As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOTS & COPILOTS INDICATED AIRSPEED DISAGREED BY 15 TO 20 KTS. COMPARED INDICATIONS WITH STANDBY AIRSPEED ADC WAS OFF BY 15 TO 20 KTS. TROUBLESHOT & FOUND THAT THE NR 1 ADC WAS DEFECTIVE & WAS REPLACED WITH AN OVERHAULED EXCHANGE UNIT. FUNCTIONAL CHECKS WERE SATISFACTORY.