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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 14th Nov 2018, 12:56
  #1181 (permalink)  
 
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Originally Posted by Gysbreght View Post
I would think that virtually ANY change to an approved type design requires an amendment to the Type Certificate. See the B737 Type Certification Data Sheet (TCDS) on the FAA website:
Yes, of course.

But the poster's point was that having to amend an existing TC is greatly preferable to the FAA/EASA saying that the manufacturer has changed so much that it's essentially a new type and has to be certificated from scratch.
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Old 14th Nov 2018, 13:07
  #1182 (permalink)  
 
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Originally Posted by A Squared View Post
So, assuming the MAX is not terribly different, you may only be 2 operation cycles of the MCAS away from having your stabilizer at full stab-up (nose down) travel.
HolyCrap. That is a chilling way to see it.

The question. Will the inclusion of the OMB solve the problem? Or is the design of MCAS insufficient, relying evidently on one AoA input. Seemingly, other sensor input did not mitigate the one vane from overruling the other parameters? Flaps, Mach, etc.?

Last edited by Concours77; 14th Nov 2018 at 13:38.
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Old 14th Nov 2018, 13:38
  #1183 (permalink)  
 
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locblue, #1146.

The linked article discusses hardware/ software changes; the option for training, human intervention and mitigation, given this event, should not be considered.
It is also questionable if the crew actions and description given in the AD will be adequate in the short term.
The regulators might judge otherwise, they must be under considerable internal pressure due to apparent weaknesses in their safety oversight. Also pressure from the wider industry, concerns over disruption and economic upset if 737MAX flying was interrupted.

A cynical view might point to overt support at high level; economically too disastrous to contemplate, so take the risk. But ensure that the risk is passed down the line; if there is an event the operator / crew will be in the firing line - ‘didn’t follow procedures’, without thought whether crews would be able to act or not.
If so then the regulatory decision process sheds all responsibility.
If the unlikely occurs then the enormity of the effect on the industry (including regulators) will be unimaginable.


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Old 14th Nov 2018, 13:49
  #1184 (permalink)  
 
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safetypee....

”...A cynical view might point to overt support at high level; economically too disastrous to contemplate, so take the risk. But ensure that the risk is passed down the line; if there is an event the operator / crew will be in the firing line - ‘didn’t follow procedures’, without thought whether crews would be able to act or not.
If so then the regulatory decision process sheds all responsibility.
If the unlikely occurs then the enormity of the effect on the industry (including regulators) will be unimaginable...”

It would only be cynical if the reality was other than blatantly apparent. I would use the word “rational”...

Who guards the guardians? “Self Certification?” Sole source sensor? Economically too disastrous? At ten million per plaintiff....

Let’s see, that’s two Billion dollars, plus another Billion for legal fees. Plus re-certification. It’s a standout airplane. The corporation not so much.
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Old 14th Nov 2018, 13:52
  #1185 (permalink)  
 
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Originally Posted by A Squared View Post
Any time you're changing the angle of a stabilizer, the potential exists for loss of control of the aircraft if you lose control of the system adjusting the stabilizer. I doubt anyone disagrees on that point.
Don't disagree per se, but this statement requires clarification. Runaway trim (from whatever cause) can cause loss of control only in a very small corner of the flight envelope (specifically, when slow, at high AOA, and with the engines at high power.) The accident aircraft was not in this corner of the envelope so the pilots had sufficient elevator authority to over ride the trim. Assuming (and yes this remains a BIG assumption) the trim ran away due to the MCAS getting erroneous AOA sensor data, the pilots should have been able to maintain control and overcome the mis trim. The mystery is why they did not.

Further, on the subject of why Boeing did not include the MCAS in the flight manual, could it be because the existing procedures for runaway trim are applicable whether the cause is a stuck switch, stuck sensor, misbehaving STS, or misbehaving MCAS. Troubleshooting the systems to determine what the root cause is for a runaway trim condition just delays the pilot from executing the runaway trim procedures. Further still, this could also explain why Boeing chose to implement MCAS the way they did, using the trim system vs a stick pusher. It makes operation of the system and any emergency procedures related to malfunction of the system completely transparent to the pilots.

