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MAXís Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAXís Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 11th Jun 2019, 19:45
  #341 (permalink)  

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The ancient maybe, though I doubt it. For the -3/4/5 there was already a full engineering gnome department below the deck to produce that old fashioned, natural feel.
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Old 11th Jun 2019, 20:44
  #342 (permalink)  
 
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Originally Posted by Smythe View Post
Sorry, but that was directly from the FAA response to Boeing on the wings, the wind loads and lack of indicators that the wings are locked.

note 'must add' means it wasnt there?

More than one means must be available to alert the flightcrew that the wingtips are not properly positioned and secured prior to takeoff. Each of these means must be unique in their wingtip-monitoring function. When meeting this condition, the applicant must add a function to the takeoff warning system, as required by ß 25.703(a)(1) and (2), to warn of an unlocked or improperly positioned wingtip, including indication to the flightcrew when a wingtip is in the folded position during taxi.
No, "must add" doesn't mean it wasn't there, it means that the FAA and Boeing didn't agree on the level of redundancy. Boeing is putting all the indications in EICAS, the FAA wants more. This is nothing new - it's a basic disagreement about EICAS that dates to the 747-400 (and in some cases to the 767/757).
The FARs say 'more than one'. Pre-EICAS this meant more than one light bulb driven my more than one monitor - because one can fail. Starting with the 747-400, EICAS is fault tolerant and multiple redundant, using inputs from multiple systems, running Level A flight critical software. Boeing thinks this complies with the multiple indication requirement, some at the FAA disagree. On previous programs (747-400,777, 767-400, 787, 747-8) this was eventually resolved with either an Equivalent Level of Safety (ELoS) or Alternate Method of Compliance (AMoC). I expect the same will be done for the 777X

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Old 11th Jun 2019, 21:03
  #343 (permalink)  
 
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Salute!

Thanks, Flight. I am thinking more of the 'bus reversion control laws, especially "direct". My understanding may have been contaminated by many discussions on the 447 Tech Log. But as you revert to lower and lower modes you might have to trim unless you wish to hold the stick out of the neutral position, right?

Our pitch law was not corrected for aircraft attitude like the bus, so a neutral stick force was what ever you had trimmed using the small wheel or the coolie hat on the stick grip. So the Thunderbird slot trims slightly less than one gee so he has good back stick “feel”. Maybe the Wingies do that too, so I’ll have to ask one. Some of our A2A guys trimmed for zero gee in order to unload and run without holding forward pressure. I even showed studs a loop by running trim all the way - about 3.5 gee. Then we did a hands off loop and watched all the limiters work (protections for you bus drivers).

I still wanna know how the bus control laws and zero mechanical feedback can be certified, but the 737 has to have “more AoA with more back pressure”. So this thing is more than yoke force, huh? Looks like borderline pitch moment problems and no motor thrust below the wings a significant contribution.

Gums sends.....

Last edited by gums; 12th Jun 2019 at 16:58. Reason: clarification and still open for critique
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Old 11th Jun 2019, 21:27
  #344 (permalink)  
 
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Yo gums, # 342.

Re Airbus certification, your ‘waivers and exceptions’ (#31)j. In practice these were alternative means of compliance for existing regulations, or proposals for new ‘equivalent level of safety’ justified by many years of research, system demonstration, and well argued reliability studies, etc. Thus over time, Airbus rewrote ‘the book’ - an expensive, international ‘gamble’, but one not planned to depend on training for exceptional circumstance and the variable human pilot.

As for equivalence in stick force approaching the stall - essentially not required because of the level of protections.

# 309 / 313,
The training position’, yes difficult to understand, even if officially declared.
Separate out the situation after MCAS fix from the problem of a deficient trim runaway drill.

MCAS II will not move the stab to an unreasonable angle due to system failure - within the bounds of certification requirements. Thus MCAS would be a background function like STS; little training requirement.

Trim runaway. Where is the limit point where the stab angle prevents recovery; speed, ht, cg, wt, thrust, manoeuvre. If not known, many test flights required to identify the boundary conditions.
At lesser stab angles how effective is the elevator, the practicality of manoeuvre procedure - speed, ht, etc, and dependence on ‘training’ for that. What is the certification acceptability of mitigation options; limit trim range, accepting flight envelope restriction; reduce the stab effect with aerodynamic change; improve elevator effectiveness; what determines an acceptable change.

What credit can be taken for crew intervention to inhibit elect trim before the limit point. Less than might be hoped for in a ‘training’ option after the accidents. This point further challenges the FAA for harmonised world opinion on Max return to service; independent action would be unacceptable both for FAA image (save face) and Boeing world wide sales.
The Max does not have a ‘trim fail’ alert, thus the rare failure situation has to be deduced. No guarantee of situation recognition or choosing the correct drill due to a range of HF considerations.

