ARTCC cleared flight xyy to descend instead of flight xxy, similar flight numbers.

Attributes
ACN	343860
Time
Date	199608
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : onl
State Reference	NE
Altitude	msl bound lower : 32300 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zmp
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 240 flight time total : 7000 flight time type : 240
ASRS Report	343860
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	faa : investigated
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

ZMP asked air carrier xyy to descend from FL330 to FL290 for crossing traffic. First officer read back clearance to FL290 and reported leaving FL330 using our correct call sign. ATC acknowledged our readback. Next we heard air carrier xxy checking in with ATC. At that time ATC called us back to confirm that we were still at FL330. Realizing what had probably happened the captain (flying) started an immediate climb out of our present altitude of FL323 back up to FL330. ATC then advised us of a possible pilot deviation and said to call ZMP administrative offices after XA00 am CDT on aug/tue/96. Extenuating circumstances include: 1) ATC issued descent clearance before air carrier xxy had even checked in on frequency. 2) was never advised (prior to the alleged deviation) that there were similar sounding call signs on frequency. 3) ATC referred to our flts as air carrier xyy and air carrier xxy instead of air carrier xxy and air carrier xyy, respectively. 4) ATC accepted our readback and the fact that we were leaving FL330. 5) warnings of similar sounding call signs for these 2 flts is normally part of the release but for some reason this warning did not appear on any of our releases. In closing, after reviewing ATC tapes the following day, ZMP accepted full responsibility for the situation and accepted as transcribed above as fact.

Original NASA ASRS Text

Title: ARTCC CLRED FLT XYY TO DSND INSTEAD OF FLT XXY, SIMILAR FLT NUMBERS.

Narrative: ZMP ASKED ACR XYY TO DSND FROM FL330 TO FL290 FOR XING TFC. FO READ BACK CLRNC TO FL290 AND RPTED LEAVING FL330 USING OUR CORRECT CALL SIGN. ATC ACKNOWLEDGED OUR READBACK. NEXT WE HEARD ACR XXY CHKING IN WITH ATC. AT THAT TIME ATC CALLED US BACK TO CONFIRM THAT WE WERE STILL AT FL330. REALIZING WHAT HAD PROBABLY HAPPENED THE CAPT (FLYING) STARTED AN IMMEDIATE CLB OUT OF OUR PRESENT ALT OF FL323 BACK UP TO FL330. ATC THEN ADVISED US OF A POSSIBLE PLTDEV AND SAID TO CALL ZMP ADMINISTRATIVE OFFICES AFTER XA00 AM CDT ON AUG/TUE/96. EXTENUATING CIRCUMSTANCES INCLUDE: 1) ATC ISSUED DSCNT CLRNC BEFORE ACR XXY HAD EVEN CHKED IN ON FREQ. 2) WAS NEVER ADVISED (PRIOR TO THE ALLEGED DEV) THAT THERE WERE SIMILAR SOUNDING CALL SIGNS ON FREQ. 3) ATC REFERRED TO OUR FLTS AS ACR XYY AND ACR XXY INSTEAD OF ACR XXY AND ACR XYY, RESPECTIVELY. 4) ATC ACCEPTED OUR READBACK AND THE FACT THAT WE WERE LEAVING FL330. 5) WARNINGS OF SIMILAR SOUNDING CALL SIGNS FOR THESE 2 FLTS IS NORMALLY PART OF THE RELEASE BUT FOR SOME REASON THIS WARNING DID NOT APPEAR ON ANY OF OUR RELEASES. IN CLOSING, AFTER REVIEWING ATC TAPES THE FOLLOWING DAY, ZMP ACCEPTED FULL RESPONSIBILITY FOR THE SIT AND ACCEPTED AS TRANSCRIBED ABOVE AS FACT.

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.