mzlin
Posts: 107
Joined: Sat Mar 31, 2012 6:32 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:28 am

speedbored wrote:
Aviation737 wrote:
Wait so the pilots didn't follow Boeing's procedure at all?

If the latest reports are to be believed then yes, they did. And they found that it couldn't be made to work, at least not quickly enough to save the aircraft.


I don't think it's accurate to say "it couldn't be made to work." In the case of ET302, it didn't work because they let MCAS continue to function after they had (temporarily) recovered the aircraft to positive vertical speed. However it could have worked if they had cut electrical power to the stabilizer a second time, while they were ascending. So they actually ALMOST made it to work.
 
mzlin
Posts: 107
Joined: Sat Mar 31, 2012 6:32 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:33 am

mjoelnir wrote:
Aviation737 wrote:
Wait so the pilots didn't follow Boeing's procedure at all?


I would say that following Boeing´s procedure killed them.

There is a need for a switch automatic trim off.

After the action of MCAS you need the electric trim to FAST trim the frame again, but Boeing's procedure compels you to switch electric trim off.


Also not quite correct. Boeing's procedure does say in the fine print that you may want to use electrical trim to get the trim to the correct position before cutting off electric trim.

I would say that MCAS activation at low altitude indeed requires the pilots to have their wits about them, as they have to know to re-trim then cut off electrical trim at the right time, and not, say, just pull back on the yoke or cut the electrical trim when the trim is down. So the pilots really need to be well prepared and have their wits about them.

So I would suggest that it was not guaranteed that a pilot in one of the US airlines (WN, AA, UA) would actually have done the right series of steps when faced with this confusing situation right after takeoff. It could be plain luck that an accident like ET302 or Lion Air didn't already happen in the US.
 
jollo
Posts: 349
Joined: Mon Aug 08, 2011 7:24 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:38 am

flybucky wrote:
mzlin wrote:
"The pilots on Ethiopian Airlines Flight 302 initially reacted to the emergency by shutting off power to electric motors driven by the automated system, these people said, but then appear to have re-engaged the system to cope with a persistent steep nose-down angle. It wasn’t immediately clear why the pilots turned the automated system back on instead of continuing to follow Boeing’s standard emergency checklist, but government and industry officials said the likely reason would have been because manual controls to raise the nose didn’t achieve the desired results. After first cranking a manual wheel in the cockpit that controls the same movable surfaces on the plane’s tail that MCAS had affected, the pilots turned electric power back on, one of these people said. They began to use electric switches to try to raise the plane’s nose, according to these people. But the electric power also reactivated MCAS, allowing it to continue its strong downward commands, the people said."

My guess it that they could not adjust the trim with the manual wheel due to stabilizer load. Satcom Guru just published a new blog article about this very topic:

A mistrim situation can result if the stabilizer is trimmed nose down and the elevator is commanded nose up. The opposing lift components combine at the jackscrew to create a large upward force, making trimming stabilizer leading edge down difficult. While electric trim motor is designed to not stall out under mistrim conditions, the loads may make trimming by the manual trim wheel very difficult. Under these circumstances, it may be preferable to release the column and let the elevator return to the neutral position, lowering the jackscrew loads and making manual trim easier.

While it's easy to say this during analysis, it's not so easy to remember to do in an emergency situation. Especially since this was probably never covered in any training.

My guess is that since they were not able to trim with the manual wheel, then they re-enabled Electric Trim. Perhaps they got it somewhat leveled out, but now MCAS is kicking in. And if you're under high workload and panic, you could easily lose track of the stabilizer position for a few seconds (especially when they were turning back), and that's all it takes at their AGL to reach an unrecoverable dive.


Well (addressing in particular member dragon6172), so it looks like ET's flight crew did read Boeing's bulletin, and did try to apply the suggestion in the "Note" (counter excessive aerodynamic loads on the trim wheel using electric trim). They just didn't to it in the correct order: they should have first brought the stabilizer back to near-neutral with electric trim and then cutoff stab trim. Of course, that's easy to say behind a keyboard and with the benefit of hindsight, much less in an aircraft diving to the ground at 1200 ft AGL.

But guess what? Non-Normal Checklists are there precisely to guide pilots through the right sequence of steps (right actions in the right order) to stabilize an abnormal situation. If the Runaway Trim NNC had actually been changed after Lion Air (introducing a mandatory step to use electric trim to neuter stab before cutting off the actuator, and amending the misleading Condition: "Uncommanded stabilizer trim movement occurs continuously", which makes applicability to MCAS runaway ambiguous) and had MAX pilots undergone specific sim training on the new NNC, then MAYBE the ET's crew would have had a fighting chance (I'm not convinced at 1200 ft AGL, but maybe).

Of course, this would have done nothing to mitigate the unbelievable decision to certify and push into service an airliner vulnerable to catastrophic upsets on the failure of a single sensor unless the crew reacts with the correct sequence of actions within seconds. But at least it would not give the message that Boeing has been playing with the lives of people (and the business of clients) to cover-up the mistake of an over-ambitious sales manager promising to a client an impossible result.
Last edited by jollo on Wed Apr 03, 2019 8:45 am, edited 3 times in total.
 
User avatar
speedbored
Posts: 2207
Joined: Fri Jul 19, 2013 5:14 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:38 am

mzlin wrote:
speedbored wrote:
Aviation737 wrote:
Wait so the pilots didn't follow Boeing's procedure at all?

If the latest reports are to be believed then yes, they did. And they found that it couldn't be made to work, at least not quickly enough to save the aircraft.


I don't think it's accurate to say "it couldn't be made to work." In the case of ET302, it didn't work because they let MCAS continue to function after they had (temporarily) recovered the aircraft to positive vertical speed. However it could have worked if they had cut electrical power to the stabilizer a second time, while they were ascending. So they actually ALMOST made it to work.

I wasn't talking about whether or not they could have possibly carried out a sequence of actions that might have recovered the aircraft. I was simply stating that it appears that they could not make the procedure that Boeing had specified work, as manual trim required too much force. IMO, Boeing should not have made the use of electric trim before cutout to correct the MCAS input an optional postscript; they should have mandated it. Expecting the pilots to work out the correct procedure by trial and error, when they have a very limited amount of time, is just negligent.
 