Worst case, there may not be any ‘training’ solution for trim runaway, as much as operators and pilots think otherwise.

_ _ Then there is the NG _ _


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Old 11th Jun 2019, 22:11
  #345 (permalink)  
 
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The question about "Proper storage", was not about the quality of the maintainers.
But everybody was expecting 'few weeks", but it is going to a few months.

Aircraft that are in cold weather can have toilets or other water systems frozen.
Static and dynamic ports that are not properly closed off can be entered by spiders, ants, mosquito's and other small animals.
Pressure systems like fuel, oil and oxygen need proper purging or risk contamination.
Aircraft in moist weather can collect water in the strangest places.

As I said, most expected some weeks, but it's going to be months.
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Old 11th Jun 2019, 22:33
  #346 (permalink)  
 
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Salute!

Thanks, PEI.

Guess Airbus did a great, not good, job getting the Part 25 cert paragraphs and such changed for their plane. I would bet that the Concorde folks provided some lessons, as it was a lot more FBW than most realize.

My main issue here is that I cannot fathom the big reason for MCAS was strictly "feel" on the yoke/column/stick. My belief is that the plane's aero does not satisfy the longitudinal stability criteria. In short, as I get to a higher AoA the plane wants to increase AoA by itself, or at least require less nose up control command than at a slightly lower AoA. I use the term "command" and not physical movement of the stick/column/yoke.

Gums sends...
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Old 11th Jun 2019, 23:40
  #347 (permalink)  
 
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Originally Posted by PEI_3721 View Post
The Max does not have a ‘trim fail’ alert, thus the rare failure situation has to be deduced. No guarantee of situation recognition or choosing the correct drill due to a range of HF considerations.


Hmm, doesn't the MAX have a "Speed Trim Fail" light, like the NG?

Later edit: it seems to have that light:



MCAS is designed as a sub-function of the STS, so in theory they could reuse that light to indicate MCAS failures as well. In my opinion it would make things easier to diagnose, especially when combined with an AoA disagree alert.
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Old 12th Jun 2019, 00:14
  #348 (permalink)  
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But what exactly would it be enunciating?
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Old 12th Jun 2019, 01:24
  #349 (permalink)  
 
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Sitting outside unused is hard on any equipment. It certainly can be properly maintained to mitigate damage but that costs money, and who is paying? If you think of it from a maintenance yard's point of view, they not only have to maintain the MAXes in dead storage, but they have to maintain the replacement fleet as well. When resources get tight, who gets priority? I'm sure that keeping the flying planes producing revenue takes precedence over tending to the sick flock of MAXes. There must be some point at which you are going to have to do a teardown to return the plane into service anyway; tires, lubricants, and sealants degrade. (How square do you imagine those tires already are?) Like diesel, Jet-A is a perfect breeding ground for microbes and partially empty fuel tanks condense water. I imagine they are going to have to pump out the fuel and replace the filters if this goes on for months. I read (I do not know plane maintanence) that it is recommended to drain the sumps every few days on an unused jet aircraft stored outside, this must get spendy when you are doing an entire fleet that is scattered hither and yon.

When the lawyers start playing, the money for this maintenance could dry up pretty fast. Obviously it is not in an airline's interest to pay to maintain planes that they will be returning to Boeing and if Boeing looks like they are going under (no new orders for two months) the contracting yard begins to wonder who is going to be paying for all of those fuel disposal fees. Common sense does not rule in cases like this, I have seen multimillion dollar yachts rot into worthlessness because nobody could agree who would pay to do a little bit of keep alive maintenance . (To be fair, shipyards go bankrupt a heck of a lot more frequently than airline manufacturers.)
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Old 12th Jun 2019, 04:18
  #350 (permalink)  
 
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Aircraft that are in cold weather can have toilets or other water systems frozen.
Static and dynamic ports that are not properly closed off can be entered by spiders, ants, mosquito's and other small animals.
Pressure systems like fuel, oil and oxygen need proper purging or risk contamination.
Aircraft in moist weather can collect water in the strangest places.
Of course, all of that is true. Why do you think that the engineers do not know this? They would be taking these steps. You seem to assume they are not aware. As far as I know it is all in the AMM.
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Old 12th Jun 2019, 04:34
  #351 (permalink)  
 
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Originally Posted by gums View Post
Salute!

My main issue here is that I cannot fathom the big reason for MCAS was strictly "feel" on the yoke/column/stick. My belief is that the plane's aero does not satisfy the longitudinal stability criteria. In short, as I get to a higher AoA the plane wants to increase AoA by itself, or at least require less nose up control command than at a slightly lower AoA. I use the term "command" and not physical movement of the stick/column/yoke.

