737 MAX

[FredK]

That is an interesting read.....

Certainly there are plenty of facts in this case that are crystal clear. 

However only Boeing can decipher all that to determine the root of the problem. Boeing has acknowledged responsibility and says that they have a handle on it all.  Hopefully for them that is the case.  Another accident would sink the 737 ship.  That has to be a lot of pressure on the people involved right now.

Fred K

[jfuenmayor]

Sure thing Fred. It is sad in all aspects. The industry will surly learn a lot from this.

An additional piece of information is the fact that Airbus had similar problems with
AOA vane malfunctioning and feeding erroneous data, and they solved it years ago. Also, the press has stated that the pilots disconnected the MCAS. This is not true. The preliminary report is clear. The system cannot be disconnected by either turning the AP or the electric trim switches off, the CND (Command Nose Down) was active with the switches off. Really scary.

BTW.  The link that i submitted link is public record. I can see that the rest of the thread has been removed. Interesting.

Trev, let me know if there is an issue with it. I am aware of your previous post regarding the decision made by the EU.

Joaquin.

[jfuenmayor]

Oops, the rest of the the thread is in the archives...sorry

[Garys]

Not scary really. The system worked exactly as it should.

05:39:45 = The system is designed to work with flaps up
05:39:55 = The system is designed to work with AP off.
05:40:35 the stab trim was confirmed cutout
05:40:41 = The system is designed to make the input. The output to the Hstab didn't happen because the cutout switches were at cutout. At this point in time they had effectively disabled the MCAS system from making any  flight control surface changes.

Its easy to be a monday morning quarter back, so I"m not going to speculate to the crews actions but I do know that they had the system beat at 05:40:35 

[Trevor Hale]

Trev, let me know if there is an issue with it. I am aware of your previous post regarding the decision made by the EU.

Actually, I did more digging and that's why my post was removed.  We don't get over a million unique users a month.  the rules don't apply to us
Trev

[KyleH]

Interesting read.
Just a factual report at this point so no conclusions, but some items I noticed:

The MCAS was disabled when the cut out switches were selected:

At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance of AND automatic trim command occurred without any corresponding motion of the stabilizer, which is consistent with the stabilizer trim cutout switches were in the ''cutout'' position

The crew didn't seem to understand that they couldn't now use the trim switches on the yoke:

At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working.

According to this, there was 8 seconds between the captain asking the question and the FO declaring it not working. I don't know if this is a long enough time to trim a 737 manually before much pressure would be relieved from the yoke when its been put into a nose down state.

In addition, this statement makes me wonder if the FO was actually manually trimming the aircraft in the wrong direction:

From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units. During this time, aft force was applied to the control columns which remained aft of neutral position....

They then put the trim cut-out switched back to the normal position!

At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002 ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units.

Now this part of the report I do find scary :

1.5.2 FIRST-OFFICER
According to Ethiopian Airlines records, the First-Officer has the following flight experience:
? Total hours: 361
? Total hours in B737: 207
? Total hours in B737-8 MAX: 56
? Flight time in previous 90 days: 207 hours and 26 minutes
? Flight time in previous 7 days: 10 hours and 57 minutes
? Flight time in previous 72 hours: 5 hours and 25 minutes

The FO started flying a 737 with only 154 hours total time. In this country that doesn't even allow me to fly a C172 for hire with only myself on board let alone a jet that can seat almost 200 passengers.

..... Also, the press has stated that the pilots disconnected the MCAS. This is not true. The preliminary report is clear. The system cannot be disconnected by either turning the AP or the electric trim switches off, the CND (Command Nose Down) was active with the switches off. Really scary.
...
Joaquin.

No.
1) As stated before; MCAS only functions with the autopilot off.
2) The report shows that the system was disabled with the trim cut-off switches in the cut-off position at 5:40.
3) The events towards the end lead me to believe that the crew put the cut-off switched back to the normal position, which would have re-engaged the electric trim and by extension MCAS system.

