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MAXs Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAXs Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 1st Jun 2019, 10:20
  #81 (permalink)  
 
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Delay

Bend alot, # 78

Boeing proposed a modification, 17 Apr. https://www.boeing.com/commercial/73...e-updates.page
This was rejected by the FAA, no specific reasons given, thus Boeing reviewed and amended the design. According to some US sources this was recently resubmitted together with a training plan; training is reported as being essentially the same as the information above - no simulator (CNN 30 May https://amp.cnn.com/cnn/2019/05/30/p...tor/index.html).

In parallel, other certification authorities have been briefed and are considering the new proposals. Although the lead certification is the FAA, there is great pressure on having a worldwide consensus due the ‘loss of trust’, procedural - oversight, self regulation embarrassments. This could be a lengthy process especially if linked with subjective assessments of procedural effectiveness as below.

The FAA has launched a separate study of procedures, assumed to be for trim runaway, this could apply to both the Max and NG. From PPRuNe discussions there appears to be significant concern about the viability of the drill which depends on quick identification and action, and difficulty in moving the trim wheel.

The NG and Max could differ in the severity of a runaway and / or effectiveness of recovery. Aerodynamically there is the difference - the need for MCAS; then there are changes in thrust levels, wings ….

Test flights might be difficult. The normal trim curve technique of trimming against stick force (constant speed / altitude - but covering the full operational environment and configuration) might find that the interpretation of stick top elect trim inhibition (EASA query) creates additional problems with the use of trim wheel - elect trim for failure, manual trim wheel for recovery. Also limiting forces might be encountered before maximum trim. In addition it might be easier to mis-trim the aircraft (away from trim) opposed to recovering from a failure condition - effect of asymmetric elevator force in aiding or opposing trim with respect to the trim wheel input.

The obvious is to avoid situations where recovery might not be assured; - evaluate the effectiveness of roller coaster manoeuvre before hand - but how.
Design quality simulation would be essential, but where did the training simulator discrepancies originate. If the source data is incorrect / unavailable, test flights would need to collect and validate new data, this too could involving the problems above.
Whilst the test aircraft might have escape doors and the crew equipped with parachutes to mitigate unforeseen risk, the associated political and commercial risks might be so great that testing will be a very slow process or alternative means of compliance are being considered, requiring worldwide agreement in the fullness of time.

P.S. Not quite the same tone or confidence which might be expected at this time :-
‘… expressed cautious optimism’
‘… hopeful that the FAA will exercise its usual due diligence and swiftly approve the recently completed software fix’
https://www.airlive.net/boeing-ceo-h...-of-the-737max 1 June




Last edited by PEI_3721; 1st Jun 2019 at 11:55. Reason: CNN & PS
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Old 1st Jun 2019, 10:49
  #82 (permalink)  
 
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Originally Posted by Bend alot View Post
As per the tread title - the delay seems to be more Boeing not officially submitting the fix to the FAA.

Why is there the delay?

Boeing say they have fixed it (not that there was ever a problem), is there fear in the test flight stage of not being able to manually move the trim wheel, when it is expected to be movable. Surely most regulators will want evidence of the trim wheel "actual flight" forces to move until it will not move.

Then since MCAS is not a part of this test flight now (had it's one input so locked out) and the MAX is essentially a NG with a trim wheel not able to move.

Nothing quite like doubling the bet - MAX grounding lifted or MAX and NG grounded.
Excellent post, Bend alot !
What if Boeing has fixed the MCAS part of its software, but is secretly negociating for the flight test to NOT show what the control forces and trim wheel ability to be moved actually are ?

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Old 1st Jun 2019, 13:52
  #83 (permalink)  
 
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PEI 3721 - This we expect to be covered then in the iPad differences training!

"The NG and Max could differ in the severity of a runaway and / or effectiveness of recovery. Aerodynamically there is the difference - the need for MCAS; then there are changes in thrust levels, wings …."

My bold.
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Old 1st Jun 2019, 14:24
  #84 (permalink)  
 
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Bend alot,
What if the difference now focuses on trim runway.
The NG in-service, apparently without incident. The Max grounded following two accidents which suggests that the trim runaway drill might be ineffective.

