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Off Topic => General Discussion => Topic started by: Glom on April 17, 2019, 05:54:34 AM

Title: Boeing 737 MAX
Post by: Glom on April 17, 2019, 05:54:34 AM
I'm surprised this hasn't been raised here already given we have knowledgeable people here.

I would be very sceptical if the outcome wasn't significantly more training on the proper how to deal with proper failures that might arise. That is after all the whole point of training. If the aircraft always worked fine, you'd only need a man and a dog.

That the MCAS only relied on one AoA sensor seems rather egregious. Someone didn't do a proper hazard analysis there.

Is there any independent test and evaluation done during the certification process?
Title: Re: Boeing 737 MAX
Post by: ka9q on April 17, 2019, 06:11:33 AM
I think Jay works for Boeing so he's probably limited in what he can say publicly.

I know a fair bit about aviation but I'm not a pilot and I'm sure I have huge gaps in my knowledge.

Some friends who are very experienced commercial pilots say that they're trained to immediately disconnect the auto-trim system in the event of any kind of pitch control instability, and so they blame the pilots in both accidents for not doing that regardless of how the plane was designed. But I don't think they have specific knowledge about the 737 MAX.

Title: Re: Boeing 737 MAX
Post by: Glom on April 17, 2019, 07:52:02 AM
Well if Jay can't talk about it, might as well forget it.

Delete thread please.
Title: Re: Boeing 737 MAX
Post by: Peter B on April 17, 2019, 09:23:20 AM
Well if Jay can't talk about it, might as well forget it.

Delete thread please.

?? Why?

Can't we have a more general discussion about aircraft safety?

I mean, for example, perfectly good pilots flying perfectly good planes can still crash them for a variety of reasons: pilot fatigue, unexpected weather, cargo fire, missile strike, incorrect trim, distraction, the list goes on. Sure, the immediate cause of many crashes may be "pilot error", but it's worth digging further to see why the pilot error occurred. In many cases I get the impression that there were other links in the chain before the pilot's error caused the crash.

In the case of the 737-MAX crashes it'll be interesting to see (a) how easy it was for appropriately trained pilots to solve the problem of the system misbehaving, (b) how closely to "appropriately trained" these pilots were, and (c) whose responsibility it was to determine that status.
Title: Re: Boeing 737 MAX
Post by: Glom on April 17, 2019, 10:21:44 AM



Can't we have a more general discussion about aircraft safety?

Never!
Title: Re: Boeing 737 MAX
Post by: Allan F on April 17, 2019, 11:20:05 AM


How to stop the runaway stabilizer.
Title: Re: Boeing 737 MAX
Post by: jfb on April 17, 2019, 11:36:19 AM
I've been following a number of discussions on the MAX, and as is often the case with these sorts of things, the problems are much deeper and more complex than deciding to use a single sensor input for this system. It's not clear that redundant inputs would help much.

There were a host of business decisions that drove the technical decisions, and some of the technical decisions were made without adequate oversight.  Boeing needed a new plane to compete with Airbus in some markets, a clean-sheet design would take too long/too much money, and the 737 was grandfathered out of some regulations, so that was the less expensive and faster option.  But the 737 had to be hacked in a way that fundamentally changed its handling at high AoA and made it prone to stall, which drove the development of MCAS.  During development of MCAS it was given more control authority than originally spec'd. 

There was oversight failure on the part of the FAA in that they allowed Boeing to self-certify the new system, and there were more business decisions that minimized the level of training required for the new system. 

What's especially damning is that after the Lion Air crash, Boeing issued directions on how to deal with an MCAS failure.  The Ethiopian pilots followed that procedure and disabled MCAS, but by that point were in an unrecoverable dive (it looks like the re-enabled MCAS because they could not manually adjust the trim). 

There's some (some informed, some not) speculation that, because of the larger and more powerful engines (and the larger lift area of the engine nacelles), the MAX is inherently unstable in flight and prone to pitching up and stalling. 
Title: Re: Boeing 737 MAX
Post by: mako88sb on April 17, 2019, 11:54:22 AM
I found this fellas videos during the Oroville Dam situation and he 's also a commercial pilot that does a great job explaining aviation related topics. Here's his Ethiopian Air preliminary report discussion that includes some of the training pilots go through in a situation similar to this albeit this was for a non-MCAS 737.
https://www.youtube.com/watch?v=HBqDcUqJ5_Q (https://www.youtube.com/watch?v=HBqDcUqJ5_Q)
Title: Re: Boeing 737 MAX
Post by: Allan F on April 17, 2019, 12:01:34 PM
Yes, the offset thrust will make a stall more severe, if the pilot just jams on the throttles. They have to get the nose down, and then gradually increase the thrust, as airspeed climbs. Which will make a low-altitude stall really dangerous.
Title: Re: Boeing 737 MAX
Post by: Echnaton on April 18, 2019, 07:01:35 PM
The web site Aviation Herald has the best coverage I've seen.  The problem is that is is heavily jargon laden and uses abbreviations without explanations. This makes it dificult to understand what they say. 

https://avherald.com/h?article=4c534c4a/0045&opt=0

What I have gleaned from reports on Ethiopian and LionAir crashes, is that in both cases, false indications recorded in the black box from the Angle of Attack vane. This activated the MCAS which contributed to the crashes.  In both cases, there was confusion with the pilots about the cause of the problem and insufficient or untimely reactions to the situation. Ethiopian apparently went into continuous stick shaker on the captain's side which was as a major distraction. 

