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Third Pilots' Union Raises Concern About Boeing 737 Max Jet

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Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#41

Post by VBprogrammer »

inferiorhuman wrote: post #36
VBprogrammer wrote: post #33

Earlier quoted context omitted.

The elevators still have some authority, you don't have to wind it from end to end to regain control. Also, the full range of mechanical motion is only available via the trim wheel, the electronic trim doesn't drive it to either extreme (although it can move it back to the centre from an extreme).

> The elevators still have some authority, you don't have to wind it from end to end to regain control. If you're at a low altitude and managing other problems will you have enough time to even recognize the problem and then wind the cranks and recover before you hit the ground? > Also the full range of mechanical motion is only available via the trim wheel, the electronic trim doesn't drive it to either extreme (alt…

> If you're at a low altitude and managing other problems will you have enough time to even recognize the problem and then wind the cranks and recover before you hit the ground?

My suspicion is that it would probably have required a well drilled crew to have handled the problem correctly. But I don't think we're up there with the extraordinary levels of piloting which we've seen demonstrated previously e.g. Flight 1549 (the miracle on the Hudson).

> Can MCAS drive the trim full down? What I've read suggests that if you give it time, it can.

I'd be surprised if it can drive it outside the normal range of electronic motion. There aren't really enough details out there for me to be sure though.

Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#42

Post by bronco21016 »

sokoloff wrote: post #13
WalterBright wrote: post #7

The pilots would have seen the nose down action as an uncommanded stabilizer trim movement. The solution is to shut off the power to the stab trim. This would work and would require no knowledge of the stall avoidance mechanism.

Exactly this. Following the existing memory items and QRH checklist items taught to every 737 pilot is (very, very likely) enough to overcome this contemplated scenario of a runaway trim from a flaw in the stability system. (It's remotely possible that the crew holds no blame in that they followed the checklist properly and the cutout switches were defective or the checklist response was otherwise insufficient.)

Would runaway trim be the thing they were reacting to? It seems to me the trim was pitching down due to the design of the stall system. I’m imagining they were getting erroneous stall warnings due to the AOA sensor feeding bad data. If I’m in an aircraft and I’m getting stall warnings, stick shakers, and stick pushers I’m definitely not going to run runaway trim memory items.

Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#43

Post by augustz »

WalterBright wrote: post #7

The pilots would have seen the nose down action as an uncommanded stabilizer trim movement. The solution is to shut off the power to the stab trim. This would work and would require no knowledge of the stall avoidance mechanism.

One question I have: on Boeing how easy is it to just jump down to secondary law to give up some of the flight envelope protections. Can that be switched manually? How exactly does that look?

If you know computer is getting garbage data / plane acting in an unusual way, you can dial things back. These planes and their engines are so reliable and maintenance is usually so good that it seems you could fall back to closer to direct law flying (power setting / pitch / etc) and at least keep plane out of the drink / gain some altitude.

Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#44

Post by sokoloff »

bronco21016 wrote: post #42
sokoloff wrote: post #13

Earlier quoted context omitted.

Exactly this. Following the existing memory items and QRH checklist items taught to every 737 pilot is (very, very likely) enough to overcome this contemplated scenario of a runaway trim from a flaw in the stability system. (It's remotely possible that the crew holds no blame in that they followed the checklist properly and the cutout switches were defective or the checklist response was otherwise insufficient.)

Would runaway trim be the thing they were reacting to? It seems to me the trim was pitching down due to the design of the stall system. I’m imagining they were getting erroneous stall warnings due to the AOA sensor feeding bad data. If I’m in an aircraft and I’m getting stall warnings, stick shakers, and stick pushers I’m definitely not going to run runaway trim memory items.

It's pretty likely that they weren't reacting to runaway trim; on that we agree.

The trim wheels are large, painted mostly black with alternating, offset white stripes (so the motion is quite visible), and have a very distinctive clacker on them. https://www.youtube.com/watch?v=cQirIH_DuAs

It's possible that the crew fought to keep the airplane in a basic attitude flying configuration for several minutes without ever noticing the trim in motion unexpectedly, but that seems unlikely, particularly when the act of holding the nose up to hold attitude was accompanied by increasing nose down trim.

Minor note: there is no stick pusher in the 73. Those tend to only be installed on T-tail aircraft. Synthetic elevator feel increases, but no pusher only a shaker.

Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#45

Post by laken »

gargravarr wrote: post #16

Okay, I've never sat in the cockpit of an aircraft, but the one thing I don't understand - if the nose of a plane suddenly drops, isn't the pilot's first instinct to pull back on the controls to raise it? From what I've read, in Boeing aircraft at least, the pilot's controls can always override the automatic systems.

Yes, but this is where it gets a little complicated, and why this accident is so fascinating to many people in aviation...

>> if the nose of a plane suddenly drops, isn't the pilot's first instinct to pull back on the controls to raise it?

