This paper describes a method for task decomposition to support function allocation between human operators and automation systems. Currently available task decompositions are not specifically designed for function allocation. Consequently, it is difficult to allocate functions and to evaluate that allocation based on current task decomposition methods. In this paper, a method for task decomposition for function allocation is introduced. The method in this paper, shows not only the hierarchical relationship between tasks, but also describes operating procedures, and conditions for the tasks within the method. Further-more, it also provides a way to explicitly call out the induced tasks created by function allocation. To demonstrate the method, a case study of the Continuous Decent Arrival (CDA) procedure is analyzed.