Was MCAS needed?

[Bergerie1]

Perhaps MCAS was not needed to all on the 737Max. Patrick Ky of EASA has said that "they pushed the aircraft to its limits during stall tests, assessed the behaviour of the aircraft in failure scenarios, and confirmed that the aircraft is stable and has no tendency to pitch up even without MCAS."

https://theaircurrent.com/aircraft-development/mcas-may-not-have-been-needed-on-the-737-max-at-all/

[Uplinker]

I obviously don't know all the ins and outs of the MAX design process, but since the beginning I have wondered why: if the longer engines caused uncommanded additional pitch-up at high AoAs, then why not just modify the artificial feel in pitch and leave the control surfaces alone? Or have the stick shaker start at a slightly lower AoA to warn of the impending pitch-up?

[gums]

Good point, Bergerie.
Unfortunately, when I looked at the FAA requirements, they were more than simply "feel" as Uplinker asks.

It was an actual aerodynamic criteria that required MCAS, hence extreme (my point) movement of the horizontal stab. The tendency to require more down stab or less "up" stab had to be corrected aerodynamically and not thru the feel system. Or am I way off base.

Gums sends..





[Uplinker]

I don't know why* Boeing didn't bring in FBW on the B737. Even if they did so only in pitch, it would have brought benefits such as auto pitch trim, no pitch/power couple, turning without needing to pull back; and MCAS would not have been needed - just a change of some variables in the software.

* well, of course, I do.

[vilas]

Making of MAX was a ruthlessly comercial act by Boeing. They weren't going to spend a penny extra if it could have been saved. If it could be certified they would have sold the dummy without MCAS, May be with some luck they would have gotten away. Afterall it was a false activation that exposed them.

[GlobalNav]

I realize that the Boeing Company has a diminished reputation, but there is one thing it is noted for. It is extremely hard to add a new “feature” to a Boeing design because in Boeing’s philosophy, “it has to buy its way on”. A lot of good ideas have been rejected over the years. Not saying MCAS was a good idea, but Boeing had to have thought it essential or they would not have expended the resources to add it. The need would have been identified by Boeing engineers. So I don't doubt there was a technical need, even if the solution leaves something to be desired.

[FlyingStone]

I don't know why* Boeing didn't bring in FBW on the B737. Even if they did so only in pitch...

It would just be yet another big patch for a very old airplane, with questionable benefits. They were better off pushing the airplane out as it was (in hindsight, with better MCAS redundancy), and rather focus on developing a 737 successor from scratch.

[Denti]

I don't know why* Boeing didn't bring in FBW on the B737. Even if they did so only in pitch, it would have brought benefits such as auto pitch trim, no pitch/power couple, turning without needing to pull back; and MCAS would not have been needed - just a change of some variables in the software.

* well, of course, I do.
Didn't they add "FBW" for the spoilers in the MAX? Anything else probably would have required a re-design of the impacted flight control system that simply was too expensive, and would have taken too much time, always worth remembering that Boeing was in quite a desperate game of catching up to the order advantage Airbus had.

That said, what puzzled me at the time was the difference in testing program, although Boeing had to change quite a lot more on its new variant than Airbus had, Airbus did more than twice the number of test flight hours, which in itself does not say all that much of course, but it was a point i noted in passing.

[Less Hair]

According to the FAA it was needed.The 737 MAX was designed to handle and feel the same to the pilot as the 737 NG. Without the MCAS function, in some small areas of the flight envelope — such as approaching a stall and during higher g-force maneuvering — the new engines contribute to the control column feeling lighter in the 737 MAX than the regulations allow. These are not areas of the flight envelope in which the airplane normally operates. However, FAA regulations, specifically 14 CFR 25.143, 25.201, 25.203, 25.251, and 25.255, still require the control column to have a higher pull-force feel in these flight regimes than would exist on the 737 MAX without the added stability from the STS and MCAS function.

For the FAA to certify the 737 MAX, the original design had to meet FAA requirements for control force feel when maneuvering or deviating significantly from trimmed equilibrium. The aircraft manufacturer is responsible for making design decisions and showing compliance to applicable regulations. In this case, Boeing elected to include an additional flight control law in the STS, which is part of the flight control software that provides required control force feel to the pilot.

This flight control law, or MCAS, enhances the feel of the column forces in manual flight, and is only operative with flaps up. MCAS provides signals to move the horizontal stabilizer at elevated angles of attack to compensate for the aerodynamic effects of the 737 MAX’s larger and more forward-located engines, resulting in the required column feel to the pilot.

Source https://www.faa.gov/news/media/attachments/737-MAX-RTS-Preliminary-Summary-v-1.pdf (page 10)

[Less Hair]

Stick force gradient must not become lighter towards a stall. But this is what supposedly happened.

[PEI_3721]

As #9 MCAS was required to meet stick force requirements; it was not directly related to the stalling characteristics. The comments about stalling could relate to acceptability if MCAS had been inhibited; thence a comparison with the NG stall, a certification consideration for the failure case.

