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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 13th Nov 2018, 16:51
  #1101 (permalink)  
 
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Originally Posted by Rananim View Post
It didnt.It trimmed the aircraft nose down in response to faulty AoA....the report from the previous commander clearly says "STS trimming the wrong way".The pilots just have to recognize that......
How do you know this is a genuine fault? The 737 STS system ALWAYS trims the wrong way - that is what it is ‘suposed’ to do. And the pilot response on every flight is to trim back the right way - which overrides the STS. Which is why the STS is widely cursed - it may be trimming into a ‘safer’ regime, but pilots like an aircraft to be in trim, not trimmed nose down - so it is still a pain when hand flying.

Silver

Last edited by silverstrata; 13th Nov 2018 at 17:10.
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Old 13th Nov 2018, 17:06
  #1102 (permalink)  
 
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Silverstrata. The theory/design is not misunderstood. It is straightforward and subject to a separate discussion relative to design and functionality?

The issue is and remains: A flight critical controls mode is installed on a fleet. It screws up, and we find out no one knew of its existence. Airbus has been subject to extreme criticism for doing similar with mode confusion the result. Boeing’s turn in the barrel. Disclosure by manufacturer is a (mandatory) minimum, understanding is up to the operator.

”handling” is done with controls. Maneuvering.

Long term stability is for TRIM.

Using a slow but immensely powerful control on climbout involves the risk of getting stuck in dangerous area of migrating neutral stick position and needing to overcome trim induced bias attitude with what amounts to a trim tab (elevator). Just my opinion. Is it fatally wrong?

Last edited by Concours77; 13th Nov 2018 at 17:17.
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Old 13th Nov 2018, 17:09
  #1103 (permalink)  
 
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At 4000 meters depth-little- no oxygen-Corrosion is related or equal to OXIDATION which requires . . . Oxygen...
Exactly, but once to the surface..oxygen!

News is now saying the lazy B knew of the issue. (WSJ at least)
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Old 13th Nov 2018, 17:34
  #1104 (permalink)  
 
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@Vessbot
The difference between nose and FPV (wind notwithstanding) is AOA
If only life were so simple! I think you need to factor in the angle on incidence. The 738 cruises at around 2 1/2 nose up but the AoA is more like 5-6 degrees? Apparently the slightly nose up attitude was to allow the fuselage to contribute some lift. Airbus, by contrast, rig their products to cruise with level cabins for passenger comfort. I've never operated the Bus though so the last bit could be B/S?
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Old 13th Nov 2018, 18:05
  #1105 (permalink)  
 
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Originally Posted by Concours77 View Post
Trying to make a point here. Attitude is displayed as degrees above/below Horizon. FPV displays degrees above/below horizon. Consolidating both elicits AoA. No?
Yes, as long as long as you're clear about what you're adding/subtracting.

You brought up wind, I didn’t.
Yes I brought it up for clarity.

It is not installed to assist manual handling. It is installed to protect the aircraft from the crew, just as shaker/pusher does.
This protection is the relevant assistance.

Originally Posted by CHfour View Post
@Vessbot

If only life were so simple! I think you need to factor in the angle on incidence. The 738 cruises at around 2 1/2 nose up but the AoA is more like 5-6 degrees?
True, but the difference between nose and wing chord is fixed, and small, and can therefore be disregarded when talking about understanding changes, i.e., if you do this with the AOA, the airplane will respond like that. The nose vs. wing difference is just the adjustment of a fixed datum, for which difference us pilots don't have any data to base on anyway. So nose symbol vs. FPV is good for a basic conception.

Plus (and I'm perfectly willing to be shown wrong about this) I'd put money on that the axis of the nose symbol is the datum in use by all the engineering anyway. Because, as you yourself pointed out, there are more components in addition to the wing that contribute to the overall AOA-dependent behavior.

Apparently the slightly nose up attitude was to allow the fuselage to contribute some lift. Airbus, by contrast, rig their products to cruise with level cabins for passenger comfort. I've never operated the Bus though so the last bit could be B/S?
I would be shocked if this is true. The performance value of note is not lift (we can easily get much more lift than we need by simply hauling back on the stick) but rather lift/drag ratio. And I cannot imagine why they would want to use any lift tied with the drag penalty of flying the tube askew to the air, as opposed to the wing, which is exquisitely designed specifically for the purpose of high L/D in the cruise condition.

