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Plane Tests Must Use Average Pilots, NTSB Says After 737 Max Crashes

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Re: Plane Tests Must Use Average Pilots, NTSB Says After 737 Max Crashes

#311

Post by Zak »

mlyle wrote: post #295
Zak wrote: post #292

Earlier quoted context omitted.

> There's some people who say that because the longer 737 is less stable in pitch it should have never been built, and I think that's over the top. I know that aerodynamic instability requiring continuous correction by fly-by-wire systems has become common on fighter jets because it's necessary to achieve some of the maneuvering characteristics necessary to make them competitive. These are, of course very different p…

I thought of a much better answer to your question: Many airplanes require functional (electronic) yaw damping to be safe in various flight conditions, because of dutch roll. There are also e.g. electronic control feel systems in some aircraft that must be operational to exceed certain speeds and/or altitudes and not be excessively vulnerable to PIO, etc.

My understanding of dutch roll (from watching a few flying videos on youtube and reading the wikipedia article) makes it seem like dealing with it is basic flight control coordination that shouldn't give a pilot experienced in a given aircraft any trouble.

Is it harder than I'm imagining in big jets, or in specific aircraft due to peculiarities of their handling characteristics?

Re: Plane Tests Must Use Average Pilots, NTSB Says After 737 Max Crashes

#312

Post by mlyle »

Zak wrote: post #311
mlyle wrote: post #295

Earlier quoted context omitted.

I thought of a much better answer to your question: Many airplanes require functional (electronic) yaw damping to be safe in various flight conditions, because of dutch roll. There are also e.g. electronic control feel systems in some aircraft that must be operational to exceed certain speeds and/or altitudes and not be excessively vulnerable to PIO, etc.

My understanding of dutch roll (from watching a few flying videos on youtube and reading the wikipedia article) makes it seem like dealing with it is basic flight control coordination that shouldn't give a pilot experienced in a given aircraft any trouble. Is it harder than I'm imagining in big jets, or in specific aircraft due to peculiarities of their handling characteristics?

Dutch roll is an oscillatory mode resulting from delayed cross-axis coupling and different axis stability. There's not really much a pilot can do about it other than trying to avoid exciting it.

Aircraft with swept, low wings exhibit dutch roll worse than other types (e.g. airliners). It's also worse at high speeds and high altitudes.

Yaw dampers vary based on aircraft and flight regime to "attenuating somewhat that annoying-bouncing-back-and-forth-feeling in the back of an airliner during cruise (imagine how bad it would be without active damping!)" to "preventing an oscillation from building in 2-3 cycles to a point where it will cause structural failure".

Re: Plane Tests Must Use Average Pilots, NTSB Says After 737 Max Crashes

#313

Post by Zak »

mlyle wrote: post #312
Zak wrote: post #311

Earlier quoted context omitted.

My understanding of dutch roll (from watching a few flying videos on youtube and reading the wikipedia article) makes it seem like dealing with it is basic flight control coordination that shouldn't give a pilot experienced in a given aircraft any trouble. Is it harder than I'm imagining in big jets, or in specific aircraft due to peculiarities of their handling characteristics?

Dutch roll is an oscillatory mode resulting from delayed cross-axis coupling and different axis stability. There's not really much a pilot can do about it other than trying to avoid exciting it. Aircraft with swept, low wings exhibit dutch roll worse than other types (e.g. airliners). It's also worse at high speeds and high altitudes. Yaw dampers vary based on aircraft and flight regime to "attenuating somewhat that…

I think some of my confusion here was related to some notable youtubers misusing the term to mean a roll-on-heading exercise. When I wrote my last question, I was thinking "there's too much, or an unpredictable amount of adverse yaw", but I now understand the problem as "the aircraft enters a self-reinforcing oscillation in response to certain poorly coordinated control inputs", which doesn't sound like a good thing at all.

Thanks for all your input in this discussion. I find both flight in general and the case of the 737 MAX fascinating. Previously the implementation of MCAS sounded absolutely insane to me, but I can mostly understand how they got there after reading your comments.

Re: Plane Tests Must Use Average Pilots, NTSB Says After 737 Max Crashes

#314

Post by Dylan16807 »

IllogicalLogic wrote: post #306
Dylan16807 wrote: post #278

Earlier quoted context omitted.

That's a tradeoff that will always exist, and cannot be eliminated. The question is where you set the tradeoff for various systems.

The tradeoff where the designer introduces an edge case where a plane crashes unless a pilot has specific additional information? From my understanding of the issue, Boeing just needs to stop the cost saving measures that led to needing software to stabilize an otherwise unstable plane.

Yes, that tradeoff always exists. There are always edge cases. The pilot will always need specific 'additional' information about the plane to avoid crashing.

The choice to make is how difficult you will allow features to be, and how many difficult features you will add.

The answer has to be at least moderately high to get the plane off the ground. If it's too high then you have a bunch of deaths.

It's okay to say Boeing went too far on the scale, but to say they never should have been on the scale is misguided. Intelligence of the operator has to cover for certain aspects of the design.

Re: Plane Tests Must Use Average Pilots, NTSB Says After 737 Max Crashes

#315

Post by ummonk »

ses1984 wrote: post #179
ummonk wrote: post #153

Earlier quoted context omitted.

It won't be someone's profitability, it'll be the ticket price that you pay.

Because there is no relationship there at all, nope none, zero.

The aviation market consistently has margins that are just slightly above zero. Change the costs and ticket prices change in response; the profits stay constant.

Re: Plane Tests Must Use Average Pilots, NTSB Says After 737 Max Crashes

#316

Post by ElonMuskrat »

chrisseaton wrote: post #51
Avalaxy wrote: post #30

Earlier quoted context omitted.

Most commonly it is used for the mean though...

Mean wouldn’t make any sense in this context. Does a mean pilot even exist? Median pilots exist by definition.

https://www.thestar.com/news/insight/2016/01/16/when-us-air-...

Re: Plane Tests Must Use Average Pilots, NTSB Says After 737 Max Crashes

#317

Post by o-__-o »

IllogicalLogic wrote: post #240
beamatronic wrote: post #159

Earlier quoted context omitted.

What type of process could be used to make sure that their experience and knowledge gets back into the mainline product?

How about Boeing stops taking cost saving measures that end up throwing unnecessary curve balls at otherwise well trained pilots? At the end of the day, this is the foundation of the problem.

But airbus has had that design philosophy since inception. The joke is a Boeing will tell you it thinks an engine has failed and ask if you want to shutdown, an airbus will tell you it thinks an engine has failed and will shutdown the engine for you. Which approach is correct? Depends on the situation but pilots will debate this everyday like emacs and vi

I think MCAS represents a change for Boeing where it will start doing things without asking.

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