COVINGTON, KY, USA
N947DL
McDonnell Douglas MD-88
On departure climb, the flight attendants smelled something burning. Then a passenger noticed a 'glow' in the right side air vent near his feet and reported that the cabin floor was warm. Halon was sprayed into the vent, and the glow disappeared. The pilot declared an emergency and returned to the departure airport. The airplane was stopped on the runway and based upon reports from emergency personnel, an emergency evacuation was performed. Thermal damage and sooting was found on 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, which consisted of fiberglass, covered on both sides with a metallized mylar, was burned. The right side, alternate static port heater lay under the insulation. The insulation on one of the wires leading to the heater was found to be deteriorated and melted where it was bent around the thermostat case. Evidence of metal transfer was found between the solid-core wire and the adjacent heater case. Soot was found on the insulation covering the wire and adjacent heater case. The heater was manufactured with the wire bend.
On September 17, 1999, about 2230 eastern daylight time, a McDonnell-Douglas MD-88, N947DL, operated by Delta Air Lines (DAL) as flight 2030, performed a precautionary landing at the Cincinnati/Northern Kentucky International Airport (CVG), Covington, Kentucky. There were no injuries to the 2 certificated airline transport pilots, 3 flight attendants, and 113 passengers. The airplane received minor damage. Flight 2030 was operated on an instrument flight rules flight plan under 14 CFR Part 121. Flight 2030 was a scheduled flight between Covington and LaGuardia Airport (LGA), Flushing, New York. The airplane was pushed back at 2150, and was airborne at 2201. At 2214, as the airplane was climbing through FL230 (23,000 feet), the flight crew reported that there was smoke in the cabin and declared an emergency. According to the captain's written statement: "...Shortly after takeoff the flight attendants reported a 'funny smell' in the cabin and described it as 'sulfurous'. This was quickly followed by a report of the fumes growing stronger and smoke. An emergency was declared and the aircraft was turned back to CVG. The first officer continued to fly the aircraft and I initiated the Smoke Identification/Removal checklist in the Pilot's Operating Manual." "During the descent, the flight attendants reported a 'glow' coming from the floor grille near the sidewall in the vicinity of seat 11E. At least one halon extinguisher was discharged in the direction of the glow. Shortly after, the flight attendants reported that smoke seemed to be dissipating." "The landing was performed on runway 18L in CVG. Fire crews immediately met the aircraft, and reported smoke and signs of a fire in the forward cargo bin. A passenger evacuation was performed." Interviews with the flight attendants disclosed that the smoke was in the forward portion of the coach class cabin. Passengers were moved away from the area, and as one passenger moved his bag, one side was observed to be "scorched." A flickering red glow was observed coming from the floor vent. While one flight attendant went to the cockpit to notify the captain what had been seen, another flight attendant sprayed the contents of a halon fire extinguisher into the vent, after which the red glow disappeared. Examination of the airplane revealed that the interior framework of the fuselage was covered with insulation referred to as thermal blankets. The blankets were separated by the ribs of the fuselage. The insulation consisted of fiberglass, overlaid by a layer of metallized Mylar coating on each side. Examination of the insulation in the vicinity of the right side alternate static port heater revealed that the metallized Mylar covering over the fiberglass had burned away in a 5-foot by 5-foot area, with the edges of the Mylar charred. The damage consisted of sooting, and heat distress to the underside floor structure and a fiberglass potable water bottle. A nearby fiberglass cargo bin wall panel was also burned. In addition, in the cabin, soot damage was visible on the right cabin sidewall in the vicinity of passenger row 11. The heating element for the primary and alternate static source heaters was controlled from a rotary cockpit switch, which could be activated on the ground or in the air. All heaters were activated together. The rotary function of the switch was used to measure current draw for each heater. A thermal sensor on each heater regulated the temperature of the heating elements within pre-determined limits. In addition, there was a thermal fuse for each heater, and a circuit breaker located in the cockpit, that had not tripped. According to DAL personnel, the right side, alternate static port heater was still operational when the airplane was ferried to Atlanta for further maintenance. According to the Safety Board Airworthiness Group Chairman's report, examination of the heater revealed the resistance of the insulation was 0.05 megaohms, instead of the specified 40 megaohms. Examination of the "A" wire revealed the thermofit wire tubing, which encased the solid-core copper wire was melted and eroded where the wire was bent around the thermostat housing, prior to reaching the thermal fuse. In addition, the insulation had also rubbed against the thermostat housing, and was melted in some areas. The internal wire was also eroded in the same area. Sooting was found on the thermostat case, and the potting compound adjacent to the case. Metal transfer had taken place between the solid-core wire, and the adjacent heater case. DAL conducted a fleet wide examination of their MD-88/MD-90 fleet to ascertain the condition of their static port heaters. Eight heaters were found with evidence of thermal damage on their wires and or connectors. As a result of this occurrence, and their fleet wide inspection, DAL removed all Mylar covered insulation blankets from around the primary and alternate static port heaters on their MD-88/MD-90 fleet. The party representative from DAL reported that they did not track the serial numbers or time on the heating units. The date stamp on the right side alternate static port heater was prior to the airplane's delivery date to DAL. The part was not life limited. The airplane had accumulated 28,033 hours and 22,934 cycles since new, at the time of occurrence. According to the party representative of Electrofilm, the position of the wire that had deteriorated insulation on the incident heater was as manufactured. He further reported that the manufacturing process had been changed, and the wire rerouted to reduce the bends induced by manufacturing. Initial reports from the Federal Aviation Administration (FAA) and DAL indicated no injuries received during the evacuation. Several months later, the Safety Board received information that there had been injuries sustained during the evacuation.
Deteriorated wire insulation and shorting at a short radius bend to the electrical wiring in the right side alternate static port heater, which resulted in electrical arcing and a fire sustained by overlaying thermal acoustic insulation.
Source: NTSB Aviation Accident Database
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