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Author Topic: This is why you don't bindly disable DTCs  (Read 11591 times)
nyet
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« on: March 13, 2019, 04:11:52 PM »

Notice the HUGE discrepancy between the two AoA sensors (20+ degrees). Notice that MCAS is *still* forcing the nose down.

In ME7, this would be noticed by the monitor, which would throw an implausibility code. At that point, it would disable anything that would use that input, unless you are stupid enough to disable implausibility checks. Have fun running your airplane into the ground.

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« Reply #1 on: March 13, 2019, 04:33:35 PM »

Sometimes when i see some complex management systems like those in planes i think 'wow this guys really badass in coding' because i cant even imagine how much situations and conditions theyre calculated in ecu, how they tested all of these and how much safety monitors / limp modes / dtc conditions etc theyre implemented because its a people lives.  (yep im comparing it with 20yrs me7 too)

But thats a really bad news how easily a stupid code (is it italian magnetty marelly btw?) can be responsibly to our lives
« Last Edit: March 13, 2019, 04:36:46 PM by fukenbroken » Logged
dal
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« Reply #2 on: March 13, 2019, 05:19:20 PM »

Thats really really sad.
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Risky
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« Reply #3 on: March 13, 2019, 05:28:42 PM »

Forgive my ignorance on the situation, but this whole incident was because someone disabled a "DTC"?

Edit: Some other people I know are saying the pilots are instructed to disable the sensor, so that way the computer doesn't get a false nose dive reading, if the sensor is faulty. Again forgive my ignorance.
« Last Edit: March 13, 2019, 05:34:50 PM by Risky » Logged
nyet
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« Reply #4 on: March 13, 2019, 05:37:38 PM »

https://www.seattletimes.com/business/boeing-aerospace/black-box-data-reveals-lion-air-pilots-struggle-against-boeings-737-max-flight-control-system/

Quote
The data confirms that a sensor that measures the plane’s angle of attack, the angle between the wings and the air flow, was feeding a faulty reading to the flight computer. The two angle-of-attack sensors on either side of the jet’s nose differed by about 20 degrees in their measurements even during the ground taxi phase when the plane’s pitch was level. One of those readings was clearly completely wrong.

This should trigger an implausibility fault and MCAS should be disabled, and both inputs ignored. It should not be up to the pilot to disable MCAS.

Quote
On any given flight, the flight computer takes data from only one of the angle-of-attack (AOA) sensors, apparently for simplicity of design. In this case, the computer interpreted the AOA reading as much too high an angle, suggesting an imminent stall that required MCAS to kick in and save the airplane.

But apparently, no such fault was triggered, so it just randomly chose a sensor to use.

Yes, this is exactly what happens when a hack ME7 "pro tuner" decides to just disable a DTC.
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« Reply #5 on: March 13, 2019, 05:56:21 PM »

Thanks for clearing that up. RIP to those 189 people that died on the flight.
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nyet
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« Reply #6 on: March 13, 2019, 10:24:58 PM »

What I don't understand is which sensor is "wrong".

Right (green) clearly can't be right, it's showing negative alpha during climbout.

But if left (red) is right, then MCAS is properly triggering, since red is showing a much higher AoA.

The only reasonable answer is that neither reading is right. Right is reading too high, and left is reading too low. Really strange.

Unfortunately, the NTSB doesn't trust the average schmo with technical information, and you'll never see the mainstream media do any useful reporting on anything technical.

Pathetic, really.
« Last Edit: March 13, 2019, 10:28:55 PM by nyet » Logged

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« Reply #7 on: March 13, 2019, 11:53:17 PM »

Well that is just crazy that there was no plausibility checking between 1. The equivalent sensor on the other side of the plan 2. A known value or typical value before take-off.  I mean how could something like that not be in place?  It seems to be the most basic of tests.  It also shifts blame entirely towards Boeing and the Boeing engineering team.  They need to understand that their error has cost > 400 lives.
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« Reply #8 on: March 14, 2019, 03:34:58 AM »

Rest assured this plane is grounded by every single country lol.. also its one thing to fuck around with ur own car,hopefully in a place with no traffic , and its one thing to fuck up something that 150+ travel on hourly...

Boeing is amazing , they are doing some good stuff but this is unacceptable.
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nyet
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« Reply #9 on: March 14, 2019, 09:06:40 AM »

Rest assured this plane is grounded by every single country lol.. also its one thing to fuck around with ur own car,hopefully in a place with no traffic , and its one thing to fuck up something that 150+ travel on hourly...

