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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Figaro » Fri Mar 22, 2019 7:51 am

This response is less about the technicalities of the cause/s of the crash/es, and more on the wider industrial implications, but I hope it is still welcome

According to this article from CNBC Garuda Indonesia has cancelled (or is seeking to cancel) an order of 49 737MAX aircraft. Only a few days ago I saw an article suggesting that perhaps Ethiopian Airlines will look to other manufacturers in the wake of the crash.

From a global perspective, it will be interesting to see how the international airline industry responds, and how Boeing is affected, by these incidents and their consequences. Have these crashes decreased confidence in Boeing, and if so, by how much?

-S
Last edited by Figaro on Fri Mar 22, 2019 7:52 am, edited 1 time in total.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby GinGin » Fri Mar 22, 2019 7:51 am

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.



That would be indeed quite usefull if the crew is now well briefed about MCAS with note about it in the FCOM and eventually additional training.

But even with a disagreement light or the AOA indicator without any informations/training on MCAS functionnalities, it would have been not so useful I think given no system was using AOA as a data for an automatic "protective" action in the 37NG ( hence in the Max without specific notes of new system implemented)




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


It depends on Airlines Training programm, but usually a huge part of training is based on understating well the AP mode and to recognize a nasty behavior that would require a quick action from crew (wrong mode for autoland for example)

Though in the 37 AP is quite simple, and controls are not fly by wire, but still mechanical with hydraulic assistance with feel sensors for yoke force feed back based on Aerodynamical conditions . So no normal and alternate law, no big surprise on aircraft handling even if a Static or Pitot tube failed.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Thorsten » Fri Mar 22, 2019 8:27 am

From a global perspective, it will be interesting to see how the international airline industry responds, and how Boeing is affected, by these incidents and their consequences.


Not much.

The A320neo is the equivalent plane of the competition - Airbus is churning those out as fast as possible and still there's a huge backlog in orders, if you cancel your Boeing order now and place an order with Airbus, you'll wait for 5 years or so till it gets delivered.

There's really not much of a choice for airlines even if they'd like to change now. Especially since the problem itself looks quite fixable, it can't cost the hell to use more than one sensor, alert the crew to disagreements and make it more transparent what the system is doing - it's not like they'd have to re-design the place from scratch.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Richard » Fri Mar 22, 2019 6:09 pm

legoboyvdlp wrote in 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.


Unfortunately two sensors isn't really a lot better than a one - as all the system can tell is that the sensors disagree - you really need (at least) 3 sensors in a redundant system before the system can decide which sensor is wrong. However I could see that using both sensors in this case could at least flash up a "disagreement sensor" or just drop the system out; but I don't fully understand the intricacies of MCAS enough to know whether that would even be possible.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Thorsten » Fri Mar 22, 2019 6:42 pm

Unfortunately two sensors isn't really a lot better than a one - as all the system can tell is that the sensors disagree


That is a lot better, because then it can prompt you to resolve the dilemma - either by de-selecting one sensor, or by switching the device off.

I'm vaguely guessing that if you have good airspeed, good vspeed and good altitude, you can derive a fairly decent AoA from that and compare it with the directly sensed one.

(Sorry, I have read a few dozen paper on redundancy management aboard my favourite spacecraft and coded most of the rules - it's not rocket science...)
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby tdammers » Fri Mar 22, 2019 10:04 pm

it0uchpods wrote in 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...


As I understand it, the problem is that the 737 MAX behaves extra badly in this particular situation (low airspeed, nose high, approaching stall); there simply isn't enough elevator authority to suffice with a stick pusher, and the normal trim controls aren't fast enough, so the Boeing engineers came up with this solution. It's not a bad idea per se, given the constraints; the major fuckup here is not having a warning indicator, not updating procedures, and not telling the pilots about it and training them to deal with MCAS malfunctioning (and I believe a major driver for this was the desire to sell the MAX as a drop-in replacement for the old 737).
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby caharpuka » Tue Mar 26, 2019 9:00 pm

legoboyvdlp wrote in 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).


I would accept this if it appeared to have been a discrete event (i.e. one dive) but it appears that at least in one case the pilots were trying to stabilize the aircraft for a while. How is it possible they didn't know how to disengage the system from the trim? Obviously Boeing have quite a lot of the blame here, but still seems quite negligent.

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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby legoboyvdlp » Tue Mar 26, 2019 10:24 pm

For a start if you cancel the MCAS manually with the electric trim switches it resets it - ie allowing it to trim a further few degrees down from the new reference position. So it's not obviously a runaway - if it keeps going nose down and you keep correcting the subsequent confusion may result in the nose trim going down to an extent where recovery is impossible before the problem is recognized and corrected.

