US National Transportation Safety Board (NTSB) investigators have found not found "any signs of burning" or "indications of smoke or other anomalous system findings" in a United Airlines A320 involved in a 4 April incident in New Orleans.
Flight 497, with 109 passengers and crew on board, departed New Orleans that morning for San Francisco, but pilots declared an emergency due to "smoke issues" when climbing through 4,000ft (1,219m), according to air traffic control recordings. The crew soon after reported that they had "lost all our instruments" and asked air traffic controllers for radar guidance back to the airport.
The NTSB had originally reported on 5 April that the crew had "reportedly received automated warnings and detected smoke in the cockpit". In its 7 April update however, investigators revealed that neither the pilots nor the flight attendants had smelled smoke or fumes on the aircraft during the 20min flight.
An attempt to use the longest runway (Runway 10) at the New Orleans international airport on return to the field proved futile due to on-going maintenance work, forcing the A320 to land on Runway 19, a shorter runway. The aircraft lost its steering after slowing, with the nosewheel exiting the side of the runway as its stopped.
During the emergency evacuation of the aircraft on the runway, NTSB says the forward right evacuation slide did not properly inflate due to a partially blocked aspirator, the mechanism that inflates the slide.
More detailed interviews with the crew will continue, with the investigators likely focusing on procedures and checklists the crew used in response to electronic centralized aircraft monitoring (ECAM) system warnings. The pilots stated that they first received an "autothrottle-related message" followed by an avionics smoke warning message that was accompanied by "instructions to land".
"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 systems," says the NTSB. "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."
Other anomalies to be investigated include the unexplained shutdown of both the cockpit voice recorder and flight data recorder before the landing.