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Old 03-24-2019, 04:41 PM   #141
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Have you seen horrific videos of these two well-known stalls of large military aircraft, one a C-17 and the other a B-52?

Both were flown by experienced hotshot pilots who were very familiar with the aircraft they were flying, and were known to push the planes to the limits.

They were practicing for an airshow, went too far, and killed themselves along with the rest of the flight crew.

PS. In both cases, the pilots entered a steep bank with the airspeed too slow for such a maneuver. The wing inside the bank stalled first, making the aircraft roll even more, and they could not level out.

Yes I have seen the B-52 crash many times and remember the story associated with it. Definitely pilot error and ego that caused this one. 'Bold pilots and old pilots...'
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Old 03-24-2019, 05:14 PM   #142
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According to some sources, pilots did not know about this new MCAS, and they tried to fly the 737 MAX just like the old 737. Not knowing about this new feature, then getting confused by the stick shaker and possible erroneous airspeed and altitude indicators caused them to not see the right corrective thing to do.

And then, allowing the MCAS to keep ratcheting its stabilizer authority by 2.5 degrees each time it activates really aggravates the problem. If the MCAS authority is strictly limited, the crashes might not happen.

From a Web site:
Quote:
It’s probably this counterintuitive characteristic, which goes against what has been trained many times in the simulator for unwanted autopilot trim or manual trim runaway, which has confused the pilots of JT610. They learned that holding against the trim stopped the nose down, and then they could take action, like counter-trimming or outright CUTOUT the trim servo. But it didn’t. After a 10 second trim to a 2.5 nose down stabilizer position, the trimming started again despite the Pilots pulling against it. The faulty high AOA signal was still present.
Thanks, I'd read about the different response the MAX had to counter-yoke, but hadn't put 2+2 together.

Still (ref my bolded section above), I'm not buying it. Let's say that these guys had instead been flying an older 737 version (no MCAS) that also had a faulty sensor for yoke pressure. A contact in the trim switch gets stuck and so the trim runs to full nose down trim. So they would die? They don't know what those two switches labelled "STAB TRIM" do? They don't know the steps required to use those very prominent manual pitch trim wheels?






And it's not a crisis situation, they've got time to figure things out. Even if they just keep countering the MCAS with electric trim every 10 seconds (as the Lion Air crew did about 20 times IIRC), they can keep doing that until somebody figures out what those switches there do.

FWIW, the correct boldface (memory) procedures for runaway stabilizer trim are:
Quote:
  1. CONTROL COLUMN - HOLD FIRMLY
  2. AUTOPILOT (if engaged) - DISENGAGE
    Do not re-engage the autopilot. Control airplane pitch attitude manually with control column and main electric trim as needed
    If the Runaway Continues
  3. STAB TRIM CUTOUT SWITCHES (both) - CUTOUT
    If the Runaway Continues
  4. STABILIZER TRIM WHEEL - GRASP and HOLD
It doesn't say "counter trim with yoke pressure and hope the trim stops running."

If the crew of either accident aircraft had taken the steps above, there would have been no crashes. These are procedures that competent crews are required to know cold--no looking in a manual.

Now, if the trim runs away long enough and the airspeed is high enough, there comes a point where it is >very< difficult to trim using the wheels (i.e. two brawny crewmembers pulling on the wheels with all their might can't move the stab to the right position). This never becomes an issue if the stab is returned to the proper spot using the switches on the yoke (which is always possible whatever MCAS is commanding), then turned off.
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Old 03-24-2019, 06:40 PM   #143
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... If the crew of either accident aircraft had taken the steps above, there would have been no crashes. These are procedures that competent crews are required to know cold--no looking in a manual...
That's why I wonder if there were other things that confused them.

Is it possible that they were too busy worrying about the false stalling, debating between themselves about whether to trust the airspeed and altitude indicators, hence neglecting to look at the trim wheel, which in other 737 aircraft never did give them any trouble?

When the autopilot is not engaged, what moves the stabilizer? In theory, the manual trim switches on the yoke could get stuck, but I am not familiar with the 737 and hope that they are dual switches. If so, the chance of a switch being stuck is fairly remote, or much less likely than an alpha vane error. The trim motor itself would be driven by 2 relays connecting to the high/low sides, and the motor also has an electrical clutch to engage it only when needed.

I would venture that run-away stabilizer trim failure is a fairly rare incidence, and the crew was preoccupied with other things happening to think of it. If anyone has any info on the frequency of stabilizer trim running away in a modern commercial jet, please share it.
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Old 03-24-2019, 07:00 PM   #144
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About limiting the authority of automatic functions on an aircraft to no more than necessary for a particular job, I remember the following flight test.

They were flight-testing our new flight control system, and I was sent on a flight as an observer. Included on the flight card that day was a test/demo of failure of the yaw damper/turn-coordination function of the autopilot.