If indeed the fuselage is pitched up (note I said the fuselage and not the nose symbol, which can be programmed to be displayed anywhere wrt. the fuselage axis) I would bet that it's because the planes are cruised slower than originally intended, or some other compromise reason... but not because the original designers wanted it.
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Old 13th Nov 2018, 18:19
  #1106 (permalink)  
 
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Originally Posted by Concours77 View Post
The issue is and remains: A flight critical controls mode is installed on a fleet. It screws up, and we find out no one knew of its existence.
It's one thing to mince rumors. Another to spout abject falsehoods. FAA, CAA, and lots of other regulatory folks were well aware of the existence of the MACS and tested it thoroughly. What Boeing did not do is include it in the pilot's flight manual. There is a vast vast difference between "not included in the flight manual" and "no one knew of its existence." VAST.
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Old 13th Nov 2018, 18:36
  #1107 (permalink)  
 
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Originally Posted by Vessbot View Post
True, but the difference between nose and wing chord is fixed, and small, and can therefore be disregarded when talking about understanding changes, i.e., if you do this with the AOA, the airplane will respond like that. The nose vs. wing difference is just the adjustment of a fixed datum, for which difference us pilots don't have any data to base on anyway. So nose symbol vs. FPV is good for a basic conception.
Yes, for the record the 737's wing root incidence is about +1°, so the difference between fuselage and wing AoA will be negligible.
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Old 13th Nov 2018, 18:42
  #1108 (permalink)  
 
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Ken, #1115, whist agreeing with the sentiment of your post, there is as yet no public evidence of the authorities’ knowledge.
It would be very surprising that there was none; however it is more important to understand their process of approval, the depth of knowledge, assessment, and validation of safety cases.
Something slipped through the net; the safety process appears to have failed us. This is a key aspect of our trust in the airworthiness of the aircraft we fly, hence the strength of the operational concern.


Last edited by safetypee; 13th Nov 2018 at 22:38.
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Old 13th Nov 2018, 18:57
  #1109 (permalink)  
 
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Salute!

Thanks, Dave, suspected as much about wing chord line. OTOH I wouldn't be using the bird versus fuselage reference for anything but gross maneuvers as we saw in AF447. That plane had the "bird" out of sight well berlow the fuselage/wing chord reference symbol

And @ Ken........ Good friggin grief, PLZ explain what good is a system that is suppoded to "help" we mortal pilots and has a fault that results in uncommanded and large trim changes at exactly the wrong time - like just after takeoff and flaps are coming up with associated trim change ( unlike Airbus, best I can see). We could care less how many "other folks" knew about MCAS, and considering that their testing and such was based on their kniowledge of how the feature was supposed to work. And did they flight test the feature with AoA sensor failure or other sensor inputs to the FCC? But the poor sob that was supposed to save the day by going "not so" manual, didn't have a chance. I especilly like the part that gives you a few seconds to get all the switches off and/or circuit breakers pulled before you get the full nose down trim once again. GASP!

Whole thing should be very scary to mortal pilots, and I am very upset with Boeing, as I always thot that made very good planes and they were pilot-friendly.

Gums sends...

Last edited by gums; 13th Nov 2018 at 19:07. Reason: typos
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Old 13th Nov 2018, 19:04
  #1110 (permalink)  
 
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IMHO BOEING has lost its virginity.
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Old 13th Nov 2018, 19:41
  #1111 (permalink)  
 
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Originally Posted by Rananim View Post
It trimmed the aircraft nose down in response to faulty AoA....the report from the previous commander clearly says "STS trimming the wrong way".
Originally Posted by silverstrata View Post
It didnt.It trimmed the aircraft nose down in response to faulty AoA....the report from the previous commander clearly says "STS trimming the wrong way".The pilots just have to recognize that......How do you know this is a genuine fault? The 737 STS system ALWAYS trims the wrong way - that is what it is ‘suposed’ to do. And the pilot response on every flight is to trim back the right way - which overrides the STS. Which is why the STS is widely cursed - it may be trimming into a ‘safer’ regime, but pilots like an aircraft to be in trim, not trimmed nose down - so it is still a pain when hand flying.

