As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAX - CREW REPORTED LEADING EDGE SLAT ASSYMETRY EICAS MESSAGE WHEN FLAPS RETRACTED. EMERGENCY DECLARED FLIGHT RETURNED LAX LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. REPLACED SENSOR S278. SYSTEM GROUND CHECK NORMAL OPERATION.