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Boeing 737 MAX crash and the rejection of ridiculous data

philip.greenspun.com

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Re: Boeing 737 MAX crash and the rejection of ridiculous data

#121

Post by bambax »

penagwin wrote: post #99
fixermark wrote: post #87

Earlier quoted context omitted.

Ah, see, I'm American. ;) The lane assist can be disabled and a cyclist who hard-brakes in front of me is taking their life in their hands because my Ford only stops if I touch the brake (it just stops as hard as it needs to to minimize risk of impact, regardless of how soft I push the pedal). (Sidebar: I almost feel like that cyclist game is something that should be solved with more sensors. If it's a common issue,…

The cyclist issue is something I don't consider a fault of software or the car's design. Driving/Cycling/Walking in front of a high speed vehicle who has the right of way to the point that they need to break means you should not have been there to begin with. The car's only other option is to hit the cyclist, so as far as I'm concerned it's doing it job correctly. Like you mention a dashcam is likely the only remedy…

I think the grandparent is talking about a situation where the cyclist is _behind_ the car and not in front of it. A modern car that brakes hard can decelerate much faster than a bike, and therefore becomes a brick wall.

When I'm on a bicycle I try to avoid cars as much as possible (by being in a lane for bikes, or on the sidewalk) but sometimes we have to share the road. Then I'd rather ride opposite to traffic because at least I see the cars incoming and can avoid them.

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#123

Post by VBprogrammer »

linuxftw wrote: post #118
VBprogrammer wrote: post #100

Earlier quoted context omitted.

That's not nearly the case. MCAS is a stupidly simple system intended to cut in during very unusual phases of flight were a normal commercial flight would not be operating.

> MCAS is a stupidly simple system So, you have reviewed the software? If it's so stupid simple, why did it kill a bunch of people?

Sigh. I've reviewed almost everything written about the accidents including the information supplied by Boeing to the airlines to explain the function of the MCAS system.

There is no lower limit on the complexity of a system required to kill people.

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#124

Post by noir_lord »

bambax wrote: post #115
chx wrote: post #70

I accidentally copypasted my one time login code into the amount of bill payment and my ebank didn't refuse the sixty seven million dollar payment (I caught it before sending it). Needless to say, I don't have and never had even one percent of that money. My brother one time actually succeeded in wiring ten million euros instead of ten million forints. The exchange ratio is 1:320. Obviously the account didn't have 10…

I sell stuff on Amazon European marketplaces. I sometimes change the price; you have to do that on each marketplace (there are 5: UK FR DE ES IT) in the interface for sellers. The decimal separator for UK/English is the dot; in all other marketplaces it's the comma. If you put a dot where a comma is expected it's silently ignored (so for example EUR 9.99 becomes EUR 999)... but "slowly": the dot you type appears norm…

I inherited a system that let you put AAA in the product price field and would persist it.

Validation is hard to get right so they simply didn’t try, not even common sense.

I’ve spent years thinking about the optimal way to structure validation and I’ve never come up with an approach I really like on an architectural level so I do the usual approach of simple sanity checks on the client and proper validation against business logic on the server but even that isn’t as isolated as I’d like.

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#125

Post by 05 »

cm2187 wrote: post #58
Diederich wrote: post #26

Earlier quoted context omitted.

Strongly suggest everyone check out the video. It's...kind of shocking.

One thing I don't understand is that if the trim is stuck in a position that pushes the plane down, shouldn't the high speed (and therefore strong air flow) help to put the trim back in a neutral position rather than making it more difficult?

Because of the nose up elevator..

Here's the explanation in one picture: [1]

Here's the article the picture came from: [2]

[1] https://3.bp.blogspot.com/-6c8hfXS8WO4/XKd93voscrI/AAAAAAAAF...

[2] https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-ra...

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#126

Post by geggam »

bambax wrote: post #121
penagwin wrote: post #99

Earlier quoted context omitted.

The cyclist issue is something I don't consider a fault of software or the car's design. Driving/Cycling/Walking in front of a high speed vehicle who has the right of way to the point that they need to break means you should not have been there to begin with. The car's only other option is to hit the cyclist, so as far as I'm concerned it's doing it job correctly. Like you mention a dashcam is likely the only remedy…

I think the grandparent is talking about a situation where the cyclist is _behind_ the car and not in front of it. A modern car that brakes hard can decelerate much faster than a bike, and therefore becomes a brick wall. When I'm on a bicycle I try to avoid cars as much as possible (by being in a lane for bikes, or on the sidewalk) but sometimes we have to share the road. Then I'd rather ride opposite to traffic beca…

Yes, the rear. I didnt make that clear.

