As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT NR 6320 - IAD-ISP - AFTER TAKEOFF, RETURNED TO IAD DUE TO THE LEFT RPM INDICATION FAILED. AIRCRAFT RETURNED TO IAD WITH NO FURTHER INCIDENTS. MAINTENANCE REPLACED THE LEFT TACH GENERATOR. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE. (M)