Drill down help

Hi Experts

In ALV, am doing drill down for a two fields that

belnr and gjahr (document and fiscal year). But its not working, pls explain how to do drill down for combining two fields.

FORM user_command USING r_ucomm LIKE sy-ucomm

r_selfield TYPE slis_selfield.

DATA belnr TYPE lfa1-lifnr.

DATA BUKRS TYPE BSIK-BUKRS.

DATA GJAHR TYPE BSIK-GJAHR.

IF r_selfield-fieldname = 'BELNR'.

belnr = r_selfield-value.

SET PARAMETER ID 'BLN' FIELD belnr.

SET PARAMETER ID 'BUK' FIELD bukrs.

SET PARAMETER ID 'GJR' FIELD GJAHR.

CALL TRANSACTION 'FB03' AND SKIP FIRST SCREEN.

ENDIF.

ENDFORM.

Thanks in advance.

Regards

rajaram