A preliminary check has found no signs of smoke or fire in the United Airlines jet that returned safely to New Orleans minutes after takeoff Monday, with the pilot first reporting a "smoke issue" _ and then that computerized instruments had failed, the National Transportation Safety Board said Thursday.
The pilots on Flight 497 for San Francisco reported that an alarm warned of smoke in the highly computerized avionics system and instructed them to land, according to the emailed update. "Despite receiving this message, neither crew member recalled smelling smoke or fumes during the flight," the NTSB said.
The 100 passengers and five crew members all got off safely, a few with what appeared to be minor abrasions from the inflatable slides, after the Airbus 320 landed on a shorter-than-requested runway about 13 minutes after takeoff. One front tire blew out and the nose ran off the runway onto grass with about 2,000 feet to spare.
Spokeswoman Bridget Ann Serchak said NTSB investigations typically take between 12 and 18 months, "so it is far too early to tell what all the next steps will be and when."
In a recording of transmissions between the airport tower and the pilot, about 4 1/2 minutes into the flight the pilot said "we have a smoke issue." About 4 1/2 minutes later, he said: "We've lost all our instruments right now."
According to the NTSB, the captain reports following an electronic checklist that included shutting down some electrical systems. "The crew reported that the first officer's display screens went blank, the ECAM (electronic centralized aircraft monitoring) messages disappeared, the cockpit to cabin intercom stopped functioning, and the air-driven emergency generator deployed," it said.
The cockpit voice recorder and flight data recorder apparently were still working at that point. But Thursday's report said both stopped recording before the plane landed back at New Orleans. Investigators have 7 1/2 minutes of voice and 18 minutes of relevant flight data, out of about 25 hours total on the flight data recorder, it said.
The captain said that when the first warning appeared, he took control of the airplane and radios while the co-pilot opened the cockpit door to tell flight attendants the plane was returning because of an emergency.
According to records at landings.com four flights on that plane, United N409UA, were aborted in the 1990s because of false smoke alarms. But those were all in the cargo area _ not the computerized communication and navigation system.
The NTSB's preliminary check doesn't necessarily mean an alarm was false, said Hans Weber a safety expert with aviation consultants Tecop International Inc.
"Sometimes you do have some little burning problem and it's very hard to find. It self-extinguishes and goes away," said Weber, who consults on aviation safety issues.
"You have to take them seriously whether they're a false alarm or not. You have no choice but to take them seriously," Weber said.
The A320 has an excellent reputation, he said, calling the aircraft reliable and well-liked.
The NTSB's statement Thursday said investigators have kept as part of their probe the front right-hand slide, which did not properly inflate during the emergency evacuation. The inflation mechanism was partly blocked, it said.
Passengers evacuated the plane on the two rear slides and one forward slide.