Air carrier Captain reported that incorrect flight ID information was being reported to ATC during flight. The aircraft transponder had incorrectly stored a previous flight number and transmitted it to the ATC system after it had been deleted and cleared.
Synopsis
Air carrier Captain reported that incorrect flight ID information was being reported to ATC during flight. The aircraft transponder had incorrectly stored a previous flight number and transmitted it to the ATC system after it had been deleted and cleared.
Narrative
I was informed ATC reported an incorrect flight ID for our flight; CVG-ZZZ. I feel this ongoing issue related to incorrect flight ID's is an issue with the transponders incorrectly storing previous codes and not deleting them when deleted/cleared. I have used the same technique ever since we have been made aware of this problem. I always clear the previous code then select enter with no code displayed. Then enter the new code and select enter again. After this I circle the flight ID on the release. At this time the First Officer has an opportunity to verify the correct ID and draw a slash through the circle. That being done if an incorrect flight ID code is being reported it would be a stored previous code that would not clear. On one occasion in the past year while waiting on the ramp to finish loading; with the preflight cockpit setup complete; our Dispatcher called to inform us that she was seeing a different flight ID than our current flight. We both verified the correct number was entered and reentered it as a precaution. It did not correct the issue. I am very suspect of our equipment.
Second reporter narrative
I received the following (abbreviated) email from the chief pilot:Good Afternoon; The FAA has notified me that you flew a flight last month with the wrong flight number in the transponder. It occurred on Day 0; Flight XXX from CVG to ZZZ. The transponder reported Flight YYY.I was not aware of this event occurring. I am a little skeptical of the allegation because I have always been; and continue to be; very diligent in ensuring proper squawk codes and flight numbers. In addition; ATC did not mention anything to us during the entire flight. However; I will take extra precaution to make sure that this mistake doesn't happen again.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.