Boeing 737 Max8 Aircraft Crashes and Investigations [Part 3] 36

[Sparweb]

This is the continuation from:

thread815-445840
thread815-450258

This topic is broken into multiple threads due to the long length to be scrolled, and many images to load, creating long load times for some users and devices. If you are NEW to this discussion, please read the above threads prior to posting, to avoid rehashing old discussions.


Some key references:

Ethiopian CAA preliminary report

Indonesian National Transportation Safety Committee preliminary report

The Boeing 737 Technical Site

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[Alistair_Heaton]

just posting updated links which are coming through pilot social media.

I also passed on the comment about the AP being in with the stickshaker going to the ECA... the reply was good point, well presented it will go on the EASA list of issues.

https://www.moonofalabama.org/2019/...severe-problem-with-older-boeing-737-ngs.html

 

[3DDave]

It's a continuing surprise that "continuous" means "forever." As in, if the steering on my car broke completely, but only for 9 seconds, that would not be the concern that it would be if it went until I crashed.

Oh. Wait.

9 seconds of broken steering on the highway would probably kill me long before I waited forever to see if it was intermittent or continuous.

The mistrim was obvious in the first 1 second of operation as the yoke force increased. It was grotesquely obvious at 4 seconds.

Something is fishy about the roller coaster maneuver simulation claim. Somehow they come closer and closer to trim and never ever gain altitude in between attempts? Even though they are carrying excess energy into the maneuver. And apparently not pulling back on the throttle to match the ever increasing pitch-up trim to slow the plane to match.

And yet another article overlooking that the Ethiopian had full electrical trim authority and threw that away when the plane was far out of trim by shutting off the motors. Properly trimming should be the default task for all pilots.

It's clear that as long as the pilots maintain trim the plane won't crash from MCAS and that the electric trim is sufficient to do that. There is zero need for any other procedure, though it would be convenient.

 

[VEBill]

Interesting.

...interrupt the electric circle that supplies the motor...

 

[VEBill]

I suspect that the opinion that no changes are required to the design will not be adopted in the final decisions.

 

[3DDave]

Yes - they will be forced to change something.

They are already changing the MCAS software - done deal. No question. Absolutely. For certain. Nothing else to do.

But that's not what the opportunists are looking for to resolve this situation. They want more. More than is offered, more than can be offered. And they will never accept that the pilots have any influence over flying the plane.

 

[VEBill]

"Nothing else to do."

No.

They'll also need to edit the procedures, especially the part where it instructs the crew to switch the electric trim switches to CUTOUT, and "...leave them there for the remainder of the flight."

Acknowledge that the procedure later helpfully mentions that the electric trim "can" be used before switching it off.But in light of the other information, the word "can" perhaps should be replaced with "must".

There will probably be changes in at least a half-dozen areas, not merely software.

 

[LionelHutz]

Runaway Stabilizer
Disengage autopilot and control airplane pitch attitude with control column
and main electric trim as required. If relaxing the column causes the trim to
move, set stabilizer trim switches to CUTOUT......

Using the electric trim to maintain control of the plane is ALREADY listed as an action to take before using the cutout switches.

 

[LionelHutz]

I have read that the stick shaker and IAS disagree would be the pilot's focus. For IAS Disagree or Unreliable Airspeed I have read at multiple places that the pitch should be 4* nose up and thrust 75% N1 if flaps are up. This is supposed to be a memory trained safe setting that will always cause a climb at low altitude or a decent from high altitude which keeps the plane safe. It's not a setting to maintain the current flight altitude and speed.

The very first line of the procedure for both; "Adjust the airplane attitude and thrust. Maintain airplane control."

The pilots never adjusted the thrust to the prescribed level.

It'd be curious to see what would happen to the plane and control column forces at the 2.1 unit trim level with 75% N1 instead of 94% N1.

 

[VEBill]

It would be surprising if the wording and procedures highlighted below would not be implicated as a contributing factor.

Especially where it says, "...ensuring..."

