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Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

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Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

Old 25th Mar 2019, 19:54
  #381 (permalink)  
 
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Originally Posted by alf5071h View Post
JPcont,

Your alternative perspective (#370) is interesting. Whilst the basic information (AoA) is the same for both ‘systems’, each system has alternative views and thus use of the information. MCAS receives a valid, but inaccurate value of AoA, the computation and activation works exactly as designed - except that the output is not what the aircraft situation, nor crew requires.
I try to explain why I feel that the MCAS is based on the rotten foundation rather than badly implemented software:
Control law works against some constraints. The simplest one is (set point - measurement)*coefficient. The control law might include integrator or there might be integrator in the system e.g. hydraulic cylinder, jackscrew etc., basically everything that acts the same manner.
When there is two control loops, there is also two active constraints.
Lets think that we have a reservoir (pitch angle) and the level of it is controlled by two independent double acting pumps (elevator, stabilizer) with distinct integrating control laws (PI controller) (jackscrew with MCAS, pilot) with slightly different level set points. The outcome is that integrator values decreases/increases until one pump is at full power (physical constraint). Then other controls the level accurately but the system acts stupidly.
I know that this is artificial and somewhat false example. However, the point is that this type of distinct control laws can have, not so nice, side effects. If the MCAS kicks only ones, pilot can easily out trim it and it has no effect. It seems to be either potential dangerous or ineffective. So, if I were regulator, I would have couple of words about this invention...

Last edited by JPcont; 25th Mar 2019 at 20:24. Reason: Typo: control loop <- actuator, not unambiguous but clear enouhg
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Old 25th Mar 2019, 20:08
  #382 (permalink)  
 
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Originally Posted by EDLB View Post



The usual hero pilot which saves the day.

There is a saying in the flying community, that it is better to have a savvy pilot who decides in poor weather conditions not to take off, than using his superior skills to fly and land in that poor conditions.

I think the same goes for the plane.

Better a plane that not tries to kill you, than one that needs superior pilot skills to stay alive.
Ah! A good saying. It is true. "There are old pilots and there are bold pilots, but there are no old, bold pilots"

But in your scenario, what happens if the weather conditions are forecast to be good and end up being much worse! As often happens. If you as a passenger were to be grounded every time weather was poor (on limits ) at destination to avoid over taxing the piloting skills of the skipper you would not be flying too often. But it would be very safe.

All winter we have pilots landing in very challenging conditions with high winds, cross winds, wet runways, low cloud base and poor visibility MANUALLY. That is because no autopilot yet devised can takeoff or land in such conditions. Max wind for auto land is circa 30 kts and 25xwind - approx. At our local CITY airport the wind is often up to 60-70 with associated poor conditions and yes there are a few go arounds, but generally the airport keeps to schedule. That takes a lot of raw skill.

And flying is very safe already. Let us get this in proportion. 2017 nobody died on a commercial flight on an airline. 3. 5 billion passengers. So this year we have had two Max planes tragically crashing. It will be very sad if they could have been avoided by learning from previous events that happened earlier but were not reported - or even the flight the previous day where it seems the same thing happened but valuable knowledge perhaps withered on the vine. We do not know yet because the investigations are not complete. But, the lessons will be learned, and they will be variety and a mix of system design, human factors and other relevant issues.

As for "heroes". I do not rate the thousands of pilots I have flown alongside over nearly 40 years as "heroes "even though they were extremely competent. Just doing the job they were trained to do. Which is what Sully said. He didn't see himself and a hero - others did that.

Cheers for now and thanks for the diverse opinions which make this forum so lively.


Y
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Old 25th Mar 2019, 23:20
  #383 (permalink)  
 
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MAX - The Fix

From AVwebFlash Responsive (Monday)


Boeing and the FAA say they expect to finish a software and training update for the 737 MAX series of aircraft shortly. Boeing said it’s been working on the update since the crash of a Lion Air MAX 8 last October but the crash of an Ethiopian MAX 8 in early March prompted the issuance of an airworthiness directive requiring Boeing to have a fix by April. “We’ve been working diligently and in close cooperation with the FAA on the software update,” a Boeing spokesman said Saturday in a statement. “We are taking a comprehensive and careful approach to design, develop and test the software that will ultimately lead to certification.”Boeing has now confirmed the software fix will focus on the angle of attack sensors and their interaction with the Maneuvering Characteristics Augmentation System, which autonomously controls the pitch of the horizontal stabilizer if data supplied by an AOA indicates an imminent stall. The MCAS currently gets data from only one of two AOAs. The fix makes both AOAs supply pitch data to the MCAS and a formerly optional disagreement warning on the PFD will become standard equipment. The update will also limit the MCAS’s ability to keep pushing the nose over in defiance of manual inputs from the pilots. The current system will relentlessly pivot the tailfeathers if the angle of attack is reported to be too high. The software update will only allow one jump of the tail position and trigger an alarm that tells the crew the MCAS has been activated. Pilot training will be part of the system updates.
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Old 26th Mar 2019, 00:15
  #384 (permalink)  
 
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I don’t understand why this was not at the very least the way the aircraft and its MCAS system should have been certified from the start.

