Incident Overview
Shortly after departure, flight attendants detected a burning odor in the cabin. Simultaneously, a passenger observed a glow emanating from the right-side air vent near his feet and noted that the cabin floor felt warm. The flight crew discharged halon into the vent, after which the glow dissipated.
Emergency Actions
The pilot declared an emergency and returned the aircraft to the departure airport. Upon landing, the airplane came to a stop on the runway. Based on reports from emergency personnel, an emergency evacuation was performed.
Post-Flight Inspection
Examination of the aircraft revealed thermal damage and sooting in the right-side underside floor structure, a nearby fiberglass bin wall panel, and a potable water bottle. A 5-foot by 5-foot area of insulation—composed of fiberglass covered on both sides with metallized mylar—was burned.
Damage Assessment
The right-side alternate static port heater was located beneath the burned insulation. The insulation on one of the wires leading to the heater was found deteriorated and melted where it had been bent around the thermostat case. Evidence of metal transfer was observed between the solid-core wire and the adjacent heater case. Soot was present on the insulation covering the wire and the adjacent heater case. The heater had been manufactured with the wire bend in place.