ACR ON GS; ON LOC IS TOLD ATC HAS LOW ALT ALERT. DETERMINES AT PROPER ALT ON APCH.

Narrative

WE WERE CLRED FOR A VISUAL APCH TO FOLLOW THE ACFT TO 34R AND TOLD TO MAINTAIN 3000 FT UNTIL ESTABLISHED AND 180 KIAS TO THE FAF. ON FINAL; ON GS AND WITHIN 1 DOT OF THE LOC; TWR CTLR SAID HE HAD A LOW ALT WARNING ON US AND HAD US AT 2100 FT. WE IMMEDIATELY CHKED OUT ALT; LOCATION; ETC; AND CONFIRMED WE WERE AT 2100 FT. WE COULD NOT DETERMINE ANYTHING WRONG SO WE CONTINUED ON THE APCH AND LANDED NORMALLY. I DID NOT CALL THE TWR CTLR AFTER LNDG TO DISCUSS THE SITUATION BUT LATER I WISH I HAD AS OVER THE NEXT 3 DAYS THE EVENT SURFACED IN OUR CONVERSATION AS TO WHY THERE WAS A WARNING. AFTER THE TRIP; I DISCUSSED IT WITH OUR SAFETY REPRESENTATIVE. HE DISCUSSED THE SITUATION WITH SEATTLE TWR PERSONNEL AND WAS TOLD THEY HAVE 3 OR 4 ERRONEOUS WARNINGS A DAY FOR SEVERAL REASONS WHICH I WON'T ELABORATE ON HERE. IF THIS EVER HAPPENS AGAIN; I WILL CALL TWR AFTER LNDG TO DETERMINE WHY THE WARNING OCCURRED; IF I MADE A MISTAKE AND MISSED SOMETHING; AND FOR THE PEACE OF MIND IN KNOWING IF I ERRED OR NOT. SUPPLEMENTAL INFO FROM ACN 204743: SUSPECT SOFTWARE ERROR IN APCH FACILITY WARNING SYS.