[Sutripta]

Originally Posted by Jeroen

With respect to the. We just do not know what, if any, changes were made to the final version of the report. The board and their then chair person have already denied buckling under pressure from Boeing. So it is one’s word against the other.

Really? You expect someone to say 'Though it was my job, I buckled under pressure', or 'I was hoodwinked'?

The 'puzzling' parts are most likely the give and take/ compromise deal part.

If the Ethiopian crash had not occurred, what do you think the LionAir crash report would have read like?

Regards
Sutripta

[Jeroen]

Response from the Dutch safety board

Reaction Dutch Safety Board on media reports in regard to the 2009 air crash investigation of flight TK1951

21 January 2020

The Dutch Safety Board does its work in strict independence. The Board decides independently on the outcome of its investigations, the content of its reports and its conclusions and recommendations.

American authorities and Boeing reacted to the concept report, which is standard procedure. In the Annex to the report their reaction and the way the Dutch Safety Board responded to their reaction is shown, in full transparency.

The report published in 2010 makes quite clear that the key-responsibility for the crash lies with Boeing, giving the failure of systems on board of the Boeing 737-800 and the way that Boeing responded to earlier warnings. Additionally, remaining possibilities for the pilots to correct these system-flaws were not used.

The technical report provided by Prof. Dekker was used by the Dutch Safety Board to substantiate its conclusions in the final report in 2010. At the time the Dutch Safety Board was not in the habit to publish underlying studies. Our current practice is different; we now publish as much as possible on our website, whenever a new report comes out. Given the current practices we have decided to publish prof. Dekker’s report today.

The key-question whether lessons of the TK1951-crash were sufficiently learned by Boeing and the American authorities, this should be part of the ongoing international investigation in the recent crashes of Boeing 737 Max.

https://www.onderzoeksraad.nl/en/pag...tigation-crash

And the Dekker report

https://www.onderzoeksraad.nl/nl/med...t_s_dekker.pdf

The Dekker report is very lengthy but makes for extremely interesting reading! A lot of insights into CRM, influence of training and simulation on pilots response, automation surprise etc.

I have not yet come to any conclusions whether the Dekker report is fundamentally different from the Investigation Board report.
Too much to read it one go.

I had not gone through all the annexes in the Dutch Investigation Board report. But it actually has all the requested/proposed textual changes from all consulted stakeholders and whether the Board approved those of not. There might have been other informal request, but the formal editorial changes are well documented it appears.

Jeroen

[Sutripta]

Originally Posted by Jeroen

Too much to read it one go.

Even how you made sense of a 228 page technical report in one night is beyond me.

Regards
Sutripta

[Jeroen]

Latest from Boeing: July it is! Nothing from the good folks at the FAA or other regulators to confirm though. Important as this is the first time under the new CEO they are making a statement regarding the return to service of the Max! He is going to have a serious issue if they don't make it!

https://www.bbc.co.uk/news/business-51200118

[vharihar]

How the Boeing 737 Max Disaster Looks to a Software Developer:

https://spectrum.ieee.org/aerospace/...ware-developer

[Thad E Ginathom]

Originally Posted by vharihar

How the Boeing 737 Max Disaster Looks to a Software Developer ...

More than anything I've read so far, that article makes me understand why I might want to not be a passenger on these planes.

[Jeroen]

By now there must be thousands and thousands of various articles on the Max floating around the net.

It is remarkable that just about every single one of them makes the same basic factual mistakes. It comes in different wording, but here it is:

1 The Max has a tendency to pitch up due to the engines being mounted further forward.

This is simply incorrect. Momentum is Force times arm. To simplify take a Max positioned horizontally: The arm is the (vertical) distance between the wing/hull and engine, not the horizontal.

In theory you could place the engines protruding past the cockpit, it would still not make it pitch up!

To date I have still not quite understood why this plane pitches up. Placing engines further forward, with everything else the same, will not have that effect. This article also mentions a few other factors, related to the new engines, which might actually be closer to the truth.

2 Everybody claims MCAS pushes the nose down, during certain conditions to avoid stalls.

As far as I have been able to make out the main reason for the introduction of the MCAS was a little more subtle:

There is a legal design requirement that defines how the control yoke needs to feel in terms of force the pilot feels. On the Max, near the extremes of the flight envelop that "feel" or rather force the pilot would feel, was not sufficient to meet the legal design criteria. Enter Max. Max would deflect the stabilizer to enhance the Force/Feel. Problem as we know now, is that due to a failed Angle of Attack sensor and poor system design it would actually push the nose down repeatedly.

