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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 27th Nov 2019, 00:24
  #4161 (permalink)  
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Huh, I'd just deleted my post because I felt it was a little harsh. On the whole, he's put a lot of work in, but there are some basic misunderstandings which rather need an update.
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Old 27th Nov 2019, 01:31
  #4162 (permalink)  
 
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Originally Posted by Mad (Flt) Scientist View Post
All DAL-A assures is that the software does what the software requirements say it should do, not that those requirements are themselves correct or complete. That's a SYSTEMS requirements issue not a software requirements issue - and indeed, can be thought of as applying to non-software aspects of design as well.
Beg to differ a bit. DAL A assurance is supposed provide convincing evidence that requirements are validated, and that they are traced to the code. The process for establishing software Design Assurance Level A is painfully extensive in time and resources. It is not an absolute guarantee of no software errors because testing to prove that is not possible. But the process, developed by manufacturers and regulators together has been in use for decades, though not without attempts to push back. Hopefully, energy to resist pushback at the rigor of DAL processes will be renewed as a result of the MAX debacle.
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Old 27th Nov 2019, 01:57
  #4163 (permalink)  
 
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Originally Posted by Loose rivets View Post
Huh, I'd just deleted my post because I felt it was a little harsh. On the whole, he's put a lot of work in, but there are some basic misunderstandings which rather need an update.
I almost quit reading after "stall prevention" and managed to grit my teeth through "thrustline" but if he doesn't know that Brady is giving the correct reason for MCAS by now, absent any stunning new revelations from Boeing, it's hopeless. My question is what is the effin envelope and can the autopilot reach that envelope? Because either MCAS is there for human pitch feel linearity and the autopilot is not bothered by any non linear effect or MCAS is not active with the autopilot on because it would not be useable in the MCAS regime. Still, I wonder if the non linearity might be a minor one that would not affect humans if told about it or it's something that we couldn't compensate for. Again, once told to be careful at .9M in the T-38, I was careful. We hear many 737 pilot accounts of how this or that dash whatever model lands better than the other dash whatever model. Those handling differences do not bother the pilots.Nor did landing the 767-300 one day and landing the 757 the next bother me.
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Old 27th Nov 2019, 09:12
  #4164 (permalink)  
 
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If Airspeed Unreliable memory items were followed, we wouldn't even know about MCAS by now.
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Old 27th Nov 2019, 09:52
  #4165 (permalink)  
 
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https://theaircurrent.com/aviation-s...-design-issue/
Re-certification sliding into 2020, FAA reissues statement it will not be rushed, Ryanair specific high density model faces issue with overwing exit
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Old 27th Nov 2019, 09:52
  #4166 (permalink)  
 
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Originally Posted by jimtx View Post
I almost quit reading after "stall prevention" and managed to grit my teeth through "thrustline" but if he doesn't know that Brady is giving the correct reason for MCAS by now, absent any stunning new revelations from Boeing, it's hopeless.
How could an article from March 2019 take into account what Brady is saying now ?

MCAS is a longitudinal stability enhancement. It is not for stall prevention (although indirectly it helps) or to make the MAX handle like the NG (although it does); it was introduced to counteract the non-linear lift generated by the LEAP-1B engine nacelles at high AoA and give a steady increase in stick force as the stall is approached as required by regulation.
I'll add that that trying to give an increase in stick force with a control slower than the stick-controlled elevator raises questions...

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Old 27th Nov 2019, 12:15
  #4167 (permalink)  
 
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Originally Posted by DaveReidUK View Post
I think you mean Type Rating, not Type Certificate.

There was never any possibility of a 737 derivative being certificated under anything other than the legacy 737 TC A16WE.
What I meant was a major Revision under A16WE (Boeing installed a brand New wing and many other major mods to the existing type certificate with the NG), a derivative that Regulators would consider substantial enough to require a new Type Rating And a new Simulator for traning the pilots.......
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Old 27th Nov 2019, 15:36
  #4168 (permalink)  
 
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Originally Posted by Fly Aiprt View Post
How could an article from March 2019 take into account what Brady is saying now ?



