Narrative:

Vv xy was the aircraft ahead of us on departure. Our flight # was vwxy. After out takeoff, ATC requested vv xy to turn to 360 degrees, then issued climb clearance to 9000' with only the xy heard (the first 2 digits were blocked out). No company prefix was used with the flight #. From our 250 degree heading we started a climbing right turn and requested confirmation of the 360 degree heading. We were told to maintain 250 degrees. Clearance to vv xy was then given to head 360 degrees and climb to 9000' (no company prefix). We immediately returned to 250 degrees and descended back to 2000' after reaching 2800' in our climbing turn. The flight continued west/O further incident, however the controller never issued an altitude warning to us. The controller continued to issue clrncs not using company prefixes until we left the frequency. I feel the absence of a company prefix with the flight # contributed to the confusion in this situation. Our assumption that xy in the clearance issued for us should have been confirmed by us before initiating any changes. Finally, the assignment of similar flight #south to flts operating in the same area contributes to situations where both controllers and flight crews more easily confuse #south and make mistakes. Supplemental information from acn 84311: considerable confusion was created due to conflicting call signs and the fact that the controller consistently omitted the company prefix.

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Original NASA ASRS Text

Title: DEP CTLR CLIPPING OR NOT USING FULL CALL SIGN CAUSED ACR-MLG TO REPLY TO CORNC FOR OTHER ACR WITH SIMILAR A/N CALL SIGN.

Narrative: VV XY WAS THE ACFT AHEAD OF US ON DEP. OUR FLT # WAS VWXY. AFTER OUT TKOF, ATC REQUESTED VV XY TO TURN TO 360 DEGS, THEN ISSUED CLB CLRNC TO 9000' WITH ONLY THE XY HEARD (THE FIRST 2 DIGITS WERE BLOCKED OUT). NO COMPANY PREFIX WAS USED WITH THE FLT #. FROM OUR 250 DEG HDG WE STARTED A CLBING RIGHT TURN AND REQUESTED CONFIRMATION OF THE 360 DEG HDG. WE WERE TOLD TO MAINTAIN 250 DEGS. CLRNC TO VV XY WAS THEN GIVEN TO HEAD 360 DEGS AND CLB TO 9000' (NO COMPANY PREFIX). WE IMMEDIATELY RETURNED TO 250 DEGS AND DSNDED BACK TO 2000' AFTER REACHING 2800' IN OUR CLBING TURN. THE FLT CONTINUED W/O FURTHER INCIDENT, HOWEVER THE CTLR NEVER ISSUED AN ALT WARNING TO US. THE CTLR CONTINUED TO ISSUE CLRNCS NOT USING COMPANY PREFIXES UNTIL WE LEFT THE FREQ. I FEEL THE ABSENCE OF A COMPANY PREFIX WITH THE FLT # CONTRIBUTED TO THE CONFUSION IN THIS SITUATION. OUR ASSUMPTION THAT XY IN THE CLRNC ISSUED FOR US SHOULD HAVE BEEN CONFIRMED BY US BEFORE INITIATING ANY CHANGES. FINALLY, THE ASSIGNMENT OF SIMILAR FLT #S TO FLTS OPERATING IN THE SAME AREA CONTRIBUTES TO SITUATIONS WHERE BOTH CTLRS AND FLT CREWS MORE EASILY CONFUSE #S AND MAKE MISTAKES. SUPPLEMENTAL INFO FROM ACN 84311: CONSIDERABLE CONFUSION WAS CREATED DUE TO CONFLICTING CALL SIGNS AND THE FACT THAT THE CTLR CONSISTENTLY OMITTED THE COMPANY PREFIX.

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.