As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT LEFT AND RIGHT TRANSPONDER INOP . A/C RETURNED TO GATE AND MTX GROUNDED A/C .MTX PERF L AND R ATC TXPNR BITE CHECKS PER AMM 34-53-01, NO DEFECTS NOTED. REMOVED AND REPLACED ATC CONTROL PANEL PER AMM 34-53-02, A/C RELEASED RVSM COMPLIANT RETURNED A/C TO SERVICE