Last edited by KenV; 14th Nov 2018 at 14:03.
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Old 14th Nov 2018, 13:57
  #1186 (permalink)  
 
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If MCAS was active, by definition your parameters were met. TRIM AND at altitude should be recoverable? Changing the focus again?

Last edited by Concours77; 14th Nov 2018 at 14:26.
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Old 14th Nov 2018, 14:01
  #1187 (permalink)  
 
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Originally Posted by A Squared View Post
Not to say that you're wrong, that may well have been the thinking. But the objections to that rationale is that the MCAS does something pretty different than the STS (almost opposite) for different reasons and in a very different flight regime ,so saying that "it's just the same "system"" is a weak reason for not disclosing it.
Just to clarify, I wasn't saying that I agree with the rationale either, just speculating as to how it could have come about, whilst also aware that I do so with the benefits of hindsight, and without the pressure of needing to design a new plane because the 320neo is eating our lunch whilst not having the time or resources to actually design a new plane.

Sometimes (in any field) the answer to "how the did we get so far of course?" is "one small step at a time, each step logical and justifiable considered in isolation".

New flight control system -->
New control system implemented "efficiently" by using existing system -->
Modification to existing system -->
Undocumented modification to existing system

Overall result: undocumented new flight control system. And crash, of course, or we wouldn't be here.
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Old 14th Nov 2018, 14:03
  #1188 (permalink)  
 
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Originally Posted by KenV
Runaway trim (from whatever cause) can cause loss of control only in a very small corner of the flight envelope (specifically, when slow, at high AOA, and with the engines at high power.)
You've said this before. Have you any proof, or is it a certification requirement? I am sure (never having actually tried it) that if I was doing > 250 KIAS (as they appear to have been doing when level and more in the dive) there is no way (not 737 but medium jet) I could pull enough backstick to hold the nose up if the stab trim was wound full nose-down.
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Old 14th Nov 2018, 14:05
  #1189 (permalink)  
 
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Just your average......

From the reporting in the Wall Street Journal (by A. Pasztor and A. Tangel) yesterday, Nov. 13:

"....company had decided against disclosing more details to cockpit crews due to concerns about inundating average pilots with too much information - and significantly more technical data - than they needed or could digest." (emphasis added)

First, what and who provided the definition of an "average pilot"? (and various extension questions, such as, is this construct of an average aviator one that is subject to refinement accounting for air carrier, extent or absence of military flying career, age and education, country of licensing, just to iterate a selection). And aren't the abilities and attributes expected of aviators for sorting through sudden, severe onsets of high spikes in information the business of other authorities in the safety system of aviation - not the airframers?

Second, have we - the global civil international aviation system - just witnessed the otherwise unheralded start of autonomous aircraft? Understanding the instrumentation, flight control and avionics components of the accident aircraft did not constitute a complete autonomous capacity - but it reportedly was autonomous enough so that the first step of the Holy Trinity seems to have been voided. [ Aviate, Navigate.....]

Third, attention General Counsel of Boeing: Remember, one central ability and attribute of a proper General Counsel is to be steadfast as "the calm presence in the room."

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Old 14th Nov 2018, 14:33
  #1190 (permalink)  
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Originally Posted by Capn Bloggs View Post
You've said this before. Have you any proof, or is it a certification requirement? I am sure (never having actually tried it) that if I was doing > 250 KIAS (as they appear to have been doing when level and more in the dive) there is no way (not 737 but medium jet) I could pull enough backstick to hold the nose up if the stab trim was wound full nose-down.
I've been in the sim when both pilots needed to fly the a/c because the runaway wasn’t recognized in a timely manner . Doable but not pretty.
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Old 14th Nov 2018, 14:35
  #1191 (permalink)  
 
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Originally Posted by Capn Bloggs View Post
You've said this before. Have you any proof, or is it a certification requirement?
This has been a basic design philosophy at both Boeing and Douglas since forever. And because that is the way it is designed, it is tested to ensure it behaves as designed and is part of the type certification. Indeed, when Boeing provides the flight training, that training includes flying the aircraft (in the sim) with a hardover trim condition. No it's not easy and may require both pilots. But yes it is very much possible.