We can't say anything clearly until we have a final report with expert analysis.

[Garys]

"3) The events towards the end lead me to believe that the crew put the cut-off switched back to the normal position, which would have re-engaged the electric trim and by extension MCAS system"

Definitely 100% the switches were moved back to normal position. Not every switch has a feed into the FDR. We know from the prelim report that they disconnected as the voice recorder had verbal confirmation with no horizontal stab movement from the MCAS input thereafter.


05:43:11 Electric trim movement came immediately after the captain said pitch is not enough. It may be in the final report that the cut out switches were heard being moved to the normal position by the cockpit area microphone, but with the stick shaker and overspeed clacker going off, it is possible that this event will go undocumented.

[jfuenmayor]

Well, I do not think that anyone here knows how the MCAS system was really  written unless there is a software engineer among us that is involved with the project and has seen the source code , but, it would seem that the crew re activated the switches in order to have access to electric trimming in a futile effort to trim faster, which of course returned the trim control to the MCAS which was already active due to the false readings.

If any of you has tried to move the trim wheel manually, in a real Level D B737 sim, I am sure you would agree that even in level flight, the number of turns and effort required is significant. Let alone in the real plane on a dive where the forces are higher.

When I say that you turn the MCAS off, I mean that there is a way to make the system inactive. The A/P was engaged at 400 ft RA, and it was so, when the MCAS system  commanded the nose down. So condition No. 1 was bypassed. Turning off the Autopilot is standard procedure when you are faced with a control problem. Automatic systems, including auto throttles  must be turned off and control returned to the crew so they can maneuver out of the situation manually.

The FO had a very low time but not the Captain (8000 hs.), who was the pilot flying.

Getting from 1.5 Units to 4.0, requires significant effort. That is what they were up against.  If the actions taken by the crew, as recommended by the manufacturer, did not correct the problem, in such a dire situation and the lack of time, they had to try something else, I would. We still have to see more information, but I am sure that out of this tragedy, many lessons will be learned. Pointing fingers is an exercise of futility, and hubris has no place.

In the mean time, the planes are still grounded, for a reason.

[Garys]

Boeing aircraft logic uses and/or gates. knowing the source code is irrelevant. For MCAS to work Autopilot must be off AND flaps must be up. There is no OR. I think you may be confusing the Flight Director, which is not an autopilot mode, so its incorrect that condition 1 was bypassed. The 1st MCAS nose down command came almost immediately after the autopilot was disengaged.

Again I"m not going to comment on the actions of the crew, but the recommendation from the manufacturer is to trim the aircraft manually into the green band  before using the cutout switches, ( MCAS is disabled during manual trim and for a further 5 seconds) disconnecting autothrottle and leaving the cutout switches in disable position. I will let you draw your own conclusions on whether that was followed.

There is so much crap in the media about the MCAS system.

From a systems standpoint, MCAS worked as it should. I'm glad to see that system is being updated. I think from a design standpoint it was absurd to only use the input from only 1 AOA and that the disagree annunciation was a customer option.

I'm only looking at these two accidents from a systems standpoint. That is all I care about. Im more concerned about the issues with the AOA.

[jfuenmayor]

