Boeing Unveils 737 Max Software Fixes (cnbc.com)

hcs_$reboot shares a report from CNBC: Boeing previewed its software fix, cockpit alerts and additional pilot training for its 737 Max planes on Wednesday, saying the changes improve the safety of the aircraft which has been involved in two deadly crashes since October. By the end of this week, Boeing plans to send the software updates and plan for enhanced pilot training to the FAA for certification approval. After the FAA approves the fix, Boeing said it will send the software update to customers. Among the notable changes to the MAX flight controls:

• The plane's Maneuvering Characteristics Augmentation System, or MCAS, automated flight control system, will now receive data from both "angle of attack" sensors, instead of just one.
• If those disagree by more than 5.5 degrees, the MCAS system will be disabled and will not push the nose of the plane lower.
• Boeing will be adding an indicator to the flight control display so pilots are aware of when the angle of attack sensors disagree.
• There will also be enhanced training required for all 737 pilots so they are more fully aware of how the MCAS system works and how to disable it if they encounter an issue.

Comments

Sensors are physical objects

[Firethorn]

Because the sensors are physical devices, and are this subject to all physical device problems. They can break, corrode, be bent by a physical impact, etc...

They're regularly inspected, which is about the best you can do.

Re:Sensors are physical objects

[viperidaenz]

No, it's intended to stop a stall from happening by automatically adjusting the stabilizer trim as the elevators don't have enough pitch authority to counteract the pitch-up caused by the more powerful engines.

The system is intended to allow the plane to be certified without redesigning the elevators.

Re: Sensors are physical objects

[viperidaenz]

thrust is what causes the stall this system is designed to mitigate.

The most thrust you apply to an aircraft the low mounted engines, the more the aircraft pitches up, making a stall more likely.

If the aircraft has tiny elevators, like the 737, there is a point where the thrust is pitching the aircraft up more than they can correct, given the current angle of attack.
In that situation, there are only two things you can do to stop a stall
1) lower the thrust that is pitching the aircraft up
2) use the stabilizer trim to change the angle of the rear stabilizer - which is what MCAS does automatically.

Re:Sensors are physical objects

[dgatwood]

What really rules the h/w angle out is the similar fault on (at least) two unrelated flights.

It only rules out hardware if you assume that the failure is a random fluke. If it is the result of a mechanical design flaw or an under-specified simple component like a resistor, capacitor, or transistor, hardware failing in the same way isn't particularly rare. For example:

GPU thermal failures often result in a small number of different sets of identical symptoms; the same solder balls break more frequently because of their location and the way that the chip expands.

At one point, I was involved in a group buy of some preamplifier hardware from a manufacturer in China. There was something like a 40% failure rate, and it was caused by a single transistor being substituted with a lower-quality part that became unstable in the presence of too little capacitance. And they all failed with the exact same symptom, en masse.

And a particular age range of certain models of TV failed en masse because of capacitor plague. In every case, the symptom was that they wouldn't turn on.

Or consider the T-Con board that drives various LCD panels in TVs. They fail with alarming regularity, to such a degree that there's actually a third-party company manufacturing new replacement boards for old TVs. There are only a few different failure modes, usually involving one color channel stuck off or on, and statistically if you buy a used board, nearly 100% of the time you'll get a bad one, because it's the #1 cause of replacing TVs that contain certain models of T-Con board.

And I can also recall a hard drive connector built by a major manufacturer that was attached by a screw on only one end, and repeatedly would work its way lose, requiring a complete redesign of the hardware in the next generation.

You get the idea.

Re:Sensors are physical objects

[ti1ion]

No, you are wrong. It is not specifically intended to stop a stall. Read up on the issue. It is intended to let all qualified 737 pilots fly the Max WITHOUT EXTRA TRAINING. This plane has different stall characteristics, meaning it does different things when it stalls. Normally, you would train a pilot to notice what it is doing and adjust accordingly. But, that requires training that Boeing told airlines they would not have to do. So, Boeing designed MCAS specifically to make the Max behave like a regular 737 when approaching a stall, ie. kick the nose down. By doing that, the pilot is supposed to be able to see a familiar characteristic and say *ding* *ding* *ding*, my plane is stalling. NO EXTRA TRAINING. MCAS is not a stall prevention system, but a Maneuvering Characteristics Augmentation System. To learn more, at least read the first three paragraphs of this article:

https://theaircurrent.com/avia...

And all the white nationalists talking about foreigners in this thread is sickening. Sad to see Slashdot being overrun by these maggots.

Re:Why wasn't it done in the first place!?

[bobbied]

MCAS wasn't *supposed* to be life critical. Quite the opposite, the Pilots where supposed to be able to override it by grabbing the controls. The problem was that it *became* life critical over time and nobody properly noted the design change's impact and then they failed to see (or just flat ignored) this fact.

Re:Encouraging news. Still nervous.

[viperidaenz]

The amount of pitch up with the newer more powerful engines got to a point where when the plane is already at a high angle of attack, the elevator don't have enough authority to counter act it. The entire rear stabilizer needs to be moved using the stabilizer trim.

Other planes have larger elevators or less pitch-up under full thrust.

Re:Why wasn't it done in the first place!?

[Chrontius]

Per recent reports, the cockpit voice recorder shows that they were in the middle of it.

And according to Boeing's simulations, they only had forty seconds between stick shaker activation and a rapid unplanned deceleration, so...