It remains to be seen if this is considered to be a training problem or design issue that puts the pilots into a overwork situation at a low altitude with insufficient time to comprehend and react.  I speculate, for no really good reason, that the angle of attack system and how the data is used will be where the change will come.

Whatever it turns out to be, you can be sure the finger pointing will continue for years. 
Title: Re: Boeing 737 MAX
Post by: Peter B on April 21, 2019, 02:00:07 AM
https://www.abc.net.au/news/2019-04-21/inside-boeings-billion-dollar-bungle-737-max/10944936

This is an interesting article that goes right back to basics - why Boeing designed the 737-MAX in the first place. It also discusses the problem of the FAA's oversight of the plane's certification - specifically, does any government organisation have the expertise to second-guess an aircraft of the complexity of the 737-MAX?
Title: Re: Boeing 737 MAX
Post by: smartcooky on April 21, 2019, 09:08:26 AM
In simple terms...

► The original 737 airframe was designed to allow a set of folding stairs to be used to disembark passengers, and to allow luggage handlers to stow luggage from tarmac level. This was in the 1960's, before passenger air bridges and tarmac luggage conveyors.

► This meant that the original airframe was very low to the ground. That suited the Pratt & Whitney JT8D engine design just fine...

(https://upload.wikimedia.org/wikipedia/commons/thumb/d/d5/United_Airlines_Boeing_737-222_Marmet.jpg/330px-United_Airlines_Boeing_737-222_Marmet.jpg)

...they were a low bypass turbofan, so they were narrow in profile and left plenty of ground clearance.

► However as engine design improved to become more powerful, and more efficient, the bypass ratio increased. By the mid 1980s, 737s were using the CFM56-3B-1 high-bypass turbofan, consequence of that is the engine had a much larger diameter. Ground clearance now became an issue, so that meant the engines had to be moved forward and upwards.

(https://upload.wikimedia.org/wikipedia/commons/thumb/6/63/Lufthansa-1.jpg/330px-Lufthansa-1.jpg)
 
► This resulted in a change to the flight characteristics. With the engine further forward, the thrust vector was also further forward, and with a more powerful engine, the aircraft had a tendency to pitch nose-up at high power settings such as TOGA (Take Off - Go Around) and could result in a stall.

► Boeing tried to get around this problem by using software in the pitch trim section of the flight control systems to autonomously push the nose of the aircraft down.

► As engines continue to become more powerful and more fuel efficient, so they got pushed even further forward, exacerbating the pitch up problem even more, so finally we arrive at the 737 MAX 8, fitted with CFM International LEAP-1B engines - higher bypass, wider profile.

(https://upload.wikimedia.org/wikipedia/commons/thumb/4/40/WS_YYC_737_MAX_1.jpg/330px-WS_YYC_737_MAX_1.jpg)

I have issues with any "autonomous" stall system - something that actively takes control away from the pilot, and keeps it away from him. IMO (and this is only the opinion of a retired aeronautical engineer) the idea of a software fix to compensate for bad flight characteristics was a blunder of monumental proportions. There should be NO system on an aircraft capable of autonomously pitching the nose down during take-off at only 1,800 feet AGL. Under those circumstances, its amazing that the flight even lasted as long as six minutes.
 
If MCAS can predict the onset of a potential stall, and take action, why not instead, just have a warning bell/horn and/or a Bitchin' Betty - "Warning: Stall Imminent!" I learned to fly in a Cherokee 140. It had a red stall warning light and a "whiny" horn that would sometimes go off intermittently about 50 to 300 feet AGL on climb-out, particularly in blustery conditions. The response was usually to just ease the yoke forwards a little to slightly lower the rate of climb. If it had a system that pitched the nose down autonomously when it detected a potential stall, I don't think I would be here to post this!
Title: Re: Boeing 737 MAX
Post by: gwiz on April 22, 2019, 06:37:32 AM
This from a former colleague of mine in the industry who is also a pilot in his spare time:
Quote
On [one of our aircraft] Autopilot, we did Failure Mode Effects Analysis, to identify what any conceivable failure of sensors, actuators, or the electronics in between could do. The most dangerous type of failures were the insidious ones that you might be hardly aware of in the cockpit. I'm not sure if I am right about this, but...it appears that the 737 MAX stall prevention algorithm took data from a single AoA sensor, and used tailplane (not elevator) trim to decrease the angle of attack. On [our aircraft], you had an obvious cue in the cockpit if the trim operated, because it moved the stick forward or backward. The stick was spring loaded so that it would move to the trim position unless the pilot put force on it... If I understand it correctly, the yoke in the cockpit of the 737 MAX does not move when the tailplane trim operates - I think it only operates the elevator. However, the phantom detection of stall due to a faulty AoA sensor (or wiring or interface or whatever) causes the stick shaker to operate. That is known to have happened on the Lion Air MAX that crashed. As a pilot, you are trained to respond to the stick shaker by pushing the nose down. The pilot's manual specifically did not mention the new stall prevention system in the MAX aircraft... What I don't know is what cue the pilots have that the tailplane trim is operating to pitch the aircraft down. Boeing assert that there is an existing procedure to switch the tailplane trim off, and that the pilots on the Lion Air flight prior to the one that crashed, followed that procedure... So faced with a very prominent cue that the aircraft is about to stall, how prominent is the evidence that you have a trim runaway?
Title: Re: Boeing 737 MAX
Post by: Echnaton on April 22, 2019, 07:49:49 AM
This from a former colleague of mine in the industry who is also a pilot in his spare time:
Quote
On [our aircraft], you had an obvious cue in the cockpit if the trim operated, because it moved the stick forward or backward. The stick was spring loaded so that it would move to the trim position unless the pilot put force on it... If I understand it correctly, the yoke in the cockpit of the 737 MAX does not move when the tailplane trim operates - I think it only operates the elevator....hat I don't know is what cue the pilots have that the tailplane trim is operating to pitch the aircraft down.

