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Thread: Breaking news: Ethiopian Airlines flight has crashed on way to Nairobi

  1. #421
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    A straightforward question. Is there a difference between the AoA and the attitude of an aircraft? If not, why can't the artificial horizon be used to verify AoA sensors?

  2. #422
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    Quote Originally Posted by Evan View Post
    So, no third ADIRU? No sdditional, backup AoA vane? Oh, but you get a light!
    You thought a third ADIRU was coming?

  3. #423
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    Quote Originally Posted by pegasus View Post
    A straightforward question. Is there a difference between the AoA and the attitude of an aircraft? If not, why can't the artificial horizon be used to verify AoA sensors?
    There is a difference. AoA measures the airflow relative to the wing. It can be very different from attitude.

  4. #424
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by pegasus View Post
    A straightforward question. Is there a difference between the AoA and the attitude of an aircraft? If not, why can't the artificial horizon be used to verify AoA sensors?
    AoA and pitch attitude are not the same.

    Pitch attitude is the angle pitch angle of the plane measured from the horizontal.
    AoA is the pitch angle of the plane measured from the feestram (i.e. airspeed vector or relative wind).
    Add one more angle, air flight path angle (the angle between the airspeed vector and the horizon), and you have that AoA = pitch attitude - flight path angle.

    For example, if an airplane after take-off has a pitch of 15 degrees nose up and the trajectory is climbing at an angle of 10 degrees (no wind), then the AoA is 5 degrees.
    If an airplane is approaching in the glide slope of an ILS that has a slope of -3deg and the airplane is pitched up 2 deg, the AoA is again 5 degrees.

    As you can see, 2 very different pitch can give the same AoA.

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  5. #425
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    What do you guys think of this? Talks about how MCAS and trim runaway are different, again, and then adds something new:

    https://leehamnews.com/2019/03/22/bj...-crash-part-2/

  6. #426
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    Quote Originally Posted by Gabriel View Post
    AoA and pitch attitude are not the same.

    Pitch attitude is the angle pitch angle of the plane measured from the horizontal.
    AoA is the pitch angle of the plane measured from the feestram (i.e. airspeed vector or relative wind).
    Add one more angle, air flight path angle (the angle between the airspeed vector and the horizon), and you have that AoA = pitch attitude - flight path angle.

    For example, if an airplane after take-off has a pitch of 15 degrees nose up and the trajectory is climbing at an angle of 10 degrees (no wind), then the AoA is 5 degrees.
    If an airplane is approaching in the glide slope of an ILS that has a slope of -3deg and the airplane is pitched up 2 deg, the AoA is again 5 degrees.

    As you can see, 2 very different pitch can give the same AoA.
    Thanks to you and others for the explanation.

  7. #427
    Senior Member Evan's Avatar
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    Quote Originally Posted by Black Ram View Post
    You thought a third ADIRU was coming?
    Did I think it was coming? No. Do I think it's needed on an aircraft with FBW functions that oppose pilot commands. Yes. So did the FAA and EASA when the A320 was being developed.

    The best Boeing can do without adding a third data source is fail-safe, meaning that if a sensor fails, the system becomes inop and thus does nothing dangerous. However, that leaves the crew with an aircraft that is unstable near the edge of the envelope under certain conditions for the remainder of the flight, and thus somewhat dangerous. I'm concerned that, somewhere down the lifespan of the Max, another crash will occur due to a stall that resulted from pilot error plus a faulty AoA sensor taking the MCAS offline. Is that likely? No. Is that greater than a one-in-one billion possibility? Certainly. The FBW approval standard for failure-leading-to-loss-of-control rate on the A320 was one-in-one-billion.

    Providing a third data source would give the Max fail-passive redundancy, meaning a sensor could fail without removing the augmented stability provided by the MCAS system. If Boeing were truly safety-focused, their solution to the current problem would include this additional hardware.

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