
They didn’t buy the DLC: feature that could’ve prevented 737 crashes was option - em3rgent0rdr
https://arstechnica.com/information-technology/2019/03/boeing-sold-safety-feature-that-could-have-prevented-737-max-crashes-as-an-option/
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cmurf
If you're not trained on the MCAS feature, an "AOA disagree" indicator is
going to tell you what? That stall warning may not work reliably?

There's more going on here than just MCAS and angle of attack sensors though.
From the KNKT preliminary report:

 _At 23:31:09 UTC, the LNI610 PIC advised the ARR controller that the altitude
of the aircraft could not be determined due to all aircraft instruments
indicating different altitudes._

Crash happens 45s later. (More correctly, the FDR stops recording.)

From the same report, four separate maintenance records containing one or more
defects in: indicated airspeed, indicated altitude, speed trim fail, mach trim
fail. These were reported by multiple crew, repaired by maintenance per
manufacturer procedure, and tested, and error state cleared.

The stick shaker was active for all of Lion Air 34 and most of 610. That is
not an airworthy aircraft, and the preliminary report states this.

Obviously something does not pass the smell test. Either there's a very
serious problem with the prescribed repair and verification procedure. Or
there's a very serious crime if the claimed repairs and/or verification are
inauthentic. Both seem incredible to me.

Common to airspeed and altimeter is the static system.

But as a pilot what really gets my attention, and not in a good way, is that
apparently automation is confused, detecting multiple current sensor
disagreements and flags, and yet it's still taking action.

~~~
olliej
Right? Especially given (per media so grain of salt maybe?) the Mcas system
was essentially engaged by a single sensor - implying a single sensor capable
of overriding all other systems, even the ones with actual redundancy.

I still don’t understand why altitude wasn’t considered - surely stalling
speed close to the ground would result in less damage than pitching towards
the ground an accelerating?

And how much can those sensors possibly cost anyway? (Real question - I have
no sense if we’re talking a few dollars, a few thousand, few million, or what)

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cjbprime
This seems grossly overstated to me.

The optional warning they're talking about is just a light in a random section
of the cockpit called "AOA disagree". That's it. It can't help the Lion Air
crew, because the world wasn't aware that AoA was hooked up to a control
surface through a new system called MCAS. And it's not in the central EICAS
error display, so it's not where the pilots are _supposed_ to be looking for
information to help them diagnose an emergency. And it doesn't explain
anything about why it might be _super bad_ that there's an AoA disagreement.

So even if you know that MCAS exists and could malfunction, you'd have to also
know that it uses AoA internally. Basically, the light only helps you if you
already know both what MCAS is and how it works, and at that point you
probably weren't going to be crashing anyway?

The correct information in the cockpit to use to help with the problem is what
the Lion Air crew did the day before the crash: get a stall warning, see and
hear that the trim wheels keep moving, notice that the yoke feels heavy, and
move to the memory item for runaway trim.

~~~
olliej
I mean the real story should be “how much did a single light to say the flight
computer was deliberately fighting you cost?”

It’s an optional extra so I suspect that one led was being charged at an
absurd rate, because it was actually necessary.

The flight crew the day before had to hunt through manuals as well, and I
haven’t seen any indication anywhere that suggested that the problem persisted
for that entire flight - which could easily be the case if you tie a pilot
overriding flight control system to a single sensor. Further I’d question a
flight control system that pushes the nose down apparently without considering
altitude

~~~
cjbprime
Hey, I don't mean to pick on you, and I'm not a pilot, but everything in this
comment seems incorrect in one way or another:

> It’s an optional extra so I suspect that one led was being charged at an
> absurd rate

The optional extra is actually an AoA visual display, and the light just comes
along for the ride with the display. It's letting you know that you can't rely
on the AoA display. It's not trying to communicate danger or emergency. That's
not its job. There's already a system called EICAS for the plane to
communicate urgent errors to the pilots, and that's where pilots look.

> because it was actually necessary

It really really wasn't. That light should not be used by pilots to diagnose
anything. We don't want pilots to have to know _how_ the airplane's internal
systems were built. The MCAS system ultimately performs trim operations. We
want pilots to notice trim aberrations, which have many possible causes
(including purely mechanical ones!), and know how to disable the trim motor if
the automatic trim is malfunctioning. If they can do that, they can solve many
more problems than just MCAS. And if they can't do that, their plane will
nosedive from many more causes than just MCAS.

> I haven’t seen any indication anywhere that suggested that the problem
> persisted for that entire flight

As I understand it, it didn't persist on the flight the day before because the
third pilot correctly noticed that the trim was misbehaving and performed the
STAB TRIM CUTOUT that disables the motor, as trained. If the motor hadn't been
disabled, MCAS would have continued to use it to mistrim.

> I’d question a flight control system that pushes the nose down apparently
> without considering altitude

Why? Wing stalls are _the most common_ cause of aviation fatalities. They
usually happen during takeoff or landing, at less than 1000ft. If they
happened at altitude they wouldn't be fatal because you have time to recover
from them.

If one is building a system to try to prevent wing stalls -- and one should
because it's the lowest hanging fruit for reducing the fatality rate of
aviation -- that system should absolutely operate at low altitudes when you're
in the critical period of a stall being effectively unrecoverable once a spin
starts, because it takes a minimum of hundreds of feet to recover. That's the
time when the system matters most.