Interested
Posts: 647
Joined: Thu May 19, 2016 12:19 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:40 am

If we forget the technical analysis for one post - basically the Ethiopian pilots found themselves in an awfully difficult situation and did their very best to save the plane and the passengers in the circumstances

And there's not one pilot or person on here that can from a distance be sure what they would have done in the exact same circumstances

I'm sure some would save the plane and some wouldn't in same situation. Regardless of nationality

There's got to be some element of luck and gut instinct involved as well
 
XRAYretired
Posts: 484
Joined: Fri Mar 15, 2019 11:21 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:47 am

mzlin wrote:
speedbored wrote:
Aviation737 wrote:
Wait so the pilots didn't follow Boeing's procedure at all?

If the latest reports are to be believed then yes, they did. And they found that it couldn't be made to work, at least not quickly enough to save the aircraft.


I don't think it's accurate to say "it couldn't be made to work." In the case of ET302, it didn't work because they let MCAS continue to function after they had (temporarily) recovered the aircraft to positive vertical speed. However it could have worked if they had cut electrical power to the stabilizer a second time, while they were ascending. So they actually ALMOST made it to work.

ALMOST kills as many people as COULDNT!

Seems 'almost' is the watchword for the whole sorry saga.

Ray
 
User avatar
SuseJ772
Posts: 874
Joined: Wed Aug 10, 2005 11:13 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:47 am

I said this about 60 pages ago and the WSJ article only reinforces my belief that, while the AoA is the initial issue, the MCAS system of course caused the crash, it was however the fact the system had a bug in it that even if you followed their post-Lion Air AD it still was not behaving as engineers would expect. This was truly the nail in the coffin that no matter what those poor pilots did they were not going to get out of it.

I think this also all the more explains why the software update is taking so long. It’s buggy and it’s s problem.
Currently at PIE, requesting FWA >> >>
 
uta999
Posts: 700
Joined: Mon Jun 14, 2010 11:10 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 9:56 am

Suppose the software 'fix' and some training fails to satisfy the authorities, the airlines, or the public. What does Boeing do next, bearing in mind the MAX is still coming off the FAL @ 50-60 per month? That could soon be 500 grounded aircraft with no Plan B. Is it possible to convert some of them back to NG if it all goes south for the MAX?
Your computer just got better
 
flybucky
Posts: 175
Joined: Tue Apr 17, 2018 7:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 10:04 am

Another bit of info: MCAS was re-engaged 4 times after the ET302 pilots turned it off.

Boeing anti-stall software on a doomed Ethiopian Airlines jet re-engaged as many as four times after the crew initially turned it off due to suspect data from an airflow sensor, two people familiar with the matter said.

https://www.reuters.com/article/us-ethi ... SKCN1RF0YU
 
SimonL
Posts: 39
Joined: Tue Mar 12, 2019 3:38 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 10:25 am

flybucky wrote:
Another bit of info: MCAS was re-engaged 4 times after the ET302 pilots turned it off.

Boeing anti-stall software on a doomed Ethiopian Airlines jet re-engaged as many as four times after the crew initially turned it off due to suspect data from an airflow sensor, two people familiar with the matter said.

https://www.reuters.com/article/us-ethi ... SKCN1RF0YU


Reengaged as in reengaged by the pilots or was it never really disengaged? (retoric)
Last edited by SimonL on Wed Apr 03, 2019 10:32 am, edited 1 time in total.
 
jollo
Posts: 349
Joined: Mon Aug 08, 2011 7:24 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 10:26 am

SuseJ772 wrote:
I think this also all the more explains why the software update is taking so long. It’s buggy and it’s s problem.


Technically, just adding the logic to disable MCAS automatically in an AoA disagree condition would be easy and safe: the MAX would fly perfectly well without MCAS for 99.999% of flight time, and an inoperative MCAS could be safely compensated by pilot training (e.g. new memory items such as speed and bank limits) for the remaining 0.001% of contingencies. I suspect (no hard data here) this logic has already been implemented in KC-767A and KC-46. I also bet (speculation here) that this logic was considered at some point during the design phase: it's a basic principle of automation design to disable the controller if inputs are invalid, and I just refuse to believe Boeing engineers ignore the basics. I also suspect (more speculation here) it's not a bug: the decision not to include this logic in the current implementation was not technical, and was driven by commercial constraints.

What's taking so long is Boeing making sure they have covered all possible contingencies: they know they will not have another chance if they bungle this fix. Making sure you've considered all possible failure modes is awfully hard, and takes time.
 
User avatar
SheikhDjibouti
Posts: 1717
Joined: Sat Sep 30, 2017 4:59 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 12:27 pm

SimonL wrote:
flybucky wrote:
Another bit of info: MCAS was re-engaged 4 times after the ET302 pilots turned it off.

Boeing anti-stall software on a doomed Ethiopian Airlines jet re-engaged as many as four times after the crew initially turned it off due to suspect data from an airflow sensor, two people familiar with the matter said.

https://www.reuters.com/article/us-ethi ... SKCN1RF0YU


Reengaged as in reengaged by the pilots or was it never really disengaged? (retoric)
You missed option 3, as mentioned up thread with a reference to HAL (or HAL 9000)
Did MCAS take matters into it's own hands and decide to re-engage itself?
It really is quite a chilling thought...….Image
Usual thx to wikipedia.

(No, I'm not actually serious. Such an idea would be totally ludicrous and not even Boeing would be that stupid. Er... would they? :duck: )
Nothing to see here; move along please.
 
User avatar
PixelFlight
Posts: 507
Joined: Thu Nov 08, 2018 11:09 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 12:35 pm

SimonL wrote:
flybucky wrote:
Another bit of info: MCAS was re-engaged 4 times after the ET302 pilots turned it off.

