Ethiopian Airlines 737 crash discussion

  • #71
nitsuj
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Feels a bit strawman peter.

The iteration Juan says in the vid is exactly all I've ever said in this thread.

Effectively so did you above. Which imo is odd and concerning; disappointing.

I actually took your earlier post as being true, and spoke to others about this stick feel requirement. Turns out it's "made up". If not "made up", not understood well enough to properly convey the point.

you're off on the stick feel. There is no stick feel issue with the 737 max. imo the below comment is irrelevant in this case. mcas is not there for that; at all. mcas is specifically for maintaining the flight characteristic.

"They are just general rules that say things like "the stick force required to pitch the aircraft up should not decrease with increasing angle of attack". There are lots of ways to satisfy that requirement, resulting in lots of different possible ways the stick will feel to the pilot in actual flight. "

Said it before, saying it again. no justification for mcas other than boeings economic concerns.
Zero need to have it from a "stability" perspective and ESPECIALLY not from a safety perspective.

It's an interesting perspective to see how you communicate; in a topic I know well. Now am curious about the replies you've made to my posts in the physics section.
 
  • #72
russ_watters
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I guess I need to go back and reread this discussion because I don't see a need for it to get heated. What I do see however is a lack of clarity of terms like "inherently stable" and "pitch-up tendancy" - they seem to contradict each other, but may not. I think it's important to remember that you can and should understand different factors separately while recognizing that the behavior of the plane as a whole is the sum of those factors. That means that saying the engines at high thrust give a "pitch up tendancy" doesn't necessarily mean the plane is pitching-up on it's own (without stick pressure or trim). The three factors are:
1. The center of lift is behind the center of gravity. This provides a constant "pitch-down tendancy".
2. The stabilizer exists to counter #1, but its "pitch-up tendancy" varies with speed.
3. The engines provide a "pitch-up tendancy". that varies with thrust and aoa.

And I guess we should add:
4...or maybe 2a: Trim adjusts the amount of pitch force applied for a given control stick input; in particular, the stick-neutral pitch-up force.

The feel of the stick or stick neutral behavior of the plane is the sum of all these separate behaviors. It would be interesting to see and compare some graphs.

This semantic argument is interesting but I don't think is particularly relevant.

If the argument is about whether the plane ever needs forward stick pressure and down-trim to avoid a stall and therefore violates FAA law, I highly doubt Boeing could get that past the FAA. In other words, I don't believe this is an inherent airframe flaw that would warrant scrapping the plane - if that's what is being suggested.
 
  • #73
russ_watters
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Going back over the discussion, some points:
That said I have no clue at what speed / alt / temp ect that the planes structure is at risk; or if pilots are informed of such high limits.
At the higher altitude at that airport they use a higher takeoff speed...
Primarily the pilots fly based on Indicated Airspeed, which is nothing more than a differential pressure reading scaled to speed. Altitude, temp, atmospheric pressure, wind and humidity are all in that reading so the limits don't change with weather and altitude. The Indicated Airspeed based takeoff speed, stall speed and Vne ("never exceed" speed) are constant and are marked on the dial (caveat: at least for light aircraft - for transport aircraft the first two might change with load).
 
  • #74
russ_watters
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Perhaps this is the bone of contention:
It requires some way to deal with the control force issue, because there are FAA regulations that require the control force required to pitch the plane up further to increase with increasing angle of attack. Those regulations are there for good reasons, which have been explained well in some of the online articles on this subject. MCAS might not be the only way to meet that requirement for the 737 MAX, but for the 737 MAX it is required to be done somehow, and that requires some kind of system to change the natural behavior of the plane because the natural behavior of the plane does not meet the requirement.
It sounds like you are saying you don't think the 737Max could get FAA certified at all without MCAS. I don't believe that's true because I think if it were it also couldn't be certified WITH MCAS!

Also, the "type certification" is the pilot's certification to fly the plane, not the plane's certification to fly at all (airworthiness certification). Keeping the type certification the same is a business convenience decision, whereas not being capable of achieving airworthiness certification would mean the plane couldn't fly at all. Note also: airworthiness certification is per plane, not per type of plane or model of plane.
 
  • #75
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you're off on the stick feel. There is no stick feel issue with the 737 max

You said you would read through the other thread, which is in the Mechanical Engineering forum and is more focused on technical questions like this. Have you done so? There is plenty of discussion there that is highly relevant to this issue. Including references on why MCAS was done for the 737 MAX which talk about making the stick feel similar enough to previous 737 models to allow the 737 MAX to be classified as the same aircraft type. The entire discussion of that topic should really be taken to that other thread; the General Dicussion forum is not supposed to be for technical questions.
 
  • #76
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It sounds like you are saying you don't think the 737Max could get FAA certified at all without MCAS

No, I'm saying the FAA wouldn't have allowed it to use the existing 737 type certification.

the "type certification" is the pilot's certification to fly the plane, not the plane's certification to fly at all (airworthiness certification).

Yes, I understand that. I have never claimed that the 737 MAX would not have received an airworthiness certification without MCAS. I have only said that MCAS was needed to allow the 737 MAX to use the existing 737 type certification--or, to put it more precisely in the light of your valid comment here, to allow pilots who had the existing 737 type certification to fly the 737 MAX without additional training.
 
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  • #77
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It sounds like you are saying you don't think the 737Max could get FAA certified at all without MCAS. I don't believe that's true because I think if it were it also couldn't be certified WITH MCAS!

Per my earlier post just now, I think we should take this discussion to the other thread, since we really shouldn't be delving into technical issues here in General Discussion.
 
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  • #80
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It's an interesting perspective to see how you communicate; in a topic I know well. Now am curious about the replies you've made to my posts in the physics section.

You really need to check references before making a statement like this.
 
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  • #81
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