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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 26th May 2019, 10:11
  #21 (permalink)  
 
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Originally Posted by MemberBerry View Post
I disagree. Safe/safer/safest. You can clearly compare safety levels, so safety is a continuum. I could even argue that this continuum is multidimensional, but for simplicity let's assume it's unidimensional.
From where I am sitting (1A, please) safety is not a continuum. It's not even a line. It's a dot where all those lines cross. What you're saying does make sense, but only as politics. Or, God forbid, policy. The law cannot scope all possible variables, of which aviation has a lot. But as long as safety is the priority for all parties involved, it's a very small dot in the universe.
If the engineer is absolutely sure he's done everything in his power and to his knowledge to make the plane safe, there is no continuum for him. He may have missed something that is impossible to check or even unknown (who knew you can't fly next to a volcano before BA9), and it very well may be the deciding factor in disembarking at the gate, but he should be sure he's done his part. The pilot must be sure he has full control of the aircraft and its systems. There should be no surprises for him, and he must have enough time to react to variables, be it a memory recall or an FCOM expedition. And for the passenger safety is an even smaller dot - will I be alive after the plane comes to a stop on the ground?

Everything else, the laws, the standards, the policies, is just politics, or worse, semantics. Bottom line that I hope everyone here agrees - if a plane is too expensive to be made safe, it mustn't fly.
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Old 26th May 2019, 12:42
  #22 (permalink)  
 
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Originally Posted by capngrog View Post
For example, walking is a relatively safe activity given normal circumstances; yet, walking on the edge of an icy precipice in a snowstorm involves more risk, requiring more caution ... hence "risk management". I could go on and on about this, but I won't.
Agreed. However in this particular case, you are walking on the edge of an icy precipice in a snowstorm while the weather forecast says sunshine and issues no warning about the precipice or it being icy. And you are pulling a sled with 200 people who rely on you to get them home safely. And the CEO of the weather forecast says it's absolutely safe because the Weather Supervisor allowed him to do that.

In you 43 years of safety investigations haven't you come to the conclusion that safety cannot exist if the people who are supposed to observe a system's safety don't understand the system or don't know it exists?
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Old 27th May 2019, 16:07
  #23 (permalink)  
 
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Way back, ‘Reevaluation of 737 Safety Procedures’,
at # 2, ‘There is no difference between the NG and the MAX in manual trim,….’
Technically - mechanically the trim system could be identical, but the installation and use, redefined by aircraft characteristics, new variants, could result in small changes which in specific circumstances are critical in safe operation.

As discussed in this thread, these changes may not be clear cut and have evolved through each generation of aircraft development. Also 737 Stuck Manual Trim Technique for some of the changes.

A key issue in safety is learning. Revisiting previous beliefs and assumptions after an accident is an important safety process - safety involves what is done opposed to a stagnant what we have.
A difficulty in reassessment is in identifying what the original beliefs and assumptions were, especially in design and certification as they may not be overtly recorded, being the conclusions of judgements about human - system interaction and human performance.
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Old 27th May 2019, 18:52
  #24 (permalink)  
 
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A clear summary of the current situation.
A disturbing view of the NG and imminent future of the MAX.
https://www.moonofalabama.org/2019/0...g-737-ngs.html
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Old 28th May 2019, 12:13
  #25 (permalink)  
 
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Despite the quirky website address the moonofalabama article is both interesting and well written. Hard to argue the 737 NG is not 'safe' given it's track record, but Boeing (and the FAA) will struggle to explain how they got to this place: 'We made the stabiliser bigger, which increased the loads it could generate, and made the trim wheel smaller, so it was harder to turn. And then deleted the procedure that told you how to use the trim wheel at high loads.'
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Old 28th May 2019, 12:35
  #26 (permalink)  
 
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Since I don't have any experience on other jetliners than the 737, can someone explain how trim runaways are sorted out on aircrafts that doesn't have a trim wheel at all. Personally I think that trim runaways happens so rarely, that once it's eliminated that MCAS can't trim full nose down anymore, I would not be to worried anymore to get on a MAX plane.
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Old 28th May 2019, 13:14
  #27 (permalink)  
 
