DC10 CARGO MAINTAINING 9000 FT. FO; PF; COPIED CLRNC TO DSND TO 3000 FT FOR A SIMILAR COMPANY CALL SIGN. CTLR QUERIED ALT AT SAME TIME CAPT QUESTIONED THE DSCNT. RETURNED TO ALT; NO CONFLICT.

Narrative

LEVEL FLT AT 9000 FT MSL IN TERMINAL AREA. I WAS CAPT; FO WAS FLYING. OUR FLT NUMBER WAS ABC. ACFT ABOUT 6-8 MI AHEAD; SAME COMPANY; SIMILAR FLT NUMBER (ABD). ATC CLRED FLT ABD TO 3000 FT. I WAS TRYING TO TUNE AND IDENT LOC AND NDB FOR APCH. I LOOKED UP AND SAW FO HAD VACATED 9000 FT AS HE SAID TO ME 'SET 3000 FT IN ALT ALERTER.' AT THIS TIME WE WERE DSNDING THROUGH ABOUT 8700 FT. JUST THEN ATC CALLED AND SAID 'ABC MAINTAIN 9000 FT.' I IMMEDIATELY DIRECTED FO TO CLB AS RAPIDLY AS POSSIBLE BACK TO 9000 FT. I NEVER HEARD A CLRNC TO 3000 FT. FO SAID HE DID. SO DIDN'T. BECAUSE FO BEGAN DSCNT WITHOUT ANYONE ACKNOWLEDGING A DSCNT CLRNC; WE NEVER GAVE ATC A CHANCE TO TELL US THAT THE CALL WAS FOR ABD. WE HAVE A VERY SPECIFIC PROC TO FOLLOW REGARDING SETTING THE ALT ALERTER; BUT THE PROC TAKES 2 PEOPLE AND MUST BE FOLLOWED CORRECTLY FOR IT TO PREVENT THIS TYPE OF INCIDENT. WHEN THE PF 'SHOOTS FROM THE HIP' AND BEGINS A DSCNT WITHOUT FOLLOWING THE PROC; WITHOUT AN ACKNOWLEDGEMENT CALL TO ATC WITH A READBACK; HE'S TAKING 2 OTHER CREW MEMBERS OUT OF THE LOOP. CONTRIBUTING FACTORS: 1) SIMILAR CALL SIGNS. OUR COMPANY HAS SIMILAR CALLS SIGNS INTO AND OUT OF MOST HUBS. 2) FATIGUE. LEFT OAK AT XA00 LCL/ARR EWR XF30. PREVIOUS REST IN OAK XA00-XN00. PREVIOUS DUTY PERIOD EWR- OAK XA30 LCL TO XA00 LCL (7 HRS 30 MINS DUTY). 3) FO FAIRLY NEW IN DC10 AND FAIRLY NEW AS FO. 4) FO EX-MIL FIGHTER PLT. USED TO 'DOING HIS OWN THING' -- NOT REALLY USED TO UTILIZING A FULL CREW. 5) BRAND NEW SO PRETTY MUCH 'OUT OF THE LOOP.'