Flight 497: The Gift of Time and Airport Proximity
When I was listening to the ATC recordings of United Flight 497's emergency in New Orleans — you can hear them here — I was overwhelmed by one fact: Even in a sophisticated, multi-million dollar FAR 25 transport category tested to a fare-thee-well, things can go to hell in a hurry. What starts out as a minor problem can quickly escalate to the life threatening, as it appears to have aboard Flight 497. One minute, you can be behind a a panel full of all the flight data you could ever want, the next, it's just so much inert plastic and silicon.
As we've discussed before, when smoke and/or fire impacts the cockpit, survival time is measured in mere minutes and in that sense, 497 had one thing going for it: The smoke appeared just four minutes after takeoff and within 12 minutes, the pax and crew were evacuating on runway 19. Had the emergency occurred two hours later, with the airplane over the mountain west, it might have been infinitely more difficult to resolve safely or at least quickly. The weather was also relatively benign, although it looks like the crew may have had to contend with some broken IMC while flying on backup instrumentation with ATC providing the navigation via vectors. Gusty conditions resulted in turbulence, according to passengers.
This incident prompted me to review the accident record to look at two other fire-in-flight accidents whose outcome wasn't as happy. Remember ValuJet 592? It took off from Miami at 2:04 p.m. on May 11, 1996. At 2:14 p.m., it plunged into the Everglades killing all aboard after a horrific fire engulfed the cabin and cockpit. It took a mere 10 minutes. Almost two years later, Swissair 111, an MD-11 enroute from JFK to Geneva, reported an urgency with smoke in the aircraft at 10:14 p.m. The emergency escalated and by 10:31, the airplane had crashed in the ocean off Nova Scotia, killing all aboard. Seventeen minutes transpired. The investigation faulted the crew in detail for its response to the emergency, but it also concluded that nothing it could have done would have changed the final outcome. The airplane was simply too far from an airport to land in time to do the occupants any good.
Fortunately, Flight 497 was not and neither the crew nor ATC wasted any time getting it vectored for an approach to runway 19. As the investigation unfolds, I'll be curious to learn if the smoke condition was escalating. If you've ever been in a simulator smoke drill, you know that it doesn't take much to completely obscure the instruments and also the view outside. Full-face oxygen masks mean you can breathe, but not being able to see well or at all complicates the emergency response.
Flight 497 lost its primary instruments, according to the crew, but its comm radios remained alive so ATC could provide assistance. It's not the first time this has happened in an Airbus A320. In 2008, another United flight had a similar experience after takeoff from Newark, losing three of the six displays and several aircraft systems. No smoke or fire reported on that one. According to this NTSB report (PDF), Airbus concedes there were 49 such events, most due to failures in one of the main electrical busses. Seven of these resulted in the loss of all six flight displays.
In other words, events like this are hardly unheard of, although given the flight hours and cycles these airplanes fly, they're still a relative rarity. There are implications for light general aviation aircraft, which are going in the direction of full glass panels. The new Corvalis TTx Cessna unveiled at Sun 'n Fun has a Garmin G2000 with no mechanical backup gyros. It does have a supplemental glass gyro. Kind of gives one pause before shoving the throttle in and launching into a 200-foot overcast.