Click to see Spoiler:
the family that the Holdens are based off of, the Coreys, Renny Corey (i.e. Michael Holden) dies overseas in Vietnam during a search for bodies of soldiers MIA in the Vietnam War. The helicopter ended up crashing due to malfunctioning equipment in the helicopter, they were in turbulence and due to the equipment were not aware of how close to a mountain they were and the helicopter crashed, killing everyone. However I don't see this happening on the show since they haven't followed the book at all, except for having them be in the Army. If anyone wants more details, feel free to ask me.