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Boeing 737 Max 8 Killed another 157 People. WTH?

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Boeing 737 Max 8 Killed another 157 People. WTH?

Old 03-18-19, 06:45 PM
  #76  
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Originally Posted by AnthonyG View Post
I still think the elephant in the room is the single sensor failure that led to a major loss of aircraft and all passengers.
Seriously. How can this get off the drawing board and passed as safe by the FAA?

In no small way this is why the black boxes got sent to France.
I think you are on to something but disagree about the black boxes. From some of the articles I've read, Boeing did a self certification with FAA approval to get the MCAS system validated in a rush to get the MAX out to compete with the Airbus 320 NEO. Single point failure in an airliner is just not done but if you ignore standard procedure, bad things happen.
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Old 03-18-19, 06:45 PM
  #77  
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Originally Posted by velojym View Post
Yeah, they can roll out (projected) statistics all they want when automating every little thing on an aircraft, but you can't beat a trained human brain when things don't go right.
At least perfect the automation on unmanned aircraft for a few years first.
Actually, a trained human brain is also fallible. Investigations of numerous crashes show the plane warning the pilot that he's in trouble, yet the pilot ignores the warnings, eg, flying into terrain. The real trick in a flight control system is to have both elements (human & computer) interact to maximize safety. It's a difficult dynamic balance to optimize, but they're still better together, as evidenced by a continually improving safety record overall.
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Old 03-18-19, 07:03 PM
  #78  
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Originally Posted by Revoltingest View Post
I can't read your article because I've reached my limit of free ones.
It would be more properly called a new design based upon an earlier airframe.
Note also that the crash appears to be a failure involving modern controls,
avionics, hydraulics & sensors. The older portion of the design appears unrelated.
A totally brand new plane would have the same risks, eg, the Airbus 330 (which is
still in the air despite unsolved problems with diving due to AOA (angle of attack)
errors....with no crashes yet, but several incidents involving severe injuries.
Sorry, let me quote some of the LA times article, hopefully not taking too much.

How a 50-year-old design came back to haunt Boeing with its troubled 737 Max jet

A set of stairs may have never caused so much trouble in an aircraft.

First introduced in West Germany as a short-hop commuter jet in the early Cold War, the Boeing 737-100 had folding metal stairs attached to the fuselage that passengers climbed to board before airports had jetways. Ground crews hand-lifted heavy luggage into the cargo holds in those days, long before motorized belt loaders were widely available.

That low-to-the-ground design was a plus in 1968, but it has proved to be a constraint that engineers modernizing the 737 have had to work around ever since. The compromises required to push forward a more fuel-efficient version of the plane — with larger engines and altered aerodynamics — led to the complex flight control software system that is now under investigation in two fatal crashes over the last five months.
....

But the decision to continue modernizing the jet, rather than starting at some point with a clean design, resulted in engineering challenges that created unforeseen risks.
....

Today’s 737 is a substantially different system from the original. Boeing strengthened its wings, developed new assembly technologies and put in modern cockpit electronics. The changes allowed the 737 to outlive both the Boeing 757 and 767, which were developed decades later and then retired.

Over the years, the FAA has implemented new and tougher design requirements, but a derivative gets many of the designs grandfathered in, Moss said.

“It is cheaper and easier to do a derivative than a new aircraft,” said Robert Ditchey, an engineer, aviation safety consultant and founder of America West Airlines, which purchased some of the early 737 models. “It is easier to certificate it.”

But some aspects of the legacy 737 design are vintage headaches, such as the ground clearance designed to allow a staircase that’s now obsolete. “They wanted it close to the ground for boarding,” Ditchey said.
....

To handle a longer fuselage and more passengers, Boeing added larger, more powerful engines, but that required it to reposition them to maintain ground clearance. As a result, the 737 can pitch up under certain circumstances. Software, known as the Maneuvering Characteristics Augmentation System, was added to counteract that tendency.
....

The entire need for the software system is fundamental to the jet’s history.

The bottom of the 737’s engines are a minimum of 17 inches above the runway. By comparison, the Boeing 757 has a minimum clearance of 29 inches, according to Boeing specification books. The newer 787 Dreamliner has 28 inches or 29 inches, depending on the engine.

