As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOS - FLT 4859 - SHORTLY AFTER TAKEOFF, CREW NOTED THE LEFT INBOARD ENGINE COWLING OPENED IN-FLIGHT. CREW RETURNED TO BOS AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE COWLING ASSEMBLY AND CHECKED FIT AND SECURITY, ALL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE. (X)