MCAS was also driven by the Boeing focus of type commonality, minimum differences training; thus a stick force tweak to achieve a 'NG like' feel (#10).

FBW might not have resolved the issue(#4). Electrical signalling was not required; the associated computation and sensor redundancy could not be justified - why not add third AoA to the existing 'mechanical' system.
Also, the Boeing FBW philosophy of keeping the pilot in the loop - stick force feel - negates the auto trim follow up. The C*U algorithm is based on trim for speed, which would not provide an additional stick force change to rectify the deficiency in manual flight. Hence the need for separate computation to drive the trim directly - MCAS.

[gums]

Awww man, this statement bugs me:

MCAS was also driven by the Boeing focus of type commonality, minimum differences training; thus a stick force tweak to achieve a 'NG like' feel (#10).

The MCAS implementation was not some gentle input to the existing column "feel". Good grief. It put in gobs of nose down trim and did it for "x" bumps and then did it again if the trigger parameters still existed. It was not well thought out and was poorly implemented, at that.

If the MCAS could make the Max "feel" like the NG, then I guess the STS in the NG is very harsh, as that system seems to be another kludge to make the pilot do something that should be part of basic trim action by the pilot as the plane increases or decreases speed. GASP!

We need to stop making excuses and simply admit the MCAS was a poor solution to an aero design that changed the stick force gradient so much that the jet would not meet the criteria.

Gums sends...

P.S. FBW computer solution is not the answer without a sh!!!tload of waivers from the certifying authorities. The 'bus is a very stable plane, as the AF crew demonstrated. They didn't even recognize that they were stalled! The military planes using FBW use it for variour reasons, and not all are to correct for a poor aerodynamic characteristic. As with the 'bus, FBW computer flight control systems can reduce workload and smooth things out (things we old farts did without HAL doing a lot except autopilot funtions when in level flight)

[CessNah]

I don't know why* Boeing didn't bring in FBW on the B737. Even if they did so only in pitch, it would have brought benefits such as auto pitch trim, no pitch/power couple, turning without needing to pull back; and MCAS would not have been needed - just a change of some variables in the software.

* well, of course, I do.
For an aircraft that is only manually flown for the best part of 30 seconds per sector, is there really a justifiable need for FBW?

[Contact Approach]

For an aircraft that is only manually flown for the best part of 30 seconds per sector, is there really a justifiable need for FBW?

Would you not say the opposite is true?

[Banana Joe]

For an aircraft that is only manually flown for the best part of 30 seconds per sector, is there really a justifiable need for FBW?
I fly a 737 manually for a lot longer than 30 seconds every sector...
And FD and AP are MEL items.

Back to your Cessna 150.

[PEI_3721]

Yo gums, #13 Let's swat some 'bugs'
The design concept of MCAS was fine. It met the objectives - as misguided as they appear to be with hindsight.
However, it was the engineering implementation that was flawed, together with weak and failed processes in testing, airworthiness, and certification; all of the holes in the Swiss Cheese lined up - they were already there just waiting for MCAS (it could have been something else).

The system operation which you describe was a failure case, not normal operation.

Yes, in hindsight, MCAS was not an ideal solution, but alternatively if the system has been well engineered, tested, certified, etc, then we would not be having this discussion - MCAS could have been hailed as a neat low-cost fix for an old design pushed too far.

Whilst the rule-makers and regulators fix, patch, kluge, the holes in regulation - swatting bugs around their cowpat, the greater concern is that they might not see the 'cowpat' which they are still standing in; that should 'bug' us.

Hindsight; 'sometimes things go wrong, so that we will know when they go right'.
Aviation assumes that the wrong things will be minor, manageable by limited capability humans, but sometimes those assumptions are wrong.

[vilas]

John Leahy ex CCO of Airbus said A380 was undone because when they launched in 2000 the engine manufacturers offered them engines which according to them was the most economical and anything better was atleast ten years away. But in three years the engine manufacturers turned out new engines for B787 which was 12% better in SFC. B737 was also undone by new engine technology in a different way. The 1960s low wing aircraft was unsuitable for high bypass engine era. Had Boeing anticipated this they should not have made 800 series itself but built a new aeroplane which being later generation aircraft may be even outlasted Airbus neo. Unfortunately they had gone for widebody 787 and by the time it turned profitable Boeing was left with no gumption to invest in another new aircraft. They hurriedly did another plastic surgery on the old lady which turned out very nasty and apart from financial damage has even destroyed their credibility and reputation.

[gums]

Far being for me to debate a certified test pilot with all the degrees and actual diplomas from the "schools".

I cannot find the "#13" ref document.... I gave up looking for technical, non-political, non-management and so forth once pPrune closed discussion here on the Tech Log. Whatever document had "#13" ? It must have been buried in all the "return to service or certification" threads that were not worth the time to look at due to legal and non-pilot posts. I tried to get tech stuff on Tech Log to no avail.

