Narrative:

Aircraft en route from atl-ord on the kokomo 1 arrival had been cleared direct okk, then direct bearz to cross at 11000 ft, then direct ord to cross 40 DME at 11000 ft. The aircraft was descending rapidly in 'VNAV' with the spdbrakes extended. The restrs were made, 'vnavcap' annunciated on the pma, spdbrakes were retracted, and VNAV level annunciated on the pma. Approach then said fly a wbound heading (280 degrees) to intercept the ord 130 degree radial. As the FMS was being programmed for the intercept both pilots noticed the aircraft descending through 10700 ft. A climb was initiated at 10600 ft and the aircraft once again leveled off at 11000 ft. Human performance considerations -- the crew was receiving numerous updated clrncs for the descent, then a turn at level off which required additional programming of the FMS. Both pilots observed the aircraft level at 11000 ft, then a few moments later it was descending. It is possible the autoplt had not fully caught up with the trim necessary for level flight or one of the pitch modes had been contacted during the wbound turn. Chicago approach called the aircraft at 10600 ft as the climb back to 11000 ft was commencing.

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Original NASA ASRS Text

Title: AN ACR FLC DSNDS BELOW THEIR ASSIGNED ALT AFTER INITIALLY LEVELING OFF AT 11000 FT. THEY WERE ON AUTOPLT AND THE PROPER ALT CAPTURE ANNUNCIATIONS WERE NOTED BY BOTH FLC.

Narrative: ACFT ENRTE FROM ATL-ORD ON THE KOKOMO 1 ARR HAD BEEN CLRED DIRECT OKK, THEN DIRECT BEARZ TO CROSS AT 11000 FT, THEN DIRECT ORD TO CROSS 40 DME AT 11000 FT. THE ACFT WAS DSNDING RAPIDLY IN 'VNAV' WITH THE SPDBRAKES EXTENDED. THE RESTRS WERE MADE, 'VNAVCAP' ANNUNCIATED ON THE PMA, SPDBRAKES WERE RETRACTED, AND VNAV LEVEL ANNUNCIATED ON THE PMA. APCH THEN SAID FLY A WBOUND HDG (280 DEGS) TO INTERCEPT THE ORD 130 DEG RADIAL. AS THE FMS WAS BEING PROGRAMMED FOR THE INTERCEPT BOTH PLTS NOTICED THE ACFT DSNDING THROUGH 10700 FT. A CLB WAS INITIATED AT 10600 FT AND THE ACFT ONCE AGAIN LEVELED OFF AT 11000 FT. HUMAN PERFORMANCE CONSIDERATIONS -- THE CREW WAS RECEIVING NUMEROUS UPDATED CLRNCS FOR THE DSCNT, THEN A TURN AT LEVEL OFF WHICH REQUIRED ADDITIONAL PROGRAMMING OF THE FMS. BOTH PLTS OBSERVED THE ACFT LEVEL AT 11000 FT, THEN A FEW MOMENTS LATER IT WAS DSNDING. IT IS POSSIBLE THE AUTOPLT HAD NOT FULLY CAUGHT UP WITH THE TRIM NECESSARY FOR LEVEL FLT OR ONE OF THE PITCH MODES HAD BEEN CONTACTED DURING THE WBOUND TURN. CHICAGO APCH CALLED THE ACFT AT 10600 FT AS THE CLB BACK TO 11000 FT WAS COMMENCING.

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.