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388 points cjr | 4 comments | | HN request time: 0.667s | source
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fsckboy ◴[] No.44537714[source]
it makes sense to me that the pilot who said "I did not do it" actually did do it without realizing it, was supposed to be putting the landing gear up when he committed a muscle memory mistake. it happened around the time the landing gear should be up, and this explanation matches what was said in the cockpit, and the fact that the landing gear wasn't retracted. I think this idea was even floated initially by the youtube pilot/analysts I watch but dismissed as unlikely.
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dyauspitr ◴[] No.44538361[source]
If you shut off the engines a couple of dozen meters above ground shouldn’t every alarm be blaring or there should be some sort of additional lever you have to pull way out of the way to enable shutting off the engine that close to the ground.
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WalterBright ◴[] No.44538978[source]
Consider a case where the engine starts to violently vibrate. This can tear the structure apart. Delaying shutting off the engine can be catastrophic.

It's very hard to solve one problem without creating another. At some point, you just gotta trust the pilot.

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russdill ◴[] No.44540677[source]
If you read through the boeing procedures, if an engine fails just after take off you delay cutting throttle or hitting the cutoff until you have positive climb and pass a certain altitude. Specifically because a mistake here would be so incredibly catastrophic. The following number of steps and verbal cross checks for then shutting down the engine are quite daunting. Not something applicable here, but still interesting to learn about
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interestica ◴[] No.44541999[source]
That’s absolutely applicable here. It means that an engine cutoff shouldn’t be allowed at all during certain parts of flight. It’s not crazy to think that a design fix would be to prevent those engagements during certain parts of takeoff (a certain window). It’s fly by wire anyway so it could presumably be done programmatically.

MCAS was basically made to prevent user input that would send the plane into a dangerous angle. The computer overrode the inputs. So there’s precedent for something like it.

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WalterBright ◴[] No.44542716[source]
> The computer overrode the inputs.

This is incorrect. The manual stabilizer trim thumb switches override MCAS.

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interestica ◴[] No.44543370[source]
Are we not in agreement? MCAS overrode the inputs and the thumb switches could override MCAS?
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invalidator ◴[] No.44546010[source]
MCAS autonomously adjusts trim downward. The trim switches override MCAS, but when released, MCAS can resume trimming down again. The trim adjustments don't "override" the pilot's elevator inputs (MCAS has no direct control over the elevators), but they can make the controls so heavy that it's impossible to pull up.
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1. WalterBright ◴[] No.44546118[source]
If MCAS is running the trim, the thumb switches override it.

MCAS affects the stabilizer, the thumb switches affect the stabilizer, the cutoff switch affects the stabilizer.

The elevators are controlled by the control column and the autopilot.

> The trim switches override MCAS, but when released, MCAS can resume trimming down again.

That is correct. That is why the procedure is to return the trim to normal with the thumb switches, then turn off the trim system. That's it. That's all there is to it.

> but they can make the controls so heavy that it's impossible to pull up.

Almost right - the trim has more authority than the elevators. The trim's ability to travel far is to provide great ability to get out of trouble. I don't really know what factors the aerodynamics guys used to calculate the max travel required. I do know there is a travel limiter on it (as I worked on that, too!) which reduces the max travel at higher speeds, because otherwise it can rip the tail section off, which is a big no-no.

There are sooo many constraints on the design of an airplane I sometimes wonder how anyone manages to make one that works at all. The Wright Bros calculated that their machine would fly, and it did, barely. Their contemporaries did seat of the pants design, which is why they failed.

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2. throwaway48476 ◴[] No.44547321[source]
It's good that you're still around to correct misinformation about MCAS. I've seen so much misinformation about it, including from paid "experts".

The Wright brothers succeeded because they were pioneers in wind tunnels and aluminum engine blocks.

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3. invalidator ◴[] No.44547601[source]
> Almost right - the trim has more authority than the elevators.

Thank you, I'll update my brain and future explanations. :)

4. WalterBright ◴[] No.44547920[source]
Thank you. I've had commercial pilots email me telling me I was correct and to keep on the good fight :-)

The Wrights did a lot more than that to be successful. Their innovations were:

1. using a wind tunnel to correctly get lift and drag coefficients for various wing sections (as you wrote)

2. first aviation engine (high power/weight ratio) (as you wrote)

3. first propeller theory, enabling 90% efficiency (other aviation propellers were 50% efficient)

4. first 3-axis control system

5. identified and solved adverse yaw problem

6. first research and development program, where problems were identified in advance, and a machine was developed to solve each problem, then the solutions were put together to make the 1903 Wright Flyer

7. kept meticulous notes on all their work and preserved the evidence of their success, such as photographs and notebooks. Exacting replicas have been built, and their flight characteristics match the Wright's results