Boeing anti-stall software on a doomed Ethiopian Airlines jet re-engaged as many as four times after the crew initially turned it off due to suspect data from an airflow sensor, two people familiar with the matter said.

https://www.reuters.com/article/us-ethi ... SKCN1RF0YU


Reengaged as in reengaged by the pilots or was it never really disengaged? (retoric)

In the schematic I have see on the Satcom Guru, both stab trim cutout switches removes the power supply to the relay that switch the main supply to the actuator. I think this was a 737 NG schematic, not a 737 MAX, but it is believed to be the same for this precise function. Unless new information changing the picture, the actuator could not move without the relay engaged, regardless of the origin of the command signal (trim switches or FCC). So either the pilots reengaged the relay (stab trim cutoff switch -> ON), or yet another fault in the system still let the relay engaged.

Obviously the investigators are now under stress to prove every single details that could matter in the crash. Why know, there is maybe a electrical fault somewhere that prevent the relay to disengage. But we know from JT043 that the stab trim cutout swicthes worked as designed at least on that flight.
 
Amexair
Posts: 56
Joined: Tue Sep 08, 2009 8:16 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 1:32 pm

flybucky wrote:
mzlin wrote:
"The pilots on Ethiopian Airlines Flight 302 initially reacted to the emergency by shutting off power to electric motors driven by the automated system, these people said, but then appear to have re-engaged the system to cope with a persistent steep nose-down angle. It wasn’t immediately clear why the pilots turned the automated system back on instead of continuing to follow Boeing’s standard emergency checklist, but government and industry officials said the likely reason would have been because manual controls to raise the nose didn’t achieve the desired results. After first cranking a manual wheel in the cockpit that controls the same movable surfaces on the plane’s tail that MCAS had affected, the pilots turned electric power back on, one of these people said. They began to use electric switches to try to raise the plane’s nose, according to these people. But the electric power also reactivated MCAS, allowing it to continue its strong downward commands, the people said."

My guess it that they could not adjust the trim with the manual wheel due to stabilizer load. Satcom Guru just published a new blog article about this very topic:

A mistrim situation can result if the stabilizer is trimmed nose down and the elevator is commanded nose up. The opposing lift components combine at the jackscrew to create a large upward force, making trimming stabilizer leading edge down difficult. While electric trim motor is designed to not stall out under mistrim conditions, the loads may make trimming by the manual trim wheel very difficult. Under these circumstances, it may be preferable to release the column and let the elevator return to the neutral position, lowering the jackscrew loads and making manual trim easier.

While it's easy to say this during analysis, it's not so easy to remember to do in an emergency situation. Especially since this was probably never covered in any training.

My guess is that since they were not able to trim with the manual wheel, then they re-enabled Electric Trim. Perhaps they got it somewhat leveled out, but now MCAS is kicking in. And if you're under high workload and panic, you could easily lose track of the stabilizer position for a few seconds (especially when they were turning back), and that's all it takes at their AGL to reach an unrecoverable dive.


It's looking more and more to be the likely case. If so, then Boeing really messed up here by not amending the RUNAWAY TRIM NNC, which would have required additional sim training.
 
User avatar
speedbored
Posts: 2207
Joined: Fri Jul 19, 2013 5:14 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 1:55 pm

Amexair wrote:
It's looking more and more to be the likely case. If so, then Boeing really messed up here by not amending the RUNAWAY TRIM NNC, which would have required additional sim training.

I don't believe that they messed up. I suspect that this was entirely deliberate in an attempt to avoid $280m of contractual penalties to Southwest, and probably additional penalties to some other airlines.

I also suspect that the additional delay to the release of the MCAS "software fix" is not due to additional changes to the software but due to discussions with the FAA and others in an attempt to avoid having to make associated changes to the differences training, which could also trigger those penalties.
 
2175301
Posts: 1437
Joined: Wed May 16, 2007 11:19 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 2:01 pm

If the WSJ article is correct; then a big question in my mind is what is the problem with the components, wiring, or maintenance procedures or practices that have resulted in these two apparently false repeated activations of the MCAS system.

Occasional failures and improper maintenance occur for all parts. Is this just rare events lining up - or is there a common cause because something is not right.

I am sure that Boeing and the investigation teams will be looking at that.


Have a great day,
 
dtw2hyd
Posts: 7070
Joined: Wed Jan 09, 2013 12:11 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 2:03 pm

If KC-46 already has a better implementation of MCAS, why can't Boeing just port it to MAX. This is not the right to keep counting beans.
 
maint123
Posts: 172
Joined: Sun Nov 04, 2018 4:18 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 2:05 pm

SheikhDjibouti wrote:
SimonL wrote:
flybucky wrote:
Another bit of info: MCAS was re-engaged 4 times after the ET302 pilots turned it off.



Reengaged as in reengaged by the pilots or was it never really disengaged? (retoric)
You missed option 3, as mentioned up thread with a reference to HAL (or HAL 9000)
Did MCAS take matters into it's own hands and decide to re-engage itself?
It really is quite a chilling thought...….Image
Usual thx to wikipedia.

(No, I'm not actually serious. Such an idea would be totally ludicrous and not even Boeing would be that stupid. Er... would they? :duck: )

You mean the trim breaker is switched off by the pilots but the breaker switches itself on again, like a auto reset breaker ? Maybe some actual Boeing experts can weigh in on this. But I doubt.
Only way would be if the breaker has a short after being switched off and allows current to flow to the motor but here the downstream switches and relays would prevent further transmission of current.
 
PlanesNTrains
Posts: 9527
Joined: Tue Feb 01, 2005 4:19 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 2:29 pm

uta999 wrote:
Suppose the software 'fix' and some training fails to satisfy the authorities, the airlines, or the public. What does Boeing do next, bearing in mind the MAX is still coming off the FAL @ 50-60 per month? That could soon be 500 grounded aircraft with no Plan B. Is it possible to convert some of them back to NG if it all goes south for the MAX?


Probably a better question in the Grounding thread.
-Dave


MAX’d out on MAX threads. If you are starting a thread, and it’s about the MAX - stop. There’s already a thread that covers it.
 
User avatar
dennypayne
Posts: 239
Joined: Tue Mar 13, 2012 3:38 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 2:36 pm

speedbored wrote:
Amexair wrote:
It's looking more and more to be the likely case. If so, then Boeing really messed up here by not amending the RUNAWAY TRIM NNC, which would have required additional sim training.

I don't believe that they messed up. I suspect that this was entirely deliberate in an attempt to avoid $280m of contractual penalties to Southwest, and probably additional penalties to some other airlines.

