The Flying Doctors - Season 3 Episode 19 Borrowed Time

A crop duster friend of Sam's named Bob gets work for Baxter but he has turned into a Enviromentalist and sprays water/milk over the crops. Baxter is not impressed and wants Constable O'Connor to arrest him. Bob tells Sam about his 8yr old son being killed when he sprayed himself with chemical from a tank. Bob decides to make a statement by threatening to empty chemicals into Canberra's water supply. bob gets killed and Sam finds out there were no chemicals aboard his plane.