Gums sends...
(One of) Mine, too. I think that the knee jerk reaction of “it’s NOT an anti-stall system”, coupled with Boeings trying to hide the system, is all the proof needed that it is in fact an anti-stall system. A rather desperate one, having to resort to taking control of the horizontal stabilizer. And I just don’t think you can cure bad aerodynamics with mediocre software.


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Old 12th Jun 2019, 10:34
  #352 (permalink)  
 
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The nuts and bolts of it

Originally Posted by Takwis View Post


(One of) Mine, too. I think that the knee jerk reaction of ďitís NOT an anti-stall systemĒ, coupled with Boeings trying to hide the system, is all the proof needed that it is in fact an anti-stall system. A rather desperate one, having to resort to taking control of the horizontal stabilizer. And I just donít think you can cure bad aerodynamics with mediocre software.


Back on the closed thread FCeng84 had some insightful information on MCAS, which went beyond what the average user knew about at the time.
Shame he hasnít been around lately.
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Old 12th Jun 2019, 12:35
  #353 (permalink)  
 
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Originally Posted by bill fly View Post


Back on the closed thread FCeng84 had some insightful information on MCAS, which went beyond what the average user knew about at the time.
Shame he hasnít been around lately.
FCeng84 has a profile saying they are a flight control engineer in Seattle. FCeng84 had a habit of posting well written and accurate technical information sometimes before you could confirm that accuracy with other public sources.

I'll go way out on a limb here and take a first wild guess: FCeng84 probably doesn't work for Airbus.

FCeng84 went dark shortly before ET prelim report release, taking another wild guess: this would be about the time the excrement really hit N1 at Boeing and everyone was probably told to shut-the-****-up on the internet/in the pub/in the bedroom, nobody say nothing except as authorised by Corp Lawyers and do NOT bother the Corp Lawyers with any requests for authorisation because they just got really busy. I sincerely hope it was that scenario and not the one where the corp lawyer turns up at your desk and says something like "can you confirm you had authorisation from legal before posting this...".

But, like I said, just a wild guess, or two...
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Old 12th Jun 2019, 13:11
  #354 (permalink)  
 
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Originally Posted by The AvgasDinosaur View Post

I think that I recall itís a -700 airframe as is the AEW variant too. I stand to be corrected.
Be lucky
David
The P8 page at boeing.com says

A derivative of the Next-Generation 737-800
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Old 12th Jun 2019, 13:34
  #355 (permalink)  
 
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The gums # 346,
You are correct in considering a wider view of stability, not just aerodynamics; cg, thrust, the complete aircraft. In the purist sense stability is more precise, and certification differentiates static and manoeuvre.
There is little information about the exact nature of the Max ‘aero’ problem; it differs from the requirements for STS and Mach trim. MCAS adjusts stick-force feel for good reason, but exactly what that is, is not clear. See Ref ‘Overview’ and ‘Definitions’.
Does MCAS address both static an dynamic stability?

Some posts refer to the horiz tail stab as a control surface, which is inaccurate; elevators control, horiz stab is associated with stability. (A secondary effect of stab can be used as a control in abnormal conditions).

MemberBerry, # 347, Trim Failure MAXís Return Delayed by FAA Reevaluation of 737 Safety Procedures
‘Speed Trim Fail’ indicates that the STS function is inoperative, not that the tail trim is electrically, uncontrollably active, and can move to full travel.

MCAS should have a similar ‘inoperative’ alert, to provide awareness of a change in aircraft ‘feel’ in some parts of the flight envelope.
The AoA Disagree alerts add clarification to other consequential problems due to AoA malfunction (air data, feel diff), but without a dedicated MCAS alert, the loss of MCAS has to be deduced.
The AOA (angle of attack) indicator provides supplementary information to the flight crew. The AOA disagree alert provides additional context for understanding the possible cause of air speed and altitude differences between the pilot’s and first officer’s displays. Information for these features is provided by the AOA sensors.
There are no pilot actions or procedures during flight which require knowledge of angle of attack.’
(Ref ‘737 MAX Flight Deck Displays’)
N.B. last sentence; perhaps this is subject to change with MCAS II

Takwis, # 351
MCAS does not ‘take control’ of the elevator, the intent is only to apply a small adjustment.
Adding to previous descriptions, consider entering a turn.
Conventional control feel requires more back stick force when turning, increasing AoA at constant speed. If the stick is released the aircraft should pitch down.
With reduced stability margin (but not unstable), the level of stick force is less than required by regulation, the aircraft pitch response is similar but less so. The aircraft might feel a bit sloppy, loose, twitchy.
Small non-pilot nose-down trim restores sufficient feel for certification.

Re speed margin to stall; MCAS appears to operate a high AoAs, but before stick shake (Vss) and stick push (stall).
Turning with increased AoA reduces the margin to stall because the in-flight AoA is closer to Vss, the stability feel requirement should cue the pilot to this change with increased stick force; however, with reduced stability the cue is less, thus the awareness of margin to Vss is reduced.
Note change in EFIS low speed awareness display, a visual depiction, whereas MCAS is the tactile depiction.

