FAA STD- Preparation of Interface Documentation

2.1 Interface Documentation
The IRD, ICD, and IR are closely related and each has a specific purpose. The Integrated Product Team (IPT) or program office is typically responsible for developing IRDs, ICDs, and IRs. IRDs identify the interface requirements between two subsystems, between a subsystem and a "user" (where the "user" can be viewed as a variable that can be filled with multiple subsystems), or between a facility and a subsystem. The requirements in an IRD are often traced to or derived from requirements in a system-level specification or system requirements document. ICDs describe the formal agreement that documents how the interface requirements between two subsystems, between a subsystem and a "user" (where the "user" can be viewed as a variable that can be filled with multiple subsystems), or between a facility and a subsystem are implemented; the as-built configuration. The design characteristics in an ICD trace to and are derived from the interface requirements in an IRD.