There are a few things where this needs some more information.

On the 737 there is a noticeable and obvious indication of the operation of the automatic trim system on all 737s.  It is the motion of wheels on either side of the center instrument console. The wheels are connected to the jack screw by wires and allow for manual operation of the trim. 

In my understanding, most or all airliners have a trim system that automatically adjusts the stabilizer, and have for decades. The MCAS is a new implementation law on the 737 for a specific circumstance beyond normal flight trim. It was developed for use on a military aircraft and has been used successfully there. One significant difference is the military version took inputs from both AoA vanes.  Faulty inputs to the flight computer from the AoA systems seems to be a significant contributor to the MCAS activation, thus the Maxs misbehavior that lead to both crashes. The faulty operation forces an extremely high workload on the pilots that they are not properly trained for.  Resulting in some guessing at at time when there is little margin for recovery from the wrong guess.

The Mentour Pilot YouTube channel has a number of videos on this topic.  The channel  owner is a 737NG captain and has discussed the 737 trim operations in detail.

https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow/videos   (https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow/videos)
Title: Re: Boeing 737 MAX
Post by: Peter B on April 22, 2019, 08:17:07 AM
So if the Angle of Attack sensor is providing dodgy data, what can cause that? How does it obtain its data?

I remember from one of those Air Crash Investigator TV shows how a plane crashed because a wasp nest blocked a pitot tube, causing it to give faulty data that confused the pilots.

And the weather at the time of the two crashes doesn't seem to have been particularly extreme - not too hot or cold, fairly humid in Indonesia, moderate humidity in Ethiopia. Both planes were fairly new, so it seems unlikely that the climate extremes which do occur in both locales would've had enough time to work any mischief.

Maybe we'll just have to wait for the experts to finish poring over the data, and hope it isn't a long-delayed solution like the 737 rudder reversals...
Title: Re: Boeing 737 MAX
Post by: Echnaton on April 22, 2019, 09:33:36 AM
So if the Angle of Attack sensor is providing dodgy data, what can cause that? How does it obtain its data?



From what I have seen on Mentour, The AoA system consists of two independent vanes that point into the airflow around the nose of the plane. One on either side of the aircraft.  The fault can be in the physical vane itself, the way the vane's physical position is translated into data, or in the transmission of that data to the flight control computer.

Crucial to the problem is that MCAS uses the pilots AoA vane only.  The Lion Air plane that crashed had a fault in the AoA system that was noticed the day before, resulting in some maintenance work.  Its significance to MCAS was not understood and, IIFC, the flight crew on the fatal flight were not notified of the fault.

On the Ethiopian plane the faulty data caused the nearly continuous activation the captain's stick shaker. While the FOs column was not affected. This caused significant pilot confusion.  According to the Aviation Herald, Ethiopian Airlines had not yet update their flight manual with the  Emergency Airworthiness Directive Boeing issued in November, after the Lion Air crash. Information that if absorbed by the crew might have prevented the crash.

So like most accidents, both were a combination of a many things related to a new design. I interpret the preliminary information to be that the MCAS was not robust enough for its implementation at a crucial time in the flight without significantly more training than was suggested by Boeing or offered by the airlines to the pilots and maintenance crews. MCAS may not have been robust enough period. The vane appears to be the weakest point. But further investigations will undoubtedly reveal more.

Title: Re: Boeing 737 MAX
Post by: Obviousman on April 22, 2019, 05:11:32 PM
It's funny, in some dark way:

There were always discussions regarding the 'automation' / AFCS approach differences between Airbus and Boeing. It was said that on a Boeing, the pilot outranks the autopilot.

And then we have the Air France 447 incident - which involved an Airbus A330 - whose contributing factors were erroneous flight condition inputs (iced pitot tube, IIRC) and the pilots forced a stall condition when they should have been lowering the nose.
Title: Re: Boeing 737 MAX
Post by: smartcooky on April 22, 2019, 06:43:58 PM
On the 737 there is a noticeable and obvious indication of the operation of the automatic trim system on all 737s.  It is the motion of wheels on either side of the center instrument console. The wheels are connected to the jack screw by wires and allow for manual operation of the trim. 

In my understanding, most or all airliners have a trim system that automatically adjusts the stabilizer, and have for decades. The MCAS is a new implementation law on the 737 for a specific circumstance beyond normal flight trim. It was developed for use on a military aircraft and has been used successfully there. One significant difference is the military version took inputs from both AoA vanes.  Faulty inputs to the flight computer from the AoA systems seems to be a significant contributor to the MCAS activation, thus the Maxs misbehavior that lead to both crashes. The faulty operation forces an extremely high workload on the pilots that they are not properly trained for.  Resulting in some guessing at at time when there is little margin for recovery from the wrong guess.

The Mentour Pilot YouTube channel has a number of videos on this topic.  The channel  owner is a 737NG captain and has discussed the 737 trim operations in detail.

https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow/videos   (https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow/videos)


There is a very good one where he does a simulation of runaway trim, and it is clearly evident that the pilots' physical workloads are quite high.

The trim wheel has to be operated by pulling out a small handle and manually cranking the wheel backwards. That wheel is in an awkward position and is difficult to operate for one pilot. AIUI, this is because they are manually cranking the trim jackscrew; a difficult enough thing to do on the ground, made much harder by the airflow over the horizontal stabilizer. The other pilot's handle is 180° out on the wheel, and its only when both pilots are cranking it that it becomes easy to do. 

