Medium large transport descends below altitude intended by ATC.

Attributes
ACN	117947
Time
Date	198907
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 8500 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute airway : ord
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 110 flight time total : 5000 flight time type : 275
ASRS Report	117947
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : overshoot other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	other

Narrative:

While descending for approach to ord, the first officer was flying the aircraft, the captain handling radio and navaids. We were cleared to descend to 8000' MSL, which was set and armed in the altitude alert. 9000 for 8000' was called out, followed shortly by ATC saying we were passing through 8700' and should maintain 9000'. We said, 'we were cleared to 8000.' he said, 'no, 9000.' the aircraft was flown to 9000', when we were immediately given 8000' as a new altitude again--end of problem.

Original NASA ASRS Text

Title: MLG DESCENDS BELOW ALT INTENDED BY ATC.

Narrative: WHILE DSNDING FOR APCH TO ORD, THE F/O WAS FLYING THE ACFT, THE CAPT HANDLING RADIO AND NAVAIDS. WE WERE CLRED TO DSND TO 8000' MSL, WHICH WAS SET AND ARMED IN THE ALT ALERT. 9000 FOR 8000' WAS CALLED OUT, FOLLOWED SHORTLY BY ATC SAYING WE WERE PASSING THROUGH 8700' AND SHOULD MAINTAIN 9000'. WE SAID, 'WE WERE CLRED TO 8000.' HE SAID, 'NO, 9000.' THE ACFT WAS FLOWN TO 9000', WHEN WE WERE IMMEDIATELY GIVEN 8000' AS A NEW ALT AGAIN--END OF PROB.

Data retrieved from NASA's ASRS site as of August 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.