Similar call signs and flight numbers result in an altitude diversion near chicago.

Attributes
ACN	491700
Time
Date	200011
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : pappi
State Reference	IL
Altitude	msl bound lower : 19500 msl bound upper : 20000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	B767 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	Light Transport
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	491700
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 controllerb other flight crewa
Resolutory Action	controller : issued advisory
Supplementary
Problem Areas	Company Flight Crew Human Performance ATC Human Performance
Primary Problem	Company
Air Traffic Incident	Pilot Deviation

Narrative:

We were given a descent clearance to descend to 12000 ft. I responded, 'air carrier xyz heavy leaving FL200 for 12000 ft. A short time later, air carrier feeder xyz said he thought someone took his descent clearance. The controller asked us what our altitude was. I responded FL195. He told us to maintain FL200. We climbed back to FL200. I asked him if there was a conflict. He said negative. I question the scheduling of air carrier xyz and air carrier feeder xyz using the same airspace at the same time.

Original NASA ASRS Text

Title: SIMILAR CALL SIGNS AND FLT NUMBERS RESULT IN AN ALT DIVERSION NEAR CHICAGO.

Narrative: WE WERE GIVEN A DSCNT CLRNC TO DSND TO 12000 FT. I RESPONDED, 'ACR XYZ HVY LEAVING FL200 FOR 12000 FT. A SHORT TIME LATER, ACR FEEDER XYZ SAID HE THOUGHT SOMEONE TOOK HIS DSCNT CLRNC. THE CTLR ASKED US WHAT OUR ALT WAS. I RESPONDED FL195. HE TOLD US TO MAINTAIN FL200. WE CLBED BACK TO FL200. I ASKED HIM IF THERE WAS A CONFLICT. HE SAID NEGATIVE. I QUESTION THE SCHEDULING OF ACR XYZ AND ACR FEEDER XYZ USING THE SAME AIRSPACE AT THE SAME TIME.

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.