If the trim stab switches have been turned off after they have run into trouble, the trim jackscrew stops in the position it is in at that moment. If that is nose down at low altitude then we have a situation were both pilots have one hand in use to crank the trim, one pilot with his other hand on the yoke, leaving one pilot's hand to operating anything else that needs doing. All this is happening with the aircraft nose down falling out of the sky at only a couple of thousand feet above the ground... not good.

Title: Re: Boeing 737 MAX
Post by: smartcooky on April 22, 2019, 08:16:45 PM
It's funny, in some dark way:

There were always discussions regarding the 'automation' / AFCS approach differences between Airbus and Boeing. It was said that on a Boeing, the pilot outranks the autopilot.

And then we have the Air France 447 incident - which involved an Airbus A330 - whose contributing factors were erroneous flight condition inputs (iced pitot tube, IIRC) and the pilots forced a stall condition when they should have been lowering the nose.


One pilot was forcing a stall condition, but because the control system was a side-stick, in a dark cockpit, with no force feedback to the other side-stick, the other pilot didn't realize the first pilot was pulling back.

Sully reckons that accident would never have happened on a Boeing because both yokes move when either pilot operates his. The yoke on your side pinning you in your seat is a pretty big clue tat the other pilot is pulling back as hard as he can.
Title: Re: Boeing 737 MAX
Post by: Bop on April 26, 2019, 12:43:41 PM
So if the Angle of Attack sensor is providing dodgy data, what can cause that? How does it obtain its data?



From what I have seen on Mentour, The AoA system consists of two independent vanes that point into the airflow around the nose of the plane. One on either side of the aircraft.  The fault can be in the physical vane itself, the way the vane's physical position is translated into data, or in the transmission of that data to the flight control computer.

Crucial to the problem is that MCAS uses the pilots AoA vane only.  The Lion Air plane that crashed had a fault in the AoA system that was noticed the day before, resulting in some maintenance work.  Its significance to MCAS was not understood and, IIFC, the flight crew on the fatal flight were not notified of the fault.

On the Ethiopian plane the faulty data caused the nearly continuous activation the captain's stick shaker. While the FOs column was not affected. This caused significant pilot confusion.  According to the Aviation Herald, Ethiopian Airlines had not yet update their flight manual with the  Emergency Airworthiness Directive Boeing issued in November, after the Lion Air crash. Information that if absorbed by the crew might have prevented the crash.

So like most accidents, both were a combination of a many things related to a new design. I interpret the preliminary information to be that the MCAS was not robust enough for its implementation at a crucial time in the flight without significantly more training than was suggested by Boeing or offered by the airlines to the pilots and maintenance crews. MCAS may not have been robust enough period. The vane appears to be the weakest point. But further investigations will undoubtedly reveal more.
From the data recovered it looks like ET302 may have had a vane detachment (they have an internal counterweight that would swing it to maximum deflection, and there was a brief period where it 'almost' returned to normal readings, this was at a period of extreme negative G forces, suggesting that the reading was from the counterweight 'floating'- of note was that at that same instant the sensor reading failed to full deflection,the heater sensor failed as well.....

Another thing that may have led to the crews confusion is that although the captains shaker only was going off, apparently the yokes are connected, so the FO yoke may have had some stickshaker bleeding through

A third point of confusion was the airlines requirements for 'no additional training' required for the MAX, but one major difference was the trim yoke switches, in the earlier 737 variants, you could disable all AP functions with one, the other disabled AP control over the stabilizers- BUT allowed electrical trim to continue working. The MAX changed this to disable all AP with both switches- this may explain why the MCAS  was turned back on again a couple of times late in the flight- at the speed they were going by that stage, it is literally impossible to trim out the MCAS input to the stabilizers by hand with the trim wheels, and they tried to activate the electrical trim motors as per previous models, only for this to not work as expected (a change which was only noted in the MAX manuals with a 'throwaway line' that the function of the yoke switches had been renamed- nothing said about the fact they had been rewired in a different configuration- no training need then!!!)

Worse when they finally reactivated what they thought was the elec trim circuits (or possibly they deliberately reactivated the entire system- they didn't much to lose by that stage) , it also reactivated the faulty MCAS- but this wouldn't have apparent at first, as it was still held off until they stopped trying to retrim, it waits 5 seconds and then starts winding even MORE trim on...

Apparently the 'official' way to get out of the overloaded trim is to decrease thrust and nose down, while winding off (anything up to a hundred turns!!!!)- not really an option when you are only 1000ft off the ground... (and some media reports have been misinterpreting their altitude to boot which doesn't help) yes they did get to nearly 9000ft before it all went pear shaped, giving the impression they had climbed a bit, what many don't seem to know is that Bole is 7625ft above sea level and where they crashed is higher again- so they were never far off the ground at all...


Of course none of this is guaranteed, but there are some hints from the released data so far that points to this possibly being the issue (I am shamelessly passing on some pretty smart peoples ideas here, I only fly private GA, but a mate flies 737NG's and there is a lot of discussion of the MAX issue obviously)

 Be interesting to see what comes out officially in the end...

Title: Re: Boeing 737 MAX
Post by: Bop on April 27, 2019, 06:40:20 AM
(https://i.postimg.cc/wMLqkk2j/giphy.gif)

This was taken from a video on a sim, showing the difficulty they would have had at that speed retrimming. remembering that they would have had to wind off tens of turns at the minimum...