Not exactly, as the correct way to get out of a stall is pointing the nose down, in order to pick up airspeed to gain more lift. The stall horns were going off, so the pilots may have thought they were stalling. In addition, as others have mentioned, the yoke alone may be unable to beat out the trim by the autopilot.

>> From what I've read, in Boeing aircraft at least, the pilot's controls can always override the automatic systems.

Historically, you are exactly right. This is the _biggest_ reason pilots are pissed at Boeing right now. It's believed that the autopilot was turned off entirely when the plane started thinking it was stalling, and trying to point itself down. This is not present on any of the original 737 aircraft, only the MAX series, and Boeing didn't inform pilots of this.

Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#46

Post by robdachshund »

gpm wrote: post #38
WalterBright wrote: post #9

Earlier quoted context omitted.

> Why hasn't the 737Max been grounded pending investigation? Because jumping to conclusions is not helpful. Let the NTSB do their job and find out what went wrong.

Exactly, jumping to the conclusion that it is safe is not helpful. Grounding the plane is exactly the opposite of jumping to a conclusion. It's declaring "we can't conclude that this plane is safe".

But you're on hn, where gog should just trust companies and bureaucrats and not ask questions or speculate in any way. Apparently using your brain here means you are a conspiracy theorist.

Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#47

Post by WalterBright »

simion314 wrote: post #30
ubernostrum wrote: post #17

Earlier quoted context omitted.

We are used from previous cases that aircrafts will get grounded until we are sure the airplane is not at fault. To be clear: you're suggesting that grounding an entire type of aircraft, either worldwide or even just within US airspace, is a common response to accidents? I ask because the last general grounding of a type was in 2013 to remedy the 787 battery issues. Prior to that , the last such grounding was the DC-…

Sorry, my experience was with incidents in my country and my memory could also play tricks on my. Anyway the question still stands, who and how decides if we should ground some airplanes?

The Smithsonian channel runs a weekly show "Aviation Disasters" which shows in detail how this is done.

Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#48

Post by WalterBright »

WalterBright wrote: post #7

The pilots would have seen the nose down action as an uncommanded stabilizer trim movement. The solution is to shut off the power to the stab trim. This would work and would require no knowledge of the stall avoidance mechanism.

Here's a picture of the cockpit, showing the location of the power switches, trim switches, and the wheel that turns when the stab trim is running.

I find it hard to understand how the pilots would not know the stab trim was moving, and how to cut it off.

https://www.nytimes.com/interactive/2018/11/16/world/asia/li...

Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#49

Post by ubernostrum »

simion314 wrote: post #30
ubernostrum wrote: post #17

Earlier quoted context omitted.

We are used from previous cases that aircrafts will get grounded until we are sure the airplane is not at fault. To be clear: you're suggesting that grounding an entire type of aircraft, either worldwide or even just within US airspace, is a common response to accidents? I ask because the last general grounding of a type was in 2013 to remedy the 787 battery issues. Prior to that , the last such grounding was the DC-…

Sorry, my experience was with incidents in my country and my memory could also play tricks on my. Anyway the question still stands, who and how decides if we should ground some airplanes?

Airlines can voluntarily ground their planes. Manufacturers can recommend it. Generally, only a government agency can force it and they only do so in truly extreme circumstances (often requiring multiple serious incidents). More commonly in the US, a directive will be issued to airlines telling them to carry out some remedy (fix/replace a part, change a procedure, etc.) and a window of time in which to complete it. They don't speculatively ground entire air fleets every time there's a potential problem.

For example, in 1991 a Boeing 737-200 crashed in Colorado with the loss of all lives on board. In 1994 there was another crash of a 737, in Pennsylvania, again killing everyone on board. In both accidents the investigation pointed to unexpected movement of the rudder.

Several other cases were identified where pilots claimed the rudder was moving unexpectedly, but they were able to land safely.

The follow-up took several years of investigative work, and eventually identified a situation where a servo could jam and deflect the rudder.

Despite two severe crashes and many other suspected non-fatal incidents, that generation of 737s was not grounded; the remedy, once the cause had been determined, was an order from the FAA to replace the servos, with a timeline by which the replacement had to be completed.

Re: Third Pilots' Union Raises Concern About Boeing 737 Max Jet

#50

Post by [deleted] »

sokoloff wrote: post #44
bronco21016 wrote: post #42

Earlier quoted context omitted.

Would runaway trim be the thing they were reacting to? It seems to me the trim was pitching down due to the design of the stall system. I’m imagining they were getting erroneous stall warnings due to the AOA sensor feeding bad data. If I’m in an aircraft and I’m getting stall warnings, stick shakers, and stick pushers I’m definitely not going to run runaway trim memory items.

It's pretty likely that they weren't reacting to runaway trim; on that we agree. The trim wheels are large, painted mostly black with alternating, offset white stripes (so the motion is quite visible), and have a very distinctive clacker on them. https://www.youtube.com/watch?v=cQirIH_DuAs It's possible that the crew fought to keep the airplane in a basic attitude flying configuration for several minutes without ever…

[deleted]
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