Hi ​@Tea Hassinen,

Is there a primary supplier defined here? I am asking you this because, in MRP, system first check whether primary supplier exist for the part if yes, then system will calculate the Leadtime considering supplier manufacturing lead time, inspection lead time, external transport lead time, transport lead time and internal transport lead time. If there are no primary supplier, then system consider the purchase lead time mention against the inventory part.

Yes, site A is primary supplier for components that site B purchase.

Are you using Exceptions in your Site to Site Supply Chain Parameters by any chance?

I have recently logged a case where I noticed MRP is not calculating the leadtime as expected when the part has an exception applied. The behaviour I saw on the exception parts, was that only the supplier for purchase part supplier manufacturing lead time was considered and all transport lead times were ignored. 

When I removed the exception, as ​@Yathartha Karunananda said, the lead time was calculated as Manufacturing Lead Time + Inspection Lead Time + External transport lead time + Transport lead time + Internal transport lead time

What kind of exceptions? Where they are determined?
 

In our case it seems that distribution order does not take in the consideration supplier manufacturing lead time at all, only transport time set on site to site parameters. This means that distribution order ship date is tomorrow and delivery date day after tomorrow since transport time is one day (&picking lead time 1day). 

The Exceptions also set up on the Site to Site Supply Chain Parameters page (e.g. I can set a different external transport lead time for parts that will be air freighted)

But sounds like this is separate to your issue. 

When you say you create the Shop Order first, is this manually created? I assume you are then running MRP and this is generating a DO with a Planned Receipt Date to match the start date of the SO as you do not hold stock of the component on site B?

MRP will always backwards schedule the DO for the component from the demand start date, so the Planned Ship Date will be the Planned Receipt Date - Transport Lead & Inspection Lead Times. If you made the Shop Order start date even earlier, you will see the planned ship date can also go into the past.

I just double checked and I am a little suprised you don’t get the ‘planned supply start date past due’ action message if the supplier manufacturing lead time takes you into the past, only if the ship date is in the past.

The Manufacturing Lead Time gets used in the MRP scheduling calculation if your inventory is below safety stock and you have “Consider Lead Time for safety stock” turned on and no open demands within part’s lead time. MRP will then generate a forewards scheduled DO with Today’s date + full lead time.