This is a transcript of the now deleted video

Quote
The original sim session transcript [C=CAPT; F=FO]:
C: We have an IAS disagree.
C: So, IAS disagree memory items.
F: Autopilot if engaged, disengage.
C: Disengaged!
F: Autothrottle if engaged, disengage.
C: Disengaged!
F: Flight directors - Both up
F: With flaps up established a flight path 4 degrees and 75% N1.
C: So, 75% N1.
F: We have 77, 76,...
C: A little bit less...
F: And, there you go.
C: 4 degrees.
F: 4 degrees.

C: So I am trying to establish this now.
F: Check!
F: We are descending...?
F: We probably... Are you feeling troubled with...
F :Any trouble with the flight control?
C: Yeah, I'm trying to trim it but...
C: It continues to trim against me when I'm trimming
C: So state the malfunction, please.
F: Yeah, this doesn't look right. Looks like uh...
F: How do you feel the stabilizer, the trim system?
F: Can you control it?
C: I'm trimming it. It is responding but...
F: It's a runaway stabilizer, if you agree?
C: For every time that I trim backward, it keeps trimming forward.
F: It's trimming forward. Yeah, it's runaway stabilizer.
C: So, runaway stabilizer memory items...
C: And i'm trying to keep this thing at 4 degrees.
F: Control column, hold firmly.
C: I am... [CAPT is holding the yoke firmly with both hands]
F: Autopilot - if engaged, disengage.
C: It's disengaged.
F: Autothrottle - if engaged, disengage.
C: It's..., if you can disengage it for me, make sure that it's disengaged.
F: It's disengaged.
F: And, do you feel that the failure stop?
F: Negative?
C: No, it's still moving.
F: Stab trim cutoff switches to cutoff.
F: OK. It stops. It looks like it stops.
C: You can see now I'm using almost full back pressure here.
F: Exactly.
C: How many degrees nose down?
F: We have 4 units nose down now
C: 4 units nose down?
F: Yup.
C: OK, I'm struggling.
C: I'm actually using almost my full force to keep the aircraft level here.
F: Do you want me to help you?
C: What I would like to do.
C: Just for the sake of exercise, can you trim this forward? [to simulate MCAS trim AND]
C: See if we can reach even zero nose down.
C: And see if I can even hold it.

[FO is trying to crank the trim wheel to reach zero nose down, simulating MCAS AND]

C: So, now we are doing this just as an exercise!
C: Do not try this at home.
C: This...
C: We are at 300 knots now.
F: I'm fighting.
C: I'm sttrugling to to keep this aircraft flying.
F: My god! [FO surprised at how hard it is to trim further nose down]
C: Yeah, the thing is with higher speed the force on the stabilizer will be higher and higher as well.
C: So it becomes almost impossible to move it.
C: So we are now at about 3 degrees.
F: Yup. [FO still tries to continue trimming nose down, the wheels is so difficult to spin]
C: We're still about 3 degrees away from full nose down trim.
C: And I am using everything that I have. [CAPT still holding on to his yoke with both hands]
F: My God ! [the trim wheel barely move for the down trim]
C: This is realistic guys.
C: This is how much of effort it would take to trim the stabilizer at this kind of speed.
C: Umph... [Capt is still trying to hold on to his yoke with his hands]
C: I'm just in control of it, though. But it's getting harder and harder.
C: And remember we're still 2.5 degrees away...
F: My God! [FO still struggles to spin the refused-to-be-spun trim wheel]
C: It's not possible, is it?
C: All right, we stop at that.

C: The reason that we have to try...
C: The reason we have to trim this manually is because the normal trim system wouldn't do this, OK.
C: It would require manual trim to get it away from this.
C: That's fine.
C: Trim it backward. [This time to illustrate the effort to trim the nose back up after "MCAS" brought the AC further nose down]
C: Trim it backward as you can.
F: Oh my God! I couldn't... [FO can't spin the wheel to trim up]
C: OK.
C: Eh...
C: Juan, press the red button! [CAPT called the sim operator...]
C: Press the red button now. [to stop the sim session]
C: This is at 340 knots.
C: And the trim is at...It's still at almost 2.5 degrees.
F: Yeah, 2.5 degrees.
Title: Re: Boeing 737 MAX
Post by: Echnaton on April 27, 2019, 04:52:15 PM
A bit of news from Aviation Herald

Quote
On Apr 27th 2019 it became known, that four independent whistleblowers, current and former Boeing employees, had called the FAA hotline for whistleblowers regarding aviation safety concerns on Apr 5th 2019. The concerns reported were wiring damage to the AoA related wiring as result of foreign object damage as well as concerns with the TRIM CUTOUT switches. The FAA believes these reports may open completely new investigative angles into the causes of the two crashes in Indonesia and Ethiopia.

https://avherald.com/h?article=4c534c4a/0045&opt=0

Faults in the AoA vane continue to be prominent in the information coming out. 
Title: Re: Boeing 737 MAX
Post by: Bop on April 28, 2019, 04:00:43 AM
Ouchies, that's exactly whats been floating around the pilotsphere for probably a week or more...
Title: Re: Boeing 737 MAX
Post by: smartcooky on April 28, 2019, 03:52:40 PM
Bop

I've nicked your post to repost at ISF in the thread there. I hope you're OK with that.
Title: Re: Boeing 737 MAX
Post by: Bop on April 29, 2019, 06:26:02 AM
Thats ok, I pinched bits myself
(waves hi over there- waves vaguely)
Title: Re: Boeing 737 MAX
Post by: smartcooky on April 29, 2019, 07:38:17 AM
Thats ok, I pinched bits myself
(waves hi over there- waves vaguely)

Aha.. the penny drops... Bop = Dabop
Title: Re: Boeing 737 MAX
Post by: Bop on May 05, 2019, 11:25:09 PM
There's been a lot of criticism of both the FAA and Boeing about the way safety testing was done, there was an article in the Seattle Times that not  only suggests that major corners were indeed being cut, but there is a noxious attitude in Boeing that led to the MAX incidents being almost inevitable....

