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>The author makes the bizarre assertion that runaway trim is only caused by short circuits That's not the only problem with TFA. I worked on the Hercules, not

by na85 5y ago

>The author makes the bizarre assertion that runaway trim is only caused by short circuits That's not the only problem with TFA. I worked on the Hercules, not any of the Boeing airliners, but this "30-year pilot" has some pretty fundamental misunderstandings of how MCAS works, what the effects of moving the engines are, and what actually went wrong with the 737 Max. Color me surprised. Regurgitating the same "MCAS prevents the aircraft from stalling because it's unstable" shlock betrays the author's surface level (at best) understanding of the issue.

alexose 5y ago
As a surface-level-understanding layman myself, what about this is wrong? The 737 MAX is unstable, no?
- na85 5y ago
  >The 737 MAX is unstable, no? No, it's not unstable. The 737 Max exhibits stable pitch behavior along the entire envelope. A lot of people think "unstable" means "it crashes" but these terms have precise meanings. The 737 Max is a stable airplane. One of the problems it exhibits is that with increasing angle of attack, the stick force does not increase (linearly is the requirement, I think, I'm writing from memory here). The way you know this is because MCAS moves the horizontal stabilizer directly, and not the control column that the pilot is holding. An anti-stall device like a stick pusher or a stick shaker provides tactile feedback to the pilot via the control column. Moving the horizontal stab directly is (basically) altering the trim of the aircraft. Thus it is a handling-qualities system.
  - alexose 5y ago
    I see. So calling it "unstable" isn't really fair. It's more that it just flies differently enough that it would feel unfamiliar to typical 737-trained pilots.
    - Dma54rhs 5y ago
      Not getting pilots retrained was the cost saving strategy for companies buying the new area aircrafts.
      - WalterBright 5y ago
        Not needing retraining was a good goal because it improves safety. Sometimes airplanes have crashed because in a crisis the pilot did the right thing for another airplane he was trained on, but was the wrong thing for what he was piloting at the moment. It's not just a cost saving measure. MCAS was a sound concept. It's implementation, however, was not sound at all.
        asd4232 5y ago
        A typical pilot switches aircraft type multiple times in their career. It's all about the cost and convenience ultimately, allowing same pilots to fly both 737MAX and the older 737NG as most 737MAX customers operate both. As far as MCAS goes, in my opinion Airbus got it right already in the 80's in their A320 with their flight envelope protection.
        wikfwikf 5y ago
        Do you understand how delusional it sounds in this specific context to say that not needing retraining improves safety? Not that it might improve safety or should improve safety, but that it does improve safety?
        rramadass 5y ago
        Rightly said!
        dpark 5y ago
        "Not needing retraining" is another way of saying "works as expected". Yes, it would likely have been safer if the 737 Max worked as expected by the pilots flying it.
        5y ago
- ummonk 5y ago
  No, it's always stable. The issue is that pulling back further on the control stick wasn't causing an increase in force feedback at high angles of attack, making it more likely for the pilot to inadvertently stall the aircraft.
deleted 5y ago
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by na85 5y ago

alexose 5y ago

As a surface-level-understanding layman myself, what about this is wrong? The 737 MAX is unstable, no?

na85 5y ago
>The 737 MAX is unstable, no? No, it's not unstable. The 737 Max exhibits stable pitch behavior along the entire envelope. A lot of people think "unstable" means "it crashes" but these terms have precise meanings. The 737 Max is a stable airplane. One of the problems it exhibits is that with increasing angle of attack, the stick force does not increase (linearly is the requirement, I think, I'm writing from memory here). The way you know this is because MCAS moves the horizontal stabilizer directly, and not the control column that the pilot is holding. An anti-stall device like a stick pusher or a stick shaker provides tactile feedback to the pilot via the control column. Moving the horizontal stab directly is (basically) altering the trim of the aircraft. Thus it is a handling-qualities system.
- alexose 5y ago
  I see. So calling it "unstable" isn't really fair. It's more that it just flies differently enough that it would feel unfamiliar to typical 737-trained pilots.
  - Dma54rhs 5y ago
    Not getting pilots retrained was the cost saving strategy for companies buying the new area aircrafts.
    - WalterBright 5y ago
      Not needing retraining was a good goal because it improves safety. Sometimes airplanes have crashed because in a crisis the pilot did the right thing for another airplane he was trained on, but was the wrong thing for what he was piloting at the moment. It's not just a cost saving measure. MCAS was a sound concept. It's implementation, however, was not sound at all.
      - asd4232 5y ago
        A typical pilot switches aircraft type multiple times in their career. It's all about the cost and convenience ultimately, allowing same pilots to fly both 737MAX and the older 737NG as most 737MAX customers operate both. As far as MCAS goes, in my opinion Airbus got it right already in the 80's in their A320 with their flight envelope protection.
      - wikfwikf 5y ago
        Do you understand how delusional it sounds in this specific context to say that not needing retraining improves safety? Not that it might improve safety or should improve safety, but that it does improve safety?
        rramadass 5y ago
        Rightly said!
        dpark 5y ago
        "Not needing retraining" is another way of saying "works as expected". Yes, it would likely have been safer if the 737 Max worked as expected by the pilots flying it.
      - 5y ago
ummonk 5y ago
No, it's always stable. The issue is that pulling back further on the control stick wasn't causing an increase in force feedback at high angles of attack, making it more likely for the pilot to inadvertently stall the aircraft.

deleted 5y ago

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