The most fundamental problem, of course, has hardly been talked about: how do you avoid thunderstorms when they are arrayed in the form of a wall hundreds of miles long? For AF447 to have avoided all thunderstorms would have required a detour of hundreds of fuel-devouring miles. I can understand why the matter wasn't seriously considered, especially after they were airborne. But that would have been the safest approach.
The pitot tube matter is likely a red herring....air speed wasn't what killed them, but rather, suddenly being faced with an insoluble problem of some sort:
Bypassing this line of storms altogether would have incurred a long detour to the west. Meanwhile, note the contours of what they had in front of them. It's possible to stay in the green (lighter precipitation and less turbulence, presumably) the whole way through. Other visual cues that indicate danger -- scallops, fingers, hooks, areas of attenuation -- look to be avoidable.
It was going to be rough, no doubt, and we'll never know for sure what their radar screens actually showed. But if the graphic is close to accurate, it becomes easier to understand why they went on through. It was a borderline call, but not a crazy one.
...My hunch is that an unusually potent lightning strike set off a cavalcade of serious electrical problems. As reviewed in this column last week, airplanes are hit by lightning fairly frequently. Although strikes aren't normally hazardous, when trouble does occur, it tends to affect the electrical system.
According to automatic status messages relayed from the airplane to its maintenance staff in Paris, the plane suffered a loss of its Air Data Inertial Reference Unit (ADIRU) and Integrated Standby Instrument System (ISIS). Other messages told of a degraded condition in the jet's high-tech, fly-by-wire flight control stem (evidently triggered by multiple electrical faults) and what seems to have been a loss of cabin pressure.
In layperson's terms, they were losing the ability to maintain speed, altitude and pressurization as well as some of their maneuverability. Under different conditions, these malfunctions aren't liable to be catastrophic. But in the throes of a storm, in darkness, it's a different story. Eventually there was total loss of control, and the plane hit the ocean in one or more pieces.
Crew incapacitation (hypoxia as a result of the decompression) is another possible factor. On the A330, the model of airplane that crashed, loss of cabin pressure can result from certain electrical failures. So the automated status message indicating depressurization may not have been a structural issue or indicator of an in-flight breakup, as many have purported.
The crew was dealing with the loss of important instruments and controls. There would be confusion at this point, with warnings going off, messages flashing and some very urgent troubleshooting. If, as part of the mix, the cabin had suddenly decompressed, it may not have been noticed right away. Without use of supplemental oxygen, the pilotswould have had about 30 seconds of useful consciousness -- maybe less.
Could they have passed out? The autopilot was off at this point, and in powerful gusts the plane could have quickly gone out of control.
Some have also posited the idea of engine failure -- the loss of one or even both engines -- caused either by hail ingestion or extreme turbulence. This could explain the loss of cabin pressure and even the loss of control. Gliding, without engines or primary instruments, is relatively easy in calm, daylight conditions, as Capt. Sullenberger showed us. But this was another situation entirely.
And over the past few days, the media has become fixated on a report that the pilots were operating at the "wrong speed" as they penetrated the bad weather. Commercial aircraft have a so-called "turbulence penetration speed" that helps ensure structural integrity and controllability during very rough air. Of course, maintaining a precise speed can be difficult under such conditions, and any discrepancy was probably a symptom of other internal failures (see electrics, above) and not by itself a cause of the accident. The news has really jumped on this topic, but I'm wary of how relevant it might be.
The speed discrepancy has been traced to the possible failure of one or more the plane's so-called "pitot tubes" during unusually heavy icing conditions. These tubes -- among the many sundry probes, ports and sensors that dot a jetliner's exterior -- help determine airspeed. Conceivably, a pitot malfunction could have caused very serious problems and, if taken to the extreme, loss of the aircraft.
All exterior probes are heated, however, and ice accretion would have to have been particularly rapid and intense to overcome them. This was possible, but not likely. If they iced over, I suspect it was due to one or more electrical failures occurring first. Again, a symptom and not a cause.
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