As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON FLIGHT 4521 AIR TRAFFIC CONTROL REPORTED THAT BOTH TRANSPONDERS FAILED AND WAS UNABLE TO RESET. THE CREW WAS NOT ALLOWED TO CONTINUE TO LGA PER AIR TRAFFIC CONTROL. THE AIRCRAFT WAS REMOVED FROM SERVICE. RESET SYSTEM. PERFORMED OPERATIONAL TEST, CHECKED GOOD PER AMM 34-52-00. NO PARTS REMOVED OR REPLACED. THE AIRCRAFT WAS RETURNED TO SERVICE.