ATX ACFT LANDS GEAR UP IN NIGHT OP.

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I WENT ON DUTY IN HOU THEN JUMPSEAT (REQUIRED BY COMPANY) TO DAL FOR FIRST LEG. I SLEPT PLUS/MINUS 2 HRS DURING LAYOVER THEN LEFT HOU FOR DAL -- GPS DIRECT. WX WAS VMC MOST OF TRIP WITH DSCNT THROUGH BROKEN LAYER FOR VISUAL APCH. ATC CLRED ME FOR VISUAL WHILE STILL IMC. I QUESTIONED THIS BY SAYING 'UNDERSTAND MAINTAIN 3000 UNTIL FIELD IN SIGHT' AT WHICH TIME THEY CANCELED THE CLRNC. I THEN HAD THE FIELD IN SIGHT AND MADE A L DOWNWIND BASE AND FINAL APCH. AT SOME POINT; I HEARD A VERY FAINT SOUND (THE GEAR HORN) BUT DECIDED IT WAS SOMETHING IN THE ELECTRICAL SYS (BEACON; ETC). IT WAS VERY FAINT. I DISMISSED IT WITHOUT EVER THINKING OF THE GEAR. I NOTICED THAT THINGS DIDN'T FEEL RIGHT WITHIN INCHES OF THE GND. I BEGAN TO ATTEMPT A GAR AND THE PWR CAME UP UNEVENLY AND THE PLANE TURNED SIDEWAYS A BIT. I DECIDED THAT A GAR COULD MAKE MATTERS WORSE; SO I RETARDED THE THROTTLES AND SLID TO A STOP ON RWY 13L. CONTRIBUTING FACTORS: I CAN'T DENY THERE IS NO EXCUSE BUT I WILL LIST SOME PROBS WHICH MADE THIS MORE LIKELY TO HAPPEN: NOT USED TO NIGHT SCHEDULE -- AFTER 4-6 WKS OF NIGHT SCHEDULE. 1830-0815 I WAS HAVING TROUBLE SLEEPING IN DAYTIME. ALSO IT HAS BEEN DIFFICULT TO ADJUST AFTER WKEND OF 'NORMAL' HRS. LONG DUTY DAYS -- 14 HRS. 1.4 HR FLT GPS DIRECT -- UNEVENTFUL VMC -- BORING AND I BECAME COMPLACENT. 3 LEGS PER NIGHT IN 3 DIFFERENT MAKE/MODEL ACFT. HAD BEEN MAKING ILS APCHS FOR LAST SEVERAL WKS -- USED TO PUTTING THE GEAR DOWN AT GS INTERCEPT. THIS TIME I JOINED THE ILS INSIDE MARKER -- MAYBE SUBCONSCIOUSLY THOUGHT GEAR WAS DOWN. HORN WAS NOT LOUD ENOUGH TO DRAW ATTN! SHOULD USE WRITTEN CHKLIST NOT JUST GUMPS -- THE OTHER SIDE OF THAT COIN IS THAT WHEN SINGLE PLT YOU WOULD RATHER LOOK OUTSIDE THAN READ CHKLIST AT LOWER ALTS IN BUSY TERMINAL AREAS.