Devil"s advocate mode:
Like BSL said don't fly over a war zone. Unless we have some sort of evidence that those Americans on board were specifically targeted because they were Americans, this plane getting shot down doesn't rise to the level of foreign policy for the US. Americans die overseas every day from being in the wrong place at the wrong time. Sad, but a fact of life.
on the situation as a whole:
Remember how everyone agrees that the borders in the Mid East don't follow ethnic or cultural lines, and as a result there tends to be long-term unhappiness with the borders and strife? Remember how we all agree it's stupid to get embroiled in those disputes because of the long history of differences and grievances on all side and in all ethnicities?
What makes you think Eastern Europe is any better?
A real quick scan of the wiki article on the Ukraine would indicate that the land we refer to as the ukraine has been settled and fought over for ~3000 years. (I'm going to assume the neolithic guys weren't invade each other just for the sake of small numbers.) It also appears that it was common to ship in ethnically <whoever won the last battle> to help hold the region since Roman times. The LONGEST it seems to have gone without fighting over it's borders was as the Ukrainian SSR. Not a banner time in history.
So it seems that some ethnically <not from Kiev> want to be politically <not from Kiev>. And the Russians, whose great aunts and Uncles may or may not be in the region see some economic political gains to be had from splitting the Ukraine and (probably) annexing the territory. The Kievan Ukrainians don't want this to happen.
Why do we care? The oil and gas into Europe thing doesn't really matter to us, except that it might make North African oil cheaper. Russia will become a little more powerful regionally, but as soon as our CinC gets a sac we can ask Putin where his Carrier Groups are. Oh, That's right. Yet Americans are all hyperventilating about some regional border spat in an area rife with regional border spats. F it. Let them sort it out.
/Devil's advocate mode.