Narrative:

Just prior to reaching hpw VOR, we were slowed by center to mach .76 and vectored to right of course. About 15 or 20 mi from the VOR, ZDC cleared us direct to hpw and then fpr. Our call sign was company eo. In our turn, we received clearance 'company eo descend to FL310.' the copilot immediately set in FL310 on the FMC and started a descent and I read the clearance back 'company eo roger, leaving FL370 for FL310.' a few seconds later, ATC asked if we could tighten up our turn. I said not at this altitude and reduced speed. As we started our turn to a northerly heading, I noticed visually and on TCASII, sbound traffic below us. At first I thought we would turn well inside of the lower traffic, but I told the copilot to ease the rate of descent as this picture did not look right. At that time ATC said 'company eo maintain FL370.' I, in turn, asked 'you want company eo to maintain FL370?' the controller responded 'I did not clear you to descend' at which I replied 'yes you did, you just cleared us to FL310.' he responded 'that was company eob I cleared to FL310.' I responded that I had understood the clearance was for company eo, was sorry for the confusion and we rapidly climbed the 600 ft or 700 ft back to FL370. The copilot and I both swear the controller indicated company eo in the clearance and he did not question my readback. We did not know that there was a company eob on frequency. The only recommendation I have is that center advise everyone that have similar call signs so that this kind of error could be avoided.

Related reports:

Google
 

Original NASA ASRS Text

Title: WDB FLC IS GIVEN CLRNC TO DSND THEN TOLD CLRNC WAS FOR ANOTHER COMPANY ACFT AND TO RETURN TO ASSIGNED ALT. READBACK HEARBACK PROB.

Narrative: JUST PRIOR TO REACHING HPW VOR, WE WERE SLOWED BY CTR TO MACH .76 AND VECTORED TO R OF COURSE. ABOUT 15 OR 20 MI FROM THE VOR, ZDC CLRED US DIRECT TO HPW AND THEN FPR. OUR CALL SIGN WAS COMPANY EO. IN OUR TURN, WE RECEIVED CLRNC 'COMPANY EO DSND TO FL310.' THE COPLT IMMEDIATELY SET IN FL310 ON THE FMC AND STARTED A DSCNT AND I READ THE CLRNC BACK 'COMPANY EO ROGER, LEAVING FL370 FOR FL310.' A FEW SECONDS LATER, ATC ASKED IF WE COULD TIGHTEN UP OUR TURN. I SAID NOT AT THIS ALT AND REDUCED SPD. AS WE STARTED OUR TURN TO A NORTHERLY HDG, I NOTICED VISUALLY AND ON TCASII, SBOUND TFC BELOW US. AT FIRST I THOUGHT WE WOULD TURN WELL INSIDE OF THE LOWER TFC, BUT I TOLD THE COPLT TO EASE THE RATE OF DSCNT AS THIS PICTURE DID NOT LOOK RIGHT. AT THAT TIME ATC SAID 'COMPANY EO MAINTAIN FL370.' I, IN TURN, ASKED 'YOU WANT COMPANY EO TO MAINTAIN FL370?' THE CTLR RESPONDED 'I DID NOT CLR YOU TO DSND' AT WHICH I REPLIED 'YES YOU DID, YOU JUST CLRED US TO FL310.' HE RESPONDED 'THAT WAS COMPANY EOB I CLRED TO FL310.' I RESPONDED THAT I HAD UNDERSTOOD THE CLRNC WAS FOR COMPANY EO, WAS SORRY FOR THE CONFUSION AND WE RAPIDLY CLBED THE 600 FT OR 700 FT BACK TO FL370. THE COPLT AND I BOTH SWEAR THE CTLR INDICATED COMPANY EO IN THE CLRNC AND HE DID NOT QUESTION MY READBACK. WE DID NOT KNOW THAT THERE WAS A COMPANY EOB ON FREQ. THE ONLY RECOMMENDATION I HAVE IS THAT CTR ADVISE EVERYONE THAT HAVE SIMILAR CALL SIGNS SO THAT THIS KIND OF ERROR COULD BE AVOIDED.

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.