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Originally Posted by FRogge View Post
Since I don't have any experience on other jetliners than the 737, can someone explain how trim runaways are sorted out on aircrafts that doesn't have a trim wheel at all. Personally I think that trim runaways happens so rarely, that once it's eliminated that MCAS can't trim full nose down anymore, I would not be to worried anymore to get on a MAX plane.
FBW planes like A320 and newer and B777 and newer have much more redundancy like several FCC with several channels each continuously comparing their output with each other, possibly more than one motor driving the jack screw, more than one signal path to the motors etc. In sum this makes it exceedingly unlikely that a runaway can happen. Think at how unlikely it is to loose both engines over water far from nearest airport on a two engine aircraft. It is not guaranteed it can never happen, but the likelyhood of it happening is so exceedingly small that the risk is deemed acceptable.

Edit: On FBW aircraft like the A320 there is no significant force required to hold say full aft stick, so less physically demanding compared to the B737 where a pilot might need to use all his force just to hold against a badly mistrimmed stabilizer. Further the elevator on say the A320 is much larger as a percentage of the stabilizer so the elevator has significantly more authority to hold against a badly mistrimmed stabilizer. In sum all these differences make the B737 much more demanding to controll when the stabilizer get significantly out of trim, and the likelyhood of it running away is probably also much larger.
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Old 28th May 2019, 15:05
  #28 (permalink)  
 
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FRogge, you then might find that the following runaway incident report is interesting.
It's a FBW airplane, of course.
Ultimately, the cause is linked to an incorrect safety risk assessment (again).

One of the manufacturer's responses was to put a button that disconnects the automation.

https://www.bea.aero/uploads/tx_elyd...0525.en_01.pdf
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Old 28th May 2019, 15:07
  #29 (permalink)  
 
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Personally I think that trim runaways happens so rarely, that once it's eliminated that MCAS can't trim full nose down anymore, I would not be to worried anymore to get on a MAX plane.
MCAS is not runaway stab. MCAS kicks in under certain conditions, MCAS was a solution for those conditions, and those conditions remain to be dealt with.

Currently, the ac has 2 sensors, one of which is used for STS and MCAS. The results a faulty or damaged AoA sensor initiated MCAS.
On the NG, the stab switches could cutoff AP and Elec stab control separately. Currently, the MAX stab switches cut off the electric stab control entirely, leaving the crew to manually trim the aircraft.
Given that it appears that in both cases, the AoA was damaged, it looks like the crew will be manually trimming the ac for the rest of the flight. That is not realistic.
Adding an AoA disagree light, so what? Changing the switches back to NG config...okay, then again, if one AoA is gone or damaged....
Adding a 3rd AoA vane, damn near impossible.
The underlying reasons and conditions MCAS was added in first place.

While it doesnt happen that often (until MCAS) when it did, it exposed the issues with the MAX AND the NG...
The "roller coaster" hasnt been in the manual since the -200 with a different stab/elev config.
Extending flying on manual trim with no AoA or limited, yet another lost art?

All adds up to a real big mess that a "software fix" is but a small part.
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Old 28th May 2019, 15:35
  #30 (permalink)  
 
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The "roller coaster" hasn't been in the manual since the -200 with a different stab/elev config
That is true. But the roller coaster method of regaining partial manual stabilizer control certainly is effective in the Boeing 737 Classic simulators despite nothing in the FCTM that specifically states how it is done. It is alluded to by the FCTM statement "In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming" The roller coaster method is designed to do just that.
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Old 28th May 2019, 16:51
  #31 (permalink)  
 
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Originally Posted by ProPax View Post
In you 43 years of safety investigations haven't you come to the conclusion that safety cannot exist if the people who are supposed to observe a system's safety don't understand the system or don't know it exists?
Accident investigators must understand all factors involved in an accident, and reaching that understanding is the point of the investigation. Accident investigators begin the process from a point of relative ignorance and, must maintain a rather steep learning curve, hopefully resulting in an understanding of the circumstances/factors of the accident. These circumstances/factors range primarily from hardware, to software, to the human element and many others; however, nobody is expert or even conversant in the intricacies of all aspects of modern technology, hence such procedures as the "Party to the Investigation" system utilized by the NTSB (USA) and others. The "Party" system employed by the NTSB, for example, relies heavily upon outside expertise, and the NTSB Investigators themselves have their specialties such as "Power Plant", Weather", "Structures", "ATC" etc. As you suggested in your above statement, to reach an understanding of complex factors in an investigation, requires the input of many competent individuals.

