As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOS-YQB - FLT 4790 - AFTER DEPARTURE OUT OF BOSTON, CREW NOTED A MUSTY, PUNGENT SMELL IN THE COCKPIT AREA. CREW DIVERTED BACK TO BOSTION AND LANDED WITHOUT INCIDENT. MAINTENANCE VENTILATED THE COCKPIT THEN GROUND RAN THE AIRCRAFT AT DIFFERENT POWER SETTINGS WITH BLEEDS AND ALL ELECTRICAL POWER APPLIED. NO DEFECTS WERE NOTED. THE AIRCRAFT WAS RETURNED TO SERVICE. (M)