Corp flight crew has altitude deviation due to similar call signs and clearance confusion.

Attributes
ACN	146329
Time
Date	199005
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dpa
State Reference	IL
Altitude	msl bound lower : 2500 msl bound upper : 4000
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 60 flight time total : 1700 flight time type : 500
ASRS Report	146329
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	other

Narrative:

Flight concerned was a short low altitude flight from mke to dpa. Initial cruise altitude was 4000'. After being handed off by milwaukee approach to chicago approach, I checked in at 4000' on a 200 degree heading. Shortly thereafter we were cleared amongst much radio clutter. Down to 2500' and a left turn to 180 degree. I read back the clearance with our full call sign. At this point we started our descent. The controller then asked if we could accept a tight turn on (to approach course) to which I responded yes. Unknown to us there was another aircraft on frequency with a very similar call sign which the controller did not alert us to. The controller then issued a right turn to 300 degree which alerted me to the fact that I had responded to another acfts call. The controller definitely confused our call signs at least once during our handling. At this point I called the controller and told him that I thought I might have responded to another acfts call sign. He then alerted us to the fact that there were two aircraft with like call signs and told us to stop our descent at 3000' which we did. I determined from this that our command to descend from 4000' to 2500' was for the other aircraft even though I read the clearance back with our full call sign. Shorty after this the controller handed us off to another approach controller and said thanks for the patience indicating to me that he had indeed made some mistakes.

Original NASA ASRS Text

Title: CORP FLT CREW HAS ALT DEVIATION DUE TO SIMILAR CALL SIGNS AND CLRNC CONFUSION.

Narrative: FLT CONCERNED WAS A SHORT LOW ALT FLT FROM MKE TO DPA. INITIAL CRUISE ALT WAS 4000'. AFTER BEING HANDED OFF BY MILWAUKEE APCH TO CHICAGO APCH, I CHKED IN AT 4000' ON A 200 DEG HDG. SHORTLY THEREAFTER WE WERE CLRED AMONGST MUCH RADIO CLUTTER. DOWN TO 2500' AND A LEFT TURN TO 180 DEG. I READ BACK THE CLRNC WITH OUR FULL CALL SIGN. AT THIS POINT WE STARTED OUR DSNT. THE CTLR THEN ASKED IF WE COULD ACCEPT A TIGHT TURN ON (TO APCH COURSE) TO WHICH I RESPONDED YES. UNKNOWN TO US THERE WAS ANOTHER ACFT ON FREQ WITH A VERY SIMILAR CALL SIGN WHICH THE CTLR DID NOT ALERT US TO. THE CTLR THEN ISSUED A RIGHT TURN TO 300 DEG WHICH ALERTED ME TO THE FACT THAT I HAD RESPONDED TO ANOTHER ACFTS CALL. THE CTLR DEFINITELY CONFUSED OUR CALL SIGNS AT LEAST ONCE DURING OUR HANDLING. AT THIS POINT I CALLED THE CTLR AND TOLD HIM THAT I THOUGHT I MIGHT HAVE RESPONDED TO ANOTHER ACFTS CALL SIGN. HE THEN ALERTED US TO THE FACT THAT THERE WERE TWO ACFT WITH LIKE CALL SIGNS AND TOLD US TO STOP OUR DSNT AT 3000' WHICH WE DID. I DETERMINED FROM THIS THAT OUR COMMAND TO DSND FROM 4000' TO 2500' WAS FOR THE OTHER ACFT EVEN THOUGH I READ THE CLRNC BACK WITH OUR FULL CALL SIGN. SHORTY AFTER THIS THE CTLR HANDED US OFF TO ANOTHER APCH CTLR AND SAID THANKS FOR THE PATIENCE INDICATING TO ME THAT HE HAD INDEED MADE SOME MISTAKES.

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.