As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED. PHL FLT 1889 EN-ROUTE PHL - MCI. AN UNUSUAL ODOR WAS NOTED IN THE AIRCRAFT CABIN SHORTLY AFTER TAKE-OFF. THE FLIGHT DECLARED AN EMERGENCY AND RETURNED TO PHL WITHOUT FURTHER INCIDENT. REPLACED APU ASSEMBLY PER J/C 43L35249001. OPERATIONS TEST AND LEAK CHECK GOOD. NO MORE ODOR NOTED WHILE RUNNING PACKS OFF OF APU BLEED.