If "allow access only to the tables specified" was unchecked then you should have access to all function modules.
Only tables are listed in the initial screen of /crystal/rls.
Try connecting your Crystal Report to BAPI_SFLIGHT_GETDETAIL. If you can then there is something wrong with your Z function module.
Download xi31_sp3_bip_sap_inst_en.pdf (SAP BusinessObjects Enterprise Integration for SAP Solutions Installation and Administration Guide).
Also, this thread should be moved to the Crystal Reports area or BusinessObjects Integration Kit area.