B737 landing atl accepts descent clearance issued to similar call sign aircraft.

Attributes
ACN	605640
Time
Date	200401
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : atl.airport
State Reference	GA
Altitude	msl bound lower : 10600 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : a80.tracon
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach descent : vacating altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : a80.tracon
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude descent : approach
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : atp
Experience	flight time total : 15750
ASRS Report	605640
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : atp pilot : commercial pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 20000 flight time type : 2500
ASRS Report	605496
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance Company
Primary Problem	Ambiguous

Narrative:

While descending into the atl area, we were aircraft abcc. Aircraft adcc was already on the frequency. We started to exercise vigilance and not take the wrong instructions from the controller. I had mistakenly read back my call sign as adcc, but immediately corrected myself in the same transmission. We received a clearance to 9000 ft and responded with our call sign 'abcc leaving 11000 ft.' the controller said 'abcc, maintain 11000 ft.' we had reached 10600 ft before we returned to 11000 ft. It is unclr whether we received the wrong clearance or the controller gave us the wrong clearance, or the right clearance was given and the controller just decided to stop us at 11000 ft. We received the clearance for the other aircraft and the controller did not catch us on the readback. The aircraft reached 10600 ft and returned to 11000 ft. No conflict was noted. Nothing further was said by this or subsequent controllers. This problem, if there was one, was brought on by the similar call signs. The atl area was very busy and the controller was very busy as were we. We had made a conscious attempt to listen for the other call sign and not to make a mistake. In that type of environment, one can't be too careful.

Original NASA ASRS Text

Title: B737 LNDG ATL ACCEPTS DSCNT CLRNC ISSUED TO SIMILAR CALL SIGN ACFT.

Narrative: WHILE DSNDING INTO THE ATL AREA, WE WERE ACFT ABCC. ACFT ADCC WAS ALREADY ON THE FREQ. WE STARTED TO EXERCISE VIGILANCE AND NOT TAKE THE WRONG INSTRUCTIONS FROM THE CTLR. I HAD MISTAKENLY READ BACK MY CALL SIGN AS ADCC, BUT IMMEDIATELY CORRECTED MYSELF IN THE SAME XMISSION. WE RECEIVED A CLRNC TO 9000 FT AND RESPONDED WITH OUR CALL SIGN 'ABCC LEAVING 11000 FT.' THE CTLR SAID 'ABCC, MAINTAIN 11000 FT.' WE HAD REACHED 10600 FT BEFORE WE RETURNED TO 11000 FT. IT IS UNCLR WHETHER WE RECEIVED THE WRONG CLRNC OR THE CTLR GAVE US THE WRONG CLRNC, OR THE RIGHT CLRNC WAS GIVEN AND THE CTLR JUST DECIDED TO STOP US AT 11000 FT. WE RECEIVED THE CLRNC FOR THE OTHER ACFT AND THE CTLR DID NOT CATCH US ON THE READBACK. THE ACFT REACHED 10600 FT AND RETURNED TO 11000 FT. NO CONFLICT WAS NOTED. NOTHING FURTHER WAS SAID BY THIS OR SUBSEQUENT CTLRS. THIS PROB, IF THERE WAS ONE, WAS BROUGHT ON BY THE SIMILAR CALL SIGNS. THE ATL AREA WAS VERY BUSY AND THE CTLR WAS VERY BUSY AS WERE WE. WE HAD MADE A CONSCIOUS ATTEMPT TO LISTEN FOR THE OTHER CALL SIGN AND NOT TO MAKE A MISTAKE. IN THAT TYPE OF ENVIRONMENT, ONE CAN'T BE TOO CAREFUL.

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.