I do not take completely agree with:

The design concept of MCAS was fine. It met the objectives - as misguided as they appear to be with hindsight.

I agree that moving the stab would change the control input gradient in order to require more aft stick for more AoA or whatever. It would not necessarily require more pounds per stick movement unless it influenced other systems in the control implementation. I do not agree that it was an acceptable concept to make the plane "feel" like the NG model. So meeting the "objective" of the Part "x" that FAA required seems to me to be the biggest bone of contention I have. How would moving the stab angle of incidence and then remain there at other parts of the envelope? "Oh, Gums, we just return to some other angle when ?" What angle?
I appreciate the implementation of moving the stab "gradually" to help with "elevator" pitch authority/movement. But my experience was with three jets that did not have "elevators" (and one that was a delta with elevators/elevons). We moved the stab for pitch control! In the "neutral" position, we followed basic FAA stability and control requirements. On autopilot, they trimmed the slab very slightly to maintain either mach hold or altitude. When we pulled hard it got harder approaching higher AoA, except for the last few degrees in the VooDoo. In the VooDoo we definitely got a "light stick" in the end game, and I wish you could have flown one to see what I mean.
----
and then I completely agree with:

However, it was the engineering implementation that was flawed, together with weak and failed processes in testing, airworthiness, and certification; all of the holes in the Swiss Cheese lined up - they were already there just waiting for MCAS (it could have been something else).

You nailed it there, PEI. And do not forget some management issues that Big B is now paying for.

[tdracer]

John Leahy ex CCO of Airbus said A380 was undone because when they launched in 2000 the engine manufacturers offered them engines which according to them was the most economical and anything better was atleast ten years away. But in three years the engine manufacturers turned out new engines for B787 which was 12% better in SFC. B737 was also undone by new engine technology in a different way. The 1960s low wing aircraft was unsuitable for high bypass engine era. Had Boeing anticipated this they should not have made 800 series itself but built a new aeroplane which being later generation aircraft may be even outlasted Airbus neo. Unfortunately they had gone for widebody 787 and by the time it turned profitable Boeing was left with no gumption to invest in another new aircraft. They hurriedly did another plastic surgery on the old lady which turned out very nasty and apart from financial damage has even destroyed their credibility and reputation.

Actually, Boeing was planning a completely new aircraft to replace the 737 (part of, IIRC, was called 'project 2016'). Problem was when Airbus announced the A320 NEO, it caught Boeing completely off guard. Not only where they resource limited (both 787 and 747-8 still a year away from type cert/EIS), if Boeing had launched the new aircraft immediately, it would have been five to six years before initial cert. Worse, both Boeing and Airbus were pushing 737s and A320s out the door at ~50/month - it would take another four to five years to get a brand new aircraft up to that sort of production rate. It would have meant giving the A320 NEO a near monopoly and the market for about five years of production - roughly 3,000 aircraft. That was too bitter of a pill to swallow, so Boeing cobbled together the MAX - which kept the A320 NEO advantage down to around 12 months.
With the benefit of 20-20 hindsight, doing a completely new aircraft looks much better than what happened on the MAX, but no one could foresee that 10 years ago...

BTW, the A380 had much bigger problems than it's engines (although they didn't help) - even now Leahy is unwilling to admit he screwed the pooch when they launched the A380 just as the market was moving to big, long range twins.

I've posted this before, but the problems with MCAS all go back to two related assumptions. First, that an MCAS malfunction was no worse than a stab trim runaway, and two that the crew could recognize and accommodate such a failure in four seconds (this second assumption pre-dating the MAX, possibly going back to the original 737-100/200). Based on these assumptions, an MCAS malfunction was judged as no worse than "Major" - same as a routine engine shutdown - and single failures are acceptable.
Turns out that both assumptions were wrong - four seconds to recognized and correct for a stab trim runaway was too optimistic (at least for some pilots), and it was not recognized as a Stab Trim malfunction. Had MCAS been originally identified as a Critical system (as it is now), it never would have been designed the way it was.

[Less Hair]

OT: With some new from scratch design Boeing would have been able to match or top the A321neo.

[chriscrepon88]

Wonder how much longer "blancoliori" will continue to defend Boeing's negligence and tortious actions? Hiding the existence of MCAS until after the first of two crashes? Sounds legit.

[gums]

Thanks, TD

The assumption that MCAS loss of sanity would be seen as runaway trim is one thing that bugs me. Most runaway trim would not be corrected by beeping the trim switches on the yoke, unless there is alot of folks out there that never had to trim using switches on the stick or yoke.

I do not put a lot of credence to the four second assumption of a big problem because the MCAS activation stopped briefly if the pilot just beeped the trim switch. Added to the implementation was undocumented changes to the trim cutout switches. Oh oh oh, how about telling the pilots that they had this thing called MCAS? How about telling them what it was supposed to do? As a pilot, I am pissed about the hold thing, and feel betrayed.

