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Faulty sensor led to horrifying ‘tug of war’ in cockpit of downed Boeing plane

A preliminary investigation on the crash of Ethiopian Airlines Flight 302 concluded a controversial software system did contribute to the downing of the Boeing plane, and the pilots followed manufacturer guidelines to no avail. Boeing said it will release a software update to fix the problem, but how did the FAA approve the plane in the first place? William Brangham talks to Miles O’Brien.

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  • Judy Woodruff:

    The first report into the Ethiopian Airlines crash came out today, and it found that a computer software system on the aircraft suspected of playing a role did, in fact, contribute to the downing of Flight 302.

    William Brangham looks at those preliminary findings and the questions that still remain.

  • William Brangham:

    The trouble began on Flight 302 within minutes of takeoff.

    According to Ethiopian investigators, a faulty sensor called the angle of attack — you can see it here in this Boeing stock footage — gave incorrect data that the plane was pointed dangerously upwards and might stall.

    That triggered the software system known as MCAS to push the nose of the plane downward at least four different times. But the report says the plane wasn't in danger of stalling.

    Ethiopian officials said that the pilots followed Boeing's protocols in flight to try and correct the plane.

  • Dagmawit Moges:

    The crew performed all the procedures repeatedly provided by the manufacturer, but wasn't able to control the aircraft.

  • William Brangham:

    In a statement today, Boeing CEO Dennis Muilenburg acknowledged that this software system appeared to play a role in this crash and in the crash last fall of another Boeing 737 MAX in Indonesia.

    Muilenburg said that, in both cases, the software was responding to erroneous sensors. He pledged the company would soon complete a software update and fix it, saying — quote — "We remain confident in the fundamental safety of the 737 MAX. When it returns to the skies, it will be among the safest airplanes ever to fly."

    Our own Miles O'Brien is back tonight to walk through this news.

    Miles, the report indicates that the software tried to push the nose of this plane downwards four different times. You're a trained pilot. Can you just help us understand what that must be like, if you're flying a plane, and you know this software is now trying to force your nose into the ground? That tug of war seems almost unimaginable to me.

  • Miles O’Brien:

    Yes. It's kind of horrifying, if you think about it, William.

    Pilots are trained to deal with what's called runaway trim, meaning the same device that kind of affects the aerodynamic surfaces, which this particular system does, kind of takes off on you, and what you do is, you disconnect it.

    In this case, however, not only did the — this system have way more authority than that and continued to kind of struggle with the pilots, but, when they disconnected it, as they were instructed to do so, the manual system, this little wheel which sits beside the captain, didn't have enough authority, enough purchase for them to overcome all the aerodynamic forces on that control surface.

    So they did everything by the book, but it wasn't good enough.

  • William Brangham:

    And as the Ethiopian officials today said, these pilots did everything Boeing instructed us to do and, still, there was this tragedy.

    What does this mean for Boeing going forward?

  • Miles O’Brien:

    Well, they have a big problem and a fundamental problem with this aircraft. And it goes right to the heart of this system.

    It begins with an aerodynamic problem with the aircraft, changing the way the engines were placed on the wing, changing the way it flies, using software to cover over that problem, but relying on only one sensor to feed that.

    It's sort of a garbage-in/garbage-out scenario that computer people talk about. Should have had multiple sensors feeding in, given the fact that it was flight-critical.

    On top of that, part of this Boeing fix that they're working on is to reduce the authority of this system, so it doesn't have this kind of monster effect on the control system and is not in — operating in a repeated fashion, getting into this tug of war with the crew.

    All of these things should help.

  • William Brangham:

    We know that Boeing has made the promises that they're going to fix this software and they're going to address these problems.

    This touches on another point that I know you have focused on in the past, which is how the FAA certified this plane was OK to fly with this software system as it is. How do you see that going forward?

  • Miles O’Brien:

    Well, I think we all imagine that, as a manufacturer of an airliner begins the design and process of building on an aircraft, that there are inspectors looking over their shoulder along the way and signing off on things.

    But there aren't enough resources in the FAA to do that. And so the FAA over the years — and this has gone on for quite some time, this is not a recent thing — has given a lot of authority to the manufacturers themselves to self-police.

    Now, it is, of course, in the interest of the manufacturer to produce a safe aircraft that doesn't fall out of the sky. But whenever you're in a competitive business such as this, and you're rushing to get an aircraft to market, and you're trying to make a buck doing that, and you're trying to do it in a way that makes it easier for the airlines to do it, and not — they don't have to recertify and retrain their pilots, the temptation to cut corners is there.

  • William Brangham:

    Miles O'Brien, thank you so much.

  • Miles O’Brien:

    You're welcome, William.

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