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Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Necolatis » Thu Mar 21, 2019 3:42 pm

https://www.nytimes.com/2019/03/21/business/boeing-safety-features-charge.html

Why on earth should you pay extra for 2 features that can save lives, sounds crazy..
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Thorsten » Thu Mar 21, 2019 5:17 pm

Why on earth should you pay extra for 2 features that can save lives, sounds crazy.


Not if you want to sell something and make money - then it sounds crazy for someone not to pay extra for something that can save lives.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby wlbragg » Thu Mar 21, 2019 5:42 pm

I think this is the perfect example of using technology the wrong way. Indicator = warning OK, Indicator = overriding the pilot control, not OK. These pilots are supposed to be experienced, they shouldn't be getting into a stall positions in the first place. It sound like a simple stall indicator is being replaced with a mechanical system that takes control as if it know best, which in potentially two cases now, it didn't.

What is the politics behind this?

Cost more money to use technology to replace what should be experience of a pilot.

So you have an airline that might be cutting cost by hiring less experienced pilots, but they spend money on a system that is supposed to augment that lack of experience, instead, it works against that lack of experiance?
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Thorsten » Thu Mar 21, 2019 6:01 pm

In hindsight it looks like the kind of design one of us would write as a quick hack into an FG FCS to make something work, not really like something that actually flies in a real aircraft or would be approved by any aviation authority.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby GinGin » Thu Mar 21, 2019 6:09 pm

Why on earth should you pay extra for 2 features that can save lives, sounds crazy..



Well, despite a very well written article, the case is a bit more complex thant being resumed to those 2 optionnal features.

Airbus or Boeing, AOA indicator are optionnals , and quite rare on companies.
That is a very useful tool though, reading the direct AOA tells a lot about the aerodynamical of the aircraft. It is massively used for Military aircraft, in approach specially.

But it is possible to have a reading of the aoa through the flight path vector present on most modern aircraft directly on the PFD or on the HUD for those whom are equipped.
Here on a 737 NG ( same on Max)

Image

The flight path vector ( circle on the horizon, level flight), and pitch indicator ( black dot at 5 ° of pitch)
You can have a picture of the AOA.

Here, the crash discussion is mainly about the MCAS system which took data from just one AOA sensor surprinsgly ( instead of 2 after the patch that will occur)
So, one faulty AOA sensor, and MCAS system is going nuts thinking the aircraft is reaching flight envelop limit with high incidence. AOA indicator or not, it would not have changed that behaviour.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby GinGin » Thu Mar 21, 2019 6:10 pm

Thorsten wrote in Thu Mar 21, 2019 6:01 pm:In hindsight it looks like the kind of design one of us would write as a quick hack into an FG FCS to make something work, not really like something that actually flies in a real aircraft or would be approved by any aviation authority.


Indeed, really surprising a so poor redundance for an invasive system like that.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby legoboyvdlp » Thu Mar 21, 2019 6:12 pm

The somewhat mistifying thing is that with two sources of AOA available the system only uses one -- it alternates between left and right each flight. That is a terrible idea - a system like that needs redundancy.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby wlbragg » Thu Mar 21, 2019 7:01 pm

So, one faulty AOA sensor, and MCAS system is going nuts thinking the aircraft is reaching flight envelop limit with high incidence. AOA indicator or not, it would not have changed that behaviour.


That is even worse, why didn't the pilots know where the big red OFF button is?
Any automated system that can control the critical control surfaces of the aircraft at such a low altitude needs to be fully understood. This new automated system effectively took thousands of hours of pilot experience and reduced it to a single switch that none of them new about.

There is really no excuse here if this second crash is understood to be the same cause as the first, pilots not understanding the system and how to shut it off.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby GinGin » Thu Mar 21, 2019 7:28 pm

Well, even if they didn't really know about the MCAS system, the procedure for an airspeed unreliable ( Following a problem with the AOA vane) and Stab trim Runaway ( consequence of the MCAS trimming down) are supposed to be known as they are memory items


Image


After the Lion Crash, Bulletin Boeing was sent to put a stress on those procedures in cas it will happen again.

https://theaircurrent.com/aviation-safety/boeing-nearing-737-max-fleet-bulletin-on-aoa-warning-after-lion-air-crash/


The switchtes to disconnect the electric motor from AP and manual electric trim ( that is used by MCAS) are there ( Stab trim cutout switches)

Image



That still didn't explain the lack of redundance, based one jsut one AOA and lack of information in the FCOM and additional training for pilot coming from 737 NG
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby WoodSTokk » Thu Mar 21, 2019 7:37 pm

wlbragg wrote in Thu Mar 21, 2019 7:01 pm:That is even worse, why didn't the pilots know where the big red OFF button is?
Any automated system that can control the critical control surfaces of the aircraft at such a low altitude needs to be fully understood. This new automated system effectively took thousands of hours of pilot experience and reduced it to a single switch that none of them new about.

