Captain of a beech super king air 300 responded to clearance for another similar sounding call sign.

Attributes
ACN	431903
Time
Date	199903
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : jot.vortac
State Reference	IL
Altitude	msl bound lower : 25500 msl bound upper : 26000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau.artcc
Make Model Name	Super King Air 300
Operating Under FAR Part	Part 91
Navigation In Use	other vortac
Flight Phase	descent : vacating altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zau.artcc
Operator	general aviation : corporate
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 6600 flight time type : 160
ASRS Report	431903
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : commercial pilot : multi engine pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued alert flight crew : returned to original clearance
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance

Narrative:

In cruise, ZAU issued a clearance for what we believe was for cpr X to descend to FL240. We read back clearance with our n-number cleared to FL240. At FL255 ATC asked us our altitude, in which I replied we were cleared to FL240. Controller stated otherwise and had us return to FL260. When I advised we had read back a clearance to FL240 the controller stated not to worry about it. I believe the clearance was issued to us, however, it was intended for another aircraft. There was a second aircraft on the frequency of cpr Y.

Original NASA ASRS Text

Title: CAPT OF A BEECH SUPER KING AIR 300 RESPONDED TO CLRNC FOR ANOTHER SIMILAR SOUNDING CALL SIGN.

Narrative: IN CRUISE, ZAU ISSUED A CLRNC FOR WHAT WE BELIEVE WAS FOR CPR X TO DSND TO FL240. WE READ BACK CLRNC WITH OUR N-NUMBER CLRED TO FL240. AT FL255 ATC ASKED US OUR ALT, IN WHICH I REPLIED WE WERE CLRED TO FL240. CTLR STATED OTHERWISE AND HAD US RETURN TO FL260. WHEN I ADVISED WE HAD READ BACK A CLRNC TO FL240 THE CTLR STATED NOT TO WORRY ABOUT IT. I BELIEVE THE CLRNC WAS ISSUED TO US, HOWEVER, IT WAS INTENDED FOR ANOTHER ACFT. THERE WAS A SECOND ACFT ON THE FREQ OF CPR Y.

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.