When backing out the bikes can be 50 ft away coming fast and the car senses they will be close so it slams on the brakes way before anyone is in danger.

Coffee spills etc

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#127

Post by linuxftw »

VBprogrammer wrote: post #123
linuxftw wrote: post #118

Earlier quoted context omitted.

> MCAS is a stupidly simple system So, you have reviewed the software? If it's so stupid simple, why did it kill a bunch of people?

Sigh. I've reviewed almost everything written about the accidents including the information supplied by Boeing to the airlines to explain the function of the MCAS system. There is no lower limit on the complexity of a system required to kill people.

> including the information supplied by Boeing to the airlines to explain the function of the MCAS system

So, you're essentially parroting Boeing's narrative IMO. Yes, they want you to think that the system is 'stupid simple' and it's 'no big deal, just one little fix' because obviously that's good for their business.

Maybe, the system required for safe operation is not so simple, and Boeing is no longer competent enough to create a system. Perhaps the 'stupid simple' system was all they were able to muster.

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#128

Post by penagwin »

geggam wrote: post #126
bambax wrote: post #121

Earlier quoted context omitted.

I think the grandparent is talking about a situation where the cyclist is _behind_ the car and not in front of it. A modern car that brakes hard can decelerate much faster than a bike, and therefore becomes a brick wall. When I'm on a bicycle I try to avoid cars as much as possible (by being in a lane for bikes, or on the sidewalk) but sometimes we have to share the road. Then I'd rather ride opposite to traffic beca…

Yes, the rear. I didnt make that clear. When backing out the bikes can be 50 ft away coming fast and the car senses they will be close so it slams on the brakes way before anyone is in danger. Coffee spills etc

Whoops my bad! I thought you meant they were purposely traveling in front of the car, knowing it's sensors would force it to stop. It'd be super moronic and dangerous, but if you recognized the car model it would at least be possible.

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#129

Post by Gibbon1 »

fixermark wrote: post #59
Gibbon1 wrote: post #34

Earlier quoted context omitted.

Unless I'm wrong disabling the MCAS system leaves the elevator at the current trim as set by the jack screw. That's really not the behavior you want. You want the control to return to neutral. Which probably isn't the way the trim mechanism is designed. This whole thing smells like a bunch of dodgy decisions. Some of them recent and others historical. For instance not being able to manually adjust trim while the elev…

Not a pilot yet myself, but I know exactly enough about flight physics and control to suspect that while you are likely correct about the MCAS jack-screw positioning being undesired, the solution is probably not to auto-return it to neutral. If we assume MCAS is only disabled in an emergency, we don't want the result of cutting out an automated system to be further automatic manipulation of the control surfaces, righ…

> we don't want the result of cutting out an automated system to be further automatic manipulation of the control surfaces, right?

You have two separate things a pilot may need to do. One is disabling the MCAS control action. In that case you do want it to return to normal trim. Second is disabling the Automatic/Electrical Trim. In that case you want it to stop and allow the pilot to set the trim manually.

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#130

Post by toast0 »

dramm wrote: post #104
linuxftw wrote: post #4

Do we actually have the raw data from the sensor in the flight recorder, or do we have the flight computer's account of that sensor's data? > IF AOA > 15 AND AOA And if the AOA is frozen at 16 due to some fault? What is a loss of signal interpreted as? Does it use last-known value? 0? 100? How often does the AOA get sampled? Is there any attempt to smooth the data? Was the data corrupted (bit errors) during transmiss…

You seem to be arguing multiple sides here. Philip Greenspun's speculation is a plausible concern, that is all it needs to be a valuable point, that type of data limit handling ought to be considered as the system is looked at. I read his post that he was talking a specific simple example, all the other types of things you mention could also be looked at. How the AoA sensors failed, any potential issues with signal h…

> not even having a standard AoA disagree alert

Sorry to nitpick on one thing here; but I don't know that having an AoA disagree alert would be that useful. There was already an airspeed disagree alert, and AoA disagree strongly implies airspeed disagree, because AoA is involved in the airspeed calculation. Furthermore, knowing an AoA sensor is broken wouldn't be super useful without a workable procedure to do something about it; in the Ethiopia crash, the procedure followed was insufficient to regain control.

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