A CANADAIR CL65 BEING VECTORED FOR A VISUAL APCH AND CLRED TO 5000 FT DSNDS TO 4400 FT AND IS ALERTED BY THE ALT ALERT SYS.

Narrative

KNOXVILLE APCH WAS VECTORING US FOR A VISUAL APCH TO RWY 23L. WE WERE APCHING VXV VOR; CLRED TO 5000 FT. WE'D JUST RPTED THE RWY IN SIGHT; BUT HAD NOT YET BEEN CLRED FOR THE APCH. I HAD MY HEAD DOWN IN THE COCKPIT; SETTING UP MY NAV RADIO OR THE FMS; I DON'T REALLY REMEMBER. I HEARD THE 'ALT ALERT' TONE AND I THOUGHT AND SAID '1000 FT TO GO.' I DID NOT IMMEDIATELY LOOK UP. WHEN I DID LOOK UP; I NOTICED THAT WE WERE DSNDING THROUGH ABOUT 4400 FT AND OUR ALT SELECTOR WAS ON 5000 FT. THIS WAS NOT GOOD; BOTH BECAUSE OF ATC CONSIDERATIONS AND BECAUSE THERE ARE HILLS IN THE NEIGHBORHOOD. RIGHT THEN; WE WERE CLRED FOR THE VISUAL. CONTRIBUTING FACTORS: POOR PLANNING; I SHOULD HAVE DONE MY SETUP WAY BEFOREHAND. ANYWAY; HOW MUCH SETUP IS REALLY NEEDED FOR A VISUAL IN GOOD VMC TO A RWY WITH NO ILS INSTALLED? LACK OF SITUATIONAL AWARENESS. THE ALERT TONE IN THE CL65 IS EXACTLY THE SAME WHETHER IT'S TELLING YOU 'YOU'VE GOT 1000 FT TO GO' OR 'HEY; DUMMY! YOU JUST PASSED UP YOUR ASSIGNED ALT.' SINCE THAT'S 2 DIFFERENT MESSAGES IT MIGHT MAKE SENSE TO HAVE 2 DIFFERENT TONES; OR A TONE FOR ONE AND A VOICE FOR THE OTHER. SUPPLEMENTAL INFO FROM ACN 539382: I LOOKED UP AND NOTICED THAT THE ALT ALERTER WAS FLASHING 5000 FT AND WE WERE AT APPROX 4300 FT MSL. AS PNF; I DID NOT THINK MUCH ABOUT IT OTHER THAN IT WAS NOT THE CAPT'S HABIT TO DSND BELOW AN ALT WITHOUT VERIFYING AN ALT. I IMMEDIATELY THOUGHT WE MUST BE CLRED FOR THE VISUAL APCH TO RWY 23L; WHICH WAS CLRLY VISUAL; WHICH I THOUGHT WOULD ACCOUNT FOR US BEING BELOW THE PREVIOUSLY ASSIGNED ALT. THE CAPT IN THE COURSE OF THE TRIP HAD ANSWERED RADIO CALLS FOR ME WHILE I WAS BUSY DOING OTHER TASKS. I IMMEDIATELY AFTER SEEING US BELOW ALT; THE CTLR CLRED US FOR THE VISUAL APCH; WHICH I THOUGHT MUST BE THE CAPT VERIFYING THE CLRNC WHICH HE HAD DONE MANY TIMES DURING THE TRIP. AFTER THE TURN AT TYS THE CAPT MENTIONED THE INCIDENT ON THE CLBOUT. HE SAID; 'I THINK I MAY HAVE DEVIATED FROM ALT ON THE DSCNT INTO TYS.' BETTER CREW COORD AND COM COULD HAVE CLRED UP THE REASON WE WERE BELOW 5000 FT. WHEN I NOTICED THE ALT FLASHING; I SHOULD HAVE QUERIED THE CAPT AS TO WHAT WAS HAPPENING.