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BBC: 737 Max - Still Not Fixed

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BBC: 737 Max - Still Not Fixed

Old 25th Jan 2021, 20:06
  #21 (permalink)  
 
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airsound10976027]Ed Pierson's own website (the paper's author) says this

Sorry - was not my intention to connect the two sentences, rather highlight this whole paragraph for reading.
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Old 25th Jan 2021, 20:33
  #22 (permalink)  

 
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Thank you for clarification, olster and Wakner
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Old 25th Jan 2021, 22:06
  #23 (permalink)  
 
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olster

Sully's CV is a bit more extensive than the Hudson in a BUS, and post that he was given the opportunity to fly the fatal MAX flights in the sim.

We can only assume he was given the same computer based differences training to supplement his original 737 type rating.
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Old 25th Jan 2021, 22:37
  #24 (permalink)  
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Allegedly, those issues with some electrical connectors/connections were found during flight line tests after the MAX left the factory, which I assume were found by internal QA.
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Old 25th Jan 2021, 22:52
  #25 (permalink)  
 
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So, reading that PDF, the MCAS anti stall system was actually doing what it was designed to do? You cant expect a computer program to work as designed with faulty inputs.
The faulty AoA sensors are the real culprits here?
(among other Boeing and Lion Air systemic failures as contributing factors)
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Old 25th Jan 2021, 23:23
  #26 (permalink)  
 
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The case filed in the U.S. Court of Appeals for the District of Columbia Circuit by the Flyers Rights group is docketed as 20-1486. It is an administrative law appeal of FAA's actions, specifically (1) the ungrounding order (I'm omitting the technical name for this order), and (2) the final AD. The underlying administrative rulings are filed, as published in the Federal Register in November. There are a number of procedural briefs and motions already in the appellate court (though without reading these, no further comment here).

The other current action by the Flyers Rights group, continuing in the federal District Court in D.C., is most definitely about the 737 MAX. It is a Freedom of Information Act lawsuit seeking disclosure by FAA of all documents relating to the ungrounding decision which, at the time the case was filed, was far from imminent. (There are cross-motions for summary judgment pending, last time I checked it out on Pacer.)

(And as SLF/attorney, I'm obliged to say, the foregoing attorney-talk is only for the purpose of clarification. Please return to the regularly conducted aviation subject matter thread.)
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Old 26th Jan 2021, 05:52
  #27 (permalink)  
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With all that said, I just returned a Max to service after 11 months in storage.
The aircraft performed well on the test flight returning without a write up.
Up until this stage I not encountered any abnormal electrical or avionics defects after the wiring mods.
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Old 26th Jan 2021, 08:40
  #28 (permalink)  
 
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Bend alot

If Sully was given the same aoa/sirspeed unreliable faults at take off why was he not able to control the aircraft applying memory items for the condition, aircraft still with flaps in take off configuration?
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Old 26th Jan 2021, 09:32
  #29 (permalink)  
 
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I am well aware that Sully is a highly experienced aviator and I completely endorse his incredible handling of the Hudson ditching. A great story mainly because everyone walked away. I am not one of them but certainly colleagues of my vintage can be a bit ahem, sniffy about the never ending Sully worship. Professional jealousy? Perhaps. However, Sully’s background while not particularly or radically different has given him a platform whereby the rest of aviation hangs on every word. He may or may not always be right. Personally I am glad I never had the misfortune to encounter corpulent Canadian geese @ 250 knots. So, to clear up any misunderstanding I have great admiration for the man but he shouldn’t be seen as the oracle without challenge either.
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Old 26th Jan 2021, 12:15
  #30 (permalink)  
 
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What agenda?
What technical innacuracies...?
Very quick to slag off the messenger with no evidence at all...
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Old 26th Jan 2021, 12:34
  #31 (permalink)  
 
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The BBC article is purely factual, reporting the stated concerns of Piersen, Sullenberger and others.

It even takes care to ensure that the judgement of the above re the lifting of the grounding, is described as "too early" (their quotes, not mine) to make it clear that the BBC itself has no view either way.
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Old 26th Jan 2021, 12:47
  #32 (permalink)  
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Couldn't agree more with Nige321 and DaveReid, Olster's views about the BBC are just plain wrong.
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Old 26th Jan 2021, 15:16
  #33 (permalink)  
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One could argue that relying on a single sensor was the original sin. At the time, it was rationalized by the fact the system was slow and not very powerful, so any competent pilot would be able to reconize it and do the runaway trim routine. However, later on, it became much more powerful, which is when they really should have turned to at least two sensors.
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Old 26th Jan 2021, 21:17
  #34 (permalink)  
 
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A man with one watch knows the time. A man with two is never sure.

In such a safety critical system, if you are using multiple sensors, you need an odd number so you can implement a voting system (and hope that there are no common-mode failures that afflict a majority of sensors, or at least engineer away the frequently occurring ones).