A Flight director is a guidance system for reference, and no, it is not the A/P, as a matter of fact, the FD is engaged normally before any flight during cockpit preparation and is an item in the checklist. And yes, the source code is important, because even though you may think  that you coded for a certain condition, in the field, it may not be so. It is called a BUG, and it is so when the code results in an unwanted action. If the possibility of a failure of one of the AOA vanes, giving conflicting information back to the MCAS subsystem was not tested for its reactions, that would be very serious indeed. At any rate, the problem has occurred twice, under similar circumstances. Now,  how do you fix it ?, you audit the source code line by line. Now, that said, as I mentioned before, the AP which is activated with the CMD  push button and shown on the  in the PFD, was activated by the FO on the CAPT's command (flying pilot), again, standard procedure. The pilot flying does not have to divert his attention to pushing a button while actively flying the aircraft, this was done at 400 ft AGL. The disturbance occurred under those conditions. In normal flight, once you engage the AP and VNAV and LNAV are active, the crew just monitors  the flight. Also, the oscillations that were noted should draw attention. Now, I do not know if it is the MCAS system that disengages the AP, in that case, it takes over, and the results are there to see.  Boeing has not yet come with the patch over six months after the first accident. They are looking at the code, of course, and this is not as easy as people may think. They cannot afford to screw up again, that would be disastrous for the MAX.

[navymustang]

Somebody correct me if I am wrong - but hasn't this occurred with U.S. airlines twice with the Max and in both cases the pilots were able to make corrective actions and fly the aircraft safely back to the airport or alternate?

[KyleH]

Joaquin you seem to be interpreting data that isn't there. There is nothing in that report that leads me to believe that MCAS wasn't working as designed. The data profile looks like a functioning MCAS system with an AOA failure.

Well, I do not think that anyone here knows how the MCAS system was really  written unless there is a software engineer among us that is involved with the project and has seen the source code , but, it would seem that the crew re activated the switches in order to have access to electric trimming in a futile effort to trim faster, which of course returned the trim control to the MCAS which was already active due to the false readings.

I'm certain no one here worked on this project and if they did they wouldn't be able to talk about it.
I have done software/circuit design in safety critical systems and do have understanding about how this kind of development is done.

When I say that you turn the MCAS off, I mean that there is a way to make the system inactive. The A/P was engaged at 400 ft RA, and it was so, when the MCAS system  commanded the nose down. So condition No. 1 was bypassed. ....

The pilot flying does not have to divert his attention to pushing a button while actively flying the aircraft, this was done at 400 ft AGL. The disturbance occurred under those conditions. In normal flight, once you engage the AP and VNAV and LNAV are active, the crew just monitors  the flight. Also, the oscillations that were noted should draw attention. Now, I do not know if it is the MCAS system that disengages the AP, in that case, it takes over, and the results are there to see.

This is not true, you cannot claim that information from the report. The report shows the MCAS system applying nose down trim at the proper time, autopilot off and Flaps up.
The very short trim down commands you can see on the chart are consistent with the autopilot commands for that phase of flight, acceleration after take-off. Then as the flaps come up slight nose up trim to maintain speed. The oscillations could simply be turbulence.

The autopilot disconnecting could have been because of the associated AOA sensor failure, or someone moving the control column. Gary would probably have a better list of the item's that could cause that.

We have to remember that these events have multiple contributing causes and we can't focus on one system to the exclusion of all the others. The MCAS may have commanded the nose down attitude, but it is only one link in the chain.

We need proper NTSB analysis to determine the probably causes of what went on.

Boeing has not yet come with the patch over six months after the first accident. They are looking at the code, of course, and this is not as easy as people may think. They cannot afford to screw up again, that would be disastrous for the MAX.

Reportedly, Boeing did have a release ready in January, however due to the FAA shutdown, could not have it reviewed. Where the process is right now, I don't know.

If any of you has tried to move the trim wheel manually, in a real Level D B737 sim, I am sure you would agree that even in level flight, the number of turns and effort required is significant. Let alone in the real plane on a dive where the forces are higher.

This is what makes me wonder if 8 seconds is enough time for the FO to declare the manual trim 'not working'

Somebody correct me if I am wrong - but hasn't this occurred with U.S. airlines twice with the Max and in both cases the pilots were able to make corrective actions and fly the aircraft safely back to the airport or alternate?

Yes, there are NASA reports to that effect. The Lyon air accident aircraft flew a couple of times with the fault before the fatal flight, and those crews successfully recovered.

