The National Transportation Safety Board continues to make progress in its investigation of United Airlines flight 497, which returned to the airport on April 4, 2011, in New Orleans, shortly after take-off due to automated warnings of smoke in the equipment bay. The airplane’s nose wheel exited the side of runway 19 upon completing the landing roll and an emergency evacuation was conducted.
The NTSB team, comprised of 3 NTSB investigators and representatives from the designated parties and advisors, arrived on scene April 4 to document and examine the aircraft and retrieve the data and voice recorders. Two other NTSB investigators, specializing in operational factors and maintenance factors, traveled to various locations to review pertinent documentation and records and conduct interviews.
After documenting the condition of the equipment in the electronics bay, investigators applied limited electrical power to various systems on the airplane. At this time, the preliminary examination has not revealed any signs of burning, indications of smoke or other anomalous system findings.
The NTSB operations group completed interviews of the flight crew yesterday. The crew indicated that, at about 4000 feet, the airplane’s electronic centralized aircraft monitoring (ECAM) system provided an autothrottle-related message, then an avionics smoke warning message, accompanied by instructions to land. Despite receiving this message, neither crew member recalled smelling smoke or fumes during the flight.
The captain indicated that he used the electronic checklist for the avionics system smoke warning indication, which included shutting down some of the airplane’s electrical system. The crew reported that the first officer’s display screens went blank, the ECAM messages disappeared, the cockpit to cabin intercom stopped functioning, and the air-driven emergency generator deployed. The captain said that he took control of the airplane at this point and managed the radios while the first officer opened the cockpit door to advise the flight attendants of the emergency and their return to New Orleans airport.
The crew also noted to investigators that they requested runway 10 for landing, but were told the runway was not available due to the presence of construction vehicles. The captain said that he was able to use the airspeed, altimeter, and attitude information on his primary flight display during the return to the airport, and that he ordered an evacuation after landing.
As previously reported, the airplane’s forward right slide did not properly inflate during the emergency evacuation. After examining the evacuation slides, investigators found that the aspirator for the forward right-hand slide was partially blocked. The aspirator component is the mechanism for inflating the slide during an emergency evacuation. Investigators have retained the slide for further evaluation.
Preliminary reports provided to investigators suggest that the flight attendants did not smell or see smoke in the cabin, but observed the cabin lights turn off and the intercom system cease to function during the flight. Interviews of the cabin crew will be conducted after the investigators complete their on-scene work to more thoroughly document the cabin crew’s observations and communications throughout the flight and emergency evacuation.
The cockpit voice recorder (CVR) and flight data recorder (FDR) arrived at NTSB headquarters in Washington, D.C. on April 5 and were successfully downloaded. The CVR is of good quality and captured approximately 7 minutes and 30 seconds of the incident flight. The FDR contained in excess of 25 hours of data and captured approximately 18 minutes of data relevant to the incident flight. Both the CVR and FDR stopped recording data prior to landing.
Investigators will remain on scene to complete their evaluation of the airplane and documentation of other factors in the incident.