Runaway Stabilizer
Disengage autopilot and control airplane pitch attitude with control column
and main electric trim as required. If relaxing the column causes the trim to
move, set stabilizer trim switches to CUTOUT. [highlight #FCE94F]If runaway continues, hold
the stabilizer trim wheel against rotation and trim the airplane manually.
[/highlight]
Note: The 737-8/-9 uses a Flight Control Computer command of pitch
trim to improve longitudinal handling characteristics. In the event of
erroneous Angle of Attack (AOA) input, the pitch trim system can trim
the stabilizer nose down in increments lasting up to 10 seconds.
[highlight #FCE94F]In the event an uncommanded nose down stabilizer trim is experienced
on the 737-8/-9, in conjunction with one or more of the indications or
effects listed below, do the existing AFM Runaway Stabilizer
procedure above, ensuring that the STAB TRIM CUTOUT switches
are set to CUTOUT and stay in the CUTOUT position for the
remainder of the flight.[/highlight]
...
Initially, higher control forces may be needed to overcome any
stabilizer nose down trim already applied. Electric stabilizer trim [highlight #FCE94F]can[/highlight] be
used to neutralize control column pitch forces before moving the STAB
TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be
used before and after the STAB TRIM CUTOUT switches are moved
to CUTOUT.

 

[LionelHutz]

Runaway Stabilizer
Disengage autopilot and control airplane pitch attitude with control column
and main electric trim as required. If relaxing the column causes the trim to
move, set stabilizer trim switches to CUTOUT. If runaway continues, hold
the stabilizer trim wheel against rotation and trim the airplane manually.

Note: The 737-8/-9 uses a Flight Control Computer command of pitch
trim to improve longitudinal handling characteristics. In the event of
erroneous Angle of Attack (AOA) input, the pitch trim system can trim
the stabilizer nose down in increments lasting up to 10 seconds.
In the event an uncommanded nose down stabilizer trim is experienced
on the 737-8/-9, in conjunction with one or more of the indications or
effects listed below, do the existing AFM Runaway Stabilizer
procedure above, ensuring that the STAB TRIM CUTOUT switches
are set to CUTOUT and stay in the CUTOUT position for the
remainder of the flight.
...
Initially, higher control forces may be needed to overcome any
stabilizer nose down trim already applied. Electric stabilizer trim can be
used to neutralize control column pitch forces before moving the STAB
TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be
used before and after the STAB TRIM CUTOUT switches are moved
to CUTOUT.

It still reads to back to the top and follow the part I highlighted - "control airplane pitch attitude with control column and main electric trim as required" and then to "set stabilizer trim switches to CUTOUT.".

The part you highlighted in red does not say to set the switches to cutout.

Sure, you could change the text to make it clearer, but saying the text says to throw the switches first before using the electric stabilizer control is simply wrong.

I don't understand the issue with the text saying to keep the switches off for the remainder of the flight since you'd want to do that in a runaway situation.

 

[Alistair_Heaton]

I think you would be surprised how little jet pilots trim the aircraft both in pitch and roll even single engine. These days they are actively told to keep the automatics in especially when the work load goes up. When the automatics come out in normal ops then the aircraft is already in trim and they only sort out there own changes of airspeed. AP in as the gear lights go out and then off when it shouts minimums at you at 200ft.


BTW there is an absolutely collosal pitch down moment when you take the power off an under wing pod jet aircraft. I will admit i have only flown one in the sim for job interviews and its always a suprise how much it pitches down and up when you take the power off/on. Which is suspect is the reason for the MCAS anyway when they go TOGA for a go-around the manual pitch up combined with the power increase pitch up takes them into the MACS area of triggering. So if they are struggling with the nose going down I can sort of understand the screwed up logic of not taking the power off which will mean further pitch down. Remember the min standard for most pilots for engineer/physics is age 14 high school level. Principles of flight is not instinctively obvious, for some of us flying an aircraft is just a big energy equation. Others its a series of SOP's which when performed result in a safe flight. Problem is when they come out of the SOP's they have nothing to fall back on.

You should see the amount of utter nonsense that's spouted about V minimum control airborne (Vmca) for asymmetric thrust situations.

BTW I have no issue with you saying it would be good for all pilots in the world to get increased training and standards. Accountants would have an issue with it as well as the pax would have to pay for it. It costs my company 10 000 euros a year to keep just one of us current but i will admit thats 1 extra 4 hour sim session above the legal minimum and an extra day in the class room.

In relation to what the finer points of manual writing complexities are. There was a move a few years ago that there should be a minimum level of English for everyone in international Aviation. You usualy see it as ICAO and then a number 4-6. 4 is the min required, 6 is a native speaker. Now in theory every pilot in commercial ops should be at least 4, you only have to look on youtube for tapes of air china in LAX to realise that the varition of level 4 standard has not really solved the issue. Some of the guys at work English is thier 4th langauage! and to be honest they are great at English and I have no complaints. But then again all recruitment is done in English and the minimum standard is ICAO 5 which means they don't have to be tested as ofen as the icao 4's. If someone gets an ICAO 6 then they never get tested again. The mucking about with wording on QRH plates for these low level ICAO 4's to be honest is not going to solve the problem. Using words like "ensuring" will mean they will miss the point. It needs to be binary, alot of QRH's are using flow charts now with yes/no logic and then if they need to go back to reassess, a line takes you back to the approprate point. After working for numerous years with none native speakers these flow chart type cards seem to work better and there is less discussion about what something means.

eg above

1. disengage auto pilot

2. trim aircraft using electric trim.

