FATIGUED FLT CREW OF A319 FAIL TO EXTEND LNDG GEAR UNTIL MASTER WARNING ALERTS WHEN FLAPS EXTENDED TO LNDG CONFIGN.

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WE WERE ON LEG 2 OF A 4-DAY TRIP IN LGA. WHILE INITIALLY TOLD LDA-A RWY 22; WE WERE ON FINAL APCH TOLD TO 'NOW EXPECT A VISUAL.' THINGS WERE HAPPENING FAST AND I WAS HEADS DOWN RE-PROGRAMMING THE BOX. FO WAS FLYING AND CALLING FOR CONFIGURING CHANGES IN ORDER TO SLOW. TFC TO FOLLOW WAS POINTED OUT. WE WERE CLRED THE VISUAL BEHIND TFC. INTERCEPTED THE LOC AND GS. SPACING STARTED TO LOOK GOOD. AT APPROX 1000 FT AGL; GOT A MASTER WARNING WITH AN UNSAFE GEAR INDICATION. WE HAD NOT PUT THE GEAR DOWN. IMMEDIATELY SELECTED THE GEAR DOWN; WARNING CEASED. DID ANOTHER LNDG CHK AND ALL NORMAL; SO LANDED. FACTORS: 1) FATIGUE -- LONG DUTY DAYS WITH SHORT OVERNIGHT. THE INSIDIOUS TYPE; IE; JUST CLOSE EYES FOR A SECOND. 2) TARGET FIXATION -- INTENT WITH TFC AND SPACING TO ARPT WITH SHORT RWY. 3) ACFT DESIGN -- I HAVE NEVER FLOWN ANY OTHER ACFT THAT WILL LET YOU GO TO LNDG FLAPS WITHOUT GIVING A GEAR WARNING. WILL STRIVE HARDER IN FUTURE TO NOT LET FATIGUE SET IN AND LOOK OUT FOR TRAPS; IE; VISUALS; ETC.