The Daily Parker

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The world panics about an airplane

Two Boeing 737 Max 8 airplanes have crashed shortly after takeoff in the last few months, killing hundreds of passengers and crew. As a result, the European Union, the UK, China, and other countries have grounded the model pending investigations. Notably, the FAA has not. In the US, only American and Southwest are flying the new plane.

This is, simply put, panic. But no one wants to be the guy who will get blamed if another one goes down, even though that is highly improbable.

The Lion Air crash in Indonesia back in October seems related to a software change in the 737 Max 8 that the pilots didn't know about. That accident is still under investigation. Obviously so is Monday's crash in Ethiopia, with the flight data and voice recorders only retrieved yesterday.

While the Washington Post runs a story about how similar the crashes appear, and the President spouting off about how planes are too complex to fly these days, I turn to fellow pilot James Fallows for a dose of reason:

In the Lion Air crash, the pilots apparently kept trying to pull the plane’s nose back up. The MCAS system kept pushing it down. The automated system eventually won. The question that’s not yet answered about that crash is why the pilots didn’t turn off or disable this system. Such fail-safe override controls are built into every automated flight system I’ve ever heard about. As Patrick Smith discusses in his post, it’s possible that the pilots didn’t understand how the new MCAS system worked, or what it would be trying to do. It’s possible that they didn’t know where the overrides were. It’s possible that … well, anything might have occurred.

Is this what happened in the Ethiopian Airlines case as well? Was the AOA-sensing system that triggers the MCAS flawed or broken? Were the automatic controls trying to push the plane down, down, down, while the pilots fought to keep it up? Did the pilots try to override or disable the system? (For instance, by lowering the plane’s flaps, which happens on every landing and is designed to automatically disable the MCAS system.) Were they caught by surprise and unaware of what that system was doing? Were they fully aware, but still unable to alter the fatal path down?

Or was something else, something entirely unrelated, responsible for this crash? Something that had nothing to do with this model of airplane, or these new automated systems? At the moment, I believe no one knows. That is what Boeing, the Ethiopian authorities, the National Transportation Safety Board, and the world’s airlines are trying to figure out. There are enough differences between the two crashes—for instance, in the fluctuations in speed and altitude before impact—that the causes could turn out to be wholly unconnected.

Fallows links to "Ask the Pilot" Patrick Smith, with this also reasonable thought:

For pilots, dealing with the unwanted nose-down command would be, or should be, straightforward. The MCAS commands, faulty or not, can be overridden quickly through a pair of disconnect switches. Why the Lion Air pilots failed to do this, if in fact they did, is unclear, but unaware of the system’s defect in the first place, we can envision a scenario in which they became overwhelmed, unable to figure out in time what the plane was doing and how to correct it.

“Though it appears there’s a design flaw that Boeing will need to fix as soon as possible,” I wrote in November,“passengers can take comfort in knowing that every MAX pilot is now acutely aware of this potential problem, and is prepared deal with it.”

The Ethiopian accident, though, makes us wonder. With the Lion Air crash fresh on any 737 MAX pilot’s mind, you’d expect the crew to have recognized the malfunction right away and reacted accordingly. Did a disconnect somehow not work? Were they so inundated by a cascade of alarms, warnings, and erratic aircraft behavior that they failed to recognize what was happening? Or was the problem something else completely?

We won't know for a long time, in any event no sooner than the FDR and CVR data gets analyzed.

Comments (1) -

  • David Harper

    3/13/2019 4:03:41 PM +00:00 |

    The article by James Fallows sensibly cautions against jumping to conclusions with insufficient evidence.  That said, according to this news article, two pilots filed incident reports last year to NASA's voluntary safety report database about the autopilot on this model making unexpected rapid descents:

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