Boeing is amazing , they are doing some good stuff but this is unacceptable.

Copy pasted from another discussion I have been participating in. This should terrify you (if true)

Quote
I asked what I think Nyet would ask - if there are two AoA sensors, but only one is being used for input, wtf is the other one there for and doing?


Response - It's doing jack shit. It's on hot standby, but unused until the pilot selects it for use during flight planning.


me - What? who chooses which sensor is the one that will used? At build, a computer, or it's actually chosen by the pilot?

Response - yes, the pilot and co-pilot during flight planning are agreeing on the settings and toggle positions for various things, and which sensor is toggled on that plane. Airbus uses an automated system that will choose one sensor for one leg, then swap to the other sensor on the next leg.

Me - But the max8 has no "argue sensor" right?

Response - correct. The airbus has a third sensor who's duty is to "argue" with the input of whatever AoA sensor is active to check it's validity.
« Last Edit: March 14, 2019, 12:07:58 PM by nyet » Logged

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« Reply #10 on: March 14, 2019, 09:10:53 AM »

Copy pasted from another discussion I have been participating in. This should terrify you (if true)


Dang..thats fucked up, but apparently Lion Air wasnt the best at maintenance either to cut costs... I'll take my car on trips Cheesy ( i know plane is one of the safest way to travel but whatever Cheesy)
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Risky
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« Reply #11 on: March 14, 2019, 12:10:33 PM »

The data I heard was the plane was going 430 knots. That is a big no no and 180 knots (I think that's what he said) at takeoff is the max that ATC allows. More than that you're speeding and you get a "ticket." (lol) They had changed the the auto-trim routines on that plane because of the increased thrust of the new engines, and changed the anti-stall programs. So the 400+ airspeed makes me think that the anti-stall was fighting the auto-pitch/trim routines, and the one system nose down's the plane, and the anti-stall kicks into push full thrust, so I think that basically both were fighting and caused the plane to pitch down and at the same time demand full thrust, driving it into the ground, which is why you end up with a massive crater, rather than a skidmark.


That is some scary shit. Can you just imagine?
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nyet
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« Reply #12 on: March 14, 2019, 02:38:45 PM »

That is some scary shit. Can you just imagine?

Pretty nuts.. btw Apologies for deleting that section from my post, but i did so because i dont see "430 knots" anywhere in the OP graph
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« Reply #13 on: March 14, 2019, 02:59:38 PM »

Pretty nuts.. btw Apologies for deleting that section from my post, but i did so because i dont see "430 knots" anywhere in the OP graph

it does, look at the end of graph ( when the plane crashes) it speed up by 200 knots or so.
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littco
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« Reply #14 on: March 14, 2019, 03:11:53 PM »

Pretty nuts.. btw Apologies for deleting that section from my post, but i did so because i dont see "430 knots" anywhere in the OP graph

Nyet, I am a pilot by profession and fly commercially, one thing that is not shown that graph is the throttle position ( speed is ). The whole reason Mcas was fitted to these new MAX aircraft was to over come the larger engines which where further forward and higher than the older NG ones, this meant with a change of power (not speed) setting the pitch moment was greater ( up or down ) and thus MCAS was fitted to correct this. Issue with these is that pilot training and conversion from the old aircraft to new ones was a 1 hour conversation including a supposed youtube video. With auto throttles, and the stage of flight they where, IE flap retractions and gear, the possibility for the MCAS to over correct is possible and then big changes in pitch to occur that the pilot due to lack of suitable training where not prepared for, leading to a war between a pilot that wants to 1 thing and a flight computer wanting to do the opposite. The planes wins and result is a non survivable pitch down. It is as much pilot lack of training, the system could of been turned off, as much as it is bad programming for allowing it, ie trip out. It could be the error was noted by the crew but the paper work allowed them to fly, The Mcas was seen , I believe as a flight enhancer rather than a safety critical item. Ie makes the crews life easier.

I agree with the AOA sensors, but generally the air date computer will take both sets of data and for the auto pilot use the sensor relating to the side which is flying, IE of the captain is flying on the left use the left hand AOA sensor, should this fail then the backup will be used, but typically a set limit of tolerance will be built in, ie 6degress then a fault flag will be given, this will be part of the whats called an MEL will give guidance to the pilots if they can fly with the error or not, and in some cases it will allow this.

I am no expert on this particular plane by any means but I know from experience until a problem happens it may have gone unnoticed for years and not been any issue. Computers are only as good as the people who program them or the people that use them.

« Last Edit: March 14, 2019, 03:15:06 PM by littco » Logged
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