Scheduling an Order Externally 
Use
You want to perform scheduling for the orders in your company using an external scheduling system.
Prerequisites
For more information on the prerequisites, see
External Scheduling.The function module
PM_ORDER_EXTERN_SCHED_DIALOG must be assigned to the fixed value D in Customizing under Plant Maintenance and Customer Service ® Maintenance and Service Processing ® Maintenance and Service Orders ® Scheduling ® External Scheduling ® Configure Communication.Procedure
Result
The dates are posted in the SAP System and in the external scheduling system.
If the external scheduling system does not find any suitable dates, you can change the basic data of the order and reschedule it.