Air carrier descend below assigned altitude resulting in less than standard separation with another ...

Attributes
ACN	132894
Time
Date	199001
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dtw
State Reference	MI
Altitude	msl bound lower : 10500 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : fll
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other
Route In Use	enroute airway : zob
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : instrument pilot : commercial pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 200 flight time total : 2600 flight time type : 800
ASRS Report	132894
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot non adherence : required legal separation other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 6000 vertical : 800
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were en route to dtw when we were cleared to slow to 210 KIAS and descend and maintain 7000 MSL. Captain read back the clearance and 7000 was set in the awi. The controller didn't respond to the captain's readback. Passing 11,000' MSL I noticed an medium large transport crossing from right to left at 10,000' MSL heading approximately 060 degree. Passing 10,500' MSL we heard the controller advise us to maintain 11,000' for traffic at 10,000'. We read back 11,000 and started to climb. We asked the controller if we had been cleared to 7000' MSL and he said no, it was 11,000 but we had already passed 10,500' MSL. No evasive action was necessary. I think the problem was due to miscom. The controller did not challenge our readback if it was in error. But I believe we were cleared to 7000' and the conflict was due to the controller clearing us to 7000' MSL.

Original NASA ASRS Text

Title: ACR DESCEND BELOW ASSIGNED ALT RESULTING IN LESS THAN STANDARD SEPARATION WITH ANOTHER ACFT.

Narrative: WE WERE ENRTE TO DTW WHEN WE WERE CLRED TO SLOW TO 210 KIAS AND DSND AND MAINTAIN 7000 MSL. CAPT READ BACK THE CLRNC AND 7000 WAS SET IN THE AWI. THE CTLR DIDN'T RESPOND TO THE CAPT'S READBACK. PASSING 11,000' MSL I NOTICED AN MLG XING FROM RIGHT TO LEFT AT 10,000' MSL HDG APPROX 060 DEG. PASSING 10,500' MSL WE HEARD THE CTLR ADVISE US TO MAINTAIN 11,000' FOR TFC AT 10,000'. WE READ BACK 11,000 AND STARTED TO CLIMB. WE ASKED THE CTLR IF WE HAD BEEN CLRED TO 7000' MSL AND HE SAID NO, IT WAS 11,000 BUT WE HAD ALREADY PASSED 10,500' MSL. NO EVASIVE ACTION WAS NECESSARY. I THINK THE PROBLEM WAS DUE TO MISCOM. THE CTLR DID NOT CHALLENGE OUR READBACK IF IT WAS IN ERROR. BUT I BELIEVE WE WERE CLRED TO 7000' AND THE CONFLICT WAS DUE TO THE CTLR CLEARING US TO 7000' MSL.

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.

Air carrier descend below assigned altitude resulting in less than standard separation with another aircraft.