After discovering his dad operating drunk and believing that to be the cause of a patient death, his dad left for Austraila. When Jack goes to find him, he finds his corpse, his dad having died from alcohol poisoning. He was transporting his father back to LA when the plane crashes. Jack is the impromptu leader of the group, making most of the decisions that affect them and leading all their attempts at surviving and getting rescued. His knowledge in medicine is VERY handy.