Material Requirement- Maint Plans

Dear All,

I have created many plans for the whole year and it has many tasklists with many components assigned. Now as per call dates order will be generated and then only material availability check will happen. May be during many call dates few material may not be available (because of larger lead times)and thats why plan can not be executed on exact dates. Now how to ensure today(know beforehand) itself that what are my future call objects(orders) requirements in terms of materials(spares).

Regards,

Raj