The 737 originally was equipped with the Pratt & Whitney JT-8 series jets, which had an inner fan diameter of 49.2 inches. “They looked like cigars, long and skinny,” Moss said.

By comparison, the LEAP-1b engines on the Max 8 have a diameter of 69 inches, nearly 20 inches more than the original. There wouldn’t be enough clearance without some kind of modification.

In the 737-300, which came after the original planes sold in West Germany, Boeing came up with an unusual fix: It created a flat bottom on the nacelle (the shroud around the fan), creating what pilots came to call the "hamster pouch.”

“They made it work,” said Ditchey, whose America West was one of the original customers of the 737-300.

But the LEAP engines required an even bigger change. Boeing redesigned the pylons, the structure that holds the engine to the wing, extending them farther forward and higher up. It gave the needed 17 inches of clearance. The company also put in a higher nose landing gear.

The change, however, affected the plane’s aerodynamics. Boeing discovered the new position of the engines increased the lift of the aircraft, creating a tendency for the nose to pitch up.

The solution was MCAS, which ordered the stabilizer to push down the nose if the “angle of attack” — or angle that air flows over the wings — got too high. The MCAS depends on data from two sensors. But on the Lion Air flight, the MCAS relied on a sensor that was erroneously reporting a high angle of attack when the plane was nowhere near a stall.

The pilots tried to counteract the nose-down movements by pulling back on the yoke. But even pulling with all their might they could not counteract the forces, according to data in a preliminary accident investigation report.

Skow criticized Boeing’s MCAS system, saying it acted only on the basis of angle of attack. The Lion Air jet was traveling so fast that when MCAS ordered the stabilizer to pitch the nose down it was a violent reaction. The software should have factored in air speed, he said, which would have better calibrated the pilots’ reaction.
....
So, it sounds like a lot of the current problems revolve around these legacy issues. I'm surprised they don't just redesign the landing gear, and put the engine thrust back to where it was supposed to be.

However, the solution will likely be more software changes, and more distancing the pilot from flying.

Overrides, so the plane automatically responds to the pilot's actions without having to switch faulty flight software on or off?
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Old 03-18-19, 07:17 PM
  #79  
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Originally Posted by CliffordK View Post
Sorry, let me quote some of the LA times article, hopefully not taking too much.

So, it sounds like a lot of the current problems revolve around these legacy issues. I'm surprised they don't just redesign the landing gear, and put the engine thrust back to where it was supposed to be.

However, the solution will likely be more software changes, and more distancing the pilot from flying.

Overrides, so the plane automatically responds to the pilot's actions without having to switch faulty flight software on or off?
Thanx for the quoted text.
The workarounds mentioned don't appear to be directly related to the crashes of the 737 Max though.
I'm only speculating based upon (unreliable) info in the news, but it appears to be control issue involving AOA (angle of attack). Whether this is a sensor or data handling issue isn't known yet. (On the A330 accidents it was a computer data handling problem rather than a sensor problem.)

It isn't widely known, but every airplane, commercial or military, is a work in progress.
The F-18 I once worked on at Northrop (in flight controls) back in the 70s is a very
different animal today. No design is ever perfect, nor will it ever be.

Disclaimer:
I'm no expert. I never knew much.
And I've forgotten even most of that.
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Old 03-18-19, 07:27 PM
  #80  
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This is the best article yet on the topic: https://www.seattletimes.com/busines...ion-air-crash/

The safety analysis:

- Understated the power of the new flight control system, which was designed to swivel the horizontal tail to push the nose of the plane down to avert a stall. When the planes later entered service, MCAS was capable of moving the tail more than four times farther than was stated in the initial safety analysis document.

- Failed to account for how the system could reset itself each time a pilot responded, thereby missing the potential impact of the system repeatedly pushing the airplane’s nose downward.