The chances of other Aviation regulators accepting any re-certification from the FAA as being above board just went through the floor....

https://www.seattletimes.com/business/boeing-aerospace/engineers-say-boeing-pushed-to-limit-safety-testing-in-race-to-certify-planes-including-737-max/ (https://www.seattletimes.com/business/boeing-aerospace/engineers-say-boeing-pushed-to-limit-safety-testing-in-race-to-certify-planes-including-737-max/)

Quote
In 2016, as Boeing raced to get the 737 MAX certified by the Federal Aviation Administration (FAA), a senior company engineer whose job was to act on behalf of the FAA balked at Boeing management demands for less stringent testing of the fire-suppression system around the jet’s new LEAP engines.

That June he convened a meeting of all the certification engineers in his unit, who collectively agreed with his assessment. Management initially rejected their position, and only after another senior engineer from outside the MAX program intervened did managers finally agree to beef up the testing to a level the engineer could accept, according to two people familiar with the matter.

But his insistence on a higher level of safety scrutiny cost Boeing time and money.

Less than a month after his peers had backed him, Boeing abruptly removed him from the program even before conducting the testing he’d advocated.

The episode underscores what The Seattle Times found after a review of documents and interviews with more than a dozen current and former Boeing engineers who have been involved in airplane certification in recent years, including on the 737 MAX: Many engineers, employed by Boeing while officially designated to be the FAA’s eyes and ears, faced heavy pressure from Boeing managers to limit safety analysis and testing so the company could meet its schedule and keep down costs.

That pressure increased when the FAA stopped dealing directly with those designated employees — called “Authorized Representatives” or ARs — and let Boeing managers determine what was presented to the regulatory agency.

“The ARs have nobody supporting them. Nobody has their backs,” said one former Authorized Representative who worked on the 737 MAX and who provided details of the engineer’s removal from the program. “The system is absolutely broken.”

FAA-designated oversight engineers are supposed to enjoy protection from management pressure. Removing one who proves a stickler for safety regulations will inevitably produce a chilling effect on others who see the consequences of being too rigid about safety concerns, said John Goglia, former member of the National Transportation Safety Board (NTSB).

“It negates the whole system,” said Goglia. “The FAA should have come down on that really hard.”

Following two deadly 737 MAX crashes off the coast of Indonesia and in Ethiopia that killed 346 people, and the subsequent grounding of the airplane worldwide, the certification of the jet has come under intense scrutiny, including a slew of lawsuits, congressional hearings and a criminal investigation.

None of the people interviewed were involved in certifying the Maneuvering Characteristics Augmentation System, the flight-control software implicated in the two crashes. But one area of scrutiny is sure to be the delegated system under which Boeing employees, paid by the company but acting as FAA designees, did the detailed certification work. It may slow down plans by the FAA and Boeing for a future certification regimen that would further erode the FAA’s oversight.

Boeing, in a statement responding to Seattle Times questions, said that FAA procedures, including regular, FAA-mandated training, “ensure Boeing employees serving in this capacity act independently on behalf of the FAA.”

It added that “there are processes in place to carefully evaluate any concerns regarding the AR’s ability to act independently.” The company declined to comment on individual cases cited in this story.

Yet as the FAA has increasingly delegated certification tasks to Boeing itself, it’s also made changes to the reporting structure that leave its designees to fend for themselves inside the company.

While a few former employees involved in certifications said they handled the pressure as a regular part of the job, others described the work environment as hostile, focused on achieving FAA approval within schedule and cost targets. Some of those workers spoke on condition of anonymity to protect professional relationships or for fear of retribution.
This echoes the findings of a Seattle Times investigation in March of what happened on the FAA side of the MAX certification. Within the FAA, its safety engineers worked under constant pressure from their managers to delegate more and more work to Boeing itself, and to speedily approve the safety assessments the Boeing designees came up with.

On the Boeing side of that process, the removal of the senior engineer acting as an FAA Authorized Rep was an extreme example that highlights the broader negative impact of two changes: The FAA no longer appoints its own ARs, instead leaving that to Boeing. And these designees now rarely interact with the FAA directly, according to former Boeing ARs interviewed by The Times.

They said these changes have stripped them of protection and given managers more opportunity to push for shortcuts.

In a statement, the FAA said it oversees the Boeing certification system “to ensure procedures are followed.” The agency also said it has “received no whistleblower complaints or any other reports … alleging pressure to speed up 737 MAX certification.”

Boeing managers are supposed to undergo “undue pressure” training to ensure that they aren’t crossing boundaries with the FAA’s representatives. And some ARs said that, despite some tensions, their managers were respectful of the role.

Fred Stong, an AR who worked on electrical systems at Boeing, said his experience was that everyone works through differences to reach common ground. He said he was always assertive in his role and didn’t face any problems.

Ouchies
I can't see any possible issues with allowing Boeing to basically control the engineers appointed to keep safety up with economics being the secondary consideration, nope, that could NEVER end in tears....
/sarcasm...
Title: Re: Boeing 737 MAX
Post by: Glom on May 07, 2019, 04:10:56 AM
I'm hearing talk about the flight crew retracting the flaps in response to potential overspeed and this is contrary to procedures because you should remove power first to arrest speed increase.

