B727 crew descends without clearance after replying to wrong call sign in ZAU airspace.

Attributes
ACN	419300
Time
Date	199811
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pia
State Reference	IL
Altitude	msl bound lower : 11000 msl bound upper : 20000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 50 flight time total : 8000 flight time type : 4000
ASRS Report	419300
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 120 flight time total : 4000 flight time type : 1500
ASRS Report	419301
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	none taken : detected after the fact
Consequence	Other
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

Approaching pia we requested a descent. We received and read back a clearance to 11000 ft. During descent we noticed we could no longer hear xmissions from ZAU. We asked another flight on frequency to relay a handoff, which was successful. Upon checking in, descended to 11000 ft, the controller advised us we had not been cleared to descend, and had accepted another flight's clearance (even though it was a response to our request). The controller stated there had been no conflict (lucky!) and indicated there was no big problem about it from their end. We feel the controller may have thought he was talking to another flight, but are near certain he used our call sign. We did read back the clearance with our call sign. We feel it was an honest, workload-related mistake that both he and we did not catch, and are glad it resulted in no traffic conflict. Supplemental information from acn 419301: I requested a descent from ZAU. Center responded 'abc XXX switch to 132.8.' she was very busy and made no mention of our descent request. I checked in on the new frequency and made another request for lower in the same transmission. ZAU responded 'abc descend to one one thousand.' I read back our full call sign with the new altitude '...roger, abc XXX leaving two zero zero for one one thousand.'

Original NASA ASRS Text

Title: B727 CREW DSNDS WITHOUT CLRNC AFTER REPLYING TO WRONG CALL SIGN IN ZAU AIRSPACE.

Narrative: APCHING PIA WE REQUESTED A DSCNT. WE RECEIVED AND READ BACK A CLRNC TO 11000 FT. DURING DSCNT WE NOTICED WE COULD NO LONGER HEAR XMISSIONS FROM ZAU. WE ASKED ANOTHER FLT ON FREQ TO RELAY A HDOF, WHICH WAS SUCCESSFUL. UPON CHKING IN, DSNDED TO 11000 FT, THE CTLR ADVISED US WE HAD NOT BEEN CLRED TO DSND, AND HAD ACCEPTED ANOTHER FLT'S CLRNC (EVEN THOUGH IT WAS A RESPONSE TO OUR REQUEST). THE CTLR STATED THERE HAD BEEN NO CONFLICT (LUCKY!) AND INDICATED THERE WAS NO BIG PROB ABOUT IT FROM THEIR END. WE FEEL THE CTLR MAY HAVE THOUGHT HE WAS TALKING TO ANOTHER FLT, BUT ARE NEAR CERTAIN HE USED OUR CALL SIGN. WE DID READ BACK THE CLRNC WITH OUR CALL SIGN. WE FEEL IT WAS AN HONEST, WORKLOAD-RELATED MISTAKE THAT BOTH HE AND WE DID NOT CATCH, AND ARE GLAD IT RESULTED IN NO TFC CONFLICT. SUPPLEMENTAL INFO FROM ACN 419301: I REQUESTED A DSCNT FROM ZAU. CTR RESPONDED 'ABC XXX SWITCH TO 132.8.' SHE WAS VERY BUSY AND MADE NO MENTION OF OUR DSCNT REQUEST. I CHKED IN ON THE NEW FREQ AND MADE ANOTHER REQUEST FOR LOWER IN THE SAME XMISSION. ZAU RESPONDED 'ABC DSND TO ONE ONE THOUSAND.' I READ BACK OUR FULL CALL SIGN WITH THE NEW ALT '...ROGER, ABC XXX LEAVING TWO ZERO ZERO FOR ONE ONE THOUSAND.'

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.