NG no events - ‘successful’ outcome, history; but this does not change the risk of a trim malfunction.
The risk in the Max could be similar if not the same, but with different history. One ‘success’ out of three does not change the system risk, but it could influence the regulatory views on crew’s contributions in recognition and action. Unfortunately the ‘success’ suggests that the Max requires three qualified crew, or conversely reinforces view that two cannot be expected to detect and manage a trim runaway in proportion to severity of the event’s circumstance (risk).

What if … this is the central topic of inter-regulator discussions; who judges, how, when, perhaps after more testing and data to assess.
Meanwhile historical risks are accepted (who bears that risk); future risk - wait and see.


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Old 1st Jun 2019, 15:40
  #85 (permalink)  
 
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Salute!
Thanks Bend and PEI.
I just have a hard time with Boeing not keeping the manual electric trim operating when MCAS does its trick.

Looks like Boeing is sticking to the "existing procedures would have prevented the crashes" story. Ditto for some of the uber pilots here. Problem is recognizing what is wrong and the magnitude/length of the MCAS commands.

PEI might be able to explain it in technical terms that some here will not fathom, but I say go for it.
- Why can't the trim commands be a function that uses "q" and mach as we did in the Viper instead of a "bang-bang" fixed amount and fixed time of application? In other words, follow a geometric plot as we did for AoA versus gee and control deflection gains.
- If MCAS is using the A/P circuits, why disable other force functions such as the control column switches for force ( not the electric switches).

Gotta be nore than meets the eye, and I do not feel training is the answer. Fer chrissakes, we are not training Top Gun fighter pilots or NASA astronauts.

Gums sends...
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Old 1st Jun 2019, 16:31
  #86 (permalink)  
 
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Originally Posted by Chris2303 View Post
When I first started in the industry in 1967 IATA was responsible for:
  • Clearing house for interline travel
  • Tariff setting
  • Inflight standards (configuration/meals/alcohol)
Amongst other things that my old brain has forgotten
To name two very important ones:
IATA's Live Animals Regulations (LAR) is the worldwide standard for transporting live animals by commercial airlines. live animals, safety, welfare, traveler's pet corner, regulations, LAR, live animal regulations, corrigendum-I, wildlife products, training, LAPB, live animals and perishables board, illegal wildlife trafficking https://www.iata.org/whatwedo/cargo/live-animals
Dangerous Goods Regulations (DGR)
IATA's Dangerous Goods Regulation (DGR) helps you classify, mark, pack, label and document dangerous shipments and hazardous materials
https://www.iata.org/publications/dgr
And many more ..
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Old 1st Jun 2019, 17:56
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If this whole unmovable trim wheel kerfuffle plays out to its full potential, Boeing is staring down the barrel of BOTH MAX and NG being grounded. And that might very well be the end not only for the 737, but for the Boeing Company. I'm not even sure their military division will be able to bail them out, unless they quickly disconnect the two parts but that would require a shareholders meeting which won't be quick. (Correct me if I'm wrong.)

So, just hypothetically, wouldn't it be safer for Boeing to simply close the 737MAX program, cut their losses, buy back the MAXes and try to cuddle the FAA into stopping the NG trim wheel inquiries? They could then concentrate on NSA, or NMA, or MOM, or whatever it is they want to do. They would likely come out of this way behind Airbus in sales and customer trust, and will have to fight back into that market, AND they have very little experience in that kind of marketing. It will be a HUGE loss and an enormous effort. But, IMHO, it's the lesser evil. The more this drags on, the less likely Boeing is to come out of this alive. As much as I like Airbus, I don't want them to be an unopposed monopolist.
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Old 1st Jun 2019, 18:27
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Salute ProPax!

You have cracked the code.

Years ago Lockheed had a design problem with their Electra turboprop. Harmonics and weak components resulted in a few fatal accidents.

Lockheed bit the bullet, grounded all the planes and then refurbished all of them at their expense. The descendants became the P-3 Orion anti-sub platform and they still have one or two flying somewhere.