[jackpilot]

May be a dumb point, but every comment, analysis, report etc is all about the MCAS and recovery procedures, no word about the original culprit IMHO which are faulty AOA probes.
Who manufactures them and what is their reliability record?
Seems to me these are not ultra sophisticated .

[mickc]

May be a dumb point, but every comment, analysis, report etc is all about the MCAS and recovery procedures, no word about the original culprit IMHO which are faulty AOA probes.
Who manufactures them and what is their reliability record?
Seems to me these are not ultra sophisticated .

Indeed.  (although hopefully more complex than a bit of red string stick to a glider window  )

There were reports of the AOA sensor on the LionAir aircraft had recently been repaired at an MRO in Florida somehwere.  (again - unconfirmed etc.)

[Garys]

Not usually a problem unless hit by lighning

[727737Nut]

Pilot Error................... Flying at or above VMO....failure to maintain control of aircraft.... Didn't follow proper procedures..............period!!

Now here is where the long investigation process comes into play,

Contributing Factors.................................................  Time will tell.  MCAS alone did not cause either crash by itself.  It is only a single chain link in the accident chain. 

add
Think about this for a moment, at one point in the middle of the FDR data, trim went to 0.4units ND!!  It didn't nose dive at that point........ then at the end when it did nose dive, trim was 0.8 - 1.1 units ND.  So why did it dive then and not when it was even more nose down earlier in the short flight?   My theory, They were flying at and above VMO for most of the short flight, they were pulling back on the yoke hard with the elevator deflected way more than normal at above VMO,  Something broke in that aft area!    Sad part was is this, all they had to do was throttle back and slow the F### down and put it to flaps 1 and turn trim back on and fly home........

I can't share my source as he is a current NG/MAX rated pilot in the US but folks, these were easily avoidable accidents

[Garys]

Pretty much sums up my thoughts as well only except I think the design of the MCAS was too aggressive. 10 secs of trim is alot when only taking the input from one sensor.  Still shouldn't have crashed though.

[727737Nut]

Pretty much sums up my thoughts as well only except I think the design of the MCAS was too aggressive. 10 secs of trim is a lot when only taking the input from one sensor. Still shouldn't have crashed though.

I agree Gary but what people must realize is that the trim button on the yoke can be held longer    Trim the plane to fly by continuous pushing of the trim button then flip the cutoff buttons.  Head home for a beer.

[Garys]

Here is the intended fix .... Interesting read.
https://www.pprune.org/10443754-post3824.html

[Trevor Hale]

If the System is going to work like it is written with the 3 layers of protection..  I am convinced this will make a difference, especially given the "Are you sure Option" LOL.

[tennyson]

I gotta say that the comments here have been both enlightening and informative.

All judgements aside, and no matter whether you are a Boeing guy (or gal) or Airbus fan, there are no winners when an aircraft gets grounded.

Personally, for me, I'm glad that the fixes are out there and that Boeing can start the recovery process of what will certainly go down in history as the most prolific aircraft in history, the 737, that is.

I say that personally, as my own 737Max 8 build is reaching certain milestones. My MIP is very near completed and should be fully functional within a week or two. I have a MAX throttle builder who is chanting at the bit to finish the job and my overheads will undergo the upgrade treatment, as soon as my MIP is finalised.

I had moments of doubt (when the two MAX crashes happened) and wondered whether a powerhouse like Boeing could endure the storm, or had I jumped the gun and sunk a significant amount of money into a dead project.

Only time will tell, but without referring to the Chrystal ball, my gut tells me that it will take some time for the tarnish to wear off.
I think that 12 months down the track, with the savings in fuel and efficiency of the new MAX technology, the world will once again embrace the Boeing name and we will all move on.


Frank

[jackpilot]

https://seekingalpha.com/instablog/398764-vaughn-cordle-cfa/5290930-boeing-737-max-8-crashes-case-pilot-error

[mickc]

Great link Jack!