ALTDEV ALT OVERSHOT IN DSCNT.

Narrative

ON DSCNT INTO SLC CLRED TO 9000 FT. CAPT AT CTLS. FO CALLED OUT ALT AT 8800 FT. ACFT BOTTOMED OUT AT 8500 FT AND CLBED BACK TO 9000 FT. CAUSAL FACTORS: CAPT NOT FEELING WELL DUE TO ILLNESS (SCHEDULED TO BE TAKEN OFF TRIP IN SLC). FO AFTER CALLING OUT 1000 FT WARNING WAS SCANNING OUTSIDE FOR TFC. SO WAS ON INTERPHONE WITH FLT ATTENDANT CONCERNING GATE ASSIGNMENT. IN HINDSIGHT; THE CAPT SHOULD NOT HAVE BEEN FLYING THE LEG. THE FO AND SO SHOULD HAVE DONE A BETTER JOB IN PRIORITIZING THEIR DUTIES. SUPPLEMENTAL INFO FROM ACN 299998: STEP DSCNTS AND REDUCED AIRSPDS WERE PROGRESSIVELY ASSIGNED BY APCH CTL. FIRST INDICATION OF A PROB WAS MY COPLT'S CALL OF 'ALT' AND I REALIZED I WAS DSNDING THROUGH 8700 FT. ALMOST IMMEDIATELY APCH CTL GAVE US A CALL AND WE CLBED BACK TO 9000 FT. A CALL TO APCH CTL ON GND IN SLC INDICATES THERE WAS NO SEPARATION PROB ALTHOUGH 8000 FT IS THE DEP CORRIDOR. I BELIEVE PRIMARY CAUSE WAS FATIGUE COMPOUNDED BY HAND FLYING THROUGH TURB. I HAD LITTLE SLEEP (2-3 HRS) THE NIGHT BEFORE IN A HOTEL IN LAX; DUE TO BEING IN THE FIRST STAGES OF A COLD. BEFORE THIS HAPPENED I HAD NOTIFIED THE COMPANY TO REPLACE ME IN SLC DUE TO COMING DOWN WITH A COLD. THE LESSON MAY BE THAT I SHOULD NOT HAVE FLOWN AT ALL; LET ALONE THESE EARLY LEGS.