As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FLIGHT DECK HAS AN ODOR IN FLIGHT, MORE SO WHEN THE POWER IS REDUCED. SMELLS LIKE DIRTY SOCKS ODOR NOT PRESENT IN THE CABIN. MAINTENANCE FOUND THE HEPA FILTERS DIRTY AND HAD A BAD ODOR. REPLACED FILTERS PER TASK CARD 26L00021001. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED WITH NO ODORS NOTED.