As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING POST-FLIGHT CHECK, THE MACH AIRSPEED WARNING SYSTEM WOULD NOT TEST PROPERLY. TROUBLESHOOTING REVEALED A BAD MACH AIRSPEED WARNING SWITCH. REPLACED SWITCH AND SYSTEM TESTED AND OPERATED CORRECTLY. SUBMITTER STATED THIS SWITCH HAS POOR RELIABILITY. THIS IS THE 3RD SWITCH REPLACED IN 12 MONTHS. FAILURE OF THE SWITCH CAUSES THE CREW TO LOSE MACH OVERSPEED WARNING.