I had my share of "firsts" in new planes, and some hairy moments in others. But this MCAS implementation in both aero design and procedural implementation simply scares me. Imagine if you were on nuclear alert back in the sixties and they changed the pre arming and actual arming of our weapons without telling us and having us practicing a few sim missions?

I relinquish the floor.

[tdracer]

Gums
Shortly after the second 737 MAX crash, I was at an event at the Seattle Museum of Flight where I ran into some old friends from Boeing (including a test pilot) who'd been involved in the MAX. One thing they all agreed on was that they'd all assumed that MCAS would be covered in the differences training from the NG.
That it wasn't was admittedly bad, but may not have made a whole lot of difference in the long run - the Ethiopian crew certainly should have known about MCAS yet still couldn't handle it.

[PEI_3721]

gums, re your post #19,
Apologies for my my cryptic #13 which was a reference to your previous post '13' in this thread, minimising thread clutter with endless quotes.

We are dancing around the same pole; but without the details of the various factors which could have influenced the goals of the people involved we cannot know their reasoning.

A minor deficiency in certification stick-force requirement could be argued with the regulator, normally the first choice - low cost. We don't know the extent of the deficiency, likely the wrong side of the line with Mach effects.

However, the second goal - NG compatibility, minimum training, then at $1M per aircraft there would be a strong incentive to improve the MAX. Particularly where the cost of MCAS as an extension of the existing STS would be small beer in the overall certification costs.

Amongst these goals it is feasible that MCAS might not be required for certification, but for commonality - training, MCAS was essential. A typical situation of conflicting goals, commercial pressures, and time constraint, cobbled together and thrown at the regulator.
Maybe the 'MAX did not required MCAS, but it had it.'

Yes Boeing are paying for this misjudgement - hard cash; the FAA can only 'pay' with loss of reputation, credibility, and worldwide trust. Which of these two, Boeing / FAA, will be back in 'profit' first ?

Flown the F101 Voodoo?! But for the toss of a coin I would have. However, the long-stab characteristics were closely studied, being typical of that generation of transonic aircraft. Extensive experience in 'the' Lightning which had similar, mild characteristics, showed how tolerant or unaware pilots can be of adverse characteristics.
These aircraft required 'MCAS', but didn't have it.

[CessNah]

I fly a 737 manually for a lot longer than 30 seconds every sector...
And FD and AP are MEL items.

Back to your Cessna 150.
I fly the 737 too actually, the only hand flying we ever do is to 1,000' AGL and it comes off at the 500 foot stabilisation gate... what's the point in having FBW for stages of flight where everything is already trimmed out and all done in straight lines?

[gums]

For all to see, PEI and Gums can discuss some of the fine points about design and aero without calling names and raising cultural aspects of aviation.

We both share some "exciting:" times in various planes, and are still here to talk about it.

I am not sure PEI has as much experience training and learning from foreighn countries as I have, but I can unnerstan those here who have flown with many of the foreign carriers and all that that involves.

I sure hope we can contribute to a great resolve not to repeat the MCAS debacle.

[George Glass]

I think this has all been done to death on other threads but it is worth reiterating the simple facts.

- MCAS was created to meet certification requirements of control column pitch force at the extreme edge of the performance envelope.
99.999 % of Pilots in normal operations would never expect to get anywhere near those conditions in 99.999 % of their total time on the aircraft.

- The inadequacy of the design was exposed ONLY after two subsequent events occurred;

- an angle of attack sensor failure
PLUS
- the incorrect application of the Non- Normal checklists expected by Boeing to resolve the issue.

Boeings assumption was that the procedures it had in place were adequate to mitigate the risk.
Subsequent events proved them wrong.
But not unreasonably so.
Took lots of cheese slices to line up to reach the outcome.

[DaveReidUK]

the incorrect application of the Non- Normal checklists expected by Boeing to resolve the issue

Boeing had a NNC to address MCAS failure ?

[Rainier]

Perhaps MCAS was not needed to all on the 737Max. Patrick Ky of EASA has said that "they pushed the aircraft to its limits during stall tests, assessed the behaviour of the aircraft in failure scenarios, and confirmed that the aircraft is stable and has no tendency to pitch up even without MCAS."


From my reading of the Boeing email in the AirCurrent article, flight test data indicated that there was not sufficient warning to the pilot that one would be entering a stall condition. The issue thereby appears to not be one of control column feel but instead that the aircraft must provide tactile feedback that a stall is imminent. If this is the actual physical behavior of the aircraft than by all means MCAS would be required.

I always wondered why it took until flight test to identify the need to use MCAS in low speed flight. This observed behavior would explain why wind tunnel data and simulation would not have predicted this beforehand.

With regards to the criminal citation, my understanding of the law is that even if failure to comply is an honest mistake, e.g. Forkner did not know of the decision to change functionality, that it would still be criminally prosecutable. This would explain why the Company is criminally liable but not the individual. It would also explain why the criminal penalty was not as severe in only ~$200 million.

Does this seem like a reasonable interpretation?

