IEAAPP00 contains the names of authorized installation-written I/O appendage routines. These appendages, when listed, can be used by any unauthorized user program. Otherwise, only programs authorized under APF or running under system protection key (0-7) may use the EXCP appendages. If your installation does not use EXCP appendages, you need not create IEAAPP00.
If the EXCP caller is not in system protection key or the job step is not authorized, the system verifies that the caller's appendage names are listed. If the names cannot be found, the system issues a 913 ABEND. If, however, the caller is authorized, the system loads the appendages without inspecting the list.