There is really no excuse here if this second crash is understood to be the same cause as the first, pilots not understanding the system and how to shut it off.


I think thats an missunderstanding (or bad wording of Boeing).
There is a NNC (Non Normal Checklist) in the handbook with the title 'Stabilizer trim runaway'.
If you follow this NNC, you will switch both to 'CUTOFF'.

But whats your meaning of 'runaway' ?
Normally a runaway is if the trimwheel continously rotate until it reach the end.
But MCAS doesn't do that. It rotates the wheel just a little bit, wait 10 seconds and rotate again a little bit.
IMHO this behavior is NOT a runaway, it's a sneakaway.
It can be that the pilots of both accident had the same meaning/understanding of 'runaway' and jump over that checklist.

Addition to that, a pilot will look in the handbook if the aircraft is stable with a nice attitude.
The problem starts directly after take off. As the problems began the aircraft was never stable and maximum 1000 AGL.
The pilots havn't time to look into the handbook. They have all tryed to stabilize the aircraft.

BTW, on the previous flight of LionAir (LNI043 from Denpasar to Jakarta) the crew has the same problems.
The Pilot switched to CUTOFF and the FO is flown manually to Jakarta.
In Jakarta all failures and problems was reported.
The alpha vane (AOA sensor) was replaced.
Thats mean the alpha vane was NEW!
I have never heared of a sensor that goes immediately wrong on the first flight.
I think the problem of the B737 MAX is behind the sensor. Can be the cables, data bus, air data module or anything else.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby GinGin » Thu Mar 21, 2019 7:42 pm

But MCAS doesn't do that. It rotates the wheel just a little bit, wait 10 seconds and rotate again a little bit.
IMHO this behavior is NOT a runaway, it's a sneakaway.


Yes, but it is also faster thant the manual electric trim. 2 Cycles of MCAS could almost move the Stabilizer at the limit of trim settings.
Sneaky situation.
Even a "little bit" for MCAS will be a huge displacement of the trim wheel
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby legoboyvdlp » Thu Mar 21, 2019 11:35 pm

That is certainly a major problem. By the time you disconnect the trim you will be massively nose down - meaning you will probably enter a nose dive with increasing speed (also straining the motor and airframe). You may just not have time to manually trim out the dive much less pull out of it (while keeping your wings on the aircraft).
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Octal450 » Fri Mar 22, 2019 2:36 am

My question.... WHY the stabilizer?
Why not use a stick pusher like the 717 and MD-80/90 have? This works much better, its impossible to not notice it, and overriding is easy. You try turning those wheels from a bad stab position while fighting with the elevator to control pitch...

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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby GinGin » Fri Mar 22, 2019 6:17 am

It would have probably required some additional training seeing the difference with a NG. The point they wanted to avoid.

@Legoboyvdlp: Indeed, tricky situation. The flight before the Lion air one had exactly the same thing and recognized the runaway luckily.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Thorsten » Fri Mar 22, 2019 7:06 am

I guess the point of the additional safety features is - how quickly does one recognize a sensor fault?

The Shuttle avionics sure is a confusing beast, but there's one thing to be said - any sensor disagreements are made glaringly obvious once they occur, and you never need to rely on the filtered state vector, you can always access the raw measurements as well - and if three out of four air data readings give you the same Mach number and one is different - you have a pretty good suspicion what is going on.

That'd be the point of the disagreement light - giving the crew extra time by alerting them quickly to the fact that AoA readings are not consistent across all systems.

It would seem the problem is fairly easy to address once you realize correctly what it is.

I believe we actually have a fairly good test case in FG - observe what people do when a virtual AP makes an attempt to kill them. I usually disconnect the AP and save such 9/10 situations - but I write AP code, I know precisely what it does when it malfunctions and how the signs of an integrator windup or so look like. But there's plenty of bug reports where people wait too long till the situation can not be saved any more - either because they do not diagnose the issue correctly, or because they trust the AP somehow has a hidden plan behind what it does.

I don't know how much mistrust against the AP is part of regular pilot training - but lack of this seems to be at the heart of the issue. And for instance the AoA disagreement alert light might have helped here.
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