I also suspect that the additional delay to the release of the MCAS "software fix" is not due to additional changes to the software but due to discussions with the FAA and others in an attempt to avoid having to make associated changes to the differences training, which could also trigger those penalties.


Getting out of this mess for $280m might be considered cheap at this point. Moreover, if I was a MAX pilot, I think I would suggest simulator training is the right thing to do, but of course none of them at this moment will be able to replicate either the current situation, or the proposed fix.
A300/310/319/320/321/332/333/343/380 AN24/28/38/148 AT72 B190
B717/722/732/3/4/5/7/8/9 742/744/752/753/762/763/764/772/773/788
CR2/7/9 D8S D9S D95 DHC2/3/7/8 D328 E110/120/135/140/145/170/175/190
F100 J31 L1011 L410 M11/80/90 RJ85 S340 SSJ100 T134/154 Y42
 
XRAYretired
Posts: 484
Joined: Fri Mar 15, 2019 11:21 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 3:33 pm

PixelFlight wrote:
SimonL wrote:
flybucky wrote:
Another bit of info: MCAS was re-engaged 4 times after the ET302 pilots turned it off.



Reengaged as in reengaged by the pilots or was it never really disengaged? (retoric)

In the schematic I have see on the Satcom Guru, both stab trim cutout switches removes the power supply to the relay that switch the main supply to the actuator. I think this was a 737 NG schematic, not a 737 MAX, but it is believed to be the same for this precise function. Unless new information changing the picture, the actuator could not move without the relay engaged, regardless of the origin of the command signal (trim switches or FCC). So either the pilots reengaged the relay (stab trim cutoff switch -> ON), or yet another fault in the system still let the relay engaged.

Obviously the investigators are now under stress to prove every single details that could matter in the crash. Why know, there is maybe a electrical fault somewhere that prevent the relay to disengage. But we know from JT043 that the stab trim cutout swicthes worked as designed at least on that flight.

I would suspect the report is a confusion of either or both the source and the reporter. Perhaps the '4 times' is in reality a number of iterations of MCAS either during T/O climb or upon re-engagement of STS (MCAS) leading to the dive.

Ray
 
User avatar
PW100
Posts: 3719
Joined: Mon Jan 28, 2002 9:17 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 3:41 pm

PixelFlight wrote:
SimonL wrote:
flybucky wrote:
Another bit of info: MCAS was re-engaged 4 times after the ET302 pilots turned it off.



Reengaged as in reengaged by the pilots or was it never really disengaged? (retoric)

In the schematic I have see on the Satcom Guru, both stab trim cutout switches removes the power supply to the relay that switch the main supply to the actuator. I think this was a 737 NG schematic, not a 737 MAX, but it is believed to be the same for this precise function. Unless new information changing the picture, the actuator could not move without the relay engaged, regardless of the origin of the command signal (trim switches or FCC). So either the pilots reengaged the relay (stab trim cutoff switch -> ON), or yet another fault in the system still let the relay engaged.

Obviously the investigators are now under stress to prove every single details that could matter in the crash. Why know, there is maybe a electrical fault somewhere that prevent the relay to disengage. But we know from JT043 that the stab trim cutout swicthes worked as designed at least on that flight.


The 737 NG has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* MAIN ELECT
* AUTO PILOT

The 737 MAX has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* PRI
* B/U

How would a MAX pilot know which one to use, what functions they have, and how they differ in functionality from the NG?
Also, was this difference covered in the one hour iPad conversion course?
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
 
hivue
Posts: 1903
Joined: Tue Feb 26, 2013 2:26 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 3:48 pm

The elevator blowback phenomenon discussed extensively up-thread may have denied the crew sufficient trim authority at the high airspeed they reached and at their altitude AGL even when they switched stab trim back on when turning the wheel didn't work. What an awful trap.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
User avatar
7BOEING7
Posts: 3038
Joined: Fri Oct 12, 2012 5:28 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 4:02 pm

PW100 wrote:

The 737 NG has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* MAIN ELECT
* AUTO PILOT

The 737 MAX has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* PRI
* B/U

How would a MAX pilot know which one to use, what functions they have, and how they differ in functionality from the NG?
Also, was this difference covered in the one hour iPad conversion course?


There are no procedures that require the flight crew to turn off one or the other switch — the only procedure is to turn off both switches. As far as the flight crew is concerned the switches could be listed as THING 1 and THING 2.
 
Unflug
Posts: 726
Joined: Wed Jan 11, 2012 5:25 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 4:11 pm

7BOEING7 wrote:
PW100 wrote:

The 737 NG has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* MAIN ELECT
* AUTO PILOT

The 737 MAX has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* PRI
* B/U

How would a MAX pilot know which one to use, what functions they have, and how they differ in functionality from the NG?
Also, was this difference covered in the one hour iPad conversion course?


There are no procedures that require the flight crew to turn off one or the other switch — the only procedure is to turn off both switches. As far as the flight crew is concerned the switches could be listed as THING 1 and THING 2.


Not that it matters much, but what is the reason to change such labels? If the name doesn't matter, why change it?
 
User avatar
7BOEING7
Posts: 3038
Joined: Fri Oct 12, 2012 5:28 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 4:16 pm

Unflug wrote:
7BOEING7 wrote:
PW100 wrote:

The 737 NG has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* MAIN ELECT
* AUTO PILOT

The 737 MAX has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* PRI
* B/U

How would a MAX pilot know which one to use, what functions they have, and how they differ in functionality from the NG?
Also, was this difference covered in the one hour iPad conversion course?


There are no procedures that require the flight crew to turn off one or the other switch — the only procedure is to turn off both switches. As far as the flight crew is concerned the switches could be listed as THING 1 and THING 2.


Not that it matters much, but what is the reason to change such labels? If the name doesn't matter, why change it?


Probably related to maintenance procedures.
 
kalvado
Posts: 1812
Joined: Wed Mar 01, 2006 4:29 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 4:17 pm

7BOEING7 wrote:
PW100 wrote:

The 737 NG has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* MAIN ELECT
* AUTO PILOT

The 737 MAX has the following TWO cut-out switches on the pedestal:
Label: STAB TRIM (NORMAL - CUT OUT)
* PRI
* B/U

How would a MAX pilot know which one to use, what functions they have, and how they differ in functionality from the NG?
Also, was this difference covered in the one hour iPad conversion course?


