Airtran Airways

Douglas DC-9

Shortly after takeoff, the airplane experienced electrical problems, including numerous tripped circuit breakers. The flight crew requested a return to airport. During the landing rollout, the lead flight attendant and air traffic control personnel reported to the flight crew that smoke was coming from the left side of the airplane; subsequently, the flight crew initiated an emergency evacuation on one of the taxiways. Examination of the airplane revealed fire damage to the left, forward areas of the fuselage, cabin, and forward cargo compartment. The greatest amount of fire damage was found just aft of the electrical disconnect panel located at fuselage station 237. There was no evidence that the drip shield normally installed over the disconnect panel was present at the time of the accident. Bluish stains caused by lavatory rinse fluid were observed on surfaces near the disconnect panel on the accident airplane and in the same areas on another of AirTran's DC-9 airplanes. Examination of one of the connectors from the disconnect panel on the accident airplane revealed light-blue and turquoise-green deposits on its internal surfaces and evidence of shorting between the connector pins. It could not be determined when the drip shield over the disconnect panel was removed; however, this likely contributed to the lavatory fluid contamination of the connectors. Following the accident, AirTran revised its lavatory servicing procedures to emphasize the importance of completely draining the waste tank to avoid overflows. Boeing issued an alert service bulletin recommending that operators of DC-9 airplanes visually inspect the connectors at the FS 237 disconnect panel for evidence of lavatory rinse fluid contamination and that they install a drip shield over the disconnect panel. Boeing also issued a service letter to operators to stress the importance of properly sealing floor panels and adhering to lavatory servicing procedures specified in its DC-9 Maintenance Manual. The Safety Board is aware of two incidents involving the military equivalent of the DC-9 that involved circumstances similar to the accident involving N826AT. Drip shields were installed above the FS 237 disconnect panels on both airplanes.

Douglas DC-9

Examination of the area of the fire origin revealed that relay R2-53, the left heat exchanger cooling fan relay, was severely heat damaged, as were R2-54 and the other relays in this area. However, the R2-53 relay also exhibited loose terminal studs and several holes that had burned through the relay housing that the other relays did not exhibit. The wire bundles that run immediately below the left and right heat exchanger cooling fans and the ground service tie relays exhibited heat damage to the wire insulation, with the greatest damage located just below the R2-53 relay. The unique damage observed on the R2-53 relay and the wire damage directly below it indicates that fire initiation was caused by an internal failure of the R2-53 relay. Disassembly of the relay revealed that the R2-53 relay had been repaired but not to the manufacturer's standards. According to the manufacturer, the damage to the relay housing was consistent with a phase-to-phase arc between terminals A2 and B2 of the relay. During the on-scene portion of the investigation, three of the four circuit breakers in the left heat exchanger cooling fan were found in the tripped position. To determine why only three of the four circuit breakers tripped, all four were submitted to the Materials Integrity Branch at Wright-Patterson Air Force Base, Dayton, Ohio, for further examination. The circuit breakers were visually examined and were subjected to an insulation resistance measurement, a contact resistance test, a voltage drop test, and a calibration test (which measured minimum and maximum ultimate trip times). Testing and examination determined that the circuit breaker that did not trip exhibited no anomalies that would prevent normal operation, met all specifications required for the selected tests, and operated properly during the calibration test. Although this circuit breaker appeared to have functioned properly during testing, the lab report noted that, as a thermal device, the circuit breaker is designed to trip when a sustained current overload exists and that it is possible during the event that intermittent arcing or a resistive short occurred or that the circuit opened before the breaker reached a temperature sufficient to trip the device.

Boeing 737-200

The first officer of AirTran Airways flight 890, which preceded AirTran flight 867 in the accident airplane, identified and reported a leak from the right engine of the Boeing 737-200 during a postflight inspection at William B. Hartsfield Atlanta International Airport (ATL), Georgia. AirTran mechanics at ATL identified the source of the leak as a chafed hydraulic pressure line to the right thrust reverser. They found the part in the illustrated parts catalog (IPC), which was not designed as a troubleshooting document and does not contain sufficient detail for such use. One of the mechanics telephoned an AirTran maintenance controller in Orlando, Florida, for further instructions. The mechanics who initially identified the source of the leak had little experience working on the Boeing 737 because they had worked for ValuJet Airlines, which flew DC-9s only, until ValuJet and AirTran merged in September 1997. On the basis of the information provided by the mechanic, and without questioning his description of the line or verifying the part number that he had provided against the IPC or some other appropriate maintenance document, the maintenance controller instructed the mechanic to cap the leaking line and deactivate the right thrust reverser in accordance with AirTran's Minimum Equipment List procedures. However, instead of capping the hydraulic pressure line, the mechanics capped the right engine hydraulic pump case drain return line. The mechanics performed a leak check by starting the auxiliary power unit and turning on the electric hydraulic pumps to pressurize the airplane's hydraulic systems; no leaks were detected. Although the mechanics were not required by company procedures to test their repair by running the engines, this test would have alerted the mechanics that they had incorrectly capped the hydraulic pump case drain line, which would have overpressurized the hydraulic pump and caused the hydraulic pump case seal to rupture. However, because the mechanics did not perform this test, the overpressure and rupture occurred during the airplane's climb out, allowing depletion of system A hydraulic fluid. Depletion of system A hydraulic fluid activated the hydraulic low-pressure lights in the cockpit, which alerted the flight crew that the airplane had a hydraulic problem. The crew notified air traffic control that the airplane would be returning to ATL and subsequently declared an emergency. The flight crew's initial approach to the airport was high and fast because of the workload associated with performing AirTran's procedures for the loss of hydraulic system A and the limited amount of time available to perform the procedures. Nevertheless, the crew was able to configure and stabilize the airplane for landing. However, depletion of system A hydraulic fluid disabled the nosewheel steering, inboard flight spoilers, ground spoilers, and left and right inboard brakes. The flight crew was able to land the airplane using the left thrust reverser (the right thrust reverser was fully functional but intentionally deactivated by the mechanics), outboard brakes (powered by hydraulic system B), and rudder. The flight crew used the left thrust reverser and rudder in an attempt to control the direction of the airplane down the runway, but use of the rudder pedals in this manner had depleted the system A accumulator pressure, which would have allowed three emergency brake applications. The use of the right outboard brake without the right inboard brake at a higher-than-normal speed (Vref for 15-degree flaps is faster than Vref for normal landing flaps) and with heavy gross weight (the airplane had consumed only 4,650 pounds of the 28,500 pounds of fuel on board at takeoff) used up the remaining friction material on the right outboard brake, causing it to fail. (The left outboard brake was still functional at this point.) The lack of brake friction material on the right outboard brake caused one of the right outboard brake pistons to overtravel and unport its o-ring, allowing system B hydraulic fluid to leak out; as a result, the left outboard brake also failed. Loss of the left and right inboard and outboard brakes, loss of nosewheel steering, and use of asymmetric thrust reverse caused the flight crew to lose control of the airplane, which departed the left side of the runway and came to rest in a ditch.