B737 flight crew responded to another aircraft's clearance and started a descent.

Attributes
ACN	524985
Time
Date	200109
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sav.airport
State Reference	GA
Altitude	msl single value : 31000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx.artcc
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zjx.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : commercial pilot : atp pilot : instrument
Experience	flight time last 90 days : 200 flight time total : 6000 flight time type : 3000
ASRS Report	524985
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : published procedure other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance controller : issued alert none taken : anomaly accepted none taken : detected after the fact other
Consequence	Other
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Our call sign was air carrier XXX. We heard a clearance to descend, read it back, heard a 'roger' from center, and began a descent. The, without any ATC request (that we heard), an air carrier YYY read back 'our' clearance. This made me question whether we had taken his clearance, and we had. We were about 200 ft below our cruise altitude, and the controller added, 'I see you're already in a descent, so you can keep on going to FL280.' my listening needed to be sharper. A similar sounding call sign can lead to confusion like this.

Original NASA ASRS Text

Title: B737 FLC RESPONDED TO ANOTHER ACFT'S CLRNC AND STARTED A DSCNT.

Narrative: OUR CALL SIGN WAS ACR XXX. WE HEARD A CLRNC TO DSND, READ IT BACK, HEARD A 'ROGER' FROM CTR, AND BEGAN A DSCNT. THE, WITHOUT ANY ATC REQUEST (THAT WE HEARD), AN ACR YYY READ BACK 'OUR' CLRNC. THIS MADE ME QUESTION WHETHER WE HAD TAKEN HIS CLRNC, AND WE HAD. WE WERE ABOUT 200 FT BELOW OUR CRUISE ALT, AND THE CTLR ADDED, 'I SEE YOU'RE ALREADY IN A DSCNT, SO YOU CAN KEEP ON GOING TO FL280.' MY LISTENING NEEDED TO BE SHARPER. A SIMILAR SOUNDING CALL SIGN CAN LEAD TO CONFUSION LIKE THIS.

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.