There are no procedures that require the flight crew to turn off one or the other switch — the only procedure is to turn off both switches. As far as the flight crew is concerned the switches could be listed as THING 1 and THING 2.

and this can be another pile of coal for Boeing grilling.
Procedure is what it is to keep grandfathered irrelevant procedure. Logically, THING A should disconnect autopilot wiring and be sufficient for MCAS/STS disabling and keeping electric trim; while THING B should kill all power.
If there would be a procedure to keep thumb switches alive while killing computer driven motion, blowback could be a lesser issue, as well as return to trim timing... But all is in the name of no extra training.
 
SimonL
Posts: 39
Joined: Tue Mar 12, 2019 3:38 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 5:53 pm

From what ive read the pilots seems to have done what they could. MCAS was activated and after the 2nd time they cut the switches, which seems quite normal. They correctly identified the issue and used the correct procedure to handle it. But now they where left with a misstrimmed aircraft they could not manually trim. And its easy to imagine one pilot holding the control column and the other desperately trying to move the trim wheel. Already here the situation has deviated from the expected and they are left to improvise. At this point they decide to reengage the electric trim, which imo is the correct thing to do in the situation. It is not clear if they disengaged it again or not but its not impossible that they came to the conclusion that the manual trim was jammed and thus saw it as their only option to fly with electrical trim enabled. Its easy to understand why it went south from here because pretty much nothing in their training are providing them with any solution and they where in the end mentally overwhelmed..
 
flybucky
Posts: 175
Joined: Tue Apr 17, 2018 7:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 6:08 pm

kalvado wrote:
Logically, THING A should disconnect autopilot wiring and be sufficient for MCAS/STS disabling and keeping electric trim; while THING B should kill all power.

Yes, that's what I first assumed when I saw the 737 NG pictures showing Main and Autopilot Stab Trim Cutoff switches. That would have made a lot of sense to be able to disable Autopilot Trim while leaving Electric Trim on.

But then I saw the checklists, and there is nothing about switching one of them only. My speculation is that if at least one of them is ON, then both Auto Trim and Electric Trim are ON. That could explain why they renamed "Main and Autopilot" to "Primary and Backup", because "Main and Autopilot" were misleading (maybe those were carryover terms from really old generations). "Primary and Backup" implies that you need to switch both of them OFF.
 
User avatar
PixelFlight
Posts: 507
Joined: Thu Nov 08, 2018 11:09 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 6:24 pm

flybucky wrote:
kalvado wrote:
Logically, THING A should disconnect autopilot wiring and be sufficient for MCAS/STS disabling and keeping electric trim; while THING B should kill all power.

Yes, that's what I first assumed when I saw the 737 NG pictures showing Main and Autopilot Stab Trim Cutoff switches. That would have made a lot of sense to be able to disable Autopilot Trim while leaving Electric Trim on.

But then I saw the checklists, and there is nothing about switching one of them only. My speculation is that if at least one of them is ON, then both Auto Trim and Electric Trim are ON. That could explain why they renamed "Main and Autopilot" to "Primary and Backup", because "Main and Autopilot" were misleading (maybe those were carryover terms from really old generations). "Primary and Backup" implies that you need to switch both of them OFF.

According to the identified publicly available schematic, your speculation is unfortunately wrong.
Both STAB TRIM CUTOFF switches have to be ON to have a powered actuator. If any of the switches is OFF, the actuator can't move.
 
XRAYretired
Posts: 484
Joined: Fri Mar 15, 2019 11:21 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 6:25 pm

flybucky wrote:
kalvado wrote:
Logically, THING A should disconnect autopilot wiring and be sufficient for MCAS/STS disabling and keeping electric trim; while THING B should kill all power.

Yes, that's what I first assumed when I saw the 737 NG pictures showing Main and Autopilot Stab Trim Cutoff switches. That would have made a lot of sense to be able to disable Autopilot Trim while leaving Electric Trim on.

But then I saw the checklists, and there is nothing about switching one of them only. My speculation is that if at least one of them is ON, then both Auto Trim and Electric Trim are ON. That could explain why they renamed "Main and Autopilot" to "Primary and Backup", because "Main and Autopilot" were misleading (maybe those were carryover terms from really old generations). "Primary and Backup" implies that you need to switch both of them OFF.

Now it all makes sense.
 
mzlin
Posts: 107
Joined: Sat Mar 31, 2012 6:32 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 6:47 pm

SimonL wrote:
From what ive read the pilots seems to have done what they could. MCAS was activated and after the 2nd time they cut the switches, which seems quite normal. They correctly identified the issue and used the correct procedure to handle it. But now they where left with a misstrimmed aircraft they could not manually trim. And its easy to imagine one pilot holding the control column and the other desperately trying to move the trim wheel. Already here the situation has deviated from the expected and they are left to improvise. At this point they decide to reengage the electric trim, which imo is the correct thing to do in the situation. It is not clear if they disengaged it again or not but its not impossible that they came to the conclusion that the manual trim was jammed and thus saw it as their only option to fly with electrical trim enabled. Its easy to understand why it went south from here because pretty much nothing in their training are providing them with any solution and they where in the end mentally overwhelmed..


Well they could have used electrical trim tabs to counter MCAS, like the Lion Air captain did 20 times before passing control over to the FO (who then didn't do it, leading to the crash).
 
BlackCat
Posts: 7
Joined: Tue Jan 15, 2019 8:18 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 7:10 pm

[url][/url]
uta999 wrote:
Suppose the software 'fix' and some training fails to satisfy the authorities, the airlines, or the public. What does Boeing do next, bearing in mind the MAX is still coming off the FAL @ 50-60 per month? That could soon be 500 grounded aircraft with no Plan B. Is it possible to convert some of them back to NG if it all goes south for the MAX?

i have same question about this... is it possible to eleminate entire Mcas system on max8 ? coz of boeing putting the big Leap engine on wing that make pitch up tendency if pilot give more power to the engine.. pilot can still control these plane by adjust the trim wheel... am i right?
 