Cheers,
Grog

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Old 28th May 2019, 17:05
  #32 (permalink)  
 
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Originally Posted by capngrog View Post
Accident investigators must understand all factors involved in an accident, and reaching that understanding is the point of the investigation. Accident investigators begin the process from a point of relative ignorance and, must maintain a rather steep learning curve, hopefully resulting in an understanding of the circumstances/factors of the accident. These circumstances/factors range primarily from hardware, to software, to the human element and many others; however, nobody is expert or even conversant in the intricacies of all aspects of modern technology, hence such procedures as the "Party to the Investigation" system utilized by the NTSB (USA) and others. The "Party" system employed by the NTSB, for example, relies heavily upon outside expertise, and the NTSB Investigators themselves have their specialties such as "Power Plant", Weather", "Structures", "ATC" etc. As you suggested in your above statement, to reach an understanding of complex factors in an investigation, requires the input of many competent individuals.

Cheers,
Grog
I'm sure I read in an initial report of the Ethiopian accident, the crew left/forgot to reduce power after takeoff. Whatever any MCAS problems, leaving full power on until you make a hole in the ground is not good practice?
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Old 28th May 2019, 17:41
  #33 (permalink)  
 
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Originally Posted by cessnapete View Post
the crew left/forgot to reduce power after takeoff. Whatever any MCAS problems, leaving full power on until you make a hole in the ground is not good practice?
One must remember that the 737 was a "certified" aircraft, and so was supposed to be trimmable at any speed within the flight envelope.
So there is nothing wrong with leaving full thrust with a stickshaker alarm at takeoff.

Duly warned and briefed pilots experienced great difficulties in the sim when confronted with the same scenario.
Even though nothing was at stakes, they say they had their hands full with dealing with the recovery and fighting tunnel vision.

What with a real unexpected alarm in a real aiplane with no previous briefing ?
And remember, the "certified" 737 was supposed to be hand trimmable at the time.

Only now do we know Boeing "autocertified" their airplanes, and there are suspicions of trim difficulties on the MAX as well as the NG.

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Old 28th May 2019, 17:48
  #34 (permalink)  
 
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Originally Posted by Fly Aiprt View Post
One must remember that the 737 was a "certified" aircraft, and so was supposed to be trimmable at any speed within the flight envelope.
So there is nothing wrong with leaving full thrust with a stickshaker alarm at takeoff.

Duly warned and briefed pilots experienced great difficulties in the sim when confronted with the same scenario.
Even though nothing was at stakes, they say they had their hands full with dealing with the recovery and fighting tunnel vision.

What with a real unexpected alarm in a real aiplane with no previous briefing ?
And remember, the "certified" 737 was supposed to be hand trimmable at the time.

Only now do we know Boeing "autocertified" their airplanes, and there are suspicions of trim difficulties on the MAX as well as the NG.
Totally aggree with above, while leaveing power up was not ideal it was not a cause of inability to trim, snip from a post in other thread:

Known facts from, report.
Airspeed at start of first MCAS input 250 kts.
MCAS applied 9 seconds ND trim the ET pilot applied 3 seconds NU trim 6 seconds later.
MCAS acitvated 5 seconds after that but was interrupted at 6 seconds by 9 seconds NU trim. (possibly interrupted by trim cutout)

Total MCAS 15 seconds ND total pilot NU 12 seconds left the aircraft severely out of trim and just under VMO in under 40 seconds and likely unrecoverable using manual/mechanical trim.
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Old 28th May 2019, 19:10
  #35 (permalink)  
 
