SMT PLT WAS SAVED FROM LNDG GEAR UP BY A VERY ALERT TWR CTLR.

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WHILE APCHING TO LAND AT SAC ARPT; I REACHED 1000 FT AGL APPROX 5 MI FROM THE ARPT. I LEVELED AT 1000 FT AND ELECTED TO DELAY LOWERING THE LNDG GEAR UNTIL I WAS CLOSER TO THE ARPT. THIS WAS A VIOLATION OF MY PERSONAL CHKLIST ITEM IN THIS AIRPLANE OF GEAR DOWN BELOW 140 MPH; 20 INCHES MANIFOLD PRESSURE; 1000 FT AGL. WHILE IN THE LNDG FLARE; THE TWR REQUESTED AN IMMEDIATE GAR; WHICH I DID. AN ACCIDENT/INCIDENT WAS ONLY NARROWLY AVERTED BY THE TWR CTLR'S OBSERVANCE AND TIMELY ACTION. THE PRELNDG CHKLIST HAD BEEN COMPLETED WITH 'GEAR TO GO.' THE CAUSE OF THIS NEAR ACCIDENT WAS RELYING ON MEMORY TO COMPLETE THE CHKLIST; AND FAILURE TO CONFIRM 'GEAR DOWN' ON SHORT FINAL. IT IS SAID THAT THERE ARE THOSE WHO HAVE; AND THOSE WHO WILL; REFERRING TO GEAR-UP LNDGS. THERE IS ANOTHER CATEGORY 'THOSE WHO ALMOST DID' THAT IS NEARLY AS HUMILIATING AS BEING 'ONE WHO DID' -- IT IS CERTAINLY A MEMORABLE EXPERIENCE. IT WILL BE A LONG TIME BEFORE I GET CLOSE TO A RWY WITHOUT HAVING VERIFIED 'BEFORE LNDG CHKLIST COMPLETE.'