Narrative:

Problem arose when center controller said in a frantic voice air carrier xx so and so (I didn't get the flight #) climb immediately to FL340 air carrier Y descend immediately to FL290. As we were Y21 and we were at FL330 we queried the controller if he meant to say Y21 instead of Y71 as we had heard no Y71 on the frequency and controllers make this particular numerical mistake with a flight # often. Instead of getting a response from the controller, we again heard air carrier xx flight XXX climb immediately to FL340 and I'll have you back down to FL330 in a couple of mins. We again transmitted to ATC re: did he mean Y71 or Y21. We heard a good 15 seconds of heterodynes, squeals and people transmitting on top of one another at which time we decided to get the hell out of FL330!!! We descended immediately to FL325 and leveled off and tried twice more to get an answer out of ATC. Then more squealing from people transmitting over each other. We transmitted our request again and received the reply, 'Y21, I'll get back to you.' there was no way I was going to go all the way down to FL290 west/O positive confirmation so we stayed at FL325 for another 15 seconds or so until the controller said, 'Y21, what can I do for you?' we asked him if he did need Y21 to go to FL290 and he said no, remain at FL330. We climbed back to FL330 and asked him about the possible flight # mixup and he said that the request to descend immediately to FL290 was for a ZZ71 on his other frequency. All 3 of us in my cockpit heard him say Y71--that's what started it all. Solution?? I don't know. Controllers are human and he said to us, 'no problem on your excursion to FL235 for a few moments.'

Related reports:

Google
 

Original NASA ASRS Text

Title: FLT CREW OF LGT HEARD THEIR CALL SIGN TO DESCEND. ATTEMPTED TO QUESTION CTLR REGARDING SIMILAR CALL SIGN SAME COMPANY. UNABLE TO CONTACT. DESCENDED 500' TO AVOID POSSIBLE TRAFFIC. EVENTUALLY CONTACTED CTLR WHO ADVISED MAINTAIN FL330.

Narrative: PROB AROSE WHEN CENTER CTLR SAID IN A FRANTIC VOICE ACR XX SO AND SO (I DIDN'T GET THE FLT #) CLB IMMEDIATELY TO FL340 ACR Y DSND IMMEDIATELY TO FL290. AS WE WERE Y21 AND WE WERE AT FL330 WE QUERIED THE CTLR IF HE MEANT TO SAY Y21 INSTEAD OF Y71 AS WE HAD HEARD NO Y71 ON THE FREQ AND CTLRS MAKE THIS PARTICULAR NUMERICAL MISTAKE WITH A FLT # OFTEN. INSTEAD OF GETTING A RESPONSE FROM THE CTLR, WE AGAIN HEARD ACR XX FLT XXX CLB IMMEDIATELY TO FL340 AND I'LL HAVE YOU BACK DOWN TO FL330 IN A COUPLE OF MINS. WE AGAIN XMITTED TO ATC RE: DID HE MEAN Y71 OR Y21. WE HEARD A GOOD 15 SECS OF HETERODYNES, SQUEALS AND PEOPLE XMITTING ON TOP OF ONE ANOTHER AT WHICH TIME WE DECIDED TO GET THE HELL OUT OF FL330!!! WE DSNDED IMMEDIATELY TO FL325 AND LEVELED OFF AND TRIED TWICE MORE TO GET AN ANSWER OUT OF ATC. THEN MORE SQUEALING FROM PEOPLE XMITTING OVER EACH OTHER. WE XMITTED OUR REQUEST AGAIN AND RECEIVED THE REPLY, 'Y21, I'LL GET BACK TO YOU.' THERE WAS NO WAY I WAS GOING TO GO ALL THE WAY DOWN TO FL290 W/O POSITIVE CONFIRMATION SO WE STAYED AT FL325 FOR ANOTHER 15 SECS OR SO UNTIL THE CTLR SAID, 'Y21, WHAT CAN I DO FOR YOU?' WE ASKED HIM IF HE DID NEED Y21 TO GO TO FL290 AND HE SAID NO, REMAIN AT FL330. WE CLBED BACK TO FL330 AND ASKED HIM ABOUT THE POSSIBLE FLT # MIXUP AND HE SAID THAT THE REQUEST TO DSND IMMEDIATELY TO FL290 WAS FOR A ZZ71 ON HIS OTHER FREQ. ALL 3 OF US IN MY COCKPIT HEARD HIM SAY Y71--THAT'S WHAT STARTED IT ALL. SOLUTION?? I DON'T KNOW. CTLRS ARE HUMAN AND HE SAID TO US, 'NO PROB ON YOUR EXCURSION TO FL235 FOR A FEW MOMENTS.'

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.