As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 1MADC HAD AN ALTITUDE COMPARATOR AT 15000 FT AND A 400 FT SPLIT FROM MADC AND STDBY AT FL230. IT ALSO HAD A 5 CKAS SPLIT IN AIRSPEED. BLOCKAGE FOUND IN LT UPPER PITOT/STATIC PROBE, OF UNKNOWN ORIGIN. BLEW OUT STATIC LINES USING DRY NITOGEN. INSTALLED NEW LT UPPER PITOT PROBE IAW GAC CMP CODE 341102. PERFORMED PITOT/STATIC SYSTEM RECONNECT CHECKS IAW GAC CMP CODE 341030. AIRCRAFT RETURNED TO SERVICE.