IMO, it should even go further and once a disagreement occurs in the AOAs, the MCAS system should be disabled.
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Old 26th Mar 2019, 03:36
  #385 (permalink)  
 
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That illustration looks fake. Does the 737 MAX have that type of airspeed display?
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Old 26th Mar 2019, 05:22
  #386 (permalink)  
 
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Not exactly fake; it is an illustration from NG manual showing optional flight instruments display mimicking the classic basic-T layout instead of far more usual PFD with speed and altitude tapes. Dunno if that option is available on MAX or which companies took that option on NG. I haven't flown round dials since 2006. and don't miss them at all.

Originally Posted by Jet Jockey A4 View Post
I don’t understand why this was not at the very least the way the aircraft and its MCAS system should have been certified from the start.
The way it was originally made was cheaper. It's "Unsafe at any speed" all over again.
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Old 26th Mar 2019, 08:55
  #387 (permalink)  

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Add a third AOA with a different software programme for both any you have solved the issue of how to make a poor aircraft design at least flyable.

I can see a lot of companies cancelling their options on this flying pig.
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Old 26th Mar 2019, 09:19
  #388 (permalink)  
 
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Add a third AOA with a different software programme for both any you have solved the issue of how to make a poor aircraft design at least flyable.

I can see a lot of companies cancelling their options on this flying pig.
Over the yeas many, many aircraft had problems, B707, B727, B747, L1011, Dc10, MD11, A320, and others in the Airbus family where all is controlled by Flight Control Laws (some of which many of us consider highly suspect)
As I understand it, the fighters of today are generally unstable, all flown by computers making 100s, if not 1,00s of successful flights every day. It is suggested in the flight where an F18 lost a considerable part of its wing and landed safely this was in a large part due to the fact the computer didn't know part of the wing was missing putting in inputs compensating for the flight parameters it was sensing.

The B737 aircraft as do all others of the Boeing family have an enviable record, similar problems have occured in the past, and no doubt will in the future, a fix will be implemented returning this aircraft to continue operating safely .

I like many others await the outcome of the investigation and report particularly the Flight Standards Department of the airlines concerned; the training, capabilities of the individual flight crew

I suggest before biased, puerile commenting, awaiting the outcome of the investigation and report is is well and truly in order including some professional, qualified, knowledgeable thinking
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Old 26th Mar 2019, 09:25
  #389 (permalink)  
 
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Why not just autodeploy the flaps instead of activating MCAS when needed?
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Old 26th Mar 2019, 09:49
  #390 (permalink)  
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Originally Posted by Less Hair View Post
Why not just autodeploy the flaps instead of activating MCAS when needed?


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Old 26th Mar 2019, 10:16
  #391 (permalink)  
 
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Well, the prototype Victor B2 auto deployed the leading edge flaps and runaway trimmed nose down, following an erroneous pitot input at very high level cruise - causing a dive into the sea with the loss of all on board.
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Old 26th Mar 2019, 10:19
  #392 (permalink)  
 
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During flight simulations recreating the problems with the doomed Lion Air plane, pilots discovered that they had less than 40 seconds to override an automated system on Boeing’s new jets and avert disaster.

https://www.msn.com/en-gb/news/world...ror/ar-BBVetZK
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Old 26th Mar 2019, 14:59
  #393 (permalink)  
 
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I've not been reading every single post so apologies if this has been asked and answered.

Since the introduction of the MAX series, and setting aside the crashes, have their been any reports of incidents that, with hindsight, we can now probably identify as MCAS related?
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Old 26th Mar 2019, 16:04
  #394 (permalink)  
 
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Originally Posted by Hartington View Post
I've not been reading every single post so apologies if this has been asked and answered.

Since the introduction of the MAX series, and setting aside the crashes, have their been any reports of incidents that, with hindsight, we can now probably identify as MCAS related?
Not AFAIK, though there have been a few 'what's it doing now' reports.

Presumably something like runaway trim would be a reportable incident, and apart from Lion Air on the day before the crash, nothing like that has come to light.
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Old 26th Mar 2019, 16:15
  #395 (permalink)  
 
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I find that quite interesting. It's tempting to suggest the system isn't as bad as we keep hearing in the press.
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Old 26th Mar 2019, 17:48
  #396 (permalink)  
 
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Originally Posted by NutLoose View Post
During flight simulations recreating the problems with the doomed Lion Air plane, pilots discovered that they had less than 40 seconds to override an automated system on Boeing’s new jets and avert disaster.

https://www.msn.com/en-gb/news/world...ror/ar-BBVetZK
Note to Moderators: Below is a copy of a post that I made within the Ethiopian accident thread earlier in response a post referencing the same article as that linked above. I know that PPRuNe operating guidelines ask that duplicate posts not be made in multiple threads, but I ask that a minor exception be made here as I feel that the comments below need to be shared with the PPRuNe community members who are following this thread and likely visited the link above. Thanks for your continued moderation of these important discussions.


