Narrative:

All 3 crew members heard clearance to descend to FL250. I verified that he wanted us to descend now to FL250. He confirmed it and it was acknowledged on the MCP as we started down. We stopped the descent when we realized we were going to descend into an aircraft at FL350. We stopped at FL360 and asked again if he wanted us to descend. He told us to stay at FL360. We believe that is when he realized that he had the wrong plane. He asked us to switch to frequency 132.51. 132.51 asked us to climb back to FL370. We believe brest center mistook us for another aircraft. The thing that bothered us was that brest told us that we were on the wrong frequency. I believe he mistook us for someone else. We did not violate anything and clearance was verified by controller before we descended. Supplemental information from acn 498488: approaching barlu intersection, the controller cleared us to descend from FL370 to FL250. We asked for and received confirmation to descend. We started a slow descent as we were over 160 mi from lhr. As we got to FL360 we got a TCASII traffic alert for traffic which was at FL350. I looked out and saw a B747 passing beneath us. We held altitude at FL360 and called the controller twice more to confirm clearance and told him we had an aircraft pass beneath us at FL350. The controller then said we were given his frequency in error and call on 132.51. We were asked to climb back to FL370 by new controller and then cleared to descend to FL250 before we reached FL370 again. The arrival was uneventful from that point but only luck and TCASII prevented a midair. Supplemental information from acn 498381: the controller was hard to understand as he had a heavy french accent.

Related reports:

Google
 

Original NASA ASRS Text

Title: B777 RECEIVE DSCNT CLRNC FROM FL370 TO FL250 FROM LFRR ACC AND CONFLICTED WITH A B747 AT FL350. STOP DSCNT BY THE B777 AT FL360 AND QUESTIONS LFRR, WHO ISSUE CLB BACK TO FL370 WITH A FREQ CHANGE.

Narrative: ALL 3 CREW MEMBERS HEARD CLRNC TO DSND TO FL250. I VERIFIED THAT HE WANTED US TO DSND NOW TO FL250. HE CONFIRMED IT AND IT WAS ACKNOWLEDGED ON THE MCP AS WE STARTED DOWN. WE STOPPED THE DSCNT WHEN WE REALIZED WE WERE GOING TO DSND INTO AN ACFT AT FL350. WE STOPPED AT FL360 AND ASKED AGAIN IF HE WANTED US TO DSND. HE TOLD US TO STAY AT FL360. WE BELIEVE THAT IS WHEN HE REALIZED THAT HE HAD THE WRONG PLANE. HE ASKED US TO SWITCH TO FREQ 132.51. 132.51 ASKED US TO CLB BACK TO FL370. WE BELIEVE BREST CTR MISTOOK US FOR ANOTHER ACFT. THE THING THAT BOTHERED US WAS THAT BREST TOLD US THAT WE WERE ON THE WRONG FREQ. I BELIEVE HE MISTOOK US FOR SOMEONE ELSE. WE DID NOT VIOLATE ANYTHING AND CLRNC WAS VERIFIED BY CTLR BEFORE WE DSNDED. SUPPLEMENTAL INFO FROM ACN 498488: APCHING BARLU INTXN, THE CTLR CLRED US TO DSND FROM FL370 TO FL250. WE ASKED FOR AND RECEIVED CONFIRMATION TO DSND. WE STARTED A SLOW DSCNT AS WE WERE OVER 160 MI FROM LHR. AS WE GOT TO FL360 WE GOT A TCASII TFC ALERT FOR TFC WHICH WAS AT FL350. I LOOKED OUT AND SAW A B747 PASSING BENEATH US. WE HELD ALT AT FL360 AND CALLED THE CTLR TWICE MORE TO CONFIRM CLRNC AND TOLD HIM WE HAD AN ACFT PASS BENEATH US AT FL350. THE CTLR THEN SAID WE WERE GIVEN HIS FREQ IN ERROR AND CALL ON 132.51. WE WERE ASKED TO CLB BACK TO FL370 BY NEW CTLR AND THEN CLRED TO DSND TO FL250 BEFORE WE REACHED FL370 AGAIN. THE ARR WAS UNEVENTFUL FROM THAT POINT BUT ONLY LUCK AND TCASII PREVENTED A MIDAIR. SUPPLEMENTAL INFO FROM ACN 498381: THE CTLR WAS HARD TO UNDERSTAND AS HE HAD A HVY FRENCH ACCENT.

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.