N826AT

HISTORY OF FLIGHT

On November 29, 2000, about 1550 eastern standard time (all times in this brief are eastern standard time based on a 24-hour clock), the flight crew of a McDonnell Douglas (McDonnell Douglas is now known as Boeing, Douglas Product Division) DC-9-32, N826AT, operating as AirTran Airways flight 956, executed an emergency landing at Hartsfield Atlanta International Airport (ATL), Atlanta, Georgia. Shortly after takeoff, the flight crew observed that several circuit breakers had tripped and several annunciator panel lights had illuminated. Subsequently, about 2 minutes after takeoff, the flight crew requested a return to ATL. After the landing, one of the flight attendants reported to the flight crew that smoke could be seen emanating from the left sidewall in the forward cabin; air traffic control (ATC) personnel also notified the flight crew that smoke was coming from the airplane. The flight crew then initiated an emergency evacuation on one of the taxiways. Airport rescue and firefighting (ARFF) personnel assisted in subduing the fire. Of the 2 flight crewmembers, 3 flight attendants, and 92 passengers on board, 13 passengers received minor injuries. The airplane sustained substantial damage. Flight 956 was operating under 14 Code of Federal Regulations Part 121 as a regularly scheduled passenger flight from ATL to Akron-Canton Regional Airport, Akron, Ohio. Visual meteorological conditions prevailed at the time of the accident.

The captain was the pilot flying. About 1541, ATC cleared the flight for takeoff. At 1543:10, as the airplane was climbing through about 3,800 feet, the cockpit voice recorder (CVR) recorded popping sounds consistent with the sound of circuit breakers tripping, which continued for about 34 seconds. During postaccident interviews, both flight crewmembers stated that during this time, they noticed that several circuit breakers had tripped. The flight crew also noted that the MASTER CAUTION light, several annunciator panel lights, the left and right fuel pressure lights, and the radio rack fan OFF annunciator lights had illuminated. At 1543:28, the captain told the first officer to tell ATC that they wanted to level off at 4,000 feet and return to the airport because "right now we have electrical problems." The captain stated that he then glanced over his shoulder to check for smoke but did not observe any smoke at that time.

The ATL north departure controller instructed flight 956 to maintain 4,000 feet and asked whether the flight would need the ARFF equipment available upon landing; the first officer replied that they would need the equipment available. The captain stated that he selected emergency power, took the generators offline, and switched the cabin pressurization to manual to stop the circuit breakers from tripping. The captain stated that during the descent, the left?side attitude directional indicator failed intermittently. He stated that, specifically, the failure flags appeared and the instrument was "jumpy." Further, he stated that the cockpit lights were flickering and that he was afraid that all of the cockpit instruments would fail.

At 1544:47, flight data recorder data ceased, and, at 1544:51, there was an interruption of audio on all CVR channels. Intermittent CVR audio returned several minutes later and continued until 1549:11, at which time, the CVR recording ended (the airplane landed about 1 minute later). Signals from the airplane's radar transponder were also lost around 1544:51 but were regained briefly until they ended around the same time as the CVR recording ended.

At 1549:40, flight 956 was cleared to land on either runway 26L or 26R. The captain stated that there was no visible smoke or smell of smoke in the cockpit before landing. About 1550, the airplane landed on runway 26R. The captain stated that the landing and rollout were normal. During the airplane's exit from the runway onto taxiway B-3, the lead flight attendant opened the cockpit door and announced that there was smoke in the cabin. A short time later, the lead flight attendant again opened the cockpit door and reported that the amount of smoke in the cabin had increased and asked the captain if he wanted to evacuate.

The captain stated that he set the brakes and told the lead flight attendant that they would evacuate and that he would make an announcement to the passengers. However, the public address system had become inoperative, and the emergency evacuation commenced with the flight attendants making announcements to the passengers and directing the evacuation.

The captain stated that the first officer completed the emergency evacuation checklist and exited the airplane. The captain then donned protective breathing equipment and proceeded through the cabin looking for any incapacitated passengers. He reported that the visibility in the first?class cabin was about 1 to 2 feet. He stated that he proceeded to the rear of the airplane to check the lavatories, at which time, he found the No. 3 flight attendant leaving with the last passenger. He reported that after ensuring that everyone had exited the airplane, he exited through the right overwing exit to further assist with the evacuation.

