AN A320 FLC ACCEPTS A LAST MIN RWY CHANGE THAT RESULTS IN A NON STABILIZED APCH TO LNDG.

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WE WERE CLRED FOR THE APCH TO RWY 23L; BUT CONTACTING TWR ON A 10 MI FINAL; WERE ASKED IF WE COULD PROCEED VISUALLY TO RWY 23R; WITH A CAUTION THAT THE APCH END WAS OBSCURED BY BLOWING DUST. WE WERE ATTEMPTING TO VISUALLY TRANSITION TO RWY 23R; WHEN I; AS PF; DELAYED MY CALL FOR GEAR EXTENSION. APCHING 1000 FT ABOVE FIELD ELEVATION; WITH RWY 23R IN SIGHT; I ASKED FOR THE GEAR AND FINAL DSCNT CHKLIST. MY CALL FOR GEAR EXTENSION WAS LATE; AND CONTRARY TO STABILIZED APCH GUIDELINES. WE WERE SLOWED TO NEAR APCH SPD; AND THE APCH WAS FULLY STABILIZED AT 500 FT ABOVE FIELD ELEVATION; AND WE CONTINUED THE APCH FOR AN UNEVENTFUL LNDG; ON SPD AND IN THE TOUCHDOWN ZONE. THE GEAR; HOWEVER; WAS EXTENDED LATE; OWING PRIMARILY TO MY DISTR WHILE TRYING TO ACQUIRE RWY 23R FOR A VISUAL APCH. THE ECAM FOR 'GEAR' SOUNDED BRIEFLY AT 800 FT AGL AS THE GEAR WAS IN TRANSIT. SOP DICTATES A MISSED APCH UNDER THESE CONDITIONS; BUT I CONTINUED THE APCH TO LNDG. I WAS A BIT BEHIND THE ACFT; AND SHOULD HAVE GONE AROUND.