Flight crew responded to another aircraft's descent clearance.

Attributes
ACN	489890
Time
Date	200010
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : iad.airport
State Reference	VA
Altitude	msl bound lower : 6000 msl bound upper : 7000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : iad.tracon
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : cfi pilot : flight engineer pilot : commercial pilot : atp pilot : instrument
Experience	flight time last 90 days : 2000 flight time total : 11000 flight time type : 4000
ASRS Report	489890
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance none taken : detected after the fact none taken : anomaly accepted
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Level at 7000 ft received descent clearance to 5000 ft. I covered controller's call. Responded with readback of descent clearance. Left 7000 ft for 5000 ft. Another aircraft asked about descent clearance, our clearance was for him to descend. We were told to stop at 6000 ft, we did. No traffic conflicts that we were aware of. I should have checked with controller about clearance because of similar call signs. We were expecting descent and heard what we wanted to hear. Will be more diligent in future.

Original NASA ASRS Text

Title: FLC RESPONDED TO ANOTHER ACFT'S DSCNT CLRNC.

Narrative: LEVEL AT 7000 FT RECEIVED DSCNT CLRNC TO 5000 FT. I COVERED CTLR'S CALL. RESPONDED WITH READBACK OF DSCNT CLRNC. LEFT 7000 FT FOR 5000 FT. ANOTHER ACFT ASKED ABOUT DSCNT CLRNC, OUR CLRNC WAS FOR HIM TO DSND. WE WERE TOLD TO STOP AT 6000 FT, WE DID. NO TFC CONFLICTS THAT WE WERE AWARE OF. I SHOULD HAVE CHKED WITH CTLR ABOUT CLRNC BECAUSE OF SIMILAR CALL SIGNS. WE WERE EXPECTING DSCNT AND HEARD WHAT WE WANTED TO HEAR. WILL BE MORE DILIGENT IN FUTURE.

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.