Narrative:

Captain's leg. Inbound on the atl sinca 8 arrival level at 11000'. We believed ATC issued us a clearance to 9000'. I acknowledged the clearance with the new assigned altitude and our full call sign. ATC did not query my response. I informed the captain of my desire to leave the #1 communication so that I could call company on #2 with our flight following information. Captain agreed. As I left the #1 communication I noticed captain started a slow descent. While talking on #2 I noticed the captain level off at 10800' and climb back to 11000'. After I came back up on #1 I asked the captain about the altitude change. He said that according to ATC the 9000' clearance was for a different aircraft. ATC queried our altitude. I told ATC that we were level at 11000'. ATC informed us that they were having some problems with their computers that evening. I acknowledged and thanked ATC for the information. I really did not think another thing about this matter until I received a call from my chief pilot several days later. He said that the feds were intending to pursue a violation in this matter. 1) mode 5 equipment would've been handy to back up a verbal ATC clearance. 2) please do not print this story in the callback magazine. 3) regional airline and major airline flight #'south are way too similar. Often an entire push will contain flight # series such as 981-972-973-961-951, etc, and also correspond to major (code sharing) flight #'south. 4) this will be the last report I send to you for the next 3 yrs. This is due to a previous fed violation on my certificate. So much for aviation safety!!! It is a shame to consider that I am a regional airline pilot and I fly probably as much or more than most other kinds of pilots. Thus, I could probably add more input to your safety database...oh well!

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Original NASA ASRS Text

Title: DESCENDED OUT OF ASSIGNED ALT.

Narrative: CAPT'S LEG. INBND ON THE ATL SINCA 8 ARR LEVEL AT 11000'. WE BELIEVED ATC ISSUED US A CLRNC TO 9000'. I ACKNOWLEDGED THE CLRNC WITH THE NEW ASSIGNED ALT AND OUR FULL CALL SIGN. ATC DID NOT QUERY MY RESPONSE. I INFORMED THE CAPT OF MY DESIRE TO LEAVE THE #1 COM SO THAT I COULD CALL COMPANY ON #2 WITH OUR FLT FOLLOWING INFO. CAPT AGREED. AS I LEFT THE #1 COM I NOTICED CAPT STARTED A SLOW DSCNT. WHILE TALKING ON #2 I NOTICED THE CAPT LEVEL OFF AT 10800' AND CLB BACK TO 11000'. AFTER I CAME BACK UP ON #1 I ASKED THE CAPT ABOUT THE ALT CHANGE. HE SAID THAT ACCORDING TO ATC THE 9000' CLRNC WAS FOR A DIFFERENT ACFT. ATC QUERIED OUR ALT. I TOLD ATC THAT WE WERE LEVEL AT 11000'. ATC INFORMED US THAT THEY WERE HAVING SOME PROBS WITH THEIR COMPUTERS THAT EVENING. I ACKNOWLEDGED AND THANKED ATC FOR THE INFO. I REALLY DID NOT THINK ANOTHER THING ABOUT THIS MATTER UNTIL I RECEIVED A CALL FROM MY CHIEF PLT SEVERAL DAYS LATER. HE SAID THAT THE FEDS WERE INTENDING TO PURSUE A VIOLATION IN THIS MATTER. 1) MODE 5 EQUIP WOULD'VE BEEN HANDY TO BACK UP A VERBAL ATC CLRNC. 2) PLEASE DO NOT PRINT THIS STORY IN THE CALLBACK MAGAZINE. 3) REGIONAL AIRLINE AND MAJOR AIRLINE FLT #'S ARE WAY TOO SIMILAR. OFTEN AN ENTIRE PUSH WILL CONTAIN FLT # SERIES SUCH AS 981-972-973-961-951, ETC, AND ALSO CORRESPOND TO MAJOR (CODE SHARING) FLT #'S. 4) THIS WILL BE THE LAST RPT I SEND TO YOU FOR THE NEXT 3 YRS. THIS IS DUE TO A PREVIOUS FED VIOLATION ON MY CERTIFICATE. SO MUCH FOR AVIATION SAFETY!!! IT IS A SHAME TO CONSIDER THAT I AM A REGIONAL AIRLINE PLT AND I FLY PROBABLY AS MUCH OR MORE THAN MOST OTHER KINDS OF PLTS. THUS, I COULD PROBABLY ADD MORE INPUT TO YOUR SAFETY DATABASE...OH WELL!

Data retrieved from NASA's ASRS site as of August 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.