Oracle 10g Fulltablescan Problem

SELECT CASE WHEN substr(xd_az,1,2) = 'SR' THEN to_char(sysdate,'YYYY') ELSE to_char(to_date(substr(xd_az,1,2),'RRRR'),'YYYY') END, 1,   
to_char(xd_eingang,'yyyymmdd'), day(vs_gebdat), month(vs_gebdat), year(vs_gebdat), '',   
xd_dok_typ, xd_az, vs_udat, xd_personal_unfall, '', vs_gebdat,   
CASE WHEN vs_abgabe IN (' ','997','998') THEN '' ELSE   
CASE WHEN xd_sammelrechnung = '0' AND substr(vs_mglnr,2,4) = '9999'   
THEN vs_abgabe ELSE '' END END, xd_ident,   
CASE WHEN xd_archiv_dok_id IS NULL THEN 0 ELSE xd_archiv_dok_id END, 
CASE WHEN xd_archiv_vorgang_id IS NULL THEN 0 ELSE xd_archiv_vorgang_id END, 
xd_dok_typ, xd_verfahren, xd_eingang, xd_post_eingang, xd_dok_name, vs_name, 
vs_vname, vs_hmkm, vs_bstand, vs_mglnr, vs_betr, vs_uart, vs_akz, 
CASE WHEN vs_abgabe IN (' ','997') THEN '' ELSE vs_abgabe END,   
pwf_ident, pwf_aktion, pwf_aktion_teil, pwf_datum_ende, pwf_datum_beginn, pwf_user_eingang, 
xd_ablage_datum, xd_sammelrechnung, '', ''   
from   xml_dokumente, verl_stamm, prog_work_flow, work_flow_aktion, term_zust 

where xd_az = vs_az AND tz_zust = 'xxxxxxxxxxx'  
 
AND (tz_sachgeb = 10 AND tz_tag2 = 0 AND tz_tag1 = day(vs_gebdat) 
AND tz_monat1v <= month(vs_gebdat) AND tz_monat1b >= month(vs_gebdat) 
OR tz_sachgeb = 9 AND tz_tag2 > 0 AND tz_tag1 <= day(vs_gebdat) 
AND tz_tag2 >= day(vs_gebdat) AND tz_monat1v <= month(vs_gebdat) 
AND tz_monat2b >= month(vs_gebdat)) 
AND xd_ident = pwf_vorgang_ident AND xd_verfahren = pwf_verfahren AND pwf_aktion = wa_ident 
AND wa_prog_modul IS NOT NULL AND wa_prog_modul = 'prog_erf'   
AND xd_ident NOT IN (SELECT dz_ident FROM dok_zust WHERE (dz_sachgeb = 10 OR dz_sachgeb = 10)) 
AND xd_az IS NOT NULL AND (pwf_aktion_teil IS NULL OR pwf_aktion_teil = 2) 
AND (vs_abgabe IS NULL OR vs_abgabe = ' ' OR vs_abgabe <> '999' )   
AND (pwf_datum_ende IS NULL OR to_char(pwf_datum_ende,'dd.mm.yyyy') = '30.05.2011')   
AND xd_az NOT IN (SELECT vm_az FROM verl_sonder)