- Assessed a failure of the system as one level below “catastrophic.” But even that “hazardous” danger level should have precluded activation of the system based on input from a single sensor — and yet that’s how it was designed.
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Old 03-18-19, 08:27 PM
  #81  
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Originally Posted by Shimagnolo View Post
This is the best article yet on the topic: https://www.seattletimes.com/busines...ion-air-crash/

The safety analysis:

- Understated the power of the new flight control system, which was designed to swivel the horizontal tail to push the nose of the plane down to avert a stall. When the planes later entered service, MCAS was capable of moving the tail more than four times farther than was stated in the initial safety analysis document.

- Failed to account for how the system could reset itself each time a pilot responded, thereby missing the potential impact of the system repeatedly pushing the airplane’s nose downward.

- Assessed a failure of the system as one level below “catastrophic.” But even that “hazardous” danger level should have precluded activation of the system based on input from a single sensor — and yet that’s how it was designed.
According to a detailed FAA briefing to legislators, Boeing will change the MCAS software to give the system input from both angle-of-attack sensors.

It will also limit how much MCAS can move the horizontal tail in response to an erroneous signal. And when activated, the system will kick in only for one cycle, rather than multiple times.
So, there are two sensors, but the system reacted to only one, or perhaps only the worst one of the two.

And, as the pilots responded, the plane repeatedly hit them with the same erroneous response.

Originally Posted by Will G View Post
The Lion Air jet crashed after 4 or 5 write-ups for a mechanical discrepancy in the trim system and their mechanics failed to properly analyze and fix the problem. The flight prior to the mishap, the crew turned off the stab system and flew the jet manually. The AOA system was not repaired and the jet flew the next morning. The mishap crew did not turn off the stab system.
Many new cars pop up with an very annoying "Service Engine Soon", or "Antilock Brake Failure" warning, and it stays up until manually reset by a technician.

The plane likely could have detected that something was amiss as the crew had turned off the control system. And, the system should have continued to collect and analyze flight data.

One would think a plane would pop up with critical errors, and perhaps a log of errors & repairs to be reviewed as part of pre-flight.



Ok, so I understand that the angle of attack sensor determines the jet's flight angle with respect to the actual air, which I presume doesn't always follow an absolute angle with respect to the Earth, especially around hills, mountains, and varying terrain. It would also naturally take into account the speed of the aircraft, so a light crosswind vector might be become relatively insignificant as the plane is flying a couple hundred MPH.

Nonetheless, I presume there are GPS, airspeed, altitude, and absolute inclination sensors that should be queried to confirm the plane's status, both in normal flight, and error conditions.

Heck, GPS should be able to have 4 quadrants on the plane + speed over land.

Perhaps even weather conditions from external sources. Satellites?

I presume the planes could be flown with one, or a couple of sensors in error. And, the pilots should be able to dynamically adjust the weight given to each sensor.

And, again, such data should be reviewed by each flight crew, as well as maintenance staff.
'
Logged comments?

I understand the evolution of aircraft. And, certainly the evolution of computer systems after the 1960's.

But, I also get Windows updates almost once a week. Wasn't there continuous evaluation of the modified flight controls following the introduction 4 years ago?

Look for potential issues and shortcomings even after the software was released? Evaluate flight data and pilot comments?
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Old 03-18-19, 09:20 PM
  #82  
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They need to totally scrap the 737 Max and redesign a new plane. That might be too expensive to do but there in no way I will get on a 737 Max.
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Old 03-18-19, 11:31 PM
  #83  
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Originally Posted by Hondo Gravel View Post
They need to totally scrap the 737 Max and redesign a new plane. That might be too expensive to do but there in no way I will get on a 737 Max.
Boeing seems to start with a base model, then over the decades steadily modify it to make it bigger.

The 737 is rapidly approaching the size of the early 757 planes (now discontinued).

Fatigue issues with the 757?

But, the 737 may retain popularity due to being about half the cost of the next larger planes.