I'll add that that trying to give an increase in stick force with a control slower than the stick-controlled elevator raises questions...
He quotes Brady in his article but expresses uncertainty about whether he is correct. Yes you have to wonder how that pencil whip actually performed in the windup turns.
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Old 27th Nov 2019, 15:56
  #4169 (permalink)  
 
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Originally Posted by jimtx View Post
I Nor did landing the 767-300 one day and landing the 757 the next bother me.
Interesting comment as the technique for both 75 and 76 were the same the result werent always the same!
75 trucks were tilted up, a stablising condition, 76 tilted down, just the opposite, could make a significant difference, guaranteed smooth touchdown every time on the 75, took what you got on the 76 !
Cant say it bothered me that much though !

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Old 27th Nov 2019, 16:31
  #4170 (permalink)  
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Originally Posted by Fly Aiprt
I'll add that that trying to give an increase in stick force with a control slower than the stick-controlled elevator raises questions...
Originally Posted by jimtx View Post
He quotes Brady in his article but expresses uncertainty about whether he is correct. Yes you have to wonder how that pencil whip actually performed in the windup turns.
It's rather striking that so many smart and experienced people have been investigating and considering MCAS for such a long time and the consensus is something like, "We're not sure what it was really supposed to deal with and definitely not sure how it would do whatever that is." And that's aside from the issues surrounding the fatal failures.

Someday, some of the insiders will be ready to tell the whole story.
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Old 27th Nov 2019, 17:01
  #4171 (permalink)  
 
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See the report of the 737 NG accident discussed in Flydubai crash at RVI final report out.

Re trim and assumptions about pilot previous experience, previous types and training, Boeing trim design philosophy.
If nothing else see the last page - the final footnote.
I hope that the FAA takes note; if not, then the other regulators; or failing that, operators and pilots.
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Old 27th Nov 2019, 17:35
  #4172 (permalink)  
 
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Originally Posted by OldnGrounded View Post
Someday, some of the insiders will be ready to tell the whole story.
In the meantime, it is hard to believe that linearizing stick force response can be achieved with a coarse one size fits all, one-shot (or repeated shots) non instantaneous movement of the stabilizer.
There might be more to it than the official theory...

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Old 27th Nov 2019, 18:21
  #4173 (permalink)  
 
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Originally Posted by Fly Aiprt View Post
In the meantime, it is hard to believe that linearizing stick force response can be achieved with a coarse one size fits all, one-shot (or repeated shots) non instantaneous movement of the stabilizer.
There might be more to it than the official theory...
I'm still having a lot of trouble getting my head around B's thought processes.
1. Don't tell the pilots about the existence of MCAS
2. Expect the pilot to respond within seconds to an unintentional MCAS activation.
3. Expect the pilot to sit quietly through an intentional MCAS trim-down and the subsequent trim-up "reset" without touching the electric trim.
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Old 27th Nov 2019, 18:40
  #4174 (permalink)  
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Originally Posted by Fly Aiprt View Post
In the meantime, it is hard to believe that linearizing stick force response can be achieved with a coarse one size fits all, one-shot (or repeated shots) non instantaneous movement of the stabilizer.
Yes, absolutely. As you say, it doesn't really make sense.
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Old 27th Nov 2019, 19:00
  #4175 (permalink)  
 
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Originally Posted by Peter H View Post
I'm still having a lot of trouble getting my head around B's thought processes.
1. Don't tell the pilots about the existence of MCAS
2. Expect the pilot to respond within seconds to an unintentional MCAS activation.
3. Expect the pilot to sit quietly through an intentional MCAS trim-down and the subsequent trim-up "reset" without touching the electric trim.
Worse than that, for (2) a response is expected in 3 (or 4, can't remember?) seconds whereas for MCAS to do it's job in (3) the pilot has to not notice the trim running for 9 seconds.

