A B767 MAKES AN APCH INTO PHL; PA; BUT THE TRAILING FLAPS STICK IN 22 DEG EXTENSION POS. CAPT EXECUTES A CAT III ILS WITH FLAPS IN THIS POS.

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ON IFR APCH TO PHL JUST INSIDE THE OM (KELEE) ON ILS RWY 9R WE SELECTED FLAPS 25 DEGS THEN 30 DEGS; AS WE WERE GIVEN AN AIRSPD OF 180 KTS TO THE MARKER. THE TRAILING EDGE DISAGREEMENT ILLUMINATED AND THE EICAS MESSAGE TRAILING EDGE DISAGREEMENT WAS DISPLAYED. FLAPS WERE STUCK AT 20-22 DEGS. PERFORMED GAR; ASKED FOR VECTORS AND PROCEEDED TO COMPLETE ALL ABNORMAL AND NORMAL CHKLISTS. WX AT PHL AND ALL SURROUNDING AREAS WAS ON A DOWNWARD TREND (FOG); WITH RVR AT PHL FLUCTUATING. BRIEFED A CAT III APCH BECAUSE OF RVR POSSIBLY BEING BELOW CAT I MINIMUMS BEFORE WE INITIATED THE APCH. ALSO OUR ALTERNATE WAS RIC AND WAS NOT EVEN CONSIDERED BECAUSE OF THE DISTANCE AND OUR FLAP SIT. PHL WITH A COUPLED APCH WAS OUR DECISION AS THE SAFEST OPTION AND NEAREST SUITABLE ARPT. WE PROCEEDED ON AN ILS TO RWY 9R AND MADE VISUAL CONTACT WITH APCH LIGHTING SYS AT 250 FT AGL AND RWY AT 200 FT AGL. CONTINUED VISUALLY TO A NORMAL AUTO-LAND. NO EMER WAS DECLARED AS THE ACFT WAS IN NO WAY IN AN UNSAFE OR EMER SIT. ONLY THE DECISION TO PERFORM A FLAPS 20-22 DEG CAT III APCH WAS A SLIGHT DEV FROM COMPANY SOP; YET THERE IS NO PROHIBITION FROM DOING SO IN ANY OF OUR FAA MANUALS; QRH; ETC.