On final approach to Islamabad in heavy fog, Airblue Flight 202 slams into the Himalayan foothills, killing all onboard.

A Boeing 737 crashes just moments after lifting off from an Algerian desert airport. For investigators, it's clear the left engine exploded after liftoff, and that a fatigue crack eventually explains why. What's less obvious is why an experienced crew of the state-owned national carrier was unable to keep their plane in the sky.