And, to be clear, MCAS, even when acting on incorrect information from the AoA sensors, never 'ran away' - it applied a one-shot adjustment which could easily be confused with normal running of STS. Unfortunately, adjusting trim with the pickle switches reset the MCAS trigger, allowing it to add another 'one-shot' adjustment, which if not fully recovered by the trim adjustment switches, added up with previous adjustments until the out-of-trim aerodynamic forces could not be overcome by use of the yoke. As history shows, this behaviour managed to fool several certified competent pilots who had not been fully informed of MCAS behaviour.

A continuous runaway is easy to recognise. An intermittent, slow piling up of small increments of unhelpful trim turns out not to have been obvious, especially in a busy work environment with falsely triggered alarms.
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Old 27th Jan 2021, 01:14
  #35 (permalink)  
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I almost started this thread after reading the BBC 'paper' on my FireFox tab. I didn't because it was filled with a LOT of technical misinformation. In particular, they'd gone to the trouble of nose angle drawings but as was so often the case, got muddled with simple pitch and AoA measurements.

Many of the statements were entirely familiar to me. This is happening at a time when Boeing know they can't have another MCAS induced incident, and now they have an entirely new incident to start a lot of heads nodding. There are some striking similarities, but hopefully not a single causal factor that is the same.

We all know pretty much what happened. What we seem to let slip into dark corners of our memories is that the two vanes failed in disparate ways. To me, this spells a very high bad luck factor in the equation. The second crash might well have been avoided had there been time, or the inclination, to practice such an occurrence after the first crash. However, it's been mooted that the psychology at that moment was probably worsened - now having the awareness of some mystery system causing problems but nowhere near enough thought and training on how to handle it. i.e., the limited knowledge causing a greater feeling of disbelief and resultant stress.

There are many factors that take some of the share of blame, though such arguments become almost philosophic.

IIRC, The first vane had been sourced from FLA from a company that sells and or refurbishes parts. If this is true, a virtually new late-model Boeing had a critical part that was not only not new, but had been serviced (then) by an unknown. Service might mean nothing more than bench testing.
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Old 27th Jan 2021, 07:10
  #36 (permalink)  
 
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Loose rivets

"I almost started this thread after reading the BBC 'paper' on my FireFox tab. I didn't because it was filled with a LOT of technical misinformation. In particular, they'd gone to the trouble of nose angle drawings but as was so often the case, got muddled with simple pitch and AoA measurements."

That's grossly unfair to the BBC.

Firstly, the article simply reports on the judgment of some individuals whose views are widely accepted as relevant. I'd be interested to know which parts qualify as "technical misinformation".

Secondly, the infographic you object to has been kicking around for a couple of years. While it's an oversimplification in that it uses the term "angle" without explaining whether it's AoA or pitch attitude, that's perfectly reasonable given (a) the target audience and (b) the fact that the distinction is arguably irrelevant in the context of the MCAS failures.
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Old 27th Jan 2021, 09:41
  #37 (permalink)  
 
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Hot 'n' High

On the contrary, my apologies. You are correct. The original incarnation of MCAS did trim again after 5 seconds if the triggering conditions continued to apply. Thank youfor the correction.

Details of MCAS here: 737 MAX - MCAS

Interesting to note FAA AD 2020-24-02 issued 2020-11-18 changed the Runaway Stabilizer wording (page 105) to "If uncommanded stabilizer movement occurs continuously or in a manner not appropriate for flight conditions:" (My italics). The document's discussion of MCAS is worth reading.

Last edited by Semreh; 27th Jan 2021 at 09:42. Reason: Add incorrectly deleted thank you
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Old 27th Jan 2021, 12:44
  #38 (permalink)  
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My pleasure Semreh! IIR, it took a while to figure out how it really worked right when all this started so I was more worried that I had lost the plot .... again! Thankfully, in this case, I remembered correctly it seems. And the rest of your Post #34 was spot on!
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Old 27th Jan 2021, 14:22
  #39 (permalink)  
 
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Semreh

AFAIK MCAS would apply up to 5ish degrees of AND trim if it sensed too high AOA. If the out of trim conditions were still there it would not apply trim again until one of several system reset triggers happened. One of those was the pilots using the trim thumb switches. If the pilots hadn’t used the trim after the first MCAS trim application MCAS would not have reactivated. Obviously, that doesn’t make MCAS okay, as we are all trained to fly with the aircraft in trim.
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Old 27th Jan 2021, 16:13
  #40 (permalink)  
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Ah, cheers hans. My memory playing tricks here it seems. I just checked and found this - https://www.faa.gov/foia/electronic_...TS_Summary.pdf. Safety Item #2, page 7. Semreh, my apologies to you - it was my poor memory after all!

As an aside, I don't recall seeing the FAA doc at the link so may be of interest to others - unless it was only me who missed that too!! It seems quite comprehensive (at first glance) covering both tech and administrative issues (such as FAA oversight). Anyway, back under my stone before I confuse people even more.
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