Background
Before departure on a scheduled passenger flight, a flight attendant noticed an electrical odor in the rear section of the airplane. The flight attendant informed the first officer, who then consulted a mechanic. The mechanic inspected the area but found no abnormalities, and the flight departed shortly thereafter.
Incident
While en route, another flight attendant reported an electrical odor in the same rear section. The captain conducted an investigation, after which the odor diminished and the rear cabin temperature was reduced. Shortly after these actions, smoke and fire became visible in the floor and side wall area. The captain declared an emergency and diverted the flight to an alternate airport. During the approach, the fire was extinguished, and an uneventful landing was made.
Investigation
Examination of the burned area revealed that an audio-entertainment system cable had shorted, resulting in minor damage to the airplane. Further investigation determined that the cable had not been properly installed and that the Supplemental Type Certificate (STC) did not provide specific instructions for cable routing, except that it should be placed under a seat rail cover.