A FATIGUED ACR PILOT REPORTS CONFUSING A HDG ASSIGNMENT FOR AN ALT. THE ACFT DESCENDED TO 6000 FT ON AN APCH GOING BELOW MIN VECTORING ALT.

Narrative

OUR DAY STARTED IN ZZZ AND WE FLEW TO LAS; CITY; AND FINISHED BACK IN LAS OVER 4 HRS LATE DUE TO WX RELATED DELAYS IN BOTH CITIES. WHILE ON VECTORS BY LAS APCH CTL; ON THE LAST LEG OF THE DAY; WE WERE GIVEN A LOW ALT ALERT BY LAS APCH CTL. I WAS THE CAPT AND PNF ON THIS LEG. WE WERE ON A HDG OF 080 DEGS AT 8000 FT; APPROX ABEAM FROM THE FIELD ON A WIDE DOWNWIND WHEN WE STARTED A DSCNT TO 6000 FT AFTER WHAT WE UNDERSTOOD AND READ BACK TO BE A DSCNT CLRNC TO 6000 FT. PRIOR TO REACHING 6500 FT; THE CTLR SAID; 'COMPANY NUMBER; LOW ALT ALERT; CLB IMMEDIATELY TO 8000 FT.' THE PF IMMEDIATELY AND AGGRESSIVELY ADDED PWR AND STARTED THE CLB TO 8000 FT. THE CTLR ASKED WHAT ALT WE WERE DSNDING TO AND WE RESPONDED 6000 FT. HE SAID HE HAD GIVEN US A HDG OF 060 DEGS AND NOT A DSCNT TO 6000 FT. NOTHING FURTHER WAS SAID ABOUT THE INCIDENT BY THE CTLR AND WE NEVER GOT A GPWS WARNING. THE REST OF THE APCH WAS UNEVENTFUL. I THINK FATIGUE PLAYED A MAJOR ROLE IN WHAT HAPPENED. WE WERE APCHING THE END OF A VERY LONG DUTY DAY WHICH INCLUDED SEVERAL HRS OF GND DELAYS; PAX ISSUES; MODERATE TURB AND HOLDING ON EVERY LEG; ICING AND ALL THE OTHER CHALLENGES ASSOCIATED WITH FLYING IN BAD WX ALL DAY LONG. THE LESSON I LEARNED IS THAT ON DAYS LIKE THIS; AS WE GET MORE AND MORE FATIGUED; WE NEED TO CONSTANTLY REMIND OURSELVES TO STAY ON OUR TOES AT ALL TIMES IN ORDER TO AVOID MAKING MISTAKES AND ALSO TO CATCH OTHER PEOPLE'S POTENTIAL MISTAKES; WHICH ARE PROBABLY OPERATING UNDER THE SAME TYPES OF PRESSURES AND STRESS.