XRAYretired
Posts: 484
Joined: Fri Mar 15, 2019 11:21 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 7:18 pm

mzlin wrote:
SimonL wrote:
From what ive read the pilots seems to have done what they could. MCAS was activated and after the 2nd time they cut the switches, which seems quite normal. They correctly identified the issue and used the correct procedure to handle it. But now they where left with a misstrimmed aircraft they could not manually trim. And its easy to imagine one pilot holding the control column and the other desperately trying to move the trim wheel. Already here the situation has deviated from the expected and they are left to improvise. At this point they decide to reengage the electric trim, which imo is the correct thing to do in the situation. It is not clear if they disengaged it again or not but its not impossible that they came to the conclusion that the manual trim was jammed and thus saw it as their only option to fly with electrical trim enabled. Its easy to understand why it went south from here because pretty much nothing in their training are providing them with any solution and they where in the end mentally overwhelmed..


Well they could have used electrical trim tabs to counter MCAS, like the Lion Air captain did 20 times before passing control over to the FO (who then didn't do it, leading to the crash).

Ah, I've tabled the question before, but perhaps you will be able to answer. With the FO in a high speed turn with AIS disagree likely and ALT disagree probable, expecting some STS trim adjustments to occur and some sink rate so easing back on the yoke to counter it, what references would the FO be using to determine the number and/or period of thumb switch operations to counter-act nose down trim possibly being applied by some unknown cause?

Thanks
Ray
 
rheinwaldner
Posts: 1709
Joined: Wed Jan 02, 2008 4:58 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:08 pm

WIederling wrote:
The "Proper" strategy to get out of the trap is (now) known.

counter MCAS introduced miss trim with manual switches once in one go and then deactivate trim hard.

Unfortunately that strategy does not yet fully resolve all possible cases: The thumb switches also lack the authority to trim the aircraft in certain corners of the flight envelope (in particular at high speeds, -> ET)

You can find the issue documented in the following EASA review findings document of the MAX certification on page 15:
https://www.easa.europa.eu/sites/defaul ... S%2010.pdf

Quote:
The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts.

In those cases, longitudinal trim is achieved by using the manual stabilizer trim wheel to position the stabilizer. The trim wheel can be used to trim the airplane throughout the entire flight envelope. In addition, the autopilot has the authority to trim the airplane in these conditions. The reference regulation and policy do not specify the method of trim, nor do they state that when multiple pilot trim control paths exist that they must each independently be able to trim the airplane throughout the flight envelope.

Boeing did not initially consider this to be a compliance issue because trim could always be achieved, even during the conditions where use of the aisle stand trim switch was required. Subsequent to flight testing, the FAA-TAD expressed concern with compliance to the reference regulation based on an interpretation of the intent behind “trim”. The main issue being that longitudinal trim cannot be achieved throughout the flight envelope using thumb switch trim only.


This means, that neither cutting off the trim and turning the wheel nor reactivating the trim and using the thumb switches might have worked anymore.

In the light of this, in some scenarios the MAX seems to be a death trap, from which the best pilots of this world wont escape.
Many things are difficult, all things are possible!
 
User avatar
qf789
Moderator
Posts: 8607
Joined: Thu Feb 05, 2015 3:42 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:14 pm

Could we please just debate the topic without trying to provoke other users or incite trouble.
Forum Moderator
 
User avatar
AirlineCritic
Posts: 1629
Joined: Sat Mar 14, 2009 1:07 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 8:59 pm

SuseJ772 wrote:
I think this also all the more explains why the software update is taking so long. It’s buggy and it’s s problem.


If the latest revelations from WSJ, Leeham, etc. are true, it would seem to me that this is more than a software problem. You can't fix too large aerodynamic loads with software. And no matter what the redundancy design is, there will always be some probability of a failure which the pilots will have to deal with. But if they can't deal with it in a the seconds they have and the trimming tools they are given?

One option to partially resolve this would be a cockpit hardware change to have separate cutoff switches for the electronic trim motors and the automated trim function. Then you could first cut MCAS and still keep trimming fast with the motors. And if they malfunction, you'd still be able to go back to the trim wheel (albeit at that point slower).
 
dampfnudel
Posts: 406
Joined: Wed Oct 04, 2006 9:42 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 9:06 pm

Well, we’ll know tomorrow at the Ethiopian news conference how guilty the people in charge at Boeing should feel.
A313 332 343 B703 712 722 732 73G 738 739 741 742 744 752 762 76E 764 772 AT5 CR9 D10 DHH DHT F27 GRM L10 M83 TU5

AA AI CO CL DE DL EA HA KL LH N7 PA PQ SK RO TW UA YR
 
SimonL
Posts: 39
Joined: Tue Mar 12, 2019 3:38 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 9:08 pm

rheinwaldner wrote:
WIederling wrote:
The "Proper" strategy to get out of the trap is (now) known.

counter MCAS introduced miss trim with manual switches once in one go and then deactivate trim hard.

Unfortunately that strategy does not yet fully resolve all possible cases: The thumb switches also lack the authority to trim the aircraft in certain corners of the flight envelope (in particular at high speeds, -> ET)

You can find the issue documented in the following EASA review findings document of the MAX certification on page 15:
https://www.easa.europa.eu/sites/defaul ... S%2010.pdf

Quote:
The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts.

In those cases, longitudinal trim is achieved by using the manual stabilizer trim wheel to position the stabilizer. The trim wheel can be used to trim the airplane throughout the entire flight envelope. In addition, the autopilot has the authority to trim the airplane in these conditions. The reference regulation and policy do not specify the method of trim, nor do they state that when multiple pilot trim control paths exist that they must each independently be able to trim the airplane throughout the flight envelope.

Boeing did not initially consider this to be a compliance issue because trim could always be achieved, even during the conditions where use of the aisle stand trim switch was required. Subsequent to flight testing, the FAA-TAD expressed concern with compliance to the reference regulation based on an interpretation of the intent behind “trim”. The main issue being that longitudinal trim cannot be achieved throughout the flight envelope using thumb switch trim only.


