Hi Matthias,
BAPI_FUNCLOC_GETLIST will give you direct equipment of a particular functional location not its sub-functional locations under the hierarchy.
If you want all equipment under the given functional location (ie., including the equipment of its descendant sub-functional locations), you need to ask an ABAP developer to develop a ZRFC for you.
In the ZRFC the developer has to create a Internal Table and recursively get the sub-functional locations and equipments of the specified functional location. He can make use of BAPI_FUNCLOC_GETLIST inside it if he feel so. He can give you a final output table with all the fields you need.
Functional Location naming conventions are not entirely sequential, rather usually the parent name is attached as prefix to it separated by "-". Using range parameters you may not get all data you need.
So let him take care of the underlying logic. You will have to pass only Functional Location name, and as a result you will get all equipments and materials if associated to it.
Note: DESCRIPT_RA has nothing to do with your requirement.
Regards,
Prashant