As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED. AT 600 FEET, STALE SOCK ODOR NOTED. TWO MINUTES LATER THE AFT FLIGHT ATTENDANT SMELLED BURNING TYPE ODOR. APU OFF, NO SMELL AT GATE. REMOVED AND REPLACED LEFT RECIRCULATION FILTER IAW AMM 21-21-41. OPERATIONAL CHECK GOOD. SEE ALSO AALA20170118005.