This means, that neither cutting off the trim and turning the wheel nor reactivating the trim and using the thumb switches might have worked anymore.

In the light of this, in some scenarios the MAX seems to be a death trap, from which the best pilots of this world wont escape.



Doesnt this means that the plane cannot be trimmed by the pilots in some parts of the flight envelope?? That alone is a major issue for the MAX..
 
flybucky
Posts: 175
Joined: Tue Apr 17, 2018 7:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 10:21 pm

XRAYretired wrote:
Now it all makes sense.

Well, according to PixelFlight, schematics show otherwise.

PixelFlight wrote:
According to the identified publicly available schematic, your speculation is unfortunately wrong.
Both STAB TRIM CUTOFF switches have to be ON to have a powered actuator. If any of the switches is OFF, the actuator can't move.

Darn, too bad. Does what you say apply to both 737 NG and MAX?

Do you have links to those schematics? I did some searching and found these links. Are any of these it?
viewtopic.php?f=3&t=1407217&p=21198009#p21198009
https://www.satcom.guru/2018/11/stabilizer-trim.html

What about this quote from the satcom.guru article?

Stabilizer trim requires power to the trim motor. A cutout switch provides a means for the pilot to remove power from the trim motor.
Autopilot trim commands are routed through a second cutout switch, which isolates the autopilot command from the trim motor.
 
morrisond
Posts: 1178
Joined: Thu Jan 07, 2010 12:22 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 10:48 pm

SimonL wrote:
rheinwaldner wrote:
WIederling wrote:
The "Proper" strategy to get out of the trap is (now) known.

counter MCAS introduced miss trim with manual switches once in one go and then deactivate trim hard.

Unfortunately that strategy does not yet fully resolve all possible cases: The thumb switches also lack the authority to trim the aircraft in certain corners of the flight envelope (in particular at high speeds, -> ET)

You can find the issue documented in the following EASA review findings document of the MAX certification on page 15:
https://www.easa.europa.eu/sites/defaul ... S%2010.pdf

Quote:
The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts.

In those cases, longitudinal trim is achieved by using the manual stabilizer trim wheel to position the stabilizer. The trim wheel can be used to trim the airplane throughout the entire flight envelope. In addition, the autopilot has the authority to trim the airplane in these conditions. The reference regulation and policy do not specify the method of trim, nor do they state that when multiple pilot trim control paths exist that they must each independently be able to trim the airplane throughout the flight envelope.

Boeing did not initially consider this to be a compliance issue because trim could always be achieved, even during the conditions where use of the aisle stand trim switch was required. Subsequent to flight testing, the FAA-TAD expressed concern with compliance to the reference regulation based on an interpretation of the intent behind “trim”. The main issue being that longitudinal trim cannot be achieved throughout the flight envelope using thumb switch trim only.


This means, that neither cutting off the trim and turning the wheel nor reactivating the trim and using the thumb switches might have worked anymore.

In the light of this, in some scenarios the MAX seems to be a death trap, from which the best pilots of this world wont escape.



Doesnt this means that the plane cannot be trimmed by the pilots in some parts of the flight envelope?? That alone is a major issue for the MAX..


At the speeds they were travelling It's possible they were well outside the flight envelope which would be a major issue for any aircraft.

It will be interesting to see the FDR traces if they are released.
 
User avatar
Super80Fan
Posts: 1525
Joined: Thu Jul 06, 2017 4:14 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 10:50 pm

I know we can trust the media when it comes to aviation as far as we can throw them but now they're saying a damaged sensor caused by a bird/foreign object hitting the plane caused the crash? That seems very odd and implausible unless it took out the pitot tubes or something....

https://abcnews.go.com/Politics/damaged ... dlines_hed
RIP McDonnell Douglas
 
morrisond
Posts: 1178
Joined: Thu Jan 07, 2010 12:22 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 10:51 pm

SimonL wrote:
rheinwaldner wrote:
WIederling wrote:
The "Proper" strategy to get out of the trap is (now) known.

counter MCAS introduced miss trim with manual switches once in one go and then deactivate trim hard.

Unfortunately that strategy does not yet fully resolve all possible cases: The thumb switches also lack the authority to trim the aircraft in certain corners of the flight envelope (in particular at high speeds, -> ET)

You can find the issue documented in the following EASA review findings document of the MAX certification on page 15:
https://www.easa.europa.eu/sites/defaul ... S%2010.pdf

Quote:
The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts.

In those cases, longitudinal trim is achieved by using the manual stabilizer trim wheel to position the stabilizer. The trim wheel can be used to trim the airplane throughout the entire flight envelope. In addition, the autopilot has the authority to trim the airplane in these conditions. The reference regulation and policy do not specify the method of trim, nor do they state that when multiple pilot trim control paths exist that they must each independently be able to trim the airplane throughout the flight envelope.

Boeing did not initially consider this to be a compliance issue because trim could always be achieved, even during the conditions where use of the aisle stand trim switch was required. Subsequent to flight testing, the FAA-TAD expressed concern with compliance to the reference regulation based on an interpretation of the intent behind “trim”. The main issue being that longitudinal trim cannot be achieved throughout the flight envelope using thumb switch trim only.


This means, that neither cutting off the trim and turning the wheel nor reactivating the trim and using the thumb switches might have worked anymore.

In the light of this, in some scenarios the MAX seems to be a death trap, from which the best pilots of this world wont escape.



Doesnt this means that the plane cannot be trimmed by the pilots in some parts of the flight envelope?? That alone is a major issue for the MAX..


I take it can be trimmed using the manual wheel - however from the FR24 traces (up to 400 Knots) it seems like they were well outside the flight envelope and that may have made it unrecoverable.
 
morrisond
Posts: 1178
Joined: Thu Jan 07, 2010 12:22 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 10:54 pm

Super80Fan wrote:
I know we can trust the media when it comes to aviation as far as we can throw them but now they're saying a damaged sensor caused by a bird/foreign object hitting the plane caused the crash? That seems very odd and implausible unless it took out the pitot tubes or something....

https://abcnews.go.com/Politics/damaged ... dlines_hed


The story also says they didn't try to use Electric Trim to counteract MCAS before hitting the cut-off switches.
 
