Narrative:

ZHU put us at FL350 (wrong altitude for direction of flight). Additionally, another company aircraft with a similar call sign was on the frequency and being handled by the same controller. ATC then told us they had to change our altitude to FL370 or FL330 for traffic. I confirmed with captain we would want FL330. Then ATC told us he would descend us when clear of traffic 2000 ft above at 2 O'clock and 2000 ft below us at 8 O'clock. I called the 2 O'clock traffic and negative contact on the 8 O'clock traffic. Moments later, ATC instructed us to descend to FL330. I verified the clearance and called descending to FL330 by call sign. Shortly thereafter (300 ft), ATC told us to return to FL350 and for the other company aircraft to maintain FL330. He then told us to again 'descend to FL330.' later, ATC informed us there might be a possible altitude deviation. I believe ATC confused the call signs. The other company aircraft never responded to any radio xmissions and I used our call sign to avoid possible confusion. There was no TCASII warning nor any aircraft in close proximity. It is always difficult to communicate effectively in a busy environment and similar call signs only add to the problem. As long as this added confusion exists, the potential for errors will not be mitigated, in spite of increased vigilance by both pilots and controllers. Supplemental information from acn 469491: eastbound, we were flying at FL330. ZHU requested and we accepted (wrong way altitude) FL350 due to anticipated traffic separation. ZHU next told us that we would have to climb to FL370 or descend to FL330. We put in our request for FL330. The very next ZHU controller descended us to FL330, and informed us that ZHU would be looking into a possible pilot deviation.

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Original NASA ASRS Text

Title: A B737-300 FLC IS ACCUSED OF ACCEPTING ANOTHER COMPANY'S FLT NUMBER AND CLRNC TO FL330 WHEN AT FL350 NW OF MSY, LA.

Narrative: ZHU PUT US AT FL350 (WRONG ALT FOR DIRECTION OF FLT). ADDITIONALLY, ANOTHER COMPANY ACFT WITH A SIMILAR CALL SIGN WAS ON THE FREQ AND BEING HANDLED BY THE SAME CTLR. ATC THEN TOLD US THEY HAD TO CHANGE OUR ALT TO FL370 OR FL330 FOR TFC. I CONFIRMED WITH CAPT WE WOULD WANT FL330. THEN ATC TOLD US HE WOULD DSND US WHEN CLR OF TFC 2000 FT ABOVE AT 2 O'CLOCK AND 2000 FT BELOW US AT 8 O'CLOCK. I CALLED THE 2 O'CLOCK TFC AND NEGATIVE CONTACT ON THE 8 O'CLOCK TFC. MOMENTS LATER, ATC INSTRUCTED US TO DSND TO FL330. I VERIFIED THE CLRNC AND CALLED DSNDING TO FL330 BY CALL SIGN. SHORTLY THEREAFTER (300 FT), ATC TOLD US TO RETURN TO FL350 AND FOR THE OTHER COMPANY ACFT TO MAINTAIN FL330. HE THEN TOLD US TO AGAIN 'DSND TO FL330.' LATER, ATC INFORMED US THERE MIGHT BE A POSSIBLE ALTDEV. I BELIEVE ATC CONFUSED THE CALL SIGNS. THE OTHER COMPANY ACFT NEVER RESPONDED TO ANY RADIO XMISSIONS AND I USED OUR CALL SIGN TO AVOID POSSIBLE CONFUSION. THERE WAS NO TCASII WARNING NOR ANY ACFT IN CLOSE PROX. IT IS ALWAYS DIFFICULT TO COMMUNICATE EFFECTIVELY IN A BUSY ENVIRONMENT AND SIMILAR CALL SIGNS ONLY ADD TO THE PROB. AS LONG AS THIS ADDED CONFUSION EXISTS, THE POTENTIAL FOR ERRORS WILL NOT BE MITIGATED, IN SPITE OF INCREASED VIGILANCE BY BOTH PLTS AND CTLRS. SUPPLEMENTAL INFO FROM ACN 469491: EBOUND, WE WERE FLYING AT FL330. ZHU REQUESTED AND WE ACCEPTED (WRONG WAY ALT) FL350 DUE TO ANTICIPATED TFC SEPARATION. ZHU NEXT TOLD US THAT WE WOULD HAVE TO CLB TO FL370 OR DSND TO FL330. WE PUT IN OUR REQUEST FOR FL330. THE VERY NEXT ZHU CTLR DSNDED US TO FL330, AND INFORMED US THAT ZHU WOULD BE LOOKING INTO A POSSIBLE PLTDEV.

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.