Narrative:

En route from abe to pit at 22000 ft getting near psb VOR, we got a new radio frequency of 121.4, which is ZOB. I (first officer) switched over and checked in with him. He acknowledged me and that was all. (It was saturday and the frequency was very quiet.) about 2 mins later I heard what I thought was for us, air carrier X, to cross grace intersection at 10000 ft, 250 KTS. I acknowledged him with a readback including call sign. This is normal at this time, at about 100 NM from grace intersection and we already had it (at this point we never heard a broadcast from air carrier Y). We programmed in on the FMC. It started getting choppy so we started down. At about going through FL210 ATC said air carrier X maintain FL200. So we stopped at FL200. I asked him if he still wanted grace intersection at 10000 ft/250 KTS. He replied we were not given grace at 10000 ft/250 KTS. I immediately questioned him saying we were and I read it back. He said no that was for air carrier Y, and stated, no problem just maintain FL200. No conflict was caused. Problem being: call signs so much alike neither the controller or the other aircraft, air carrier Y, caught this. We were not informed that there was an air carrier Y on frequency. These call signs, air carrier X and air carrier Y sound so much alike, much more than most. They should not be used in the same airspace. When you say air carrier X not air carrier xx it sounds so much like air carrier Y that the captain, myself, the other aircraft, and the controller never picked up on wrong aircraft getting wrong clearance.

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Original NASA ASRS Text

Title: CREW IN B737-300 INBOUND TO PIT TAKE DSCNT CLRNC MEANT FOR COMPANY WITH THE SAME LAST 2 NUMBERS OF THE FLT IDENT.

Narrative: ENRTE FROM ABE TO PIT AT 22000 FT GETTING NEAR PSB VOR, WE GOT A NEW RADIO FREQ OF 121.4, WHICH IS ZOB. I (FO) SWITCHED OVER AND CHKED IN WITH HIM. HE ACKNOWLEDGED ME AND THAT WAS ALL. (IT WAS SATURDAY AND THE FREQ WAS VERY QUIET.) ABOUT 2 MINS LATER I HEARD WHAT I THOUGHT WAS FOR US, ACR X, TO CROSS GRACE INTXN AT 10000 FT, 250 KTS. I ACKNOWLEDGED HIM WITH A READBACK INCLUDING CALL SIGN. THIS IS NORMAL AT THIS TIME, AT ABOUT 100 NM FROM GRACE INTXN AND WE ALREADY HAD IT (AT THIS POINT WE NEVER HEARD A BROADCAST FROM ACR Y). WE PROGRAMMED IN ON THE FMC. IT STARTED GETTING CHOPPY SO WE STARTED DOWN. AT ABOUT GOING THROUGH FL210 ATC SAID ACR X MAINTAIN FL200. SO WE STOPPED AT FL200. I ASKED HIM IF HE STILL WANTED GRACE INTXN AT 10000 FT/250 KTS. HE REPLIED WE WERE NOT GIVEN GRACE AT 10000 FT/250 KTS. I IMMEDIATELY QUESTIONED HIM SAYING WE WERE AND I READ IT BACK. HE SAID NO THAT WAS FOR ACR Y, AND STATED, NO PROB JUST MAINTAIN FL200. NO CONFLICT WAS CAUSED. PROB BEING: CALL SIGNS SO MUCH ALIKE NEITHER THE CTLR OR THE OTHER ACFT, ACR Y, CAUGHT THIS. WE WERE NOT INFORMED THAT THERE WAS AN ACR Y ON FREQ. THESE CALL SIGNS, ACR X AND ACR Y SOUND SO MUCH ALIKE, MUCH MORE THAN MOST. THEY SHOULD NOT BE USED IN THE SAME AIRSPACE. WHEN YOU SAY ACR X NOT ACR XX IT SOUNDS SO MUCH LIKE ACR Y THAT THE CAPT, MYSELF, THE OTHER ACFT, AND THE CTLR NEVER PICKED UP ON WRONG ACFT GETTING WRONG CLRNC.

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.