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Comment by MDWolinski | Hacker News Reader

All software is buggy. The problem with the MCAS system is that pilots were not informed that it was there, nor were they given a way to override it and take full control of the airplane. Also, while the MCAS system relied on two sensors, if either failed, the MCAS system itself failed, so there was no built in back-up for it.

Bugs in software happen because situations where they arise are sometimes hard to predict. You can test your software all you want but it's not until it's in the field that you start discovering new issues because people tend to do things in ways developers didn't consider.

Tesla's software has over a billion miles of data on it and it still has issues in some basic functionality. And let's not talk about Iowa which in itself was a major failure in software release management.

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@MDWolinski “.. while the MCAS system relied on two sensors ..”

MCAS used only the one sensor, this decision made so as to avoid recertification.

http://www.b737.org.uk/mcas.htm

“Are we vulnerable to single AOA sensor failures with the MCAS implementation or is there some checking that occurs?”

https://www.aviationtoday.com/2019/11/02/boeing-ceo-outlines...

Not all software is buggy to the point of killing almost four hundred people. Comparing some shit app some interns built for Iowa with avionics software is frankly insulting to the people who work hard to make avionics software. The same goes for Tesla. The avionics industry, including Boeing, used to have a great record in this area. Even if the mcas bugs were unavoidable, the fact still is that the design was fatally flawed due to either sensor being a single point of failure. And of course, the main problem that the whole, entire airplane is unstable in the air. How can you still make excuses for Boeing at this point in time? The only reason this bug should be irrelevant is because this plane should never carry another commercial passenger. But I'm sure profits will prevail over lives once again starting this summer or whenever the FAA gives their go ahead.

> And of course, the main problem that the whole, entire airplane is unstable in the air.

That's not really true. The airframe is fine, except it doesn't handle like a 737. MCAS was meant to make the MAX handle like a 737.

Mentour Pilot, a 737 instructor with a youtube channel, has covered this fairly extensively: https://youtu.be/TlinocVHpzk?t=951

Great video. But he says the exact same thing I did. The MCAS is necessary because of the different engine placement. So the airplane cannot recover from a stall without it. That, to me, makes the entire airplane unstable and improper for commercial flights as this is an expected condition at times that the plane should be able to recover from. The airplane cannot function without a deeply flawed software system no one understands and no one knows how to operate. Changing the software doesn't change any of these things.

It is possible to recover from a stall without MCAS, but the handling characteristics have changed. The requirement is that the force on the yoke increases with the angle of attack, but in the case of the MAX, the stick force becomes lighter at a certain point. As I understand it, Boeing was mainly trying to avoid training pilots for any changes.

> That, to me, makes the entire airplane unstable

That's fine, but know that the way you're choosing to use the word "unstable" doesn't square with how it's actually used in the aviation industry.

Ok. I should have said completely unsafe for commercial passenger use instead.

There is one specific Iowa which (if it was still in service) could become very deadly if it was using a buggy app.

> All software is buggy.

Assuming that's not hyperbole and just to be pedantic:

  mov ax,cs
  mov ds,ax
  mov ah,9
  mov dx, offset Hello
  int 21h
  xor ax,ax
  int 21h
  
  Hello:
    db "Hello World!",13,10,"$"

Bug report for you...

Expected: "Hello, World!"

Actual: "Hello World!" (missing comma)

See spec: https://en.wikipedia.org/wiki/%22Hello,_World!%22_program

Don't know why I thought this was so funny, but I did. =)

Sad thing we have little insight on microcode and the exact way machine code gets interpreted, for all we know there might still be a resulting bug from any step asm to execution.

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