As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE PILOTS ALTIMETER AND ALTITUDE ALERTER WERE FLAGGED AND THE OVERSPEED HORN WAS GOING OFF. THE ADC WAS FOUND TO BE DEFECTIVE AND REPLACED. THE SYSTEM WAS TESTED AND INSPECTED IAW MFG AND FOUND TO COMPLY WTH FAR 91 AND TO REMAIN RVSM COMPLIANT. THERE HAS BEEN ONE PRIOR REPORT OF THE ADC FALLING ON THIS AIRCRAFT. (K)