Possibly the assumption was that in an intentional MCAS trim-down the pilots would be otherwise occupied with impending stall, warnings, feel-shift etc. - this was proved correct...

Intentional but erroneous MCAS activation was never considered (if I understand JTAR correctly).
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Old 27th Nov 2019, 20:17
  #4176 (permalink)  
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FAA Takes Back Control Of Key Safety Step From Boeing

FAA Takes Back Control Of Key Safety Step From Boeing As Questions Linger On 737 MAX Fix

The Federal Aviation Administration is taking back the sole authority to issue airworthiness certificates for new 737 MAX aircraft for an indefinite period, marking a reversal in a program that had transferred responsibility to Boeing, even as questions linger on the re-launch of the troubled airplane.

As Reuters has reported, the FAA issued a letter to Boeing on Tuesday notifying them of the decision. Citing the large number of 737 MAX planes that will need vetting that have piled up in storage as Boeing has continued production despite the global grounding of the plane, the FAA said it will “retain authority to issue airworthiness certificates and export certificates of airworthiness for all 737 MAX airplanes” for an indefinite period, until the Administration is satisfied that Boeing has “fully functional quality control and verification processes.”

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Old 27th Nov 2019, 21:51
  #4177 (permalink)  
 
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Originally Posted by GlobalNav View Post
Beg to differ a bit. DAL A assurance is supposed provide convincing evidence that requirements are validated, and that they are traced to the code. The process for establishing software Design Assurance Level A is painfully extensive in time and resources. It is not an absolute guarantee of no software errors because testing to prove that is not possible. But the process, developed by manufacturers and regulators together has been in use for decades, though not without attempts to push back. Hopefully, energy to resist pushback at the rigor of DAL processes will be renewed as a result of the MAX debacle.
Differ on your "differ".

As you say, DAL-A is fundamentally a SOFTWARE assurance process not a systems design assurance process. For a holistic systems design process with rigour with regard to requirements, one has to look to something like ARP4754 instead. DAL-A starts with the assumption that the systems designer knows what he is doing, and makes sure the software does what he intends. DAl-A requirements validation will typically validate the software requirements against the systems requirements, but go no further into the design. ARP4754 more fundamentally questions the systems design and the assumptions therein.

True, the DAL-A process can sometimes highlight deficiencies in the higher level requirements - muddled thinking there may cause a muddle at the software level, and software design assurance will probably catch that, and if the breadcrumbs are followed (and the software folks will be motivated to do so, to prove it's not their fault!) then the problem may be found. But if the problem is not muddle but rather being wrong, but consistently so, then all DAL-A ultimately proves is that the SW does what it's supposed to.

A lot of what we sometimes lazily call a "software problem" is actually a systems design problem, and would have occurred whether the design were implemented in software, analogue electronics or even hardware. In other words, DAL-A is a necessary but not sufficient condition for correct design execution.
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Old 27th Nov 2019, 21:55
  #4178 (permalink)  
 
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Other than politics (which is obviously huge) I fail to see how the issuance of CofAs or similar has any relationship to design approval and TC issue. It's not even the same groups of people involved or responsible.
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Old 27th Nov 2019, 23:36
  #4179 (permalink)  
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Originally Posted by safetypee View Post
See the report of the 737 NG accident discussed in Flydubai crash at RVI final report out.

Re trim and assumptions about pilot previous experience, previous types and training, Boeing trim design philosophy. [Emphasis Added]
If nothing else see the last page - the final footnote.
I hope that the FAA takes note; if not, then the other regulators; or failing that, operators and pilots.
Absolutely spot on, safetypee. Strongly suggest reading section "2.2. On the peculiarities of the trim (relief) of forces" beginning on page 159.

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Old 28th Nov 2019, 00:07
  #4180 (permalink)  
 
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A further consequence,

Europe demands approval of new Boeing 777X in snub to US regulators

According to the UK Daily Telegraph newspaper. Sorry, can't post the link.
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