As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL (FL 993) - DURING CLIMB-OUT WITH FLAPS RETRACTED,THE NR 4 LEADING EDGE FLAP TRANSIT LIGHT ILLUMINATED. AIRCRAFT RETURNED TO FIELD (PHL). NO EMERGENCY WAS DELCARED AND THE AIRCRAFT LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED NR 4 KRUEGER FLAP PROXIMITY SENSOR. OPERATIONAL CHECK OF SYSTEM GOOD. (X)