BA3200 FLC ON APCH IS ALERTED BY GPWS 'TOO LOW; GEAR.' THEY EXTEND GEAR AND COMPLETE THE LNDG.

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WE WERE CLRED FOR THE VISUAL APCH TO RWY 30L AT STL. THE FO WHO WAS THE PF; CALLED FOR FLAPS 10 DEGS. THE TWR CLRED US TO LAND ON RWY 30L; HOLD SHORT OF RWY 24. WE DID NOT KNOW IF WE HAD THE PERFORMANCE FIGURES FOR THAT; SO I TOLD THE TWR I WOULD CHK ON THE HOLD SHORT PERFORMANCE. ON CHKING THE PERFORMANCE; I FOUND WE COULD LAND AND HOLD SHORT OF RWY 24. JUST AS I WAS ABOUT TO TELL THE TWR; HE CLRED US FOR THE VISUAL TO RWY 30R; AND ASKED US TO CONTACT THE TWR ON 120.05. I PREFERRED TO LAND ON RWY 30L BECAUSE WE WERE ALREADY ESTABLISHED ON THE APCH AND ALSO WE WOULD HAVE A SHORTER TAXI. I TOLD THE TWR CTLR WE COULD LAND ON RWY 30L AND HOLD SHORT OF RWY 24 IF THAT IS WHAT HE NEEDED. HE SAID; 'NAH; WE'VE GOT SOMETHING ELSE GOING ON HERE -- GO TO RWY 30R AND CONTACT THE TWR ON 120.05.' I ACCEPTED; AND THE FO BEGAN THE SIDESTEP MANEUVER TO RWY 30R. I CALLED THE RWY 30R TWR AND GOT LNDG CLRNC. AS THE FO ALIGNED HIMSELF WITH THE RWY 30R EXTENDED CTRLINE; WE ENCOUNTERED WHAT SEEMED LIKE WAKE TURB; ALTHOUGH THE PREVIOUS ARR HAD BEEN 4 MI AHEAD OF US. IN ADDITION; WE STARTED DROPPING BELOW THE GLIDEPATH. WE HAD TUNED IN THE ILS TO BACK UP THE VISUAL APCH; AND IN SPITE OF THE FO'S ATTEMPT TO MAINTAIN THE GLIDEPATH; WE MOMENTARILY DSNDED ABOUT 2 DOTS BELOW THE GS. AS I WAS CONSIDERING A GAR; THE APPARENT WAKE TURB/WINDSHEAR ABATED AND THE FO WAS ABLE TO GET BACK ON THE GLIDEPATH. AT THIS TIME WE HEARD 'TOO LOW; GEAR' ON THE GPWS. I REALIZED I HAD NOT HEARD THE FO CALL FOR 'GEAR DOWN; FLAPS 20 DEGS; BEFORE LNDG CHKLIST.' I IMMEDIATELY EXTENDED THE LNDG GEAR; CONFIGURED THE AIRPLANE AND COMPLETED THE BEFORE LNDG CHKLIST. THE REMAINDER OF THE APCH AND LNDG WERE WITHOUT INCIDENT. ON THAT APCH; BOTH THE FO AND MYSELF WERE DISTRACTED TO THE POINT THAT WE DID NOT CONFIGURE THE ACFT FOR LNDG UNTIL WE HEARD THE GPWS WARNING. THE FO SAID HE WAS ABOUT TO MAKE THE CALL WHEN WE WERE ASKED TO GO TO RWY 30R. THE SUBSEQUENT DISCUSSION WITH THE RWY 30L TWR AND TURB/SHEAR ON RWY 30R FURTHER DISTRACTED HIM AND CAUSED HIM TO MISS THE REQUIRED CALL. AS THE PNF I SHOULD HAVE BEEN MONITORING THE APCH MORE CLOSELY BUT I TOO WAS DISTRACTED WITH: 1) CHKING THE PERFORMANCE FOR THE HOLD SHORT OP; 2) TRYING TO SECURE RWY 30L FOR US AFTER THE TWR TOLD US TO GO TO RWY 30R; 3) CALLING THE RWY 30R TWR FOR LNDG CLRNC; AND 4) THE ALT EXCURSION DUE TO THE TURB/SHEAR AFTER ALIGNMENT WITH RWY 30R. THERE WAS A LOT GOING ON DURING THAT APCH. CTLRS SHOULD NOT MAKE CHANGES IN RWY ASSIGNMENT DURING THE LATTER PART OF THE FINAL APCH UNLESS ABSOLUTELY NECESSARY. AT THAT TIME RWY 30L WAS COMPLETELY CLR AND THE CTLR COULD EASILY HAVE LET US LAND ON RWY 30L AS ORIGINALLY CLRED. WHATEVER ELSE HE HAD 'GOING ON' COULD HAVE WAITED ANOTHER 2 MINS. LNDG ACFT AFTER ALL HAVE PRIORITY. HOWEVER; NOTWITHSTANDING ATC VAGARIES; IN ORDER TO PREVENT MY OVERLOOKING KEY ITEMS SUCH AS ACFT LNDG CONFIGN; I WILL CONSIDER THE FOLLOWING: 1) FOLLOW STANDARD PROCS. OUR OPERATING PROCS HAVE US BRING PROP RPM FROM A CRUISE SETTING TO 100% AS PART OF THE BEFORE LNDG CHKLIST. WE STARTED THIS APCH HIGH (DUE TO OUR INITIAL ASSIGNED ALT); AND IN ORDER TO HELP SLOW THE AIRPLANE AND LOSE ALT FASTER THE FO HAD ASKED FOR 100% RPM WHEN WE STARTED THE APCH. AS A RESULT; THE AIRPLANE SOUNDED AND FELT LIKE IT WOULD AFTER THE BEFORE LNDG CHKLIST. THIS COULD HAVE SUBCONSCIOUSLY CAUSED US TO MISS THE REQUIRED CALLOUT. 2) AVOID LOOKING AT PERFORMANCE CHARTS WHILE ON FINAL APCH. IF I AM NOT SURE OF A HOLD SHORT PERFORMANCE LIMIT; I WILL SIMPLY DECLINE THE CLRNC RATHER THAN TRY TO LOOK IT UP ON FINAL. 3) GAR IF WAKE TURB OR WINDSHEAR IS AFFECTING ACFT CTL. THIS WILL REDUCE THE POSSIBILITY OF MISSING KEY ACFT ITEMS DUE TO THE DISTR OF DEALING WITH THE TURB/SHEAR. 4) DO NOT ALLOW ATC COM TO INTERFERE WITH THE OP OF THE ACFT. REMEMBER AVIATE; NAV; COMMUNICATE.