[George Glass]

Yup.

Initial failure of Angle of Attack sensor leads to NNC “Airspeed Unreliable.”

Continued motion of Stab Trim leads to NNC “ Runaway Stabilizer.”

Challenging, but doable. Fly thrust and attitude.
But if you leave the autothrottle engaged at T/O thrust , try to re-engage the autopilot AND try to re-engage stab. trim you are screwed.
As a matter of interest , the flight data recordings from the initial Ethiopian report seem to have disappeared from the internet.
Why ?

[Less Hair]

However it used to be some intermittent motion of stab trim. Starting over and over again. MCAS had been kept unknown to the pilots. And those AoA indicators were not displayed as advertised.
Not only the training got changed but the hardware and software.

[vilas]

Yup.

Initial failure of Angle of Attack sensor leads to NNC “Airspeed Unreliable.”

Continued motion of Stab Trim leads to NNC “ Runaway Stabilizer.”

Challenging, but doable. Fly thrust and attitude.
But if you leave the autothrottle engaged at T/O thrust , try to re-engage the autopilot AND try to re-engage stab. trim you are screwed.
As a matter of interest , the flight data recordings from the initial Ethiopian report seem to have disappeared from the internet.
Why ?
The question was did Boeing had NNC for MCAS? When MCAS itself was not disclosed how will they have a procedure for its abnormality?

[DaveReidUK]

As a matter of interest , the flight data recordings from the initial Ethiopian report seem to have disappeared from the internet.

I'm not sure exactly what you mean - the Preliminary Report, complete with the FDR traces that were widely discussed here on PPRuNe, is still downloadable from the Ethiopian CAA website.

[FlightDetent]

For the record, as well I find G.G.'s summary markedly off the centre-line. That's from a person who agreed on all observations made by 737driver and fdr. For the latter it is certainly not a surprise, however, the former had received a lot of friendly and undeserved fire IMHO. With so many lives lost unnecessarily, the aim for everyone is taking as many lessons as possible for their own job.

At the edge of the envelope, an aeroplane must behave in a predictable manner and provide tactile resistance of sufficient and increasing magnitude.
Encountering unreliable airspeed event at take-off, a pilot shall assure for the necessary power + pitch to continue climbing safely.

Each of them being correct does not make the other one less true. Two gas pedals, two feet.

[George Glass]

I'm not sure exactly what you mean - the Preliminary Report, complete with the FDR traces that were widely discussed here on PPRuNe, is still downloadable from the Ethiopian CAA website.

Is it ?
Last time looked the link wasn’t there.

For those that are wondering I have personally experienced an “ Airspeed Unreliable” event in flight.
After the initial “what the f#ck “ moment the NNC worked just fine.
It will NOT work if you leave the autothrottle engaged.

My understanding is that MCAS was certified on the basis that the existing checklists and procedures would be carried out by a properly trained crew and would mitigate any risk.

Clearly they were wrong.

[DaveReidUK]

Is it ?
Last time looked the link wasn’t there.

Aircraft Accident Investigation Preliminary Report Ethiopian Airlines Group B737-8 (MAX) Registered ET-AVJ 28 NM South East of Addis Ababa, Bole International Airport March 10, 2019 (http://www.ecaa.gov.et/home/wp-content/uploads/2019/07/Preliminary-Report-B737-800MAX-ET-AVJ.pdf)

[FullWings]

I thought that most of us had agreed over this one but the trigger for the runaway trim NNC was “continuous uncommanded movement”. For those who haven’t flown the 737, the trim moves quite a lot in bursts in normal operation, without a command from the pilots, as it is driven by STS, MCAS on the MAX and the autopilot. How could you tell that the trim moving then stopping was a) normal operation or b) a dangerous system failure? Answer: you couldn’t, without (secret) prior knowledge and continued observation. If you disconnect the trim every time it moved under its own accord you might as well pull the circuit breaker on the ground. It’s many years since I flew one but I still remember the “clunk clunk clunk” which was the most common sound on the flight deck.

It was asking too much of pilots dealing with a complex failure plus tactile and aural alerts, during a critical phase of flight where the trim was actually responding to their inputs, to immediately diagnose a failure of a system that wasn’t even documented and work out what to do. We now know that the sim trials were unrepresentative due to prior coaching.

[Sailvi767]

John Leahy ex CCO of Airbus said A380 was undone because when they launched in 2000 the engine manufacturers offered them engines which according to them was the most economical and anything better was atleast ten years away. But in three years the engine manufacturers turned out new engines for B787 which was 12% better in SFC. B737 was also undone by new engine technology in a different way. The 1960s low wing aircraft was unsuitable for high bypass engine era. Had Boeing anticipated this they should not have made 800 series itself but built a new aeroplane which being later generation aircraft may be even outlasted Airbus neo. Unfortunately they had gone for widebody 787 and by the time it turned profitable Boeing was left with no gumption to invest in another new aircraft. They hurriedly did another plastic surgery on the old lady which turned out very nasty and apart from financial damage has even destroyed their credibility and reputation.