But even so, how did this contribute to the crash? They had plenty of energy, the aircraft would have still flown clean.
Title: Re: Boeing 737 MAX
Post by: smartcooky on May 07, 2019, 08:41:55 AM
I'm hearing talk about the flight crew retracting the flaps in response to potential overspeed and this is contrary to procedures because you should remove power first to arrest speed increase.

But even so, how did this contribute to the crash? They had plenty of energy, the aircraft would have still flown clean.

It looks like they had the power setting at 94% for take-off, and it remained there for the entire duration of the flight until it crashed. That would be very usual, it means means the aircraft was traveling much faster than it ought to have been... its no wonder they had the over-speed clacker going off. High speeds like that make it very difficult to manually trim using the trim-wheels because of the excessive airflow over the horizontal stabilizers.

According to the report I read, the flaps were extended 0.019° - an insignificant amount.
Title: Re: Boeing 737 MAX
Post by: smartcooky on May 07, 2019, 08:33:14 PM
https://www.theverge.com/2019/5/2/18518176/boeing-737-max-crash-problems-human-error-mcas-faa

Longish article - well worth the time to read for aviation tech enthusiasts
Title: Re: Boeing 737 MAX
Post by: Glom on May 08, 2019, 03:50:25 AM
It seems that it was the retraction of the flaps that caused MCAS to engage, so those who wish to blame the pilots are saying that had they followed the procedure and not retracted the flaps, they wouldn't have died.

The problem is that Boeing still designed a plane that actively tries to kill you if you retract the flaps.

You shouldn't retract the flaps with a stick shaker because a stick shaker is supposed to mean you're near the stall.  Clearly that was incorrect in this case. It was obvious they were nowhere near the stall so blindly following the procedure because duh stick shaker would not problematic too.
Title: Re: Boeing 737 MAX
Post by: Obviousman on May 08, 2019, 04:59:33 AM
Always have to remember the 'flappy' mantra:

- Gear up
- Flaps up
- Shut up
Title: Re: Boeing 737 MAX
Post by: bknight on May 08, 2019, 09:11:03 AM
Always have to remember the 'flappy' mantra:

- Gear up
- Flaps up
- Shut up

Nothing about the throttle?
Title: Re: Boeing 737 MAX
Post by: smartcooky on May 08, 2019, 08:00:38 PM
It seems that it was the retraction of the flaps that caused MCAS to engage, so those who wish to blame the pilots are saying that had they followed the procedure and not retracted the flaps, they wouldn't have died.

The problem with that theory is that the pilots would have to already know that retracting the flaps would cause MCAS to engage; and since retracting flaps is a standard part of climbout, they would not have realised that it was the cause of their pitch down problems. Its going to be difficult for the pilots to know that when they didn't even know MCAS was even a thing - it wasn't in the Flight Manual, the QRH or any of the 737 Max documentation such as the training manual. Nor was there any mention of it in the 2½ hour iPad course about the 737 Max. The only people who even knew MCAS existed were the engineers who designed it, and even they had no idea that it could cause this problem.

To be clear, MCAS was implemented to make the flight handing characteristics of the 737 Max as near as possible the same as the 737 NG.  Its was supposed to be something that worked in the background.

The problem is that Boeing still designed a plane that actively tries to kill you if you retract the flaps.

You shouldn't retract the flaps with a stick shaker because a stick shaker is supposed to mean you're near the stall.  Clearly that was incorrect in this case. It was obvious they were nowhere near the stall so blindly following the procedure because duh stick shaker would not problematic too.

Tragically, had the pilots been briefed as to what MCAS was and how it works, they MIGHT have been able to figure out that extending the flaps to the minimum setting, Flaps 1, would have disengaged the MCAS, full control would have been restored, and as long as they kept their speed below the overspeed limit for that flap setting (about 200 kias IIRC)  they could have circled back to the airport for an emergency landing.

As it was, they had no idea what they were fighting. The aircraft appeared to have a mind of its own, and at low speed and low altitude, they just didn't have enough time work it out.
Title: Re: Boeing 737 MAX
Post by: Glom on May 09, 2019, 01:12:54 PM
And of course these are the types of scenarios you train for. But no training was a design objective.
Title: Re: Boeing 737 MAX
Post by: smartcooky on May 12, 2019, 07:43:19 AM
Oh dear, it looks like Boeing committed another unforgivable blunder; they changed the functionality of the stab trim switches on the 737 Max without telling anyone.

Those following the story will recall these two switches on the back right of the centre console...

(https://www.dropbox.com/s/yntgr47fa9ihlzt/MCAS-Disable.jpg?raw=1)

On previous versions of the 737 such as the 737 NG the left switch only deactivates the yoke trim switches that pilots use to control the horizontal stabilizer, and the right switch only deactivates autopilot control of the horizontal stabiliser.

However, on the 737 MAX , this was changed so that both switches performed the same function - setting either one to cut-out would disable the yoke trim switches and the autopilot functions, such as MCAS.

This means that, in the case of a runaway trim problem, a pilot flying the 737 NG could set the right switch to cutout, to turn off autopilot trim inputs, and still have manual electrical control of the horizontal stabiliser with the trim switches on the yoke. However, if they were flying the 737 MAX, this would not work - setting either switch to cut-out turned the whole stab trim system off!