As Boeing eventually catches up with Dreamliner 787 orders, I'd imagine they'd continue to experiment with composites, perhaps eventually replacing the 737 with a smaller version of the Dreamliner.
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Old 03-19-19, 12:21 AM
  #84  
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My dad the autopilot engineer liked to joke about the Boeing fuselage machine, they feed in aluminum at one end and out the other end comes 3+3 fuselage and they just slice off as much as they need for each plane
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Old 03-19-19, 08:31 AM
  #85  
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CliffordK, I haven't flown the 737 MAX so I'm not sure of the warnings that might be different from the 737-800NG. The 737 MAX could not be too terribly different than prior 737 models or it would require a new type certificate, i.e., the pilots would have to go through training in order to fly that model specifically and the FAA does not usually allow a commercial carrier to schedule pilots to fly 2 different aircraft types. So, if Boeing added a lot of new systems, the jet would have to go through the ENTIRE certification process and then the pilots would have to train on the new jet and then ONLY fly that new jet. This would be financially prohibitive for most airlines, specially Southwest with only 737s. What drives a new or different type rating? I'm not sure because I've flown the 757 and the 767 under a common type rating. The differences in systems and operations were different but minor, the landing technique was different, and handling was different in that the 757, max weight of 250K-ish, was a lot more nimble than the 767, max weight of 400K-ish.

You offer up some common sense ideas but those were probably thrown under the bus due to rules, regulations, timing, but mostly money.
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Old 03-19-19, 09:02 AM
  #86  
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Originally Posted by Darth Lefty View Post
My dad the autopilot engineer liked to joke about the Boeing fuselage machine, they feed in aluminum at one end and out the other end comes 3+3 fuselage and they just slice off as much as they need for each plane
lol like a play-doh 'pasta' extruder
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Old 03-19-19, 10:06 AM
  #87  
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Originally Posted by Will G View Post
CliffordK, I haven't flown the 737 MAX so I'm not sure of the warnings that might be different from the 737-800NG. The 737 MAX could not be too terribly different than prior 737 models or it would require a new type certificate, i.e., the pilots would have to go through training in order to fly that model specifically and the FAA does not usually allow a commercial carrier to schedule pilots to fly 2 different aircraft types. So, if Boeing added a lot of new systems, the jet would have to go through the ENTIRE certification process and then the pilots would have to train on the new jet and then ONLY fly that new jet. This would be financially prohibitive for most airlines, specially Southwest with only 737s. What drives a new or different type rating? I'm not sure because I've flown the 757 and the 767 under a common type rating. The differences in systems and operations were different but minor, the landing technique was different, and handling was different in that the 757, max weight of 250K-ish, was a lot more nimble than the 767, max weight of 400K-ish.

You offer up some common sense ideas but those were probably thrown under the bus due to rules, regulations, timing, but mostly money.
The reason the plane has the nose up tendencies is because the much larger though far more efficient engines sit higher up on shorter nacelles (you can't take off with stuff dragging like those fake bull danglers on the hitch of your truck).

If the engines had been longer instead of fatter this may not have been the problem. And when was the last time an L-1011 did something like that? You seem to have reached some limitations for this 1967 plane.

And yes, Boeing decided against designing a new plane.

Now I've heard that the main failure of the MCAS is that it cycles up to four times in rapid succession and should at the least be left off during takeoff and initial ascent. While I had an inkling of this, I have no experience as a pilot so I needed to know this to confirm at least parts of my suspicions. It sounded like the new software eliminates so much hard re-cycling to let the pilot control the plane better and also without proper training these two crews had no clue while US and Canadian crews knew a little bit more and knew to turn MCAS off at least temporarily if a problem occurred.

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Old 03-19-19, 10:51 AM
  #88  
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Originally Posted by Will G View Post
Boring and unfulfilling? I've been doing the commercial thing and flown fighters in the military. I'll admit flying upside down and blowing stuff up is both exciting and demanding but I definitely would not call commercial flying boring and/or unfulfilling. If I can take people halfway around the world over some of the most harsh terrain on the planet and the passengers major complaint is the long flight, I've made the difficult look easy.
There's a quote about flying being long moments of boredom punctuated by the occasional sheer terror that comes to mind here, and I'm sure they phrased it a little different. .
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Old 03-19-19, 11:03 AM
  #89  
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That quote sounds like the job of driving a train. Or manning a nuclear missile silo.
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Old 03-19-19, 03:32 PM
  #90  
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Originally Posted by no motor? View Post
There's a quote about flying being long moments of boredom punctuated by the occasional sheer terror that comes to mind here, and I'm sure they phrased it a little different. .
Sounds about right. Or maybe long moments of boredom punctuated by occasional bad airplane food. Commercial aviation is quite sedate in the grand scheme of things. Military flying, however, had more than it's fair share of WTF moments.
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Old 03-19-19, 06:19 PM
  #91  
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Bloomberg: Pilot Who Hitched a Ride Saved Lion Air 737 Day Before Deadly Crash