It not being a standard runaway (such as e.g. the electric motor failing stuck on) might cause confusion
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby tdammers » Wed Mar 27, 2019 10:19 am

Yes, that is probably exactly it.

The "runaway stab trim" memory items from the classic 737 work just fine on the MAX: it amounts to shutting down the electrical trim system entirely, or, worst case, "overriding" it by physically holding on to the trim wheel with brute force. MCAS or not, this will prevent the aircraft from inputting any kind of trim from any system (including the yoke switches). So it seems logical that if the pilots had recognized the runaway, they would have done the right thing - but they didn't, meaning they probably didn't recognize the problem quickly enough.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby V12 » Fri Apr 05, 2019 5:52 am

At http://avherald.com/h?article=4c534c4a/0022&opt=1024 is preliminary report with FDR graph. Very interesting data, probably pilots made procedure stab trim runaway, but again switched on that 2 CUT-OUT switches and after 5 seconds MCAS made his final kamikaze attack.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Isaak » Fri Apr 05, 2019 6:39 am

Unbelievable. Thanks for the article, it clarifies a lot for me.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby V12 » Fri Apr 05, 2019 7:29 am

We need wait for final report, but FDR data are very interesting, especialy about :
1) at 5:40:35 on CVR is recorded that the First-Officer called out “stab trim cut-out” two times. Captain agreed and First-Officer confirmed stab trim cut-out.
2) at 5:40:41 on FDR is recorded MCAS command without stab movement what is clear evidence of stab trim cut-out switches are OFF
3) at 5:43:11 on FDR electric trim and stab movement , what is clear evidence of stab trim cut-out switches are ON
Why pilots when know that they are in stab trim runaway situation did not switched off that switches ? Strange. We don't know...
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby Johan G » Fri Apr 05, 2019 3:52 pm

Isaak wrote in Fri Apr 05, 2019 6:39 am:Thanks for the article, it clarifies a lot for me.

+1

There is some things there that raises my eye brows. In particular (my emphasis): :?
On Mar 21st 2019 the airline stressed that all pilots underwent the Boeing recommended and FAA approved differences training from the Boeing 737 NG to the Boeing 737 MAX aircraft before the MAX aircraft joined the Ethiopian Airlines fleet and before the pilots started flying the MAX. The pilots were also briefed on the EAD by the FAA concerning the LionAir accident. The airline further stressed: "The B-737 MAX full flight simulator is not designed to simulate the MCAS problems." The FAA had earlier, in February 2018, pointed out differences between the NG and MAX systems in their Flight Standardization Board (FSB) Report. This report notes as the only and only difference with respect to the trim system: "STABILIZER TRIM: Stab Trim cutout switches panel nomenclature".

It seems like the pilots was not trained to handle MCAS system faults and in that sense was fighting partially blind.

I also want to quote one of the comments to the article:
Phantom Phreek wrote:I read today:
CEO Dennis Muilenberg was addressing Wall Street on a conference call on April 26, 2017. He boasted about how quickly the company had brought the 737 Max to market — and praised the Federal Aviation Administration's "streamlined" certification process. He attributed that to the pro-business philosophy of the new administration.

Looks like the FAA will be taking on more certification testing soon.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby legoboyvdlp » Fri Apr 05, 2019 9:07 pm

Oh wow - according to an article I read (sorry, can't find the link again), the answer is in a procedure that was in the manual years ago for the -200 but was since removed.

The combination of full aft column and almost full nose down trim will result in extreme load on the jackscrew preventing it from moving easily. So in the -200 they developed a procedure where you release the column and trim rapidly, then pull the column again to stop the nose dropping and repeating until trim is normal. But that was removed many years ago.

So, think about the situation - the crew disconnect electric trim but due to nose down trim they can't climb but are holding back column. They can't manually trim due to high loads on the jackscrew. They're doing everything right - but something not described in the manual (again) prevents them from recovering the situation. So they reengage electric trim and MCAS pushes the nose down again making it impossible to recover.

Boeing has a lot to answer for if this is true.
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Re: Boeing Jets Lacked 2 Safety Features sold as Extra

Postby V12 » Sat Apr 06, 2019 4:19 am

The plane was flyable with 10 degs column pull around 3 minutes, but was heavy on the nose. If You can see FDR graph, the crew switched stab ON, used man elec trim nose up, stab surfaces moved, but they did not switched OFF again. After 5 seconds MCAS engaged again.
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