Narrative:

Air carrier flight departed dca at approximately XY20L. Immediately after takeoff, contact with departure control was established. The controller requested a change of the transponder code from that set prior to departure. The flight progressed normally toward lga. During the latter portion of the climb, I looked at my scratch pad and noticed a clearance from that morning's earlier trip to lga. Although the computer stored clrncs invariably remain the same, transponder codes do vary from flight to flight. At this time, it occurred to me that the code set at departure on this particular flight was that used earlier in the day. I pondered this peculiarity for several mins, and it strangely dawned on me that we may never had confirmed the transponder code with dca clearance delivery. We did call for our clearance at approximately XX50L, and was told to standby as we were #2 in sequence. We continued to monitor clearance delivery and at the same time conducted our cockpit business. At departure time of XY00L, we switched to ground control, obtained our pushback clearance, and hence a normal and uneventful sequence of events transpired for this flight. The only peculiarity of this day was a request to change transponder codes, which in itself is not unusual. However, the code set in was that given to us 2 flts prior that same day. My only conclusion to this matter is that the clearance was read to us, not having waited for our acknowledgement, another flight possibly stepped on or inadvertently interfered with communications. This, combined with other pre-departure business, may have created an oversight to insure that the clearance was properly obtained. During busy times at dca, 2 frequencys should be used to insure that readbacks are proper. Controllers must slow down sufficiently to insure that all flts acknowledge clrncs properly.

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Original NASA ASRS Text

Title: FLC OF AN LGT ACR ACFT INADVERTENTLY TAKE OFF WITH THE WRONG XPONDER CODE DUE TO NOT HEARING THEIR FILED CLRNC FROM CLRNC DELIVERY.

Narrative: ACR FLT DEPARTED DCA AT APPROX XY20L. IMMEDIATELY AFTER TKOF, CONTACT WITH DEP CTL WAS ESTABLISHED. THE CTLR REQUESTED A CHANGE OF THE XPONDER CODE FROM THAT SET PRIOR TO DEP. THE FLT PROGRESSED NORMALLY TOWARD LGA. DURING THE LATTER PORTION OF THE CLB, I LOOKED AT MY SCRATCH PAD AND NOTICED A CLRNC FROM THAT MORNING'S EARLIER TRIP TO LGA. ALTHOUGH THE COMPUTER STORED CLRNCS INVARIABLY REMAIN THE SAME, XPONDER CODES DO VARY FROM FLT TO FLT. AT THIS TIME, IT OCCURRED TO ME THAT THE CODE SET AT DEP ON THIS PARTICULAR FLT WAS THAT USED EARLIER IN THE DAY. I PONDERED THIS PECULIARITY FOR SEVERAL MINS, AND IT STRANGELY DAWNED ON ME THAT WE MAY NEVER HAD CONFIRMED THE XPONDER CODE WITH DCA CLRNC DELIVERY. WE DID CALL FOR OUR CLRNC AT APPROX XX50L, AND WAS TOLD TO STANDBY AS WE WERE #2 IN SEQUENCE. WE CONTINUED TO MONITOR CLRNC DELIVERY AND AT THE SAME TIME CONDUCTED OUR COCKPIT BUSINESS. AT DEP TIME OF XY00L, WE SWITCHED TO GND CTL, OBTAINED OUR PUSHBACK CLRNC, AND HENCE A NORMAL AND UNEVENTFUL SEQUENCE OF EVENTS TRANSPIRED FOR THIS FLT. THE ONLY PECULIARITY OF THIS DAY WAS A REQUEST TO CHANGE XPONDER CODES, WHICH IN ITSELF IS NOT UNUSUAL. HOWEVER, THE CODE SET IN WAS THAT GIVEN TO US 2 FLTS PRIOR THAT SAME DAY. MY ONLY CONCLUSION TO THIS MATTER IS THAT THE CLRNC WAS READ TO US, NOT HAVING WAITED FOR OUR ACKNOWLEDGEMENT, ANOTHER FLT POSSIBLY STEPPED ON OR INADVERTENTLY INTERFERED WITH COMS. THIS, COMBINED WITH OTHER PRE-DEP BUSINESS, MAY HAVE CREATED AN OVERSIGHT TO INSURE THAT THE CLRNC WAS PROPERLY OBTAINED. DURING BUSY TIMES AT DCA, 2 FREQS SHOULD BE USED TO INSURE THAT READBACKS ARE PROPER. CTLRS MUST SLOW DOWN SUFFICIENTLY TO INSURE THAT ALL FLTS ACKNOWLEDGE CLRNCS PROPERLY.

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.