Caution, some of the above is supposition - conjecture based on the little information available to date.

Ref: https://www.boeing.com/commercial/73...e-updates.page




Last edited by PEI_3721; 12th Jun 2019 at 16:31. Reason: typo
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Old 12th Jun 2019, 16:18
  #356 (permalink)  
 
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Originally Posted by infrequentflyer789 View Post
FCeng84 has a profile saying they are a flight control engineer in Seattle. FCeng84 had a habit of posting well written and accurate technical information sometimes before you could confirm that accuracy with other public sources.

I'll go way out on a limb here and take a first wild guess: FCeng84 probably doesn't work for Airbus.

FCeng84 went dark shortly before ET prelim report release, taking another wild guess: this would be about the time the excrement really hit N1 at Boeing and everyone was probably told to shut-the-****-up on the internet/in the pub/in the bedroom, nobody say nothing except as authorised by Corp Lawyers and do NOT bother the Corp Lawyers with any requests for authorisation because they just got really busy. I sincerely hope it was that scenario and not the one where the corp lawyer turns up at your desk and says something like "can you confirm you had authorisation from legal before posting this...".

But, like I said, just a wild guess, or two...
Hi Infreq

That is what I thought as well - and was alluding to.

It was good to get some horses mouth stuff but in the face of mucho uninformed guff he probably gave up - or as you say...

Now what about 737driver?
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Old 12th Jun 2019, 18:18
  #357 (permalink)  
 
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Bill fly and infrequentflyer, it probably goes at bit further than that. During an active investigation, the participants are under what's basically a gag order - all public information releases should come from the lead investigating agency (or at least be cleared with them before hand). We were not even supposed to talk about it with co-workers who where not involved in the investigation or didn't have a 'need to know'.
Note, this gag order doesn't come from Boeing - it comes from the investigating agency - although it was Boeing's responsibility to enforce it. So FCeng may have been 'reminded' not to discuss things in public (consequences could be pretty serious - up to and including getting fired).
Add to that the pending lawsuits - during the discovery phase of the lawsuits they can (and will) ask for copies of every written communication you had regarding the accident - and we had to keep track of and save everything - especially emails. It got so bad during the investigation of the BA 777 that landed short at Heathrow that I simply stopped writing anything down - if I wanted to discuss something I'd go find the person and just talk.
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Old 12th Jun 2019, 18:42
  #358 (permalink)  
 
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Salute!

Nice, Racer , you nailed it.

One example now is the complete silence of the Lion Air crew that handled the rogue MCAS the flight before. Their testimony regarding knowledge of MCAS will be interesting. Of course, they also have a potential liability problem for not letting next crew and maintenance folks that the shaker was on all the time.

Finally, some of the active pilots here have to be careful in the arena( think Driver). A good lawyer will quote every positive or negative statement/opinion to make their point. As a potential trial expert witness in a major aviation lawsuit, I was damned glad I had not commented publically about the issues. Of course, that was before widespread internet and email! Nevertheless, when the suit was settled as a “draw”, I was required by law to turn over every shred of research papers, correspondence, etc. and my floppies, even at that early stage of Word Perfect and other tet editing programs.

Gums sends...



Last edited by gums; 12th Jun 2019 at 19:56. Reason: typo
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Old 12th Jun 2019, 18:47
  #359 (permalink)  
 
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Is this the cause of the delay ?

"Let's build a Dream-Liner" :-


The final video (Second flight) is tragic - 5 months work down the pan.

N

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Old 12th Jun 2019, 19:17
  #360 (permalink)  
 
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Originally Posted by gums View Post
Salute!

Nice, Racer , you nailed it.

One example now is the complete silence of the Lion Air crew that handled the rogue MCAS the flight before. Their testimony regarding knowledge of MCAS will be interesting. Of course, they also have a potential liability problem for not letting next crew and maintenance folks that the shaker was on all the time.

Finally, some of the active pilots here have to be careful in the arena( think Driver). A good lawyer will quote every positive or negative statement/opinion to make their point. As a potential trial expert witness in a major aviation lawsuit, I was damned glad I had not commented publically about the issues. Of course, that was before widespread internet and email! Nevertheless, when the suit was settled as a ďdrawĒ, I was required by law to turn over every shred of research papers, correspondence, etc. and my floppies, even at that early stage of Word Perfect and other tet editing programs.

Gums sends....

Gums sends...

Well itís a shame that knowledgeable people can get warned off - although using a pseudonym - whether I agree with them or not (I didnít always).

It starves a thread of funded info and opens it to repetition and lay questions.

Maybe the solution would be a new pseudonym - although I guess it would become clear in time...
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