Thursday is an official day of mourning in Azerbaijan as an investigation is underway to determine what caused an airplane carrying 67 passengers to crash on Christmas Day in Kazakhstan, killing 38 and leaving at least 29 survivors. [time-brightcove not-tgx=”true”] Video posted by CNN shows the plane crash-landing, exploding into a fireball and plumes of black smoke. Here’s what to know about the devastating accident and the latest on the possible causes.