This paper clarifies the EWIS scheduled and un-scheduled maintenance tasks of aircraft in service according to the concept of the Electrical Wiring Interconnection System (EWIS) as a special functional system of the aircraft, relying on the type development practice. Based on this, some special maintainability qualitative requirements were presented, a set of new process and method of allocating the maintainability requirements to EWIS design zones were innovatively delivered, and some feasible means of EWIS maintainability evaluation or verification were studied.