One of the key elements to the baseline MCAS logic is that it will only put in a single increment of stabilizer motion as long as no pilot trim command is given. This goes in over no more than 10 seconds (less if operating at Mach number greater than 0.4 where MCAS single increment authority is less than 2.5 degrees). The amount of elevator needed to balance one MCAS increment of stabilizer motion will be approximately 5 degrees due to the 2:1 ratio of stabilizer to elevator pitch control power. That amount of elevator can readily be commanded via the column with plenty of additional pitch control authority available to perform any maneuvers needed to maintain desired flight path and speed (if, for instance, climbing with a fixed throttle while varying path to maintain speed). Even in the presence of errant AOA data causing MCAS to activate when actually at AOA well below the intended MCAS activation point, MCAS will not move the stabilizer more than one increment without the crew making a pitch trim input. The only path to compromised pitch control authority via the column is for the crew to make pitch trim inputs but not make sufficient pitch trim inputs to return the stabilizer to the proper trimmed position.

Where this notion of "40 seconds" comes from is a total mystery - particularly when coupled with the statement "... without the crew using the trim switches". The scenario that led to problems after 40 seconds must have included short, ineffective periods of crew pitch trim switch commands that did not establish column force free pitch trim but did enable MCAS to insert another increment of airplane nose down stabilizer.

FCeng84 provides clarity ...
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Old 26th Mar 2019, 18:24
  #397 (permalink)  
 
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"40 seconds without trim switches" statement depends on "which trim switches exactly".
If it is to mean "without touching any trim switches and without touching the mechanical trim wheel", this may well be true.
Otherwise, it is not.
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Old 26th Mar 2019, 18:26
  #398 (permalink)  
 
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Originally Posted by Hartington View Post
I find that quite interesting. It's tempting to suggest the system isn't as bad as we keep hearing in the press.
How is system B supposed to be better than system A, if system B with 100% certainty kills everyone onboard given a certain failure mode. While system A can be combated, logged and reported in 90% of similar cases, and only in 10% of those cases kills people? I am just not sure what you are getting at.
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Old 26th Mar 2019, 18:32
  #399 (permalink)  
 
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Originally Posted by FCeng84 View Post
Where this notion of "40 seconds" comes from is a total mystery - particularly when coupled with the statement "... without the crew using the trim switches". The scenario that led to problems after 40 seconds must have included short, ineffective periods of crew pitch trim switch commands that did not establish column force free pitch trim but did enable MCAS to insert another increment of airplane nose down stabilizer.
Spot on: just a blip on the pitch trim doing nothing more than stopping the uncommanded trim. That is how I read it too. After 5 seconds of wait, MCAS will get back into action. But certainly a highly unrealistic scenario, one would think.
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Old 26th Mar 2019, 18:44
  #400 (permalink)  
 
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Originally Posted by NutLoose View Post
During flight simulations recreating the problems with the doomed Lion Air plane, pilots discovered that they had less than 40 seconds to override an automated system on Boeing’s new jets and avert disaster.

https://www.msn.com/en-gb/news/world...ror/ar-BBVetZK
Ok, so we finally have some "we tried this in the sim and...", albeit sim and scenario were under Boeing control (but apparently not under Boeing NDA...). Apparently these were first-world pilots, forewarned, MCAS expected, and obviously with knowledge of the potential implications (smoking crater / large splash).

Things that jumped out at me (my emphasis):

Those involved in the testing hadn’t fully understood just how powerful the system was until they flew the plane on a 737 Max simulator, according to the two people.
Under conditions similar to the Lion Air flight, three engagements over just 40 seconds, including pauses, would send the plane into an unrecoverable dive
MCAS was surprisingly powerful once tested in the simulator
So, 40 seconds to unrecoverable dive due to a system that the pilot does not know about (before), or (now) even with knowledge will not appreciate how powerful it is until they have experienced it in the sim. Which they won't have, because there are no sims outside Boeing because there don't need to be because no max-specific sim training is needed and an NG sim doesn't have MCAS. So the first time a line pilot encounters this "surprisingly powerful" control law is, inevitably, in the air with a plane load of pax behind them (WTF are sims for?), and they have 40s to figure it out - and it is not clear at what altitude that is...

Before the Lion Air crash, Boeing and regulators agreed that pilots didn’t need to be alerted to the new system, and training was minimal.
So, that was before Lion Air. Now, having established in tests with line pilots (presumably not done before?) that the "surprisingly powerful" MCAS cannot be appreciated until experienced in the sim (or presumably in the a/c, however briefly), the fix is, drum roll..............:

Pilots will be required to complete a training on the updated system on their iPads.
I really don't know what to say.

I'm sure plaintiffs lawyers will though - they're going to have a ****ing field day in court with this.
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