3. Electric trim switches ......... cut out until landing

4. Is trim wheel moving? Yes hold and trim manually. No. fly manually (do not move cutout switches)


The above is not what the procedure should be, its only a suggestion of how the procedure should be given and the extremly low level of English that should be used. No lists which required grammar knowledge use only "and" or "or" to separate.

Write the cards using KISS principle. Why the hell do they use "conjunction" instead of "addition" or even "and" when they know fine the bulk of their market are none native speakers of dubious ability.

Oh and plan for the pilot reading it at 3 am after 6 days of 12 hours shifts.

 

[VEBill]

"...do the existing AFM Runaway Stabilizer procedure above, ensuring that the STAB TRIM CUTOUT switches are set to CUTOUT..."

This extract can be (mis)interpreted to mandate that the switches are set to cutout while executing the procedure.

By way of explicit clarification of this point: If the wording had also included the word "while" after the comma then it'd be more-explicitly wrong. Now it's merely very badly worded. The present participle (continuous tense) of the word "ensuring" (with the -ing) very nearly includes an implicit 'while'.

The final report will almost certainly make the exact same point as I'm making here. It remains to be seen if this contributed to the incident.

The point that started this was that these procedures are not optimally worded, and they'll be yet another example of something that'll need to be corrected. It's precisely incorrect to claim that there's nothing to fix but the software.

 

[itsmoked]

That was an eye-opener Alistair.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[GregLocock]

So, has the FMEA for this system been disclosed? or are we still guessing as to what Boeing thought it was supposed to do? Putting my conspiracy hat on, fit big engines, write FMEA, find high severity index for high AoA conditions, identify Permanent Corrective Action can be software, define software fix, sign off FMEA. They needed a new FMEA done after that on the fix.


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[waross]

Thank you Alistair.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Lou Scannon]

I predict, that this MCAS debacle, quite possibly with great enrichment from this thread, will become one of history's object lessons in system engineering (in the largest sense) gone wrong, or perhaps better put, done ignorantly and/or negligently.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[Alistair_Heaton]

The reason why shall we say the procedures are so immature and geriatric compared to the other cards I suspect is because the original system from outset was pretty much bullet proof.

You have a great big lump of a DC jack screw powered off the emergency battery bus, way more robust than it needs to be mainly because it acts as ballast weight down the back for trim, saves having a lump of depleted uranium in the tail which in the old days when they used it for ballast. Three wires, one rocket switch, CB, and cut out switch (which I suspect was only used by technicians, never in anger). The manual trim system is "fly by wire" all of which are steel and the control runs are over pulleys.

I suspect the whole 737 series has had issues with that trim system that you can count on one hand since the 1960's. Nobody ever used that card so there was never a need to update it. The option of going paperless flight deck like the 777 and 787 was discounted due to grandfather issues. Just finding the QRH book behind the captains seat takes time. Then finding the correct page takes time. Paperless as soon as it see's that the trim has been running more than 5 seconds the QRH card will pop up on the 6th screen. 737 is a Memory item which is never trained for in the sim.

I suspect that a solo software fix onto the screw jack input wasn't the first solution either, a secondary motor onto the trim line with a clutch that could be over powered by the main trim system I suspect was looked at. But they were struggling with weight so that got ditched.
Yaw damper systems (which are used on the rudder to counter act dutch roll) were initially like this screw jack setup, they took the data off the Captains heading double integrated it, and then waggled the rudder to counter act the issue. When it was in the rudder pedals were solid you couldn't move them, to the point I had a US trained FO going into Dubai similar to the calibrator that's crashed recently who hit vortex and ripped his thigh muscle trying to push the rudder pedal to lift the wing. His crime was forgetting to press the AP disconnect twice to kill the yaw damper as well as the AP on a J41.

These days you can use the rudder pedals normally to there full limits with the yaw damper in and you never think about it really until a cap comes up and you have to slow down to the YAW damper u/s limits. To the extent you can actually have an engine failure and if you spot it winding down you can feed in the rudder to counteract the yaw and the AP never needs to come out. The BAe Jetstream rudder system was a wire analogue system. You really didn't want to play with swapping your heading flux valve input though with yaw damper in, this could give instantaneous heading changes which the yaw damper system would drive the rudder hard over to the yaw damper limits. You tended to only make that mistake once.

