THE FLC OF AN LGT CARGO FLT DISCOVERED THAT THEY WERE TOO LOW WHEN THEY RECEIVED A RADAR ALTIMETER 1000 FT CALL. WHILE THE CREW WAS CLBING TO A HIGHER ALT; THE APCH CTLR INTERVENED. ALTDEV ALT OVERSHOT.

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ON AN IFR FLT FROM MKE TO ATW; WE WERE AT CRUISE AT 12000 FT. WE WERE TALKING TO ZAU. THEY GAVE US DISCRETION TO 10000 FT. HAVING STARTED OUR DSCNT; THEY THEN GAVE US DISCRETION TO 4000 FT. PASSING THROUGH ABOUT 7000 FT THEY GAVE US DSCNT TO 2000 FT. AT THIS TIME THEY HANDED US OVER TO GRB APCH. WE CONTINUED DOWN AND LEVELED AT 2000 FT. LEVELING; WE GOT A 1000 FT CALL ON THE RADAR ALTIMETER. RIGHT AT THIS TIME GRB APCH CAME BACK TO VERIFY OUR ALT. I HAD TOLD THEM WE RECEIVED 2000 FT FROM ZAU. I REMEMBER ALL MY READBACKS FOR EVERY DSCNT AND REMEMBER CLRLY WHAT I HAD SAID. ANYWAY; WE WERE ALREADY IN A CLB TO 3000 FT WHEN WE HEARD OUR RADAR ALTIMETER CALLOUT 1000 FT. GRB APCH SAID NO PROB. NOTHING WAS SAID. I HAD LITTLE SLEEP THE FOLLOWING DAY DUE TO A NOISY HOTEL. SUPPLEMENTAL INFO FROM ACN 326511: PROB AROSE DUE TO MISCOM BTWN CREW AND ZAU. DISCOVERED BY VISUAL PERCEPTION OF BEING TOO LOW AND RADAR ALTIMETER VOICING 1000 FT WHILE APCH CTL SIMULTANEOUSLY STATED THAT THE ASSIGNED ALT WAS 3000 FT.