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by spangry
881 days ago
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Pretty chilling reading. A disturbingly similar situation occurred in AirAsia Flight 8501 (Airbus A320): https://en.wikipedia.org/wiki/Indonesia_AirAsia_Flight_8501#.... Similar to the AF incident, the autopilot disengaged and the flight control switched to alternate Law. The aircraft began to roll and the first officer over-corrected back and forth while also pitching the nose up and causing the plane to stall. The pilot and the first officer were both providing opposite inputs (nose down and nose up respectively) which cancelled each other out, preventing recovery from the stall condition. The plane crashed into the ocean, killing everyone onboard. I'm starting to wonder if there's something inherent in the design of the Airbus side-stick that makes this sequence of events (i.e. banking, overcorrecting, climbing) more likely if the aircraft suddenly switches from normal to alternate law. |
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I think it’s less something specific to the Airbus sidestick implementation and more over-reliance on cockpit automation in general. Airbus alternate law flies more like (not exactly like) a non-FBW traditional airplane, and pilots who never train that skill (because they always fly normal law) become overloaded when thrown into that situation unexpectedly.
A primary problem is that your muscle-memory is all wrong. Holding the stick to the side no longer gives a constant-bank turn. You have to re-center the stick when you get to the desired bank angle. Pulling all the way back doesn’t give you a constant near-maximum rate of climb (You can stall the airplane), and need to apply a little less back pressure when you get to the desired pitch. You also need to manually adjust pitch trim for any speed or power changes. So a failure that induces alt law means that you took off in one airplane and are now flying a different airplane.
The event that precipitated alt law is nearly always an emergency or near-emergency on its own. So not only are you flying a different airplane than the one you’re used to, you’re also diagnosing system failures at the same time.
If there’s anything to blame with Airbus’s implementation, I would argue it’s that the normal law is too dissimilar to how airplanes actually fly.
Edited for clarity.