Remember the 737 flight control system was designed in the 60s and is fully mechanical. The 737 has a measure of SCAS (Stabililty Control Augmentation System) with STS and MCAS, but those systems act entirely thru the mechanical flight control system (more specifically, the trim portion of the mechanical flight control system). Further, the exact action (though not the reason why) of these systems is easily discernible by looking at the trim wheel, the action is over ridden/cancelled with the push of the trim switch on either pilot's yoke, can be cut out completely with a cutout switch, and if all else fails, can be overpowered by applying high stick forces. The Boeing and Douglas design philosophy is to always give the pilots the ultimate say and the ability to overpower whatever an electronic system wants to do. Indeed that is why these systems only operate through the trim system, because the base flight control system can overpower trim. Yes, this means that unlike many Airbus aircraft, the pilots of Boeing/Douglas aircraft can do stupid things and endanger the aircraft. It's not like the A320 where if you have the wrong flight control mode selected the pilots cannot simply overpower the system by pushing on the stick and/or the throttle to over ride envelope protection, and must instead deselect the current mode and select another. I'm not saying or even suggesting one design approach is "better" or "safer" than the other, I'm saying the approaches are fundamentally and significantly different.

Last edited by KenV; 14th Nov 2018 at 15:04.
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Old 14th Nov 2018, 14:48
  #1192 (permalink)  
 
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Originally Posted by WillowRun 6-3 View Post
From the reporting in the Wall Street Journal (by A. Pasztor and A. Tangel) yesterday, Nov. 13:

"....company had decided against disclosing more details to cockpit crews due to concerns about inundating average pilots with too much information - and significantly more technical data - than they needed or could digest." (emphasis added)

First, what and who provided the definition of an "average pilot"? (and various extension questions, such as, is this construct of an average aviator one that is subject to refinement accounting for air carrier, extent or absence of military flying career, age and education, country of licensing, just to iterate a selection). And aren't the abilities and attributes expected of aviators for sorting through sudden, severe onsets of high spikes in information the business of other authorities in the safety system of aviation - not the airframers?
You appear to be very ignorant of the certification process. Yes, the airframers decide that, and no the regulators do not. Airbus for example assumes a significantly lower skill level pilot than either Boeing or Douglas, provides more automation, and provides/imposes more protections that cannot be over ridden by the pilots. Further, I've already said it multiple times. The emergency procedure for a 737 runaway trim condition (whatever the root cause be it STS, MCAS, or magical gremlins) is the same. Inundating the pilots with checklists and troubleshooting procedures to determine root cause is pointless and just delays execution of the procedure. Perform the procedure, fly the airplane, get it on the ground, and let the maintainers do the trouble shooting. As it is, the vast majority of pilots don't understand STS and indeed don't understand what it does nor why even after hundreds of thousands of pilots have flown the aircraft for multiple decades and millions upon millions of safe flight hours. The point is they don't really need to understand STS. They only need to recognize a runaway trim condition, need to be trained to recognize it in a timely manner, and need to know the procedures to overcome it. The same applies to MCAS.

Last edited by KenV; 14th Nov 2018 at 15:15.
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Old 14th Nov 2018, 15:09
  #1193 (permalink)  
 
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Concours, #1194, OK rational.
The economic view considered aircraft grounding.
Add dented corporate and aircraft images, effect on all sales.

“through inaction, do not allow a human being to come to harm” Asimov



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Old 14th Nov 2018, 15:10
  #1194 (permalink)  
 
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KenV

I might be less knowledgeable than you are but I'm not making broad assumptions in these questions. It remains to be determined whether disclosure of the MCAS subsystem would or would not have made a substantial difference in this crash. Yeah, I don't claim expertise in type certification processes but then, I'm also not asserting clairvoyance as to what the CVR - and probable cause analysis of the AIB - will show.

As to differences in Boeing and Airbus, this still begs the question. You didn't get any sense from statements by officials of pilots' unions that references to an "average pilot" were a bit objectionable?

As for the definition itself, read my post and see if this time you can spot where I said this point is up to regulators... ( hint, I didn't).

