If you are using the master model method (the part is added as a component to the drawing file), the component (model file) will need to be fully loaded. Once the model is fully loaded, you can reference the feature collection in the model part file.
re: component modeling features
If you are using the master model method (the part is added as a component to the drawing file), the component (model file) will need to be fully loaded. Once the model is fully loaded, you can reference the feature collection in the model part file.