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Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

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Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#141

Post by mannykannot »

VBprogrammer wrote: post #138
mannykannot wrote: post #137

Earlier quoted context omitted.

Let's work through an example. You are in level, trimmed, manual flight and the trim system suddenly starts pitching the nose down. As a consequence, the aircraft will begin descending and accelerating. Your first response, even before you have recognized that you have a trim runaway situation rather than just some turbulence, is to pull back, to restore level flight level and bring the speed down to where it is supp…

Unfortunately I think you may be misinterpreting that section in the manual. From your senario when the trim moves nose down. You apply nose up on the elevator which makes the trailing edge of the elevator go up which applies a downwards force on the trailing edge of the stabilizer. In order to move the trim back towards neural you need to lift the trailing edge against this force. If the trim is extreme you may have…

You have a point, but I am not sure that this is a complete analysis of the situation, because it does not consider the changing moments as the centers of pressure of the wing and stabilizer move in response to the changing airspeed. Furthermore, when one moves the elevator of a subsonic airplane, it does not just change the force generated by the elevator, but also the force generated by the stabilizer it is attached to (by affecting the airflow over it), so that is another potential source of changing moments.

Perhaps the phrase "aerodynamically relieve the air loads" means to minimize the aerodynamic force generated by the stabilizer? The stabilizer of a conventional airplane will invariably generate a downwards force when the aircraft is in pitch equilibrium at high speed, but it may be upwards at low speed, even with the C of G within limits. In such cases, the speed at which it has no load will be an intermediate one, and therefore could be either above or below the speed to which the airplane is currently (mis-)trimmed.

The quoted passage says it is referring to correcting what it calls a mis-trim, so if your interpretation is correct, then where it says "in-trim speed", it actually means "the speed to which the airplane is mis-trimmed", while the general usage of the term "in trim" means trimmed to fly at the intended speed, and I would take the phrase "in-trim speed" to refer to that speed - the speed that the pilots intend to fly at, or, in other words, the speed that this out-of-trim airplane would tend to fly at when put back in trim.

Furthermore, if things are as you describe, then the rule could have been more simply and clearly phrased as "reduce your pressure on the control yoke". Maybe your interpretation is correct, but if so, it seems to me to be an unnecessarily confusing way to describe it.

Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#142

Post by jquery »

dang wrote: post #124
jquery wrote: post #102

Earlier quoted context omitted.

It’s boring to read HN wildly speculate on the crash and trash Boeing as if they know what went wrong. Historically speaking, early speculation has nearly always been notoriously bad at predicting what went wrong in a given crash scenario. Despite this happening twice it is still a sixth sigma event, there is no reason to think the exact same set of circumstances occurred twice, especially after pilots were well awar…

No doubt many people will turn out to be wrong about this. You simply need to make your points without breaking the site guidelines, as do we all. You've unfortunately broken them again just now. It's explicitly against the guidelines to insinuate that people you disagree with are astroturfers. Would you mind re-reading https://news.ycombinator.com/newsguidelines.html and following them carefully when posting here? W…

Nice to see HN finally has a semi-active moderator. As you can see I’ve taken quite the hiatus from HN because the noise to signal ratio got really bad.

I don’t care about downvotes, if I did I wouldn’t post my actual opinions here, I just found it silly that people were trying to bury a comment that wasn’t the standard doom and gloom and ignorance I see around the crash.

Interestingly as soon as I edited my post the downvotes stopped and I started getting upvotes so some people found the edit interesting. :thinking emoji:

If you care to hear from someone who has been part of this community since early days, too many people are able to vote on comments. They don’t lurk, they are attracted here from a controversial link and stick around, reflexively treating upvotes/downvotes as a disagree/agree button instead of interesting/not-interesting like it used to be. Maybe the eternal September has finally arrived for good, or perhaps I’ve drifted from the core values of your typical HNer while this site stayed the same or drifted in a different direction. Only you would have the traffic and usage stats to know. I’m curious what percent of active HNers have an account created within a standard deviation of mine.

-posted from my phone so forgive typos

Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#143

Post by mannykannot »

cjbprime wrote: post #107
VBprogrammer wrote: post #54

Earlier quoted context omitted.

I think it's unlikely that this crash will be attributed to the same set of circumstances as the lion air crash. I don't find it credible that an experienced pilot would fail to catch what, in essence, is a trim runaway event. There is a reason trim runaway is a memory item on almost all aircraft. Even in the Lion air case the previous flight experienced difficulty with the system and dealt with it. This was before t…

> I don't find 1 particularly compelling, it would have been noted by now if it was impossible to trim the aircraft using the manual trim wheels. It has been noted: 737 Flight Crew Training Manual, chapter Non-Normal Operations/Flight Controls, sub heading Manual Stabilizer trim: "Excessive air loads on the stabilizer may require effort by both pilots to correct mis-trim. In extreme cases it may be necessary to aerod…

This appears to be the case for 737 NG models, as well as the MAX. If it is a dangerous flaw, it is so for all of them.

The bit about the 'effort by both pilots' raises the issue of the 200-hour first officer.

https://www.pilot18.com/wp-content/uploads/2017/01/B737NG_FC...

Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#144

Post by cjbprime »

mannykannot wrote: post #141
VBprogrammer wrote: post #138

Earlier quoted context omitted.

Unfortunately I think you may be misinterpreting that section in the manual. From your senario when the trim moves nose down. You apply nose up on the elevator which makes the trailing edge of the elevator go up which applies a downwards force on the trailing edge of the stabilizer. In order to move the trim back towards neural you need to lift the trailing edge against this force. If the trim is extreme you may have…

You have a point, but I am not sure that this is a complete analysis of the situation, because it does not consider the changing moments as the centers of pressure of the wing and stabilizer move in response to the changing airspeed. Furthermore, when one moves the elevator of a subsonic airplane, it does not just change the force generated by the elevator, but also the force generated by the stabilizer it is attache…

For what it's worth, my reading matches VBprogrammer's, though I agree with you that much of the language seems unnecessary.