As this function was deemed non-critical, the autopilot only needed single inputs from the sensor suite, and drove the rudder through a series actuator whose movements were not reflected at the pilots' pedals. The series actuator by design had a limited authority and could drive the rudder only +-2.5 degrees.

To prove that it was safe, the test engineer in the back, while in flight, flipped a prewired switch that shorted 28V across the series actuator motor, driving it hard to its stop. There was no failure mode of any sensor or electronics that could cause the motor to go faster than that!

I heard a "thunk" from the tail of the jet, which was followed by a mild turning and rolling of the jet. The test pilots let it go for a few seconds, then made the manual correction to straighten out the aircraft. The test engineer then flipped the "failure insertion" switch back to its normal position.

And that was that. No big deal.

For landing the aircraft, the autopilot needed access to the parallel servo that had full rudder authority. It was called "parallel" because its action was reflected in the pilots' pedals, and they would want to know what it was doing. In order to engage in the autoland mode and drive all the control surfaces to max deflection, the autopilot had to have a full complement of all redundant sensors. Everything had to be at least dual and in agreement. And the autopilot was also dual-channel. And the parallel servos were also dual in all axes of control.
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Old 03-24-2019, 07:51 PM   #145
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To alert the crew that the stabilizer is moving, is there any aural warning in the 737?

Some McDonnell Douglas aircraft have the CAWS (Central Aural Warning System) that cries out "Stabilizer Motion... Stabilizer Motion..." whenever the stabilizer motor is running, whether commanded manually or by the flight control system.
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Old 03-24-2019, 08:38 PM   #146
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I would venture that run-away stabilizer trim failure is a fairly rare incidence, and the crew was preoccupied with other things happening to think of it.
I'm sure it is very rare in flight, but in my experience it is a "favorite emergency" in the simulator. It is quite an attention-getter. And, in some planes/failure modes, the trim does not just go one way and stop at the limit switch, but instead cycles back the other way reversing direction repeatedly. I would be very surprised if no one onthe flight deck had seen this in the sim.

But, 737 MAX simulators are still not common, and they are not required (crews current in other 737 models generally go through a short period of "difference training" academics). I'm assuming that these older sims have the pre-MAX feature of ceasing the trim actions when a crewmember applies opposite yoke pressure. If so, crews exposed to this emergency could have developed habits that would not serve them well in the 737MAX. Ideally, the "runaway trim" routine at the sim's instructor console would keep the trim running despite yoke pressure, to reinforce use of the cutoff switches (as called for in the memory procedure).


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To alert the crew that the stabilizer is moving, is there any aural warning in the 737?

Some McDonnell Douglas aircraft have the CAWS (Central Aural Warning System) that cries out "Stabilizer Motion... Stabilizer Motion..." whenever the stabilizer motor is running, whether commanded manually or by the flight control system.
I don't know if there is an aural warning on the 737, but it is hard to believe it would be required. Between the actions of the plane itself, the yoke pressures, and the large spinning wheels with the white stripes--well. If the CAWS activates every time the stabilizer is moving (autopilot, manual electric trim, etc) it must be very distracting (or the crews mentally tune it out because it is so common).
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Old 03-24-2019, 08:49 PM   #147
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... I'm assuming that these older sims have the pre-MAX feature of ceasing the trim actions when a crewmember applies opposite yoke pressure. If so, crews exposed to this emergency could have developed habits that would not serve them well in the 737MAX...


If this is how the actual old 737 aircraft works in normal flight, then why should the sim be different?

I would think that for a run-away trim simulation, they would keep the motor running until the power switch is turned off.

PS. I talked about simulators built by CAE of Montreal earlier. They used the real avionics hardware as on the aircraft whenever possible. And that included all the flight control systems, displays, warning systems, etc... Of course they had to simulate all the sensors and actuators interfaced to the flight control computers in addition to the aircraft aerodynamics, so that the latter thought they were flying the real aircraft. Hence, all man/machine interactions were as with the real aircraft.
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Old 03-24-2019, 08:59 PM   #148
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If this is how the actual old 737 aircraft works, then why should the sim be different?

I would think that for a run-away trim simulation, they would keep the motor running until the power switch is turned off.
Let's say the co-pilot's trim switch is calling for nose-down trim (contacts malfunctioning or not). If the captain applies opposite yoke-- (pulling the yoke aft), does the trim in the aircraft cut out? I think it does, but I'm not sure. Now, if you want to train crews in the proper by-the-book procedure (which call for use of the cutout toggle switches), then in the simulator, when the console operator calls for a runaway trim malfunction, the sim should >not< stop the trim motor from running when opposite yoke pressure is applied, instead it will only stop when the cutout toggle switches are used.
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Old 03-24-2019, 09:02 PM   #149
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... when the console operator calls for a runaway trim malfunction, the sim should >not< stop the trim motor from running when opposite yoke pressure is applied, instead it will only stop when the cutout toggle switches are used.
Yes.