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Remember the trim works at two speeds too. The pilots can command a slow speed trim with flaps up and fast with flaps not up. MCAS works at fast speed I believe? 9 seconds at full speed and 3 seconds back at half speed wouldn't end well....
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Old 28th May 2019, 21:12
  #36 (permalink)  
 
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Hard to argue the 737 NG is not 'safe' given it's track record
This was exactly the argument used for the Nimrod MR2 until 14 aircrew were killed by a latent airworthiness problem that had not manifested to the point where it had been recognised in the previous 25 years. (Yes, the number of aircraft and hours flown were a couple of orders of magnitude different but it's the same logic.) As ever, it's the combination of unforeseen circumstances that are the killer but if the manufacturer had foreseen and ignored, you have a very different equation.
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Old 28th May 2019, 22:07
  #37 (permalink)  
 
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there's still the issue if MCAS is disabled under certain circumstances. how can the MAX meet the certification requirement about consistently increasing forces on the Yoke as the aircraft approaches a stall, which seems a very desirable attribute!

And the liability/fraud issue about the Boeing paperwork that stated MCAS authority would be limited to 0.4 units, thus justifying much less scrutiny and code that wasn't level 1, then actually allowing it 2.5 units of authority? It would be even worse if it was found that B deliberately wrote in 0.4 to get it passed under the radar whilst knowing/having a good guess it would need much much more in actual use. That counts as gaming the regulator.

G
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Old 29th May 2019, 00:54
  #38 (permalink)  
 
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That is true. But the roller coaster method of regaining partial manual stabilizer control certainly is effective in the Boeing 737 Classic simulators despite nothing in the FCTM that specifically states how it is done.
Of course, in the classic.

The NG has a larger stab, and a smaller elevator....

What is the procedure for this configuration?

It appears the FAA has finally caught up, and well,

the lazy B has been caught.

In reality, I am far over this shit. The aircraft industry is held back by all of the bullshit regulations, that when you read them, are so old, dont relate, or are so vague to be unusable.
New designs and technology are hampered by attempts to fit into 1950s capabilities, (or abused by compliance)

If you want to let the aviation business really soar, fix the regulatory process to allow technology to expand as a NEW FN system, rather than a legacy bullshit system. FK the " its the same and no new training is required or type" It is not....

I would much rather be trained on a new fightdeck capabilities, and the intricacies of the AP, than they tell me it is the same as a -700 or -800, FK an iPAD and I am cert'd, and expect me to react when the FN nose points down......

I WANT to know the differences, I WANT to know when the shit hits the fan, what I need to do about it. This bullshit about hand flying the aircraft, is becoming just that, bullshit.
The MTOW and thrust alone between these variants should tell someone with "experience' that it just doesnt work that way anymore...

Last edited by Smythe; 29th May 2019 at 01:15.
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Old 29th May 2019, 01:46
  #39 (permalink)  
 
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Originally Posted by SLF3 View Post
Despite the quirky website address the moonofalabama article is both interesting and well written. Hard to argue the 737 NG is not 'safe' given it's track record, but Boeing (and the FAA) will struggle to explain how they got to this place: 'We made the stabiliser bigger, which increased the loads it could generate, and made the trim wheel smaller, so it was harder to turn. And then deleted the procedure that told you how to use the trim wheel at high loads.'
They also put a damper in there as well because there was also a new trim motor.


Regarding the trim wheels: When the NG was being introduced, I happened to be the Lead Engineer in charge of them and a whole lot of other stuff. There were some issues. The new display system created a pinch point between the dash and the wheel. We had to make the wheel smaller. And the new trim motor resulted in the wheel, which is directly connected to the stabilizer by a long cable, springing back when electric trim was used. It was an undamped mass on the end of a spring. We had to add a damper.
Result: Depending on the flight conditions, the force to manually trim can be extremely high. We set up a test rig and a very fit female pilot could barely move it.
International Skeptics Forum - View Single Post - [Ed] 737 Max Crashes (was Shutdown caused Boeing crash.)

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Old 29th May 2019, 08:12
  #40 (permalink)  
 
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Originally Posted by Smythe View Post
The NG has a larger stab, and a smaller elevator...
The elevator has stayed the same size on every 737 variant as the size of the stab gradually grew.
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