https://www.bloomberg.com/news/articles/2019-03-19/how-an-extra-man-in-cockpit-saved-a-737-max-that-later-crashed
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Old 03-19-19, 08:14 PM
  #92  
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Originally Posted by Shimagnolo View Post
Bloomberg: Pilot Who Hitched a Ride Saved Lion Air 737 Day Before Deadly Crash

https://www.bloomberg.com/news/articles/2019-03-19/how-an-extra-man-in-cockpit-saved-a-737-max-that-later-crashed
As the newscaster on that link says, "creepy". Yes. That the only reason that same plane didn't crash the day before of the exact same failure was because an off-duty pilot in the cockpit jump seat recognized what wa happening, turned off the autopilot and instructed the pilot to reduce the engine throttle. Wow! So this was known and Boeing didn't make it a point to bring it to the attention of all airlines and flight crews?

I have respected Boeing (and always felt creeped out flying DC-10s knowing what caused the Iowa City crash with my best friend's wife and two kids aboard), but sorry, Boeing, you just lost me. This doesn't even qualify as an accident, just and event waiting to happen.

Ben

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Old 03-19-19, 11:20 PM
  #93  
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Originally Posted by 79pmooney View Post
That the only reason that same plane didn't crash the day before of the exact same failure was because an off-duty pilot in the cockpit jump seat recognized what wa happening, turned off the autopilot and instructed the pilot to reduce the engine throttle. Wow! So this was known and Boeing didn't make it a point to bring it to the attention of all airlines and flight crews?
The problem has nothing to do with the autopilot, in fact, the suspect system (MCAS) is disabled if the autopilot is engaged. As we have been discussing, the problem appears to be that the flight crews are not correctly diagnosing a trim system issue (driven by the MCAS receiving faulty angle-of-attack data). All pilots are trained to recognize a trim system malfunction but the MCAS system appears to be complicating the diagnosis by virtue of the way it intervenes sporadically as the crew tries to figure things out. Note the highlighted text below in the article you referenced.

"The so-called dead-head pilot on the earlier flight from Bali to Jakarta told the crew to cut power to the motor driving the nose down, according to the people familiar, part of a checklist that all pilots are required to memorize."

These things are often more subtle than they appear on the surface.

- Mark
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Old 03-20-19, 08:16 AM
  #94  
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The "memorize" thing are called Red Box items because those things are in the checklist enclosed in a red box and are things that, if not done correctly and quickly (i.e. not enough time to pull out the book with all the malfunction checklists, find the problem item checklist, and run the checklist), could lead to loss of the aircraft. Runaway Stabilizer is one of those red box checklists.
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Old 03-20-19, 12:08 PM
  #95  
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On most aircraft systems there are levels of redundancy. A Left system and a Right System usually and sometimes even a Center system. I'm surprised the FAA let this single point of failure get by.

The FAA usually has a very high level of safety required. When we started trading 30 pounds of paper charts and operating manuals in our kitbags for iPads, the FAA required the iPad survive a 9 G force in a bracket in the cockpit and a 60,000 foot cabin decompression. If I ever encounter 9Gs in an airliner or a decompression at 60,000 in a jet that even lightweight might get to 41,000 feet, I've got a lot more pressing issues to deal with than a non-functioning iPad.

Regarding drones or automated flight, I'm not sure you would want to ride on something with such a high accident rate.
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Old 03-20-19, 12:45 PM
  #96  
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Originally Posted by 79pmooney View Post
As the newscaster on that link says, "creepy". Yes. That the only reason that same plane didn't crash the day before of the exact same failure was because an off-duty pilot in the cockpit jump seat recognized what wa happening, turned off the autopilot and instructed the pilot to reduce the engine throttle. Wow! So this was known and Boeing didn't make it a point to bring it to the attention of all airlines and flight crews?

