THE CREW OF A BE1900 FLEW INTO A TSTM ON APCH TO FLL AND EXECUTED A MISSED APCH AT 700 FT DUE TO A MICROBURST.

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I WAS OPERATING FLT TO FLL AND WAS CLRED TO ENTER A HOLDING PATTERN FOR AT LEAST 45 MINS DUE TO HVY WX APCHING THE FLL ARPT. AFTER HOLDING FOR APPROX 30 MINS; I WAS GIVEN THE OPPORTUNITY TO TRY THE ILS 9L DESPITE HVY RAIN AND RPTS OF WINDSHEAR. I DECIDED TO TRY THE APCH AND ABOUT 1000 FT AGL WE RECEIVED HVY TURB AND RAIN AND CONTINUED THE APCH. AROUND 700 FT AGL RECEIVED WINDSHEAR +/-40 KTS WITH HVY TURB AND RAIN THAT SEEMED TO BE ASSOCIATED WITH A MICROBURST. THE DECISION WAS MADE TO TERMINATE THE APCH AND GAR; HOWEVER; THE AIRPLANE WOULD NOT CLB WITH NORMAL CLB PWR AND WE EVEN BEGAN TO DSND TO APPROX 300 FT AGL. I RECEIVED NUMEROUS GPWS WARNINGS DUE TO THE MICROBURST ACTIVITY. I PUSHED THE PWR LEVERS UP TO THE MAX POS AND RECEIVED 'T6' AND 'OIL' MASTER AURAL WARNINGS; HOWEVER; WAS UNABLE TO IDENT THE AFFECTED ENG DUE HVY TURB AND DIRE ATTEMPTS TO CTL THE ACFT. WE WERE SUCCESSFUL WITH THE CLBOUT AND EXITED THE MICROBURST DUE TO THE EXCESS PWR OBTAINED BY USING TRANSIENT PWR. THE PWR FOR THE ENGS WAS IMMEDIATELY REDUCED AFTER WE WERE ABLE TO CTL THE ACFT SAFELY. I TOOK A NOTE OF ALL ENG PARAMETERS AND FOUND THEM TO BE NORMAL INDICATIONS. WE PROCEEDED TO LAND AGAIN IN FLL AFTER THE HVY WX MOVED AWAY FROM THE FIELD AND WAS FINALLY SUCCESSFUL.