Silver
Not a Boeing driver, frequent lurker here, but:

From reading this thread and the Boeing alert, it seems that a big part of the issue is that the crew was not aware of MCAS. The writeup for STS "trimming the wrong way" may very well have been written by a captain that thoroughly understood STS and was aware of which way it should normally trim....but what he was seeing was the undocumented MCAS feature trimming opposite to the direction STS would be expected to trim in a given flight regime. The writeup mentioning STS may just be because this was the only feature of which he was aware that would cause the trim to run in manual flight.
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Old 13th Nov 2018, 19:58
  #1112 (permalink)  
 
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Some Google Fu reveals a document called "OPERATIONAL EVALUATION REPORT – BOEING 737" "ORIGINAL – JANUARY 10, 2018" from ANAC (Brazilian civil aviation authority). In "Appendix 2 – OPERATOR DIFFERENCE REQUIREMENTS (ODR) TABLES" MCAS is listed as "No" on both flight characteristics (FLT CHAR) and change of procedures (PROC CHNG).
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Old 13th Nov 2018, 20:29
  #1113 (permalink)  
 
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Having flown the 737 and the 777 several,things are noticeable:

Firstly, Boeing are getting more and more reticent about what information is provided in the FCOM - the exact info about TOGA at low alt/touchdown that caught the EK crew out was present in older editions of the manual but not recent ones. I often learn things that aren’t in the manuals from people who were trained on the aircraft some time back.

The 737 is a 60s design out of which Boeing have wrung every single knot and .02% fuel efficiency increase. They have done so while being forced to keep a common type rating with the Classic. They have added a lot of stuff in the background while maintaining a flight deck with an archaic and complex Caution and Warning system that has zero prioritisation and requires much more cognitive processing simply to identify the correct checklist than the EICAS that Boeing have been supplying with newer aircraft since the 80s.

This is not a happy collection of circumstances, partially driven by customers (SWA I’m looking at you...) but also a consequence of what seems to be a new philosophy at Boeing.
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Old 13th Nov 2018, 20:47
  #1114 (permalink)  
 
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The shape of a commercial airplane wing (twist, sweep, variation in cord and camber along the span, etc.) is very complex. As such it would be quite a trick to define a true "zero AOA" reference. What ever metrics used for such a calculation would undoubtedly be impacted by flap position and wing spanwise droop that is a function of payload/fuel distribution and wing lift loading. AOA as determined from the body mounted vanes (with correction for known local flow distortion) is presented with respect to the fuselage.

As has been mentioned, transport aircraft that are optimized to maximize L/D are designed to fly with a small, positive pitch attitude. To design an airplane to fly with deck angle of exactly zero in cruise would be to leave unrealized performance on the table! Separately, optimization of takeoff, landing, and ground operations usually results in a slightly negative deck angle when taxiing. I strongly doubt that any commercial transport airplane has ever been designed to have exactly zero deck angle either during ground taxi or cruise.
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Old 13th Nov 2018, 20:47
  #1115 (permalink)  
 
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Originally Posted by KenV View Post
It's one thing to mince rumors. Another to spout abject falsehoods. FAA, CAA, and lots of other regulatory folks were well aware of the existence of the MACS and tested it thoroughly. What Boeing did not do is include it in the pilot's flight manual. There is a vast vast difference between "not included in the flight manual" and "no one knew of its existence." VAST.
Correct. During Part 25 Certification a requirement for MCAS was identified. It was then added. As you stated, the current brouhaha relates to the lack of any form of reference material that’s visible to pilots.

