycle: the change in wing-shape means that the plane has to maintain a higher airspeed to keep flying, even as drag and loss of power are slowing it down.