DC9 CREW EXPERIENCED AN ALTDEV IN ZHU CLASS E.

Narrative

THE INCIDENT OCCURRED DURING THE INITIAL DSCNT PHASE FOR LNDG AT BROWNSVILLE; TX. DSCNT INSTRUCTIONS WERE RECEIVED AT FL330 WITH STEP-DOWN TO FL230; FL190; AND 16000 FT BEFORE THE INCIDENT TOOK PLACE. WHEN THE CLRNC TO 16000 FT WAS RECEIVED; I; THE PNF; ACKNOWLEDGED AND DIALED THE CORRECT ALT ON THE ALT ALERTER. THE CAPT ACKNOWLEDGED BY STATING '16000 FT' AND POINTING TO THE ALT ALERTER. SHORTLY THEREAFTER; THE CAPT BRIEFED THE APCH AND CALLED FOR THE DSCNT CHKLIST. WHILE I WAS INVOLVED WITH THE EXECUTION OF THE CHKLIST; THE CTR CTLR ALERTED US TO OUR ALTDEV; AT WHICH TIME WE HAD ALREADY DSNDED TO APPROX 14500 FT. THE CTR CTLR DID NOT SEEM OVERLY CONCERNED WITH THE INCIDENT AS THERE WERE NO OTHER ACFT IN THE VICINITY. INSTEAD; AFTER A SHORT PAUSE; HE ASSIGNED US A DSCNT TO 6000 FT. CONTRIBUTING FACTORS INCLUDED NOISE LEVEL; AUTOMATION; DISTR; AND FATIGUE. THE NOISE LEVEL IN THIS PARTICULAR ACFT IS SIGNIFICANT DUE TO ITS AGE AND THE REMOVAL OF INSULATION IN THE MAIN CABIN. WE WERE UNABLE TO HEAR THE AURAL ALERT OR SEE THE AMBER LIGHT. AUTOMATION; OR LACK OF IT; PLAYED AN IMPORTANT ROLE IN THIS INCIDENT. BOTH; THE CAPT AND I CAME TO OUR PRESENT EMPLOYER FROM ACFT THAT INCORPORATED FULLY AUTOMATED (ALT CAPTURE) GLASS COCKPITS. ADDITIONALLY; OUR INVOLVEMENT WITH THE CHKLIST DREW OUR ATTN AWAY FROM OUR ASSIGNED ALT. BUT THE MAJOR CONTRIBUTING FACTOR TO THE INCIDENT WAS FATIGUE. AFTER ARRIVING AT CHICAGO AT XA30; CHKING INTO A HOTEL AT XB00; AND GETTING A WAKE-UP CALL AT XE00 TO RPT FOR DUTY AT XH00 IN DETROIT; THE CAPT HAD BEEN GIVEN AN 'OPPORTUNITY' TO REST FOR ONLY 3 HRS DURING THE PRECEDING 24 HRS. ALTHOUGH HE ACKNOWLEDGED THE CLRNC TO 16000 FT; HIS COGNITIVE AWARENESS LED HIM TO BELIEVE THAT THE ASSIGNED ALT WAS 11000 FT.