Jumping the helicopter
There are many reasons a writer might choose to kill a character. Characters can die nobly for a cause; some die as part of another character's development. On television, characters sometimes die because the actor dies or wants to leave the show, though again this can be handled well or poorly. (On Judging Amy—yes, I know, I know, but it was showing on TNT at the exact time of day that I wanted to avoid working on my dissertation—the actor playing Tyne Daly's fiancé died; the writers worked the character's offscreen death into the script terrifically. Compare that to, say, Tasha Yar on ST:TNG. Similarly, on a TV show I watch, a character dies rather unexpectedly in a later season, but it's done over a few episodes and is written into the plot with some care.)

Far and away the worst reason to kill a character, IMHO, is "we kind of needed to get rid of him." The two most glaring instances of this, I think, are Rosalind Shays (Diana Muldar, L.A. Law, who rather suddenly falls down an elevator shaft; and Robert Romano (Paul McCrane, ER), who had a helicopter fall on him. I never saw the second—I didn't watch the show (in spite of the fact that my uncle co-produced the first season of it), and I've only seen the occasional bits and pieces. But as I was leaving for work the other day, my wife was watching the episode, and when I commented on Romano firing someone, she said, "Don't worry, a helicopter's about to fall on him." In both of these cases, the character was (I gather) too unpleasant to keep around: that is, the writers/producers decide that, well, they just needed to get rid of them.

I mention this because I'm two-thirds of the way through something I've been reading (I won't name it, because, you know, spoilers) in which a character, one who's been fairly central to the plot so far, gets shot, in a relatively random and thoroughly unexpected way. And it happens just after he's delivered a message to one of the central characters, so in fact it's very much the case that the author is done with him and having him still hanging around would only get in the way. In fact, in case there was any doubt, another (morally ambiguous) character who watched it happen admits that he could have stopped it, but didn't because "his task was over". At the end of the chapter, I turned to my wife, who'd finished reading it already, and said, "I can't believe the author just dropped a helicopter on him."

Dropping a helicopter isn't like jumping the shark: the book is still terrific (and I suppose that ER didn't stop being a good show at that point). But I can't pretend it's unflawed, and one of the glaring flaws, in my opinion, is this sudden, random, unexpected, and wholly unnecessary character death.