Posted on 04/19/2019 7:26:18 PM PDT by the_daug
On Apr 19th 2019, as result of the initial assessment released on Apr 16th 2019, The Aviation Herald received pages out of the 737-8 System Schematic Manual showing the circuitry involving the TRIM PRI CUTOUT and TRIM B/U CUTOUT Switches more clearly. The TRIM PRI CUTOUT switch appears under various different names on several pages of the manual, always being referenced as S272 however, the TRIM B/U CUTOUT switch also appears under different names in different locations always being references as S149 however. The graphics of chapter 27-41-11 page 101 makes clear both CUTOUT switches have more than one contact. One set of contacts delivers a signal to both FCC A and FCC B named "AUTO STAB TRIM CUTOUT" and thus would seem to support a possible re-activation of the Trim, however, a second set of contacts switches power supply to both control columns' Trim Up/Trim Down swiches (effectively disabling those switches with either of the CUTOUT Switches in CUTOUT position) as well as the power supply to relay R64, which in turn disconnects the TRIM MOTOR Unit from its power supply (three phases of 115V) leaving the trim motor without any power if either of the CUTOUT Switches is in position CUTOUT. Unless this schematic diagram does not agree with the actual wiring or another fault exists in the electrical wiring, it thus appears impossible the trim motor gets energized or could re-activate with either of the CUTOUT switches in CUTOUT position. For ease of understanding we have marked the 28V signal path in magenta and the power path to the trim motor (115V) in green on the system schematic diagram provided below.
Coverage released on Apr 16th:
If I’m reading it correctly this is indicative of piss-poor design in the control interrelationships. They either had an idiotic electrical engineer designing this or they had multiple engineers working at cross-purposes and not communicating. Of course, I could be missing something.
Pi$$ Poor FMEA analysis too.
Someone needs to drain the swamp at Boeing. Now.
It finally landed, loaded up and took off on one engine.
insha'Allah
Moving HQ to RhamTown was a large mistake.
It’s not just the 737 MAX 8’s (those planes should not fly period) but even its latest batch of military planes are showing trouble. And tip of the iceberg with regard to corrupt ethics, cutting corners, and revelations regarding this once great company as of late.
Boeing SWAMP must be drained, FAA too.
Ever since the first generation of the 737, stabilizer trim runaway was such an important condition to recognize and resolve as a pilot that the procedure is a "memory item" instead of a checklist item. This means that the pilot must be trained to recognize stab trim runaway, and know exactly what to do in order to correct the issue immediately, without running through a written emergency troubleshooting checklist.
The Ethiopian pilots appear to not have been properly trained to be certified for ANY version of the 737.
I sure hope the guys at The Aviation Herald aren’t called upon to make the manual more understandable!
Oh please. First of all, their latest batch of military aircraft also has problems, please look it up. And must we wait for an American 737 MAX to crash before holding Deep State Boeing accountable? Gamble with more lives? Being a frequent flier, I would prefer NOT.
There is so much coming out about the company now, and none of it pretty. This is not to say things were always bad...But beginning in the 2000s, Boeing had the opportunity to design and build a whole new innovative plane!!! But their rush to compete with sales of Airbus latest offering in the short term made them scrub their initial plans and instead ‘MAXimize’ their existing (and outdated) 737 model.
The problem is: to make the plane model more fuel efficient and competitive, they adjusted things like engine placement and challenged the inherent aerodynamics of the plane...And to counteract this, they installed anti-stall software. And decided to sell essential safety features as ‘add-on’ parts to prospective airlines.
With the corrupt FAA’s help, they self-regulated and self-inspected their way to quick approval. And voila you have the release of the MaX 8.
If Boeing believes its latest planes go ‘above’ the heads of so called 3rd world pilots then they should not be a) outsourcing their maintenance to other countries b) growing in their reliance on Chinese-manufacturing input and c) selling their planes to foreign airlines...Ethiopian Air is one of the few 1st World level things Africa’s got and thousands of first worlders are passengers in its planes.
First world governments, first world corporations, first world institutions are not beyond ENORMOUS corruption in case you haven’t noticed. And Boeing has spent massive cash to be in bed with Deep State and FAA is equally a mess. As I have stated already on board Drain the Boeing swamp!
I believe Boeing’s donation toward Barack Obama’s Presidential Library is upwards of about $10 million.
If you read the comments dated today you’ll see other people in the industry’s comment on this information that was posted om Aviation Herald today. The comments post in reverse order of FR.
