Narrative:

We were operating air carrier XXXX and upon checking on to ny center; the controller properly notified us to be aware that air carrier XXXY was also on frequency. While in cruise at FL230 roughly 80 nm southwest of syr; ATC issued the following clearance; 'air carrier XXXX descend and maintain niner-thousand.' as the non flying pilot; I read back the clearance providing the call sign and assigned altitude. I set the altitude into the preselect; the captain verified it and then began a descent. Upon reaching 21;500 ATC queried us as to our assigned altitude. I read back that we were assigned niner-thousand. He quickly responded with a 'negative that clearance was for air carrier XXXY; for now descend and maintain FL200 air carrier XXXX.' I read that back. He then cleared air carrier XXXY down to niner thousand. When air carrier XXXY read back their descent clearance; he clearly stated that he also heard the previous clearance as being for air carrier XXXX and thus didn't respond or query it. We then descended to FL200 and completed the remainder of the flight without incident. Safety was never compromised during the event as there was no other traffic in our vicinity. Suggestions; this event could be avoided my a major overhaul of the assignment of flight numbers. While it could never be 100% avoided due to delays and other airlines. It would be possible for this air carrier to make sure that no two similar sounding call signs would be airborne at the same time or at least not in the same ATC environment. Since we knew that air carrier XXXX and air carrier XXXY were both on frequency; we could have each clarified every clearance given to each other; but that would have been a communications nightmare leading to frequency congestion. While it didn't prevent the deviation in this instance; it was very good that the controller advised us of the possible confusion.

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Original NASA ASRS Text

Title: Air carrier with four digit call sign initiated a descent issued to another same company aircraft with similar four digit flight number; ATC did caution both aircraft regarding number similarities prior to event.

Narrative: We were operating Air Carrier XXXX and upon checking on to NY Center; the controller properly notified us to be aware that Air Carrier XXXY was also on frequency. While in cruise at FL230 roughly 80 nm Southwest of SYR; ATC issued the following clearance; 'Air Carrier XXXX descend and maintain niner-thousand.' As the non flying pilot; I read back the clearance providing the call sign and assigned altitude. I set the altitude into the preselect; the captain verified it and then began a descent. Upon reaching 21;500 ATC queried us as to our assigned altitude. I read back that we were assigned niner-thousand. He quickly responded with a 'negative that clearance was for Air Carrier XXXY; for now descend and maintain FL200 Air Carrier XXXX.' I read that back. He then cleared Air Carrier XXXY down to niner thousand. When Air Carrier XXXY read back their descent clearance; he clearly stated that he also heard the previous clearance as being for Air Carrier XXXX and thus didn't respond or query it. We then descended to FL200 and completed the remainder of the flight without incident. Safety was never compromised during the event as there was no other traffic in our vicinity. Suggestions; this event could be avoided my a major overhaul of the assignment of flight numbers. While it could never be 100% avoided due to delays and other airlines. It would be possible for this Air Carrier to make sure that no two similar sounding call signs would be airborne at the same time or at least not in the same ATC environment. Since we knew that Air Carrier XXXX and Air Carrier XXXY were both on frequency; we could have each clarified every clearance given to each other; but that would have been a communications nightmare leading to frequency congestion. While it didn't prevent the deviation in this instance; it was very good that the controller advised us of the possible confusion.

Data retrieved from NASA's ASRS site as of April 2012 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.