WINDSHEAR ENCOUNTER ON APCH TO ATL; GA.

Narrative

I WAS FLYING AS THE FO ON A FLT TO ATL. WE WERE BEING VECTORED TO AN ILS TO RWY 9R. THE WX WAS MARGINAL; CEILING 300 FT OVCST; WIND VARYING 140-210 DEGS AT 12 KTS GUSTING TO 18 KTS. APCH ADVISED THAT A 15 DEG CUT INTO THE WIND WAS NEEDED TO HOLD FINAL. WE WERE AT 5000 FT MSL; HDG 180 DEGS; WITH AUTOPLT COUPLED UP TO ILS RWY 9R. DUE TO THE HVY WIND; WE WERE GIVEN A VECTOR OF 150 DEGS TO JOIN THE LOC; CLRED FOR THE APCH. THE AUTOPLT QUICKLY CAPTURED THE LOC AND MADE A HARD TURN TO THE L TO KEEP CTRED. COUPLED WITH THE STRONG WIND; WE BLEW THROUGH THE LOC TO THE N. THE AUTOPLT STRUGGLED BUT CORRECTED BACK. JUST PRIOR TO RE-CENTERING; WE CAPTURED THE GS AND BEGAN A SLOW DSCNT TO THE OM. AFTER JUST PASSING 3500 FT MSL; WE EXPERIENCED A HUGE DSCNT AND DEGRADING PERFORMANCE FOLLOWED BY A WINDSHEAR WARNING AND; SECONDS LATER; A GPWS WARNING. WE IMMEDIATELY BEGAN A GAR ON THE FIRST WARNING; BUT DID NOT ARREST THE DSCNT UNTIL 1000 FT LOW. TWR IMMEDIATELY RPTED OUR 'LOW ALT' WARNING; FOLLOWED BY A LLWAS ALERT THEN BY A 'MICROBURST' ALERT. TOTAL TIME FROM ONSET TO RECOVERY WAS 15 SECONDS MAX. OUR GAR TOOK US OUT TO THE S (180 DEG HDG) THEN OUT TO THE W (270 DEG HDG). ALT CTL WAS IMPOSSIBLE FOR THE NEXT 5+ MINS -- +/-200 FT UNTIL WE CLBED TO 5000 FT MSL. 20 MINS LATER; EVERYTHING SETTLED OUT.