On the Manage Load screens it is one of those orange buttons across the top of the page.

The original idea for this service was to allow a User to add a non-inventory item to a shipment without taking the effort to fully enter that item into the Inventory System. A typical example would be a Skid used to consolidate cartons. However as Users are wont to do, they started finding all manner of alternative uses for this function. Originally just a few Users were making use of the tool so working around some of the screens “known issues” seemed OK at the time. Now however we have a whole new generation of expanded Users and they have been creating issues for themselves and us, so at long last we have taken a stab at addressing those “know-bugs”.
Here is what you can do now with On The Fly:
Existing Asset
If you select an Asset that is in the Inventory you can edit the Asset's Contents, Weights & Dims, etc. and post information to the selected instance’s Record. This information will save, update the Project and update the file for the Asset in the database. This should prove very handy if you are using empty cases and packing them with random pieces for a given Project. Just remember the database is updated and until you make a second edit the contents will remain.New Non-Inventory Asset
You can make a true On The Fly item, the original intent, which will not be entered into the database. At the time you do so you can determine if it is a One Way Item or Will Return item. This is a onetime choice and is non-editable after the first save. If you select One Way the item will not be made available on the Manage Load from screen of return packing list.
Note: If you plan to Transship this Asset you should enter it into the Company's Inventory, as On The Fly Items are not programed to Tranship. They are what they are. A convenience not a replacement for the Asset Management system.