Just a small point on the engine issue. The Airbus A320 and 321 NEO’s suffer from a similar if not the same issue and it’s actually worse on the Airbus because the aircraft could in fact become unstable. This was not caught until the aircraft was in service and it required the CG be restricted by blocking the last seat rows on many configurations. They were attempting to address this and remove the CG restriction via software. I am not sure if this has been completed. MCAS was primarily designed to insure the aircraft handled like the 800 and would not require any pilot simulator training for the transition. In fact Boeing promised SWA that no simulator differences training would be required. SWA wrote a 1 million dollar per aircraft penalty into their purchase contract if even 1 sim session would be mandated by the FAA. The rest is history.

[George Glass]

A B737 simulator instructor at a carrier I used to work for used to do an exercise when we had some time left over.
He’d position us at about 7nm on final to a lit runway , at night , in flight freeze , and then turn all the lights off on the forward panel.
When we were happy he’d let us go.
After a while he would stop the sim. and ask us how we thought it was going.
”Bit fast and a fraction low” I said.
”Correct. Continue”
After a normal landing we discussed what had been an interesting exercise.
It demonstrated several things;
1) How well thought out the Boeing cockpit is and how visual cues and muscle memory can get you a long way.
2) That old f@rts like myself know more than we think we do , just by virtue of years of experience.
3) What a confidence building exercise it was for new F/Os , particularly those coming from Airbus , as to what the aircraft can actually do.

Another exercise was to take the aircraft to 20,000 ft and turn off every unguarded switch on the overhead panel.
The aircraft still flies.

The point is that the B737 is an analogue aircraft with lots of nice to have , but not necessary , digital add ons.

Reading all that has been written about the MCAS debacle I now realise that the B737s time has passed , not because it is fundamentally unsafe , but because the world has moved on. I don’t think its going to far to say that the time of Piloting as a highly regarded , valued profession is over.
The accountants have won.
Airbus philosophy has won.
Time to retire the B737 ASAP.
Very sad.

[jimtx]

Wonder how much longer "blancoliori" will continue to defend Boeing's negligence and tortious actions? Hiding the existence of MCAS until after the first of two crashes? Sounds legit.
I not sure MCAS was hidden. The Brazilian Authority had a differences document for the MAX that listed MCAS as a cat B training item. Forkner was listed as a contributor to the document. Why other states authorities did not have MCAS listed I don’t know. But it would be interesting to see what the Brazilian training involved.

[jimtx]

The question was did Boeing had NNC for MCAS? When MCAS itself was not disclosed how will they have a procedure for its abnormality?
What’s interesting is now that they do have a NNC procedure they don’t reference any caution about handling in any flight regime when you end up without MCAS. The tail wagged the dog. The solution was eliminate MCAS. The autopilot doesn’t need it and pilots don’t need it. But too late for that.

[Less Hair]

They now compare two AoA-vanes anytime so the indication in order to stay away from a stall is more reliable. The whole thing is a move back from fly by wire to manual flying. Mixing two worlds didn't add up.

[megan]

Since he MCAS was there to alleviate longitudinal handling qualities I would have though some sort of note would have been incorporated in some check list to advise what a crew may face with respect to handling qualities upon failure. Some helicopters (S-76 and Blackhawk) had longitudinal handling qualities that didn't comply with FAR's and had what was called a pitch bias actuator (PBA) in order to satisfy the FAR. Experience on the line showed the PBA wasn't necessary and was removed.

[DaveReidUK]

But it would be interesting to see what the Brazilian training involved.


https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/545x757/brazil_mcas_differences_ac0d3a45fbfa0000528c34d0164efe4e6e06 a3c0.jpg

[jimtx]

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/545x757/brazil_mcas_differences_ac0d3a45fbfa0000528c34d0164efe4e6e06 a3c0.jpg
Yes, So what did the Brazilian Authority require GOL to train and check?

[jimtx]

Since he MCAS was there to alleviate longitudinal handling qualities I would have though some sort of note would have been incorporated in some check list to advise what a crew may face with respect to handling qualities upon failure. Some helicopters (S-76 and Blackhawk) had longitudinal handling qualities that didn't comply with FAR's and had what was called a pitch bias actuator (PBA) in order to satisfy the FAR. Experience on the line showed the PBA wasn't necessary and was removed.
As far as I can tell there is no note or caution in the new procedure and in the simulator session I don't know if they just RTB with no MCAS and thus don't get into whatever regime it was designed to alleviate. It would seem that they should take the simulator into the relevant handling regime to show the non linear stick force to the crew when they do have a MCAS failure.

[RVF750]

Anyone hazard a guess as to why they didn't try an aerodynamic solution. Let's face it a tab or smallish strake glued onto the upper sides of the nacelles wouldn't look too bad and kill the lift at high AoA? I take it KISS doesn't go far at Boeing.....

