Narrative:

We were flying from peoria, il, to ord and had been cleared direct to ord and to descend to and maintain 11000 ft. Descending through 13000 ft, chicago center told us to maintain 13000 ft. We acknowledged the clearance and said we would go through 13000 ft but climb back up to and maintain 13000 ft. Chicago center then told us to just maintain 12000 ft. At this point we heard chicago center say that ord had shut off arrs and aircraft were going into holding, and the center controller got very busy. The controller came back and cleared us direct to shooz intersection and hold southwest on victor 10, right hand turns, and gave us an efc time of XA00. Since we were going direct ord, the arrival data was no longer in our FMS and we were directly abeam shooz intersection at that time. During our scramble to slow down, turn towards the holding fix, and program the FMS, the autoplt descended through 12000 ft, which we had set in upon receipt of the altitude clearance. We received an altitude alert and descended to 11500 ft before establishing an immediate climb back to 12000 ft. At this point center told us again to maintain 12000 ft and said he showed us at 11400 ft. We were now leveling at 12000 ft and told him we were maintaining 12000 ft. The controller then offered us radar vectors as it was apparent we were having problems with the clrncs at such short notice. When we got the FMS programmed, we were only 5 mi from entry with right hand turns and the remainder of the flight progressed uneventfully! We feel the entire situation arose because of a sudden high workload placed on the controller and consequently placed on us. We went from a simple descent and direct to clearance, to a compound altitude clearance and complicated holding instructions with less than 2 mins to the holding fix, all at the same time. Also, for some unknown reason, our autoplt failed to capture the altitude which was set at 12000 ft. We attribute this altitude deviation to the combination of these different altitude clrncs, last min holding instructions, attempting to program our FMS, the failure of our autoplt to capture the selected altitude, and the fact that the center controller was extremely busy -- as well as we were.

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Original NASA ASRS Text

Title: DSNDED THROUGH ASSIGNED ALT.

Narrative: WE WERE FLYING FROM PEORIA, IL, TO ORD AND HAD BEEN CLRED DIRECT TO ORD AND TO DSND TO AND MAINTAIN 11000 FT. DSNDING THROUGH 13000 FT, CHICAGO CTR TOLD US TO MAINTAIN 13000 FT. WE ACKNOWLEDGED THE CLRNC AND SAID WE WOULD GO THROUGH 13000 FT BUT CLB BACK UP TO AND MAINTAIN 13000 FT. CHICAGO CTR THEN TOLD US TO JUST MAINTAIN 12000 FT. AT THIS POINT WE HEARD CHICAGO CTR SAY THAT ORD HAD SHUT OFF ARRS AND ACFT WERE GOING INTO HOLDING, AND THE CTR CTLR GOT VERY BUSY. THE CTLR CAME BACK AND CLRED US DIRECT TO SHOOZ INTXN AND HOLD SW ON VICTOR 10, R HAND TURNS, AND GAVE US AN EFC TIME OF XA00. SINCE WE WERE GOING DIRECT ORD, THE ARR DATA WAS NO LONGER IN OUR FMS AND WE WERE DIRECTLY ABEAM SHOOZ INTXN AT THAT TIME. DURING OUR SCRAMBLE TO SLOW DOWN, TURN TOWARDS THE HOLDING FIX, AND PROGRAM THE FMS, THE AUTOPLT DSNDED THROUGH 12000 FT, WHICH WE HAD SET IN UPON RECEIPT OF THE ALT CLRNC. WE RECEIVED AN ALT ALERT AND DSNDED TO 11500 FT BEFORE ESTABLISHING AN IMMEDIATE CLB BACK TO 12000 FT. AT THIS POINT CTR TOLD US AGAIN TO MAINTAIN 12000 FT AND SAID HE SHOWED US AT 11400 FT. WE WERE NOW LEVELING AT 12000 FT AND TOLD HIM WE WERE MAINTAINING 12000 FT. THE CTLR THEN OFFERED US RADAR VECTORS AS IT WAS APPARENT WE WERE HAVING PROBLEMS WITH THE CLRNCS AT SUCH SHORT NOTICE. WHEN WE GOT THE FMS PROGRAMMED, WE WERE ONLY 5 MI FROM ENTRY WITH R HAND TURNS AND THE REMAINDER OF THE FLT PROGRESSED UNEVENTFULLY! WE FEEL THE ENTIRE SITUATION AROSE BECAUSE OF A SUDDEN HIGH WORKLOAD PLACED ON THE CTLR AND CONSEQUENTLY PLACED ON US. WE WENT FROM A SIMPLE DSCNT AND DIRECT TO CLRNC, TO A COMPOUND ALT CLRNC AND COMPLICATED HOLDING INSTRUCTIONS WITH LESS THAN 2 MINS TO THE HOLDING FIX, ALL AT THE SAME TIME. ALSO, FOR SOME UNKNOWN REASON, OUR AUTOPLT FAILED TO CAPTURE THE ALT WHICH WAS SET AT 12000 FT. WE ATTRIBUTE THIS ALTDEV TO THE COMBINATION OF THESE DIFFERENT ALT CLRNCS, LAST MIN HOLDING INSTRUCTIONS, ATTEMPTING TO PROGRAM OUR FMS, THE FAILURE OF OUR AUTOPLT TO CAPTURE THE SELECTED ALT, AND THE FACT THAT THE CTR CTLR WAS EXTREMELY BUSY -- AS WELL AS WE WERE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.