I have respected Boeing (and always felt creeped out flying DC-10s knowing what caused the Iowa City crash with my best friend's wife and two kids aboard), but sorry, Boeing, you just lost me. This doesn't even qualify as an accident, just and event waiting to happen.

Ben
I read the article linked quite differently.

That extra pilot, who was seated in the cockpit jumpseat, correctly diagnosed the problem and told the crew how to disable a malfunctioning flight-control system and save the plane, according to two people familiar with Indonesia’s investigation.
...
The so-called dead-head pilot on the flight from Bali to Jakarta told the crew to cut power to the motor in the trim system that was driving the nose down, according to the people familiar, part of a checklist that all pilots are required to memorize.
...
However, the pilots on the harrowing Oct. 28 flight from Bali to Jakarta didn’t mention key issues with the flight after they landed, according to the report.

Their request for maintenance didn’t mention they had been getting a stall warning since about 400 feet after takeoff as a result of the faulty angle-of-attack sensor. It was still giving false readings the next morning on the flight that crashed, according to flight data.
So, the MCAS isn't exactly the "autopilot".

And they didn't cut power to the main engine, but rather cut power to the servo motor that was disrupting the flight controls, I think.

And, there was poor communication with the maintenance staff.

It is a little surprising that maintenance crews don't conduct test flights when they're struggling to diagnose sensor failures, although I could imagine the complexities of extra takeoff/landing attempts.
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Old 03-20-19, 01:18 PM
  #97  
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I think it is also important to realize that despite these two recent accidents, commercial aviation on major airlines is extremely safe. In fact, in 2017 there were ZERO fatalities in commercial jets in over 37 MILLION flights. Think about that for a second before you think we're in some kind of crisis situation with respect to commercial aviation safety. They are certainly flaws in airplanes and crews, but in general, the system, with all the checks and balances, has produced truly extraordinary levels of safety.

The MAX and its training system will be fixed in a few weeks (or few months), and with the intense scrutiny, it will likely be one of the safest airplanes in the sky.

- Mark

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Old 03-20-19, 01:49 PM
  #98  
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Originally Posted by CliffordK View Post
And they didn't cut power to the main engine, but rather cut power to the servo motor that was disrupting the flight controls, I think.
I think they did both which is standard procedure in runaway trim malfunctions. When you point the nose of an airplane towards the ground, it gains speed dramatically and can quickly exceed safe structural limits. So if any kind of uncommanded descent situation, you immediately chop power to reduce speed buildup while you sort the problem. But as Will has mentioned, things can get pretty confusing as they crew was likely getting faulty indications (via the bad sensor) that the airplane was stalling and increasing power is what you need in this situation.

- Mark
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Old 03-20-19, 03:36 PM
  #99  
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Originally Posted by Revoltingest View Post
Actually, a trained human brain is also fallible. Investigations of numerous crashes show the plane warning the pilot that he's in trouble, yet the pilot ignores the warnings, eg, flying into terrain. The real trick in a flight control system is to have both elements (human & computer) interact to maximize safety. It's a difficult dynamic balance to optimize, but they're still better together, as evidenced by a continually improving safety record overall.
Yeah, as an aircraft mechanic, I dealt with the results of fallible pilots, and am aware.
However, I also know how "dumb" even the best automation can be. I do agree that the best solution is going to be a mix.
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Old 03-20-19, 05:26 PM
  #100  
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Originally Posted by velojym View Post
Yeah, as an aircraft mechanic, I dealt with the results of fallible pilots, and am aware.
However, I also know how "dumb" even the best automation can be. I do agree that the best solution is going to be a mix.
Time will illuminate, as automation becomes more sophisticated, capable & robust.
Human beings aren't so upgradable.
Note also that the F-16 is aerodynamically unstable, so the pilot actually provides only
inputs to a computer, which does the flying. (A human cannot react quickly enuf.)
Yet it's a very reliable system.

Last edited by Revoltingest; 03-20-19 at 05:35 PM.
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