[gums]

We went thru this a few years back RVF.

The mods closed the threads to new posts.

Unless they deleted all the posts, you may find some stuff there, but the basic rational was aero fixes deleted the better performance from the new motors and their mounting.

[tdracer]

Anyone hazard a guess as to why they didn't try an aerodynamic solution. Let's face it a tab or smallish strake glued onto the upper sides of the nacelles wouldn't look too bad and kill the lift at high AoA? I take it KISS doesn't go far at Boeing.....
Not to contradict the esteemed gums, but they did try aero fixes - various strakes on the inlet and add-ons to the wing. None of them worked sufficiently well to alleviate the loss of stick gradient at high AOA. At some point - with huge barn doors on the inlets to spoil the lift - they probably could have made the aero fix work, but it was deemed impractical due to costs, weight, and fuel burn. Then they tried MCAS and it worked like a charm.
The problem wasn't so much the concept of MCAS, it was the implementation.

[gums]

Thanks, TD......

I got the impression from the Boeing "mole" who I will not name but you can see many posts if we have not deleted them.

If you move that big stab you get a ton of change in pitch moment. The normal mode is small changes for the stab and use changes to the elevator. We saw an extreme example with AF447 when the system moved the stab over and over because the pilot held back stick.

Up to me, I would change the FAA 25 rules to account for mechanical feel at the cockpit and then deal with the Airbus stick that has zero feedback. I flew a few thousand hours in jets with zero feedback that did not come from mechanical connections to control surfaces that then let me know the pressure on them. I estimate that 95% of most commercial jets since 1950 never had direct feel of the control surfaces ever.

I have no problem with the stick getting a little light when approaching a high AoA, but that should be shown to the pilots and if deemed a serious problem , use a pusher and or a horn.

The MCAS was a poorly implemented kludge that should have been dealt with using a waiver for its purpose , but then have procedures for the chance it would go rogue.

Logging.... have a great weekend, and geaux Saints.

[tdracer]

Gums, in the aftermath of the second MAX crash, I believe it was the Canadian authorities who basically argued for just that - get rid of MCAS and get an exemption for the stick force gradient.
For some reason, it never got any traction with the other authorities.

[Less Hair]

Well sort of. EASA is on the record that the MAX is safe to fly with MCAS (version 2.0) off.
And that is their verdict after recent test flights with their own pilots.

[PEI_3721]

td, "For some reason, it never got any traction with the other authorities."

Perhaps Boeing didn't put this option up front because it wasn't a solution to their $1M/aircraft 'min differences training' incentive.

[DaveReidUK]

Well sort of. EASA is on the record that the MAX is safe to fly with MCAS (version 2.0) off.
And that is their verdict after recent test flights with their own pilots.

However MCAS must be operative for dispatch.

[tdracer]

td, "For some reason, it never got any traction with the other authorities."

Perhaps Boeing didn't put this option up front because it wasn't a solution to their $1M/aircraft 'min differences training' incentive.
This was well after the second crash - when Boeing had conceded that simulator training would be required.

[FlightDetent]

Up to me, I would change the FAA 25 rules to account for mechanical feel at the cockpit and then deal with the Airbus stick that has zero feedback. Puzzling. While true it's not a feedback loop, such shorthand description obscures the simple fact that on AB - aerodynamically an entirely conventional craft - to get higher AoA
+ more elevator is needed, achieved by
+ greater stick displacement, for which
+ still increasing force needs to be overcome.
The end result is a fixed correlation between AoA and force on the stick. During a commanded maneuver, the requirement for the A/C to resist a push towards the envelope's edge ever more aggressively is well satisfied.

[gums]

Thank you, Detent. You have opened the door we had here long ago.

You have described the basis of the problem most folks have RE: FBW

to get higher AoA
+ more elevator is needed, achieved by
+ greater stick displacement, for which
+ still increasing force needs to be overcome.
The end result is a fixed correlation between AoA and force on the stick. For a commanded maneuver, the requirement for the A/C to resist a push towards the envelope's edge ever more aggressively is well satisfied.

The situation 25 years ago with the ;bus ( most widely used FBW plane by many carriers, and at least two variants), was much more than a simple electric voltage or syncrho angle from a control stick to a servo that moved the elevator or aileron or rudder.

I do not have the tech manual for the 'bus stick, but I do not beleive the 'bus stick had any force feedback nor any change in the gradient for gee command dependent upon AoA or even Q. In short, it was like an old Atari game. You got used to the gee command that your stick movement made after pulling on the stick a few times.

The MCAS requirement was as you described. Higher AoA should required more aft stick. That requirement was based upon decades of conventional aircraft designs and control systems. The Airbus 320 and on changed all that.

Many very educated and experienced pilots and engineers are here from the AF447 threads. They will talk at length about the issuues. I prolly screwed up a few assertions about FBW related to current planes, but I can come back and elucidate at length. Unless we have a Concorde pilot here, or an original Viper pilot, I shall continue to pull rank RE: FBW
RE: for the veterna here of all the commercial planes I have ridden in for 60 years, I shall bow to their experience and knowledge and we can discuss. Many of them have flown the same high performance planes that I flew. Some may even been students of mine.