Apparently, the 800 and 900 and such have been big sellers, and only reason I see for the MAX was better fuel economy.

Gums sends...
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Old 1st Jun 2019, 18:33
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SLF here who worked for the UK government for too long. Please don't shoot me, it kept me off the streets.

It seems possible that when the FAA allowed Boeing to self certify they assumed a level of Trust. Speculation, but they *may* now feel that Boeing did not act entirely in line with that level of trust. In which case I wouldn't be surprised if the FAA (et al) are now reviewing every document, email and report they received from Boeing ref the newer 737 offerings with a fine tooth comb, in the light of recent experience. Depending on the time scales, they may also feel that now is good time for a detailed review of the stuff they were sent on the Drainliner and perhaps the also 777X. Could take a while.
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Old 1st Jun 2019, 18:43
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Originally Posted by ProPax View Post
If this whole unmovable trim wheel kerfuffle plays out to its full potential, Boeing is staring down the barrel of BOTH MAX and NG being grounded. And that might very well be the end not only for the 737, but for the Boeing Company. I'm not even sure their military division will be able to bail them out, unless they quickly disconnect the two parts but that would require a shareholders meeting which won't be quick. (Correct me if I'm wrong.)
Not to say that there is never room for improvement, but such a drastic action would have to be reconciled with the fact that the 737NG has one of the best safety records of any commercial aircraft ever built.
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Old 1st Jun 2019, 18:52
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Yo, gums,
Why not use ‘q’
I don’t know; superficially speed for trim would be a logical association.
However, as much as Boeing sticks to the stability line, the aircraft’s sensitivity at low speed suggest that AoA is required for avoiding a stick force reduction with decreasing speed (pre stall region), particularly at high altitude where Mach is also used in the computation (restriction).

Given the above, there is nothing in the accidents to indicate that MCAS did not work as expected, except for the ‘single’ sensor failure - rubbish in rubbish out. We must assume that this error path is now completely shutdown with cross checking etc, and does not introduce any further contribution to trim failure than in previous aircraft.
MCAS fades into the background similar to STS; crew knowledge required, no immediate action except awareness of areas of reduced stability. For that, a MCAS ‘off’ alert would be preferred, opposed to a deduction from AoA Disagree. Would MCAS shut down for any other reason.

ProPax,
There could be many intermediate alternatives.
Why is such a large trim range required; if this could be reduced then the trim wheel force might be reduced. This might require cg, speed, altitude restrictions; room for compromise.
Reduced elect trim speed (trim motor electrics - runaway scenario) could be another option, or an increased lever arm for manual wheel operation, or increased gearing for wheel speed.
Adjust the elevator effectiveness - might be a bit drastic, but if needs must.




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Old 1st Jun 2019, 18:54
  #92 (permalink)  
 
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Pro Pax

I just dont see this trim wheel kerffufflle as you put it, the method of bringing the trim back into the normal range has been known since the days of the B707 and has not been an issue.

The issue is that training departments in airlines have forgotten the lessons of the past.
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Old 1st Jun 2019, 19:01
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Boeing is staring down the barrel of BOTH MAX and NG being grounded. And that might very well be the end not only for the 737, but for the Boeing Company.
The NG has nearly 7,000 aircraft in service and has been in the air for 22 years with zero crashes due to runaway trim.

The chances that the NG will be grounded: zero. It has proven itself to be a very safe aircraft.

With MCAS disabled (post fix), the MAX's safety profile from a trim runaway is the same as the NG.

The "end of Boeing" scenario being posed here is pure fantasy.
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Old 1st Jun 2019, 19:08
  #94 (permalink)  
 
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A and C,
The difficulty appears to be with the ability of the elevator to control pitch - nose up, before the procedure can be used.
Larger tail area - trim, same elevator, changes in aerodynamics, hydraulic jack stall. Perhaps small changes, but incrementally eroding the margin for recovery.
Inaccurate simulation, false assumptions based on previous, smaller aircraft.

futurama, ‘zero accidents’ does not affect the inherent risk of system failure - outcome bias.
Never a zero chance of anything, particularly in aviation.



