EMB120 flight crew responded to another aircraft clearance during downwind leg.

Attributes
ACN	521379
Time
Date	200108
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : atl.airport
State Reference	GA
Altitude	msl bound lower : 5000 msl bound upper : 6000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : atl.tracon
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 26r
Flight Phase	descent : approach ground : maintenance
Route In Use	approach : instrument precision arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 250 flight time total : 2300 flight time type : 1500
ASRS Report	521379
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Experience	flight time last 90 days : 150 flight time total : 800 flight time type : 350
ASRS Report	520908
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	atc equipment other atc equipment : radar other controllera
Resolutory Action	controller : separated traffic controller : issued new clearance
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance Environmental Factor
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On downwind for runway 26R atlanta hartsfield, we were at 7000 ft 095 degree heading. My first officer and I both thought we heard our call sign and 'turn right 180 degrees, descend and maintain 5000 ft.' we were beyond the OM and it seemed like the correct position for this clearance to be given. My first officer read back the clearance. No response was given to us until we were descending through 6000 ft. Approach came back and said, 'level off at 6000 ft, then left to 050 degrees. You took someone else's clearance.' this is an easy mistake to make in busy environments with similar call signs. If approach would have told us on the readback the clearance was not for us, this could have been prevented. I guess he made the same mistake we did.

Original NASA ASRS Text

Title: EMB120 FLC RESPONDED TO ANOTHER ACFT CLRNC DURING DOWNWIND LEG.

Narrative: ON DOWNWIND FOR RWY 26R ATLANTA HARTSFIELD, WE WERE AT 7000 FT 095 DEG HDG. MY FO AND I BOTH THOUGHT WE HEARD OUR CALL SIGN AND 'TURN R 180 DEGS, DSND AND MAINTAIN 5000 FT.' WE WERE BEYOND THE OM AND IT SEEMED LIKE THE CORRECT POS FOR THIS CLRNC TO BE GIVEN. MY FO READ BACK THE CLRNC. NO RESPONSE WAS GIVEN TO US UNTIL WE WERE DSNDING THROUGH 6000 FT. APCH CAME BACK AND SAID, 'LEVEL OFF AT 6000 FT, THEN L TO 050 DEGS. YOU TOOK SOMEONE ELSE'S CLRNC.' THIS IS AN EASY MISTAKE TO MAKE IN BUSY ENVIRONMENTS WITH SIMILAR CALL SIGNS. IF APCH WOULD HAVE TOLD US ON THE READBACK THE CLRNC WAS NOT FOR US, THIS COULD HAVE BEEN PREVENTED. I GUESS HE MADE THE SAME MISTAKE WE DID.

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.