I was wondering why the xf32 lost to the now F22.
it’s a three-way switch? up, neutral, down?
After reading that I fell into a comma.
Here is Obama back in 2011 hailing new Boeing-Lion Air deal in hopes of boosting economy in time for election season.
I am not pinning the blame on him for Boeing’s current predicament. As the Mueller debacle reminds us, most everyone is part of ‘the swamp’ in some way...and it’s a fact that many a major American institution from Boeing to NASA, private and public —- have gone downhill or become insanely corrupt from power (Silicon Valley, Monsanto, the mainstream media, Big Pharma.) —
Trump is doing his best to reboot our country and often by means of our most cherished economic and technological entities...but companies like Boeing need a MAJOR overhaul /cleanout before USA can move full speed ahead in the work of Making America Great Again. We can’t MAGA with pre-Trump operational parts! To use an analogy.
Meanwhile, China, Japan, Russia, and Brazil are releasing their own commercial aircraft offerings to the world in the hopes of breaking the Boeing-Airbus duopoly. We shall see how that unfolds.
Possibly contributing factors into the accident:
- Corporate Culture within Boeing in designing aircraft
- Corporate Culture within FAA in certifying aircraft
- Corporate Culture in Ethiopian Airlines, which did not ensure their flight crew were fully aware of the implications of the LionAir Crash and the related EAD as well as Boeing and FAA approved emergency procedures
- Less than optimal crew performance, e.g. loss of situational awareness with respect to speed and thrust
...and blind faith in their tech.
Well, you are wrong. So is anyone who is blaming the pilots in either 737 Max crash.
The Boeing MCAS is the culprit in both. It is an automated system that can trim nose down beyond the point of recovery....except using the manual trim wheel.
MCAS can trim down beyond the point where electric trim (on the yoke) cannot bring trim back to neutral.
That is something no 737 has except the Max.
The other fault is that the MCAS system uses only 1 angle of attack sensor to decide if it will automatically introduce nose down trim. That is bad design for many reasons, but the Ethiopian flight lost the angle of attack sensor on takeoff, making MCAS think the plane was 70 degrees nose up (a stall).
So, the yoke starts shaking, alarms are going off as you are 1000 feet off the ground. The plane is telling you that you are going to stall. You know that you are not because the other angle of attack sensor and airspeed indicator is working and telling you all is good.
Suddenly, the nose is pitching down (MCAS), so you try to use electric trim to bring it back while pulling back on the yoke to keep the nose up and to keep climbing.
You are still trying to address all the shakes, bells and warnings going off.
You shut off the Auto Stab Trim switches, but the plane is still pitching down. You just killed your electric trim by throwing those switches.
You are pulling back on the yoke hard to try and keep level, but the plane has been trimmed down.
You try to use the manual trim wheel, but it will not move. The forces across the stabilizer are so strong that you cannot move the wheel (remember, it is a cable that runs the length of the plane to a small wheel in the cockpit. The air across the stabilizer has a tremendous amount of air pressure across it, so turning a small wheel is impossible. The typical procedure is to let the nose down by stopping your pull back on the yoke, manually trim a bit, then pull back on the yoke again. This is called "roller coaster" and it only works if you have lots of altitude, which neither crew had.
The Ethiopian crew turns Auto Stab Trim switches back on, in hopes of using the electric trim to correct what MCAS has done. But MCAS is also activated by those switches and adds in more nose down trim to a point where the electric trim cannot move.
One design fault is that the yoke switch electric trim can only move the trim so much, not within the full range of nose up or nose down trim. MCAS has no such limitation and can add full nose-down trim, which is outside the operating range of the electric trim on the yoke.
Your fate is sealed. The automated system created a situation that is unrecoverable when you are so close to the ground.
Boeing and other pilots have confirmed (using the simulator) that in this situation, you have less than 40 seconds after wheels up to turn off the Auto Stab Trim and correct the situation.
Remember, the Ethiopian crew was being told they were stalling, not that trim was running away. By the time they realized what was happening, MCAS put in so much nose down trim that nothing could recover it.
Boeing's software correction does 2 things:
1) MCAS will use both angle of attack sensors. If they disagree, MCAS will shut off.
2) MCAS can only apply a small amount of nose down trim....it cannot take trim to its maximum, nose-down setting.
These crashes had nothing to do with bad flight crews or their training. It is sickening to see so many blame them.
two way switch.
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