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Old 1st Jun 2019, 19:41
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Salute!

Prolly should discuss the technical stuff on other forum, but if I were on the review cmte for releasing the MAX for widespread use I would question Boeing about several aspects of their MCAS implementation from tht of a user viewpoint and an aero engineer and experienced pilot having flown half a dozen jets with various "gotchya's" and such.
@PEI I propose "q" because it appears MCAS uses mach to determine the amount of deflection and such. Gotta review, but seems mach became a player above 0.65 M or so.Without a good diagram of the function, we can only guess. But FCeng indicated that at higher mach the incrememntal stab movement is not only less but maybe not even as long of application.If the thing can use mach, then it can use "q'. That would avoid the severe forces that cause problems with the manual wheel trim, heh? It is not hard to design a simple analog chip that integrates AoA and Q to determine how much and how fast to move the stab in order to meet the requirements.

Let's face it. 10 seconds of nose down trim at a quarter degree per pulse is harsh!!! Yeah, yeah, yeah, the Yeager folks here will simply "go manual" as R2D2 is melting. But seriously, Boeing has to do more than recommend training and more adjustments to the kludge.

Gums sends...
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Old 1st Jun 2019, 19:41
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safetypee, no where did I write that the risk is zero. Very safe is not zero risk.

Also, "outcome bias" does not mean what you think it means.
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Old 1st Jun 2019, 19:42
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Originally Posted by PEI_3721 View Post
ProPax,
There could be many intermediate alternatives.
Why is such a large trim range required; if this could be reduced then the trim wheel force might be reduced. This might require cg, speed, altitude restrictions; room for compromise.
Reduced elect trim speed (trim motor electrics - runaway scenario) could be another option, or an increased lever arm for manual wheel operation, or increased gearing for wheel speed.
Adjust the elevator effectiveness - might be a bit drastic, but if needs must.
In case the forces have increased the complete mechanical system might be unsafe. First thing that comes to my mind are the steel cables... but is not limited to those only
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Old 1st Jun 2019, 20:30
  #98 (permalink)  
 
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gums
I just have a hard time with Boeing not keeping the manual electric trim operating when MCAS does its trick.
sorry to be a pedant, but the B737 has manual trim, aileron trim, rudder trim, main electric trim, auto trim, mach trim, and speed trim - (of which MCAS is a subsystem)

there is no such thing as manual electric trim
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Old 1st Jun 2019, 20:45
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There are many solutions to this problem, indeed. Add a few switches, string a few cables, reduce/enlarge, install a motor, etc. BUT!!! Any of those would need to be certified. And that won't be easy. There are at least three disgruntled parties involved - China with increased tariffs, Europe with increased tariffs, and Canada with a badly enginnered attempt to increase tariffs. So whatever Boeing does, whatever solution they come up with, it will hit the wall worse than Dale Earnhardt.

EASA, TCCA, and CAAC will, with almost 100% probability, demand full re-certification if any new systems are added to an already troubled airplane. And actually, I don't think FAA will be too accomodating, either, after Boeing humiliated them with this whole "self-certify" calamity. The political climate is such that the current administration needs to "do something right". And Boeing may just as well serve as an object lesson.

I just don't see a different way out of this for Boeing. They were late grounding the MAX when it was apparent that MCAS was involved in both accidents, and were forced to take action. They blamed the crew. They enraged the pilots community. Their reputation is badly damaged. If they are again forced to re-certify the MAX and then the NG, it may become the proverbial nail in the coffin. They should really bite the bullet and make a proactive move. Considering that many MAXes were sold with incredible discounts, buying them back won't be such a terrible expense.

It still leaves the issue of the NG trim wheel loads, but considering it's been in the skies for quite some time, and provided Boeing acts fast, certifies the modification, and modifies the fleet at their own expense, they may get away with it.
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Old 1st Jun 2019, 20:51
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article from NYT on the foundation of MCAS...very interesting

https://www.nytimes.com/2019/06/01/b...max-crash.html
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