MildBlueYonder
Posts: 11
Joined: Sun Apr 08, 2018 6:30 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 11:00 pm

dtw2hyd wrote:
If KC-46 already has a better implementation of MCAS, why can't Boeing just port it to MAX. This is not the right to keep counting beans.


Yeah, I’ve been wondering the same. Seems like the engineering and failure mode analyses for the KC-46 version of MCAS yielded all of the protections now being retrofitted into the MAX implementation. Kinda argues circumstantially in favor of external influence being applied to the latter.

Also, it just seems a bit circular and stupid that MCAS, which is a safety measure intended to catch pilots with poor training who decide to firewall the throttles rather than push the nose forward on the approach to stall, should itself be designed to rely entirely on stellar training to prevent catastrophe in the event of malfunction.
 
User avatar
scbriml
Posts: 17263
Joined: Wed Jul 02, 2003 10:37 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Wed Apr 03, 2019 11:30 pm

Super80Fan wrote:
I know we can trust the media when it comes to aviation as far as we can throw them but now they're saying a damaged sensor caused by a bird/foreign object hitting the plane caused the crash? That seems very odd and implausible unless it took out the pitot tubes or something....

https://abcnews.go.com/Politics/damaged ... dlines_hed


The article says it damaged the AOA sensor which caused bad AOA data (like the Lion flight), which eventually activated MCAS.

morrisond wrote:
The story also says they didn't try to use Electric Trim to counteract MCAS before hitting the cut-off switches.


https://leehamnews.com/2019/04/03/et302 ... more-29790
Time flies like an arrow. Fruit flies like a banana!
There are 10 types of people in the World - those that understand binary and those that don't.
 
User avatar
PixelFlight
Posts: 507
Joined: Thu Nov 08, 2018 11:09 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Thu Apr 04, 2019 1:07 am

flybucky wrote:
XRAYretired wrote:
Now it all makes sense.

Well, according to PixelFlight, schematics show otherwise.

PixelFlight wrote:
According to the identified publicly available schematic, your speculation is unfortunately wrong.
Both STAB TRIM CUTOFF switches have to be ON to have a powered actuator. If any of the switches is OFF, the actuator can't move.

Darn, too bad. Does what you say apply to both 737 NG and MAX?

Must be formally verified but this is my understanding from what I have read so far. And the schematic have a "MCAS ENGAGE" function into the FCC A/B box (center bottom). MCAS only exists on the 737 MAX.

flybucky wrote:
Do you have links to those schematics? I did some searching and found these links. Are any of these it?
viewtopic.php?f=3&t=1407217&p=21198009#p21198009
https://www.satcom.guru/2018/11/stabilizer-trim.html

In fact the schematic was posted by "fadecfault" (and not in the Satcom Guru blog, sorry for the confusion)
viewtopic.php?f=3&t=1407217&start=1650#p20886627
The same discussion is here:
viewtopic.php?f=3&t=1417545&start=4300#p21247403

flybucky wrote:
What about this quote from the satcom.guru article?

Stabilizer trim requires power to the trim motor. A cutout switch provides a means for the pilot to remove power from the trim motor.
Autopilot trim commands are routed through a second cutout switch, which isolates the autopilot command from the trim motor.

The schematic say something a bit different: as the STAB TRIM CONTROL signal (From P6 CB PANEL) pass trough both switches, both provides a means for the pilot to remove power from the trim motor.
 
mzlin
Posts: 107
Joined: Sat Mar 31, 2012 6:32 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Thu Apr 04, 2019 3:42 am

Per WSJ (https://www.wsj.com/articles/pilots-tak ... 1554347116)
"Preliminary findings from the second crash, which occurred last month in Ethiopia, are expected to stoke criticism from pilots that Boeing and U.S. regulators fell short in highlighting steps crews are supposed to take BEFORE turning off a stall-control feature implicated in both crashes... Other pilots said executing such manual controls to first get the plane into a stable position was instinctive piloting, and there is no need to revise the current checklist. “That’s flying the airplane,” one U.S. pilot said."

At least there is now awareness that one should retrim (using electrical trim tabs) before cutting off the power to the stabilizer. Sadly it's a bit late; maybe it wouldn't have hurt to have emphasized this in the FDA directive.

IMO the WSJ and Seattle Times have provided the best coverage of this crisis so far, with detail and with accuracy. It's refreshing to read these news articles after reading inaccuracies, finger-pointing, statements of indignation, and pronouncements of doom bounce back and forth on various forums.
 
SuperEighty
Posts: 9
Joined: Mon Mar 11, 2019 11:19 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Thu Apr 04, 2019 4:09 am

Super80Fan wrote:
I know we can trust the media when it comes to aviation as far as we can throw them but now they're saying a damaged sensor caused by a bird/foreign object hitting the plane caused the crash? That seems very odd and implausible unless it took out the pitot tubes or something....

https://abcnews.go.com/Politics/damaged ... dlines_hed


Several outlets are reporting that the AOA sensor was indeed damaged by a bird or other foreign object on takeoff.

Big news if true.
 
Backseater
Posts: 478
Joined: Fri Aug 19, 2005 3:20 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Thu Apr 04, 2019 5:37 am

Super80Fan wrote:
I know we can trust the media when it comes to aviation as far as we can throw them but now they're saying a damaged sensor caused by a bird/foreign object hitting the plane caused the crash? That seems very odd and implausible unless it took out the pitot tubes or something....

https://abcnews.go.com/Politics/damaged ... dlines_hed

Bole Int airport was/is(?) known for bird strikes by pigeons, doves, black kites, ... A study in 1995 found 33 bird strikes in a year, many early in the morning. And in 1998 at an airport in Northern Ethiopia, a 737 crashed after ingesting 15 pigeons!
If they are looking for an act of God to explain why they are not responsible, that is indeed a good possibility.
Let us see whether the FDR recorded a sudden spike during the latter part of the take-off roll when there may be enough combined kinetic energy to do the deed (unless they have low flying, Mach 0.3 birds out there!)
If they cannot find the sensor's swept vane that is supposed to have been hit, maybe they can provide the autopsy report of the incriminated bird because it was probably sliced in half by the sharp profile of the vane.

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos