An airline crew smuggling a $2 million diamond on board begins to get murdered one by one. [Title: Fight or Flight}

This could? be a mixed genre crime thriller with horror as the second genre. Something comes on to the plane with the diamonds. Could be a curse, a demon guardian, an alien,etc.

Who is the main character and why must they do whatever it is their goal so happen to be?

Check out the 'Formula' tab up top for some logline basics.

... and what will the lead character do about this situation?

I like the short, simple style of this logline, but I would agree with the last reviewer that it needs a little more personality. Maybe allude to the murders, but don't let us know so much of what will happen.

Think about what makes this different than any other smuggling film. That's what I would want to hear in the logline.