It's still a valid question: how is this baseline defined, based on what data, and with what level of transparency.
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Old 14th Nov 2018, 16:17
  #1195 (permalink)  
 
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Originally Posted by DaveReidUK View Post

Max downwards stab (i.e. a/c nose up) angle: -12.9°
Max upwards stab (i.e. a/c nose down) angle: +4.2°

A stab angle of 0° corresponds to 4 units of nose-up (ANU) trim at the lever. Presumably the purpose of ANU units is simply to avoid confusion between positive and negative values, so it may well be that each ANU unit increment = 1°.
Ah, well that clears up the small mystery.
The Classic has 17 units of trim, which equates very nicely to your 17 degrees of trim.

Silver.
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Old 14th Nov 2018, 16:26
  #1196 (permalink)  
 
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Originally Posted by KenV View Post
Don't disagree per se, but this statement requires clarification. Runaway trim (from whatever cause) can cause loss of control only in a very small corner of the flight envelope (specifically, when slow, at high AOA, and with the engines at high power.) .
Disagree entirely, the mighty stab trim can overpower the piddling elevator.
Especially if you were on the front of the flight envelope to start with.
Have you ever tried giving max nose down trim at 250 kt...?

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Last edited by silverstrata; 14th Nov 2018 at 16:52.
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Old 14th Nov 2018, 16:33
  #1197 (permalink)  
 
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A layman's question: As this MCAS trim behaviour seems to be designed as an emergency measure in lieu of a stick pusher, is there any information feedback to the pilots that it's been activated? Visual, auditory? Apart from the normal feedback of the trim wheels turning and clacking?
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Old 14th Nov 2018, 16:34
  #1198 (permalink)  
 
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Originally Posted by A Squared View Post
So, assuming the MAX is not terribly different, you may only be 2 operation cycles of the MCAS away from having your stabilizer at full stab-up (nose down) travel.
Which is why you want a stick push, rather than a stall trim.

A pusher can give you full stick forward, but as soon as you reach flying speed it will relent and give you normal control with normal trim. So you fly away with a few beads of sweat, and get some tea and bisuits with chiefy. But a stall-trimmer on the forward stop is going to take an age and a half to retrim - even if you recognise what has happened - resulting in salty tea and soggy biscuits with Davey Jones...!

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Last edited by silverstrata; 14th Nov 2018 at 16:53.
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Old 14th Nov 2018, 16:49
  #1199 (permalink)  
 
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Originally Posted by Sriajuda View Post
A layman's question: As this MCAS trim behaviour seems to be designed as an emergency measure in lieu of a stick pusher, is there any information feedback to the pilots that it's been activated? Visual, auditory? Apart from the normal feedback of the trim wheels turning and clacking?
One imagines that the stick-shaker might also operate (there is no stall alert-tone or warning-lamp). Depends how close to the stall this stall-trimmer system starts to operate. Other than that, I presume the new system is like the STS, and all you get is the clunking and clanking of the trim-wheel. If it had a new warning tone or light, it would have needed a separate section in the manual.

And bearing in mind that this was a spurious warning, would the stick shaker even operate..?

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Old 14th Nov 2018, 16:57
  #1200 (permalink)  
 
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Originally Posted by silverstrata View Post


The STS normally trims nose down after take-off.
It is safer that way....

Silver
From you posts it is obvious you know more about the 737 than I, so apologies for going on about this, but I feel it is an important point:
The main reason for the STS is to make the airplane more speed stable, so it artificially flies the airplane back to a reference speed with trim inputs. If the STS trims AND after T/O your speed must have been below the reference speed, and the STS trims to get the nose in the direction of the speed change back to reference speed.
It does not trim AND just because it is safer, it is flying the aircraft with the trim to get the aircraft back to reference speed. Most pilots seem to blip the trims to set a new reference speed, and stop the STS from trimming in that direction. As the pilot starts to accelerate the STS will try to keep the reference speed so it will trim ANU, while the pilot wants to accelerate and trims AND.
What I think happened with the write-up is that after they raised the flaps and were accelerating the MCAS kept trimming AND and that is the unexpected trim direction the previous captain was referring to, because the STS would still be trying to trim ANU normally. I am inclined to believe he knew what the expected trim direction was in this situation based on the fact he was able to continue without crashing.
Again, all just based on an A pilot reading about B planes, so if I am incorrect about the technology please correct me.

Last edited by hans brinker; 14th Nov 2018 at 17:16. Reason: Adding words
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