Anyway, water under the bridge, it wont undo the two crashes and those that perished. Nor does it make a material change in the way Boeing/FAA messed up.

But in terms on defining what the solution needs to be, any problem needs to understood in depth. Otherwise you will not be able to design a correct solution.

In all honesty, I have stopped reading the various Max threads on the pilot forums. I used to check them frequently, but it is rare to see anything new coming to light.

Jeroen

[vharihar]

Originally Posted by Jeroen

Momentum is Force times arm. To simplify take a Max positioned horizontally: The arm is the (vertical) distance between the wing/hull and engine, not the horizontal.

Torque (not momentum) is Force times distance.

Originally Posted by Jeroen

This is simply incorrect. In theory you could place the engines protruding past the cockpit, it would still not make it pitch up!

To date I have still not quite understood why this plane pitches up. Placing engines further forward, with everything else the same, will not have that effect.

I think you're wrong. The way I rationalize this with myself is this:

• Torque is force times distance from fulcrum (which in this case is the center of gravity (CG), which is presumably at some point along the centerline of the fuselage, somewhere around the wings area). Now if the powerplant is mounted a bit forward, then that distance increases (well, the CG also moves ahead, but not by that much I'd imagine). Hence the torque increases. So the aircraft will tend to rotate about a horizontal left-right axis. Meaning it'll pitch up. Makes sense to me.
• Another thing, and which is stated quite clearly in the Spectrum article, is that the nacelle shape (flattened bottom) makes the engine shape itself act a bit like a wing in itself, meaning it offers some lift (This has nothing to do with the engine placed a bit forward. But its just due to the recent nacelle shapes). Hence, when the engine is revved more and results in increased airspeed, it would offer more lift. And due to the above torque and CG considerations, it would pitch up even more aggressively than "had it not been nacelled but just mounted forward".

[Sutripta]

Originally Posted by Jeroen

By now there must be thousands and thousands of various articles on the Max floating around the net.

It is remarkable that just about every single one of them makes the same basic factual mistakes. It comes in different wording, but here it is:

Have you posted this on any of the more professional aviation forums? What replies did you get?

Momentum is Force times arm.

Think there is a mixup between moment and momentum.

To date I have still not quite understood why this plane pitches up.

Engine positioning - spool centreline to wing distance - how does it vary between the various 737 models? I would have thought that if the critical dimension was the 'ground clearance' of the engine, then a larger diameter engine would have pushed the engine centreline closer to the wing.


2 Everybody claims MCAS pushes the nose down, during certain conditions to avoid stalls.

As far as I have been able to make out the main reason for the introduction of the MCAS was a little more subtle:

There is a legal design requirement that defines how the control yoke needs to feel in terms of force the pilot feels.

IIRC, previously you gave a different statutory requirement as the reason for the MCAS

Nor does it make a material change in the way Boeing/FAA messed up.

But in terms on defining what the solution needs to be, any problem needs to understood in depth. Otherwise you will not be able to design a correct solution.

The 737Max saga reminds me of three automotive cases
Toyota unintended acceleration - sloppily written code
GM ign key problem - design changed keeping same part #
Ford Powershift problems - Not merchandisable but too much invested to pull back (reminiscent of the Pinto fuel tank case. I think Ford has to pay compensation by next month.
https://www.freep.com/in-depth/money...ct/1671198001/
But note first world users get compensation. Third world users get goodwill warranty if they are lucky!

The IEEE article is a slight updating (Nacelles acting as canards) of an earlier article. Wonder why it was essentially reprinted.

Regards
Sutripta

[Jeroen]

Originally Posted by Sutripta

Have you posted this on any of the more professional aviation forums? What replies did you get?

It was discussed extensively on various forums across the net. The biggest problem with many aviation forums is that they have so many people on it, that it becomes difficult to make up your mind who to believe so to speak. Many people come with elaborate statements, but some of this stuff is very difficult for me to really validate as I am no expert either.

I have been a member for about two decades of one very small, very specialised aviation forum. There is probable about 30-40 active members. But many of them are real pilots, aviation engineers etc. And I have known them for so long and met with some of them over the years f2f. So I tend to go with what I pick up there as points and general concessions.