BTW the MCAS system is only the tip of the iceberg in relation to the Elevator system now. Its what the media and discussions are focusing on because its what's highlighted the issues with the elevator system design. The whole NG series is now under the microscope. If the FAA are making them tackle the elevator size and power and the size of the trim wheel in the cockpit its a whole different ball game. The FAA might have no option if its proved it certified the NG's as compliant when they weren't. The FMEA for the increasing the size of the stab and keeping the same sized elevator and reducing the size of the trim wheel in the front is the one that's going to be interesting. I suspect the MCAS software change has already been done. The delay is dealing with the bigger picture with the whole of the NG series, which is a tyrannosaurus in a china shop issue, there are over 7000 of them out there on the planet. They have an extremely good safety record mechanically. The only thing that pulls them down is the number of pilots that have taken them off road on landing due to poor decision making in regards to weather conditions and/or pushing a unstabilised approach. Personally I see no point changing them. They have proved themselves safe the hard way.

What they are going to do with the max's tail I really don't have a clue. Its a catch 22. The system works fine and pilots don't screw it up as proved by history of type if there is no external input to the trim system. Add in external input and it vastly increases the chances of system irregularities which vastly increases the chances of the pilots screwing it up. The current control and power is more than fine for normal operations and likely failure modes as the NG has proved. The new mode of failure its not. Get rid of the external input problem solved but then the aircraft isn't stable at high alphas. Which to be fair does happen way more often than passengers know or expect. And if your expecting 737 NG pilots to swap between the 800 and max sometimes in the same day its going to bite at some point if there is a change in control forces. There are things called noise abatement procedures which most airports have in built up areas. It requires you to fly a sub optimal profile to try and reduce the noise. It usually has you climbing at high draggy alphas at V2 +10 until 3000ft sometimes with a low level power reduction as well as cleaning up the flaps. This leads to highish alphas but I don't have a clue if they would be in the MCAS zone. here is a link to the Boeing noise profiles. The only time you can deviate from them is if you have an emergency or weather related issue. Zurich in Europe the company will get a 5000 euro fine if you don't comply with them. And if the company doesn't pay then they will come chasing after the Captain for the cash. They are particularly trouble some because they require a hard turn at low level as well requiring a 25 angle of bank as well because of rich powerful locals that live off the ends of the runways. There are something like 30 noise microphones as well dotted about which if you trigger them you also get a fine even if you have carried out the procedure to the letter. So your angle is high anyway to get V2 +10 and increases again because your in a 25 deg banked turn which gets you to within 20knots of Vs which is really high alphas and I pretty certain you would have the MCAS in action if you were stupid enough to try and fly a NDAP2 manually.

http://www.b737mrg.net/downloads/B737MRG_noise.pdf

You just have to look at EK521 777 crash in Dubai, that was 14000 hours experience on the flight deck and they still screwed up something which is trained for and done 3-4 times in the sim every 6 months. Although I have my suspicions that the temperature was way above what the airport was reporting due to local labour laws. Add in variations in control forces into the equation which occur on no other type from Cessna 150 trainer through to 747-800 and its not going to be pretty. Go arounds are not that common at most airports. The likes of Gatwick they are aiming at 1 an hour. If its more than 2 then the controller will be looked at, 0 and they will also be looked at because they are not pushing the traffic in hard enough. 1-2 an hour and they are doing great. But for a pilot you looking at 1 or 2 a year outside the sim for a regional pilot flying 4 sector days and 800 hours.

So I agree Hemi that this will be the subject of case study's for years both from design POV and from The pilot side of things. Hopefully lessons will be learned and money doesn't override safety.

 

[VEBill]

Bloomberg: Pilot warned Ethiopian bosses

 

[Alistair_Heaton]

That Captain has an interesting history, one which is no fault of his own from what I can tell.

Bernd Kai von Hoesslin is German and had issues in India with Jet Airways a few years ago if its the same guy. From all accounts he is a man of moral fibre and knows his stuff. His name rang a bell when I read the article.

 

[3DDave]

Ethiopian Airlines published a rebuttal to the Bloomberg article on Twitter. Condensed "Nuh Uh"

https://twitter.com/flyethiopian/status/1133680645568454657

I can see some reason for being disgruntled and for Ethiopian Airlines to keep pointing to Seattle as the entire source of the problem. But I think their cover got removed when they said their crew did everything per the AD, even though the flight data record showed they clearly did not. If this is true and it has the ring of truth to it, no wonder they wanted the spotlight so many miles away.