As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 6272 - IAD-BOS - DURING CRUISE, MADE A UNSCHEDULED FLIGHT DUE TO LEFT RPM INDICATION FAILED. AIRCRAFT RETURNED TO GATE WITH NO FURTHER PROBLEMS. MAINTENANCE INSPECTED AND REMOVED ANE REPLACED TACH GENERATOR. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE. (M)