Frustrating to have a question that could be answered quickly by a 737 pilot! (Whether the trim wheel becomes much harder to turn after you set STAB TRIM CUTOUT to cutout, mistrim down, and pull up.)

Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#145

Post by cjbprime »

VBprogrammer wrote: post #130
cjbprime wrote: post #129

Earlier quoted context omitted.

> It certainly doesn't say it's impossible. What would it have to say? It says you might have to do X before Y, where Y is a thing that you need to do quickly while at low altitude to avoid dying and X is a thing that gives you even less time to do it in and makes the problem worse.

Ok let's look at it another way. Do you think it's even remotely likely that Boeing haven't had one of their 737 Max aircraft try this out at a safe altitude? They staked the future of the aircraft by saying they believe they are safe to fly. I've never suggested having a trim runaway close to the ground is trivial. It's certainly going to result in brown trousers when it happens, but it should be within the abilitie…

I mean, the answer could be that you do that three times, then you remember that the emergency AD said that you should trip STAB TRIM CUTOUT when this happens, so you do, and then you realize that you're mistrimmed at less than 1000ft AGL, you just disabled the motor that was allowing you to fix the trim, and now you can't fix it without losing 600ft in the process while you release the yoke.

I am not saying this is likely to be what happened! But given that Boeing didn't even mention any of this in the manual before Lion Air, it seems plausible that they either didn't test it carefully, or tested it at high altitude and imagined that it would never happen at low altitude?

Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#146

Post by VBprogrammer »

mannykannot wrote: post #141
VBprogrammer wrote: post #138

Earlier quoted context omitted.

Unfortunately I think you may be misinterpreting that section in the manual. From your senario when the trim moves nose down. You apply nose up on the elevator which makes the trailing edge of the elevator go up which applies a downwards force on the trailing edge of the stabilizer. In order to move the trim back towards neural you need to lift the trailing edge against this force. If the trim is extreme you may have…

You have a point, but I am not sure that this is a complete analysis of the situation, because it does not consider the changing moments as the centers of pressure of the wing and stabilizer move in response to the changing airspeed. Furthermore, when one moves the elevator of a subsonic airplane, it does not just change the force generated by the elevator, but also the force generated by the stabilizer it is attache…

You make a couple of very good points. And your right, if it were that simple they hopefully would have described it that way.

In general pitch trim runaway incidents are easiest to control at low speeds. It gives you more aircraft configuration options available to try and reduces the aero loads general.

But perhaps they were just not ruling out either.

Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#147

Post by mannykannot »

VBprogrammer wrote: post #135
mannykannot wrote: post #82

Earlier quoted context omitted.

I think there is a certain amount of hindsight in your response to scenario 1. While there is a good case to be made that Boeing was wrong to minimize the differences between the latest models and their predecessors, the Lion Air crash investigation did not produce any evidence that an MCAS fault could not be remedied by following the published procedure, and as far as I can tell, no other incidents prior to the Ethi…

Perhaps it's just because I've been trying in vain to make similar points but I don't understand why you've been down voted here. It seems the only acceptable response is that Boeing deliberately killed people by trying to subvert the certification requirements and/or failing to inform pilots of a new system.

I am wondering why, if it was obvious that the 737 MAX should be grounded after the Lion Air crash, no one seemed to be saying that until the Ethiopian Airlines crash?

Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#148

Post by tyingq »

cjbprime wrote: post #116
CydeWeys wrote: post #106

Earlier quoted context omitted.

Why would AOA indicators be a paid upgrade? Isn't that a pretty fundamental display needed to safely fly the plane? And wouldn't having disparities here between planes create more confusion among pilots?

Airlines and general aviation aircraft have totally ignored AoA as a relevant indicator until very recently. You won't find an AoA indicator in even a modern Cessna. As a student pilot you're taught about unsafe low airspeeds instead, even though AoA can technically cause a wing to stall at any airspeed, and even though that memorized stall airspeed ($V_s1$) actually varies with factors like plane weight. AoA is not…

Looks like that changed. AoA is standard equipment on Cessna 172's since 2016: https://www.flightglobal.com/news/articles/aoa-indicator-bec...

Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#149

Post by Moru »

Sylamore wrote: post #133
dredmorbius wrote: post #74

Earlier quoted context omitted.

Try; http://archive.fo/Qk7PU The .is domain has been occasionally problematic.

archive.is/fo basically doesn't work with cloudflare DNS due to a misconfiguration by whomever runs the archive.today service. It has been reported by multiple people to the site operator and at this point it seems likely intentional.

I just used my normal DNS server to get the correct IP and put that IP in my pi-holes hosts file and now it works just fine.

Re: Boeing 737 Max Hit Trouble Right Away, Pilot’s Tense Radio Messages Show

#150

Post by mannykannot »

VBprogrammer wrote: post #146
mannykannot wrote: post #141

Earlier quoted context omitted.

You have a point, but I am not sure that this is a complete analysis of the situation, because it does not consider the changing moments as the centers of pressure of the wing and stabilizer move in response to the changing airspeed. Furthermore, when one moves the elevator of a subsonic airplane, it does not just change the force generated by the elevator, but also the force generated by the stabilizer it is attache…

You make a couple of very good points. And your right, if it were that simple they hopefully would have described it that way. In general pitch trim runaway incidents are easiest to control at low speeds. It gives you more aircraft configuration options available to try and reduces the aero loads general. But perhaps they were just not ruling out either.

I have asked around, and the consensus is that you are correct.
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