Here an image that was used for the engine forward issue on my forum:



To your point below, the pitch moment is related to the distance between the CG of the engine and wing (or hull/wing). In this image the vertical distance. How far apart the CG are horizontally so to speak (e.g. mounting the same engine further forward) does not have any effect on the pitch moment.

Although I am not a hundred percent sure, the total centre of gravity of the Max is not any different from the previous versions.

A lot of people assume moving the CG of the engine forward (away from the CG of the rest of plane) creates a pitch moment. Simply not true. The Max, apparently does have a bit of this pitch upward tendency, but it is not related to thrust (pitch moment) forces, but to aerodynamic forces.

Adding a little snippet from the same forum:

however it is the fact that the nacelles are further forward of the CG which gives rise to the issue (at high AoA the lift created by the nacelle has a longer arm to work with ahead of the CG and this gives a greater pitch-up effect).

This is incompatible with the longitudinal static stability requirements in FAR25 which requires stick forces to increase at a given rate as airspeed is reduced away from the trimmed airspeed. Hence MCAS - in the problem region some nose down trim is introduced, the pilot has to pull back harder to maintain or reduce airspeed and everyone is happy, until the AoA data used to compute the MCAS demand is faulty...

Originally Posted by Sutripta

Think there is a mixup between moment and momentum.

Well spotted.

Originally Posted by Sutripta

Engine positioning - spool centreline to wing distance - how does it vary between the various 737 models? I would have thought that if the critical dimension was the 'ground clearance' of the engine, then a larger diameter engine would have pushed the engine centreline closer to the wing.

Spot on, see above: As it is an actual larger engine (diameter) then previous ones, you would think the CG ends up slightly higher due to ground clearance, which would actually even reduce the pitch up moment / tendency!

Originally Posted by Sutripta

2 Everybody claims MCAS pushes the nose down, during certain conditions to avoid stalls.

IIRC, previously you gave a different statutory requirement as the reason for the MCAS

I have changed my mind before! It is a case of lurking around some of the forums and see what comes up and who to believe. On the big forums these big threads have a sort of natural cycle on how the discussions take place

Initial phase: Everybody throws in everything, lots of opinions, lots of discussions on what the facts are, partly due to that early on little facts are knows.

As time moves on, more information becomes available you get to a sort of serious phase: This is where a lot of the initial posters have lost interest and the really knowledge and sharp cookies continue. This is where you can find most relevant information and things tend to get more clear on what is what really.

The third phase on these forum threads is where we are now: Posts still continue, little to nothing new, endless repeats and nitpicking and in the Max case, quite a bit of Boeing / FAA bashing

So as times moves on, so do my thoughts/insights etc.

Again, if anything it shows how complex these things are, certainly for laymen and amateurs to really follow and come to some sort of conclusion. But it also shows that once a certain point is made (forward place engines push plane up) it is rare/difficult to see that point in mainstream media change.

Jeroen

[Sutripta]

Nacelle as canard/ lifting body should be easy enough to design round - make it symmetric about the horizontal axis. Will add a slight amount of drag. I would think there is more to it than that.
Surprised that no one in universities have put various models of the 737 in wind tunnels and let us know the results.

Regards
Sutripta

[ds.raikkonen]

Originally Posted by Sutripta

Have you posted this on any of the more professional aviation forums?

Refer thread on Airliners.net:

Regulators knew prior to 737MAX crashes that trim control was confusing in some conditions

https://www.airliners.net/forum/view...b2517765d9875f

[Sutripta]

Originally Posted by ds.raikkonen

Refer thread on Airliners.net:

Could you be a bit more specific pls. wrt. my question?

Regards
Sutripta

[Jeroen]

Next time when you board a plane remember this:

https://www.scientificamerican.com/a...ay-in-the-air/

Lots of people will tell you how lift works, but unfortunately none of that is the true, full understanding of lift. We simply do not know how planes stay up!

[V.Narayan]

Originally Posted by Jeroen

Next time when you board a plane remember this:

https://www.scientificamerican.com/a...ay-in-the-air/

Lots of people will tell you how lift works, but unfortunately none of that is the true, full understanding of lift. We simply do not know how planes stay up!

Jeroen, Beautiful article. Thank God I retired before I read this

All, The wings of a bird are far far far more efficient and versatile than the most advanced airplane wing. In some ways we are only now learning how to fly