DAMAGE TO AIRPLANE

Examination of the airplane revealed fire damage to the left forward areas of the fuselage and cargo compartment from fuselage stations (FS) 237 to 313 and damage to the cabin floor and sidewall. Fire damage was concentrated in an area just aft of the electrical disconnect panel located at FS 237, which is a junction panel for seven wire bundles. The fuselage exterior also exhibited heat discoloration in an area beneath the lavatory service panel located between FS 237 and 256 and a soot trail that extended aft from the radio rack vent, located just aft of the lavatory service panel. Soot was also present throughout the forward cargo compartment and on the cabin outflow valve near the rear of the airplane.

The floor structure and carpet of the passenger cabin exhibited fire damage from the left sidewall to the centerline of the airplane from FS 237 to 313. The seat tracks under seats 1A and 1C were buckled from heat exposure, the carpeting in front of seats 2A and 2C was burned and melted, and the floor in the aisle next to row 3 was spongy and buckled.

Further examination of the interior area between the forward cargo compartment and the fuselage revealed bluish stains, similar in color to lavatory rinse fluid (also known as blue water) on sidewall insulation blankets and components near FS 237. No drip shield, which was designed to protect the connectors at FS 237 from overhead fluid leakage, was installed over the FS 237 disconnect panel at the time of the accident, although the support brackets for the drip shield were in place. The drip shield was incorporated into the design of DC-9 series airplanes beginning with fuselage line number 271, which included N826AT. N826AT was delivered with the drip shield installed, but investigators could not determine why the shield was not in place at the time of the accident. Of the first 270 DC-9s manufactured, 80 included a forward lavatory.

The damaged wiring from the area around FS 237 was removed and sent to the Safety Board's materials laboratory for detailed examination. Beading was observed on the ends of many individual wires, which is consistent with heat damage from arcing. Each of the seven electrical connectors from the removed wire bundles was opened to determine the internal condition of the connector pins and grommet material. One connector exhibited more thermal damage than the other six and contained light-blue and turquoise-green crystalline deposits on the mating surfaces of its two sides and around nearly all of its pins. This connector also exhibited evidence of pin-to-pin shorts. Laboratory tests of the grommet material from this connector revealed elevated levels of sulfate (a basic chemical constituent in lavatory rinse fluid, which can be very conductive) as compared to undamaged grommet material.

Examination of Other Airplanes

Safety Board investigators examined the area around the FS 237 disconnect panel on another AirTran DC-9 and on two DC-9s from another operator. Although a drip shield was installed above the FS 237 disconnect panel on the AirTran DC-9, protecting the components directly beneath it, bluish dried stains were observed on many surfaces near the FS 237 disconnect panel, including the bulkhead at FS 218 and on the ducts, wiring, insulation blankets, and sidewall. Neither of the DC-9s from the other operator had a drip shield installed over the FS 237 disconnect panel, and it was not determined whether these airplanes originally had the drip shields installed. Although no blue stains were observed on or near the area of the FS 237 disconnect panels in these airplanes, many components were covered with a white, mottled substance, which suggests that a fluid other than lavatory rinse fluid may have leaked from above.

AIRCRAFT INFORMATION

AirTran's records indicate that the accident airplane, serial number 47359, was manufactured on April 2, 1969, by McDonnell Douglas Corporation. The airplane was delivered to Delta Airlines new, where it was operated from 1969 to 1993. The airplane was bought back by Boeing in 1993 and stored from 1993 to 1994. In 1994, the airplane was bought by ValuJet and placed into revenue service until June 18, 1996, at which time it was placed in storage because ValuJet ceased operations. The airplane remained in storage until January 8, 1997, when it was returned to revenue service under AirTran Airways (ValuJet merged with AirTran Airways in 1997). At the time of the accident, the airplane had accumulated 78,255.3 flight hours and 88,367 cycles.

Maintenance Information

Records from the airplane's most recent C check, which was completed in October 1999, were reviewed for nonroutine maintenance actions acc...