AN A300 REV UNLK LIGHT ILLUMINATED ON FINAL AT 4200 FT. THE CREW CONTINUED THE APCH; ENG RUNNING; MAKING AN ABNORMAL FLAP CONFIGURATION (15/20) LANDING IN THE EVENT OF AN ENG SHUT DOWN AND GAR.

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FO WAS FLYING LEG. AT LEVELOFF OUTSIDE ZZZZZ; CLRED FOR ILS XXL; THE CAUTION CHIME ANNOUNCED A CAUTION; WITH NO ECAM RESPONSE SEVERAL TIMES. WE VERIFIED A REV UNLK LIGHT R ENG. WE WERE CONFIGURED AT FLAPS 20 DEGS; GEAR UP; WITH CLRNC TO ZZZZZ. THE AUTOPLT AND AUTOTHROTTLES WERE ENGAGED. THE CAUTION CHIME CONTINUED WITH NO CAUTION LIGHT; NO ECAM FOR SEVERAL SECONDS AS I RETRIEVED THE QRH. THE FO CONTINUED THE APCH. THE ECAM THEN RESPONDED WITH THE REV UNLK ECAM ITEMS WHICH WE PERFORMED. I FOLLOWED UP THE COMPLETION OF THE QRH CHKLIST. WE DECIDED TO CONTINUE THE APCH; MONITOR THE ENG; AND PREPARE FOR AN ENG SHUTDOWN ON FINAL. I CHOSE TO CONFIGURE ONLY TO FLAPS 15/20 ONLY FOR THE FOLLOWING REASONS: THE CHANCE OF AN ENG SHUTDOWN ON FINAL. WE WERE RATHER LIGHT WT; AND THE 10000 FT RWY EASILY SUPPORTED THE FASTER APCH SPD; LOWERING THE OVERALL THRUST REQUIRED FOR APCH; THUS ALLOWING MINIMAL ENG AXIS-SYMMETRIC THRUST IN CASE OF ENG SHUTDOWN. I ALSO THOUGHT THAT THIS WOULD SAFEGUARD A POSSIBLE GAR IF THE APCH GOT UGLY WITH A SHUTDOWN DURING THE DSCNT TO TOUCHDOWN. I ALSO THINK THAT THIS CONFIGN MORE CLOSELY FOLLOWED OUR TRAINING FOR LNDG WITH AN ENG SHUTDOWN; SHOULD THAT END UP BEING THE CASE IF THE REVERSER DEPLOYED DURING THE DSCNT. THE ARR WAS NORMAL; THE LIGHT STAYED ON UNTIL SHUTDOWN; AND WE ENTERED THE LOGBOOK WRITE-UP. I CONSULTED WITH THE DUTY ACP (ASSISTANT CHIEF PLT) AT ZZZ AND DECIDED TO RPT CONSIDERING IN RETROSPECT THAT THE AOM BULLETIN CONCERNING THE USE OF 15/20 FLAPS FOR LNDG AS NOT SUPPORT FOR NORMAL OPS; AND I HAD NOT DECLARED AN EMER TO ALLOW MYSELF AUTH TO DO SUCH. I THINK THE CHOICE FOR FLAP SETTING WAS THE BEST OPTION CONSIDERING THE POSSIBILITY OF AN INFLT DEPLOYMENT OF A THRUST REVERSER ON THE APCH; AND WAS BEST INSURANCE TO SAFEGUARD THE CONTROLLABILITY OF THE ACFT IN SUCH A CASE; AND ALLOWING THE FO FLYING A CONFIGN WHICH WAS FAMILIAR IN FLYING A SUDDEN SINGLE ENG APCH. I DID NOT REALLY CONSIDER THE POSSIBILITY THAT I WAS VIOLATING THE AOM PER THE BULLETIN UNTIL I BOUNCED THE SITUATION OFF THE ACP; AND DECIDED A RPT MIGHT BE THE BEST COURSE. I DO NOT THINK IN THIS SITUATION; WITH NO DEPLOYMENT; AND CONSIDERING HOW MUCH TIME WE HAD; THAT DECLARING AN EMER WAS NECESSARY. MY POSTFLT CONVERSATION WITH THE FO; SHE AGREED. DURING MY IOE; A COUPLE OF 15/20 FLAP APCHS WERE DEMONSTRATED. I THINK THAT THE COMPANY POLICY DISCOURAGING THESE FLAP SETTINGS FROM NORMAL OPS IS OVER MGMNT OF OPERATING THE ACFT FOR WHAT IS A NORMAL LNDG FLAP SETTING. CREWS SHOULD BE ALLOWED THE FLEXIBILITY TO USE ALL NORMAL PROCS OF CERTIFICATION; CONSIDERING CIRCUMSTANCES SUCH AS WT; WINDS AND TERRAIN. I WOULD THINK THAT USING A 15/20 FLAP FOR LNDG IS NO DIFFERENT DECISION THAN THAT OF USING ONE OF THE THREE TKOF FLAP SETTINGS WE CAN USE IN NORMAL OPS.