But you also need to train the crew how the aircraft behaves in normal flight, when things work normally. And indeed you want the "normal condition" to prevail in the real aircraft.
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Old 03-26-2019, 04:37 PM   #150
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Southwest Boeing 737 Max makes emergency landing in Orlando; FAA cites engine issue unrelated to recent crashes
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Old 03-26-2019, 06:30 PM   #151
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An expert says not all B-737 MAX planes can fly until July or August 2019.

That's because although the software fix can be uploaded by an engineer from a laptop to an aircraft in one hour, not every foreign aviation agency will follow the lead of the FAA to approve the fix, and will want to conduct their own review.

See: https://www.msn.com/en-us/money/comp...ove/ar-BBVgitT.
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Old 04-09-2019, 07:38 AM   #152
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... If the crew of either accident aircraft had taken the steps above, there would have been no crashes. These are procedures that competent crews are required to know cold--no looking in a manual.

Now, if the trim runs away long enough and the airspeed is high enough, there comes a point where it is >very< difficult to trim using the wheels (i.e. two brawny crewmembers pulling on the wheels with all their might can't move the stab to the right position). This never becomes an issue if the stab is returned to the proper spot using the switches on the yoke (which is always possible whatever MCAS is commanding), then turned off.


Recent report on the Ethiopian crash: https://www.bbc.com/news/world-africa-47553174.

Pilots did switch off the electric drive to the stabilizer drive, but then were not able to move the stabilizer using manual wheels.

The article has a time history plot of the readings from the two alpha vanes. The left sensor used by the MCAS went hardover to 60 deg after take-off. The MCAS software took this ridiculous reading at face value!
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Old 04-09-2019, 08:25 AM   #153
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Pilots did switch off the electric drive to the stabilizer drive, but then were not able to move the stabilizer using manual wheels.
Yes, but from the timeline they fought the trim ( control input opposite the trim) for about 3 minutes. That is an incredibly long time. During this time the electric trim should have been turned off and they could have been trimming using the wheel. The pressures on the jackscrew and trim system built up as speed increased. This would not happen if the plane was kept in trim (using either the wheel or through repeated use of the switches). As I mentioned, there comes a point where neither the manual wheel nor the trim motors are effective. This isn't a design failure.
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Old 04-09-2019, 08:33 AM   #154
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I dunno.

I am not sure that even an expensive fancy motion base simulator would have some hardware to simulate how the stabilizer manual wheels behave under different speeds.

How did Boeing turn a supposedly benign MCAS into something so critical with their design?

If they insisted that their design was right, they would have stood steadfast and not changed the software to now require two sensors in agreement. They could just issue more bulletins to tell pilots what to do.
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Old 04-09-2019, 09:13 AM   #155
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It is a bit disingenuous for officials/press reports to say that the crews followed procedures and the procedures didn't work. They (apparently) only attempted to use the procedures after it was far too late. An extreme analogy would be if they got a fire indication for the number one engine and watched it blink for 3 minutes before cutting the fuel and discharging the extinguisher. Did they follow the procedure? I guess, eventually. Do we blame Boeing if the fire burns through the wing spar ? (Bad design to put that spar so close to the engine nacelle, and all that fuel stored right above an engine--why would they do that!!?)
Boeing is going to make the software better, along with the crew training. It can all certainly be improved.
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Old 04-09-2019, 09:14 AM   #156
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Originally Posted by stepford View Post
... My question is, how large do you allow a single equity position to get before you rebalance?

my largest holding is over 10% ( but under 15% ) ( the second largest 5% )

at one stage it was closer to 25% but i reduced the large holding because the company was making a series of bad decisions ( but i was still in healthy profit ) not solely because the holding was so large

if a small holding had of made a similar run of bad decisions i would have exited it completely ( take the money and run )

regarding Boeing , i would probably wait a little longer , some impacted airlines might sue for losses or reduce the number of planes ordered
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Old 11-08-2019, 12:26 PM   #157
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This thread started out as a stock-picking idea, then evolved into some technical discussions. We ran out of things to talk about, and the thread died.

I am still curious about this subject, so still follow the story on the news. What I thought should be a simple fix turned out to be a long delay. So, there is apparently more to the story, and we will not know the technical details for a while.

Just now, saw an article on Bloomberg which I cannot read without a subscription. The introduction is tantalizing:

Quote:
Delays in Boeing Max Return Began With Near-Crash in Simulator

Boeing Co. engineers were nearly done redesigning software on the grounded 737 Max in June when some pilots hopped into a simulator to test a few things.

It didn’t go well...
And then,
Quote:
You have reached your free article limit
Hmmm... Do they track readers' computers by IP address or by cookies? Should I fire up my desktop to see if I can read above article?
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Old 11-08-2019, 02:24 PM   #158
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OK, here's the same article, but found on another Web site.

It sounded like Boeing has been addressing other issues more complex, and not directly related to the alpha vane failure and the MCAS.

https://www.heraldnet.com/business/d...or-near-crash/
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