Operational error between 2 air carrier's due to similar call signs and controller phraseology.

Attributes
ACN	470612
Time
Date	200004
Day	Thu
Local Time Of Day	1801 To 2400
Place
State Reference	IN
Altitude	msl bound lower : 20800 msl bound upper : 22000
Environment
Flight Conditions	Mixed
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zau.artcc
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : enroute altitude change
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zau.artcc
Operator	common carrier : air carrier
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
Experience	flight time last 90 days : 150 flight time total : 10000 flight time type : 500
ASRS Report	470612
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 80 flight time total : 7160 flight time type : 26.2
ASRS Report	470329
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : published procedure non adherence : required legal separation non adherence : clearance
Independent Detector	aircraft equipment : tcas other controllera other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : took evasive action flight crew : took precautionary avoidance action flight crew : returned to assigned altitude
Miss Distance	horizontal : 12000 vertical : 300
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

While level at cruising altitude of FL220 received a partially blocked transmission from ZAU to descend to 15000 ft. In the transmission we heard 'xx,' our call sign. We read back our call sign 'understand cleared to 15200 ft.' center then cleared us direct mie VOR. We turned direct and initiated our descent. At approximately FL210 received a TA, shortly followed by an RA to climb. Immediately disconnected the autoplt and initiated a climb back to FL220. Received TCASII clear of conflict. Never made visual contact with the traffic. We passed 300 ft above according to TCASII. Not exactly sure of mi lateral separation, but we think it was about 2-3 NM. Supplemental information from acn 470329: controller called the air carrier X flight #xx, air carrier Y flight #xx. 'I' verified he meant air carrier X flight #xx -- the answer was 'whatever, air carrier X flight #xx direct mie.' before we could call center, he was telling us to level at FL220. It appears that the descent clearance was issued to the wrong aircraft.

Original NASA ASRS Text

Title: OPERROR BTWN 2 ACR'S DUE TO SIMILAR CALL SIGNS AND CTLR PHRASEOLOGY.

Narrative: WHILE LEVEL AT CRUISING ALT OF FL220 RECEIVED A PARTIALLY BLOCKED XMISSION FROM ZAU TO DSND TO 15000 FT. IN THE XMISSION WE HEARD 'XX,' OUR CALL SIGN. WE READ BACK OUR CALL SIGN 'UNDERSTAND CLRED TO 15200 FT.' CTR THEN CLRED US DIRECT MIE VOR. WE TURNED DIRECT AND INITIATED OUR DSCNT. AT APPROX FL210 RECEIVED A TA, SHORTLY FOLLOWED BY AN RA TO CLB. IMMEDIATELY DISCONNECTED THE AUTOPLT AND INITIATED A CLB BACK TO FL220. RECEIVED TCASII CLR OF CONFLICT. NEVER MADE VISUAL CONTACT WITH THE TFC. WE PASSED 300 FT ABOVE ACCORDING TO TCASII. NOT EXACTLY SURE OF MI LATERAL SEPARATION, BUT WE THINK IT WAS ABOUT 2-3 NM. SUPPLEMENTAL INFO FROM ACN 470329: CTLR CALLED THE ACR X FLT #XX, ACR Y FLT #XX. 'I' VERIFIED HE MEANT ACR X FLT #XX -- THE ANSWER WAS 'WHATEVER, ACR X FLT #XX DIRECT MIE.' BEFORE WE COULD CALL CTR, HE WAS TELLING US TO LEVEL AT FL220. IT APPEARS THAT THE DSCNT CLRNC WAS ISSUED TO THE WRONG ACFT.

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.