Boeing made this change without informing pilots, and without including it in the iPad "Differences Training" course or any of the training documentation.
 
https://www.seattletimes.com/business/boeing-aerospace/boeing-altered-key-switches-in-737-max-cockpit-limiting-ability-to-shut-off-mcas/ (https://www.seattletimes.com/business/boeing-aerospace/boeing-altered-key-switches-in-737-max-cockpit-limiting-ability-to-shut-off-mcas/)
Title: Re: Boeing 737 MAX
Post by: Bop on May 12, 2019, 12:13:00 PM
I mentioned that  previously, and I suspect it was why the MCAS was re-enabled towards the end, they tried to get the electric trim working 'as per spec' as manual trim was by this stage out of the question, and in the process re-enabled the MCAS, dooming them...
Problem was that Boeing 'changed the spec' without telling anyone...
I have a diagram of the wiring system floating around somewhere at home, when I get back, I'll see if I can dig it up, it clearly showed the MAX now has both switches now wired together in series, where previous versions had them separated, with one switching off all electrical assist (what the MAX now has with BOTH switches) and the other switching off AP functions, but leaving the pilots trim switches on the yoke able to drive the electric motor (now nonexistent on the MAX!!!!)

Boeing apparently didn't consider this to be a major enough change to mention in their ipad slideshow, past 'we renamed the switches'...

:-O
Title: Re: Boeing 737 MAX
Post by: smartcooky on May 12, 2019, 09:53:32 PM
I have a diagram of the wiring system floating around somewhere at home, when I get back, I'll see if I can dig it up, it clearly showed the MAX now has both switches now wired together in series, where previous versions had them separated, with one switching off all electrical assist (what the MAX now has with BOTH switches) and the other switching off AP functions, but leaving the pilots trim switches on the yoke able to drive the electric motor (now nonexistent on the MAX!!!!)

Well that is appalling. If one of my tech bosses asked me to do it that way, I would refuse, and I certainly would not sign off on it.

The correct way of doing this would be to remove the second switch, and make a new switch panel with only the single remaining switch on it. The only reason I can see for doing it the way they did is to save a few dollars on new panelling. Its another clear attempt the cut corners and costs.
Title: Re: Boeing 737 MAX
Post by: Glom on May 13, 2019, 04:07:31 AM
Is that verified?

That sounds too ridiculous to be true.
Title: Re: Boeing 737 MAX
Post by: smartcooky on May 13, 2019, 06:55:46 AM
Is that verified?

That sounds too ridiculous to be true.

(https://www.dropbox.com/s/t3oid26nzrlm531/737NG-Stab-Trim.png?raw=1)
Stab Trim block diagram for 737NG

(https://www.dropbox.com/s/kqze9q4xsu32h7d/737MAX-Stab-Trim.jpg?raw=1)
Stab Trim wiring diagram for 737MAX

Please note that the top diagram is a block diagram rather than a wiring diagram but it will get the point across (I can't find an actual wiring diagram for the 737NG Trim system, but I know enough about these sorts of documents to have a fair idea what it will look like.

You can see that in 737NG (top diagram) the two switches are separate. The left ("Main Elect") switch kills electrical power to the Stab Trim motor (so stops the whole stab trim system from working) while the right ("Autopilot") switch only turns off the autopilot inputs to the Stab Trim motor, leaving the pilots able to electrically operate the trim system.

However on the 737MAX (bottom diagram) the two switches are wired in series. Also note that A on the left switch connects to A on the Electric Stab Trim Motor Block (on the right side), and B on the right switch connects to B on the FCC (Autopilot) block (bottom centre). As I understand this diagram, switching off either the left or right switch will turn off power to the Stab Trim motor, and this means the pilots will have no manual electrical control of the trim system from their yoke trim switches. Their only option then is to use the trim wheels and we have already seen what a difficult task that is.
Title: Re: Boeing 737 MAX
Post by: Bop on May 13, 2019, 10:04:24 AM
Well that is appalling. If one of my tech bosses asked me to do it that way, I would refuse, and I certainly would not sign off on it.

The correct way of doing this would be to remove the second switch, and make a new switch panel with only the single remaining switch on it. The only reason I can see for doing it the way they did is to save a few dollars on new panelling. Its another clear attempt the cut corners and costs.
From the various pilots, it was more a training issue, one of the contract requirements was that the planes had to be a 'standard 737' ie no retraining/re-certifications for the pilots necessary, and there was a major penalty if this was not achieved (from memory just over 100 million dollars- for one airline alone!)
This obviously led to management pushing for the software to correct the trim issues 'invisibly' so the pilots simply didn't have to be told...
In fact even after the first crash, where I suspect Boeing management had a pretty good idea what had gone wrong very quickly- they simply did a quick 'here's what to do' briefing on an Ipad and called it good enough and still didn't release much info on the new system

Is that verified?

That sounds too ridiculous to be true.
Unfortunately yes
(I see Smartcooky has already put up some diagrams, I believe I still have the NG circuit diagrams as well at home when I get back there ...)
Title: Re: Boeing 737 MAX
Post by: Glom on May 13, 2019, 10:22:46 AM
Well then. Boeing are in for a right boening.
Title: Re: Boeing 737 MAX
Post by: Bop on May 13, 2019, 05:38:47 PM
Yes indeed, and the FAA along with them (due to the whole 'selfcertification' thing- which is also a relatively new thing...

It's looking like many other countries regulators are going to be far less 'trusting' of FAA declarations, with the UK , EU and China to date saying that may require 'additional' certification checks before lifting the flying ban in their countries- a real slap in the face to the FAA!

 :o

It could lead to the 737MAX being allowed to fly in the USA only, and banned from international flights until Boeing gets re-certified in each individual country that demands it

Here in Australia, Virgin was supposed to be getting 50 new hulls  by mid/end of this year, they have pushed them out to 2021- which doesn't look good for any continuing orders either, they obviously aren't expecting to be able to use them any time soon...