Gotta go now.

[jimtx]

This was well after the second crash - when Boeing had conceded that simulator training would be required.
If Boeing concluded simulator training would be required, what training would that be? Flying the simulator and having MCAS run away and deal with it, then take an airplane without MCAS and land somewhere, and on the way let the crew see how the airplane handled without MCAS in the regime it was supposed to pencilwhip? Lives and money spent over a pencil whip that wasn't needed.

[FlightDetent]

gums Best wishes, sir. I am half-convinced the door better stay shut for the clarity of the nice discussion within the scope of this thread, and definitely so for our weekend enjoyments in the offline life. :)

If we manage to find some knowledgeable folk later, perhaps there are stones to be overturned still. The shirt I'll be wearing says: "Driver of a Bus (with force gradient on the stick for varying AoA)", colour yet to be determined.

4. In Direct Law - stick to surface, the aircraft is conventionally stable and requires manual trim operation to trim out forces when the speed is changed. Stick force per G is conventional.My underline. While FBW could render all the requirements for flight control characteristics not applicable or obsolete, in the particular case of mid 1980s design - the small 'bus - the manufacturer decided and suceeded to design a plane that actually fulfills them. Both in its natural, raw aerofoil form, and as well once the HAL is powered up.

[zzuf]

Gums I enjoy your posts and as FlightDetent says this is probably not the place for flight control discussions except for MACS but....
1. A320 has spring feel for artificial feel as in F86 without the bob weight.
2. Longitudinal control is manoeuvre demand, eg stick force per G or per pitch rate, or a blend of the two depending on speed/alpha.
3. Beyond the autotrim envelope a pull force is required for lower speeds, a push force is required for higher speeds.
4. In Direct Law - stick to surface, the aircraft is conventionally stable and requires manual trim operation to trim out forces when the speed is changed. Stick force per G is conventional.
5. My first aircraft with an electronically signalled flight control mode was the Mirage111 in Autocommand, circa 1969 plenty of Mirage pilots earlier.
6. My first FBW airliner was Airbuse's A300 FBW F-BAUD March 1986.
7. There were literally years of negotiations/ discussions on what FBW characteristics would be considered as acceptable as "Equivalent Safety" to the then current stability and control standards standards US FAA/ UK CAA/ French DGAC.
Links may help - the sidestick link is from a serious flight simmer with an OEM sidestick which he stripped for repairs.
https://sim-on-a320.com/blog/2016/08/12/original-sidesticks/
https://davi.ws/avionics/TheAvionicsHandbook_Cap_12.pdf
Thank you for your interesting posts - and your service.
Cheers mate.
Oh https://sim-on-a320.com/blog/2017/03/28/sidestick-springs-repair/

[gums]

Thanks a bunch, ZZ you too, Detent.
I am remiss by not going back to all the AF447 data and such to see the gradients.
My main point about discussing FBW is too many folks do not understand exactly what it is and how it can be implemented differently in different planes. I really liked the Canadian approach concerning the Max, and seems to me that the 727 had to use a pusher or similar implementation due to its characteristics at high AoA. Ditto for other commercial planes.
=====
Off topic, but I would have loved to have had a hop in the F-86. Our sqd checked out the last two U.S. Air National Guard units that were flying the thing, but USAF would not let us try it, heh heh. Ditto for the Mirage, and my first fighter was the F-102, so would have been neat to compare the deltas.

[PEI_3721]

gums, Detent, et al, caution with specific comparisons.
Following on from zzuf, good refs; - associating the A320 with feel and bob wts could be misleading.

Airbus chose the combination of electrical signalling, digital computation, and side stick as their FBW system. All of these challenged the certification status quo; this required adaptation, interpretation, and new regulations. Airbus designed the future, rewrote the regulations.
Conversely, Boeing, using the improved technologies where possible, chose to follow history. Moving sticks, trim based force-feel, fleet commonality.

The piloting differences matter little (avoiding endless opinionated debate); these aircraft meet the safety requirements, and are flown as any aircraft can be.

Airbus chose a manoeuvre demand algorithm C*, a combination of pitch rate and 'g', with rate dominating low speed, 'g' higher. The trim followup restores a stable condition and minimises drag. (Military systems may favour 'g' more than rate)

Boeing is similar except the trim followup had to maintain the speed-dependent force-feel; this is the basis of the C*U algorithm, where U is the speed aspect.

The 737 Max with MCAS extended previous trimming adjustments (STS), to compensate for aircraft weaknesses; in no way is this FBW (electrical signalling at best). Post modification, MCAS fails safe, no trim demand or incremental runaway (although separately, the stab still could).

Relating this to AF447; the A330 did exactly what the pilot demanded, for the situation, as the crew interpreted it - UAS - pitch/ power. The