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Old 13th Nov 2018, 20:57
  #1116 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Yes, for the record the 737's wing root incidence is about +1°, so the difference between fuselage and wing AoA will be negligible.
So the AoA is around 3.5 degrees in the cruise? (seems a bit low). BTW (and off topic) I've just googled for some Airbus PFD images and it would seem that the Bus cruises at 2.5 just like the 738.
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Old 13th Nov 2018, 21:13
  #1117 (permalink)  
 
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Originally Posted by FCeng84 View Post
The shape of a commercial airplane wing (twist, sweep, variation in cord and camber along the span, etc.) is very complex. As such it would be quite a trick to define a true "zero AOA" reference. What ever metrics used for such a calculation would undoubtedly be impacted by flap position and wing spanwise droop that is a function of payload/fuel distribution and wing lift loading. AOA as determined from the body mounted vanes (with correction for known local flow distortion) is presented with respect to the fuselage.
Exactly, and this is the flip side of all the non-wing "total airframe" components I mentioned that make any zero-AOA datum, arbitrary. So you might as well choose a convenient one, that is not separated, as you note, by the AOA vanes by a floppy piece of structure (and, I'll add, from the IRS).

As has been mentioned, transport aircraft that are optimized to maximize L/D are designed to fly with a small, positive pitch attitude. To design an airplane to fly with deck angle of exactly zero in cruise would be to leave unrealized performance on the table!
This I disagree with. Why can't a plane be designed for the cruise condition with an exactly-level fuselage attitude (least drag) and wing incidence set for an AOA that yields best performance?

(I understand that after the basic design is "locked in" and it would be too time consuming and expensive to change the incidence, customer requirements or fuel prices or max gross weight or many other factors could change the cruise condition, and therefore the AOA, and therefore fuselage attitude; but I'm talking about the design process at the very beginning, before it's molested by such changes.)
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Old 13th Nov 2018, 21:15
  #1118 (permalink)  
 
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Originally Posted by JPJP View Post


Correct. During Part 25 Certification a requirement for MCAS was identified. It was then added. As you stated, the current brouhaha relates to the lack of any form of reference material that’s visible to pilots.


Will you elaborate? “A requirement for MCAS was identified. It was then added.” What is not included in the statement is:

“It was then certified to the C of A....” How? By Boeing memo? Or did it just sound like a good idea?

In the AD, “After manufacturer’s research, it was ‘discovered’ (sic) that Trim could continue Nose Down after receiving sensor data related to a high and erroneous AoA value...” Can we review the research? Because I am not buying that it was ever “unknown”.




Last edited by Concours77; 14th Nov 2018 at 03:39.
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Old 13th Nov 2018, 21:17
  #1119 (permalink)  
 
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Originally Posted by CHfour View Post
So the AoA is around 3.5 degrees in the cruise? (seems a bit low). BTW (and off topic) I've just googled for some Airbus PFD images and it would seem that the Bus cruises at 2.5 just like the 738.
Given what me and FCeng84 have written, it seems especially fruitless to compare displayed AOA across not only different airframes, but different avionics systems.
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Old 13th Nov 2018, 21:21
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Originally Posted by Vessbot View Post
Exactly, and this is the flip side of all the non-wing "total airframe" components I mentioned that make any zero-AOA datum, arbitrary. So you might as well choose a convenient one, that is not separated, as you note, by the AOA vanes by a floppy piece of structure (and, I'll add, from the IRS).



This I disagree with. Why can't a plane be designed for the cruise condition with an exactly-level fuselage attitude (least drag) and wing incidence set for an AOA that yields best performance?

(I understand that after the basic design is "locked in" and it would be too time consuming and expensive to change the incidence, customer requirements or fuel prices or max gross weight or many other factors could change the cruise condition, and therefore the AOA, and therefore fuselage attitude; but I'm talking about the design process at the very beginning, before it's molested by such changes.)
No airplane can fly with zero AoA. Let’s don’t do Bernoulli. If the centerline of chord is the same as the fuselage longitudinal line, and the fuselage is level, the airplane will sink. The angle of incidence of the wing allows less nose up when close to level. It is “baked in” AoA. No?

There was an aircraft with “variable incidence wing”. It allowed Nose Down level flight, or even very Nose Down glide slope. It was useful for seeing the deck on the aircraft carrier when landing. Vought F-8 Crusader.
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