A B727 crew misinterped clearance and continued descent through assigned altitude.

Attributes
ACN	503790
Time
Date	200102
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	msl bound lower : 6000 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other vortac
Flight Phase	descent : vacating altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : flight engineer pilot : commercial
ASRS Report	503710
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 50 flight time total : 12000 flight time type : 8000
ASRS Report	502125
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During approach to runway 9L in VFR conditions at ord, we were given a descent from 10000 ft to 5000 ft by the approach controller. The captain was working the radios and the first officer was flying. The captain read back 5000 ft and the first officer confirmed 5000 ft. As we approached 6000 ft, the controller told us to level off at 6000 ft and that our assigned altitude was 7000 ft. We complied with the new instructions and the captain replied 'we read back 5000 ft.' nothing else was said regarding the matter and the flight was completed normally. I think the controller said 5000 ft. It was our first leg of the day with 10.5 hours of rest at private the night before. I was not tired and I don't think the rest of the crew was either. As a crew, we worked well together and had a normal schedule. I would like the controllers to return to confirming the assigned altitudes in case the crew reads back the wrong altitude. Also, we were not in a high workload situation, and there was not a lot of traffic on the radio.

Original NASA ASRS Text

Title: A B727 CREW MISINTERPED CLRNC AND CONTINUED DSCNT THROUGH ASSIGNED ALT.

Narrative: DURING APCH TO RWY 9L IN VFR CONDITIONS AT ORD, WE WERE GIVEN A DSCNT FROM 10000 FT TO 5000 FT BY THE APCH CTLR. THE CAPT WAS WORKING THE RADIOS AND THE FO WAS FLYING. THE CAPT READ BACK 5000 FT AND THE FO CONFIRMED 5000 FT. AS WE APCHED 6000 FT, THE CTLR TOLD US TO LEVEL OFF AT 6000 FT AND THAT OUR ASSIGNED ALT WAS 7000 FT. WE COMPLIED WITH THE NEW INSTRUCTIONS AND THE CAPT REPLIED 'WE READ BACK 5000 FT.' NOTHING ELSE WAS SAID REGARDING THE MATTER AND THE FLT WAS COMPLETED NORMALLY. I THINK THE CTLR SAID 5000 FT. IT WAS OUR FIRST LEG OF THE DAY WITH 10.5 HRS OF REST AT PVT THE NIGHT BEFORE. I WAS NOT TIRED AND I DON'T THINK THE REST OF THE CREW WAS EITHER. AS A CREW, WE WORKED WELL TOGETHER AND HAD A NORMAL SCHEDULE. I WOULD LIKE THE CTLRS TO RETURN TO CONFIRMING THE ASSIGNED ALTS IN CASE THE CREW READS BACK THE WRONG ALT. ALSO, WE WERE NOT IN A HIGH WORKLOAD SIT, AND THERE WAS NOT A LOT OF TFC ON THE RADIO.

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.