Air carrier flight crew reported the transponder malfunctioned after takeoff from SNA and began to transmit the wrong code and flight number. At the destination; line maintenance informed the crew they had other similar reports from other aircraft regarding John Wayne/Orange County Airport Santa Ana.
Synopsis
Air carrier flight crew reported the transponder malfunctioned after takeoff from SNA and began to transmit the wrong code and flight number. At the destination; line maintenance informed the crew they had other similar reports from other aircraft regarding John Wayne/Orange County Airport Santa Ana.
Narrative
During climb out in busy airspace; approximately 2-3 minutes after takeoff; received EICAS caution message: XPDR 1 IN STBY. Complied with QRH and re-selected TA/RA mode (turned transponder back on). Upon turning transponder back on; we missed approximately two ATC calls because we thought they were using the wrong callsign. We then realized that our ADSB callsign had changed on the MCDU (Multipurpose Control Display Unit) to a random callsign which was not even close to our actual callsign or the previous flight's callsign. While changing the callsign back; ATC asked us to 'verify transponder code'. We had already noticed and were changing that back to the PDC assigned code as well. We informed ATC we were changing it back. We are quite certain that these were set and cross-checked correctly prior to and during departure. On arrival; we entered the discrepancy into the Electronic Aircraft Maintenance Logbook and line maintenance troubleshot and deferred the transponder 1. Maintenance noted that they'd been seeing this exact issue approximately weekly (not specific to this tail number) and it seemed to be happening specifically climbing out of the same airport we departed from.Equipment malfunction / automation issue - unknown cause.This sounds like it is not an isolated incident. Suggest informing flight crews with a notice as well as attempting to track and troubleshoot in coordination with equipment manufacturers. The fact that it switches the ADSB callsign specifically was confusing and can lead to both distraction and missed radio calls as well as momentary 'ADSB noncompliance'.
Second reporter narrative
MCDU malfunction. Spontaneously; and with no discernible trigger of cause; our transponder switched to standby; ADSB-code became a random flight number (not the last flight number); and our transponder squawk code also became random. All three of those changes happened simultaneously; randomly; and without a known reason. This caused us to initially question if an ATC instruction was for us and make the correction to our transponder; squawk; and ADSB; communicate that we had a glitch with our transponder; and run a QRH procedure for transponder in standby. No additional threats were encountered and communication and surveillance was reestablished with ATC within seconds of noticing the issue.Equipment malfunction / automation issue - unknown cause.Flight crews should be notified by a notice about this possible glitch.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.