It's true, fratricide was common during a period of the Ottoman Empire. It did not exist in the beginning, it was instituted later in order to protect the continuance of the throne. Towards the end of the empire however, this tradition was ended and the eldest brother started taking the throne.
Sons of the sultan were always in rivalry for the throne. They thought that if the other brother remained alive, he would then rebel and build his own military forces to fight the brother with the throne. They felt that this would put the future of the empire at risk and would cause chaos and civil war. So brothers started killing one another and the one left alive simply became sultan.
When I say fratricide, of course, they didn't do this with their own hands. They had others do it for them. But the saddest part of this terrible tradition was that after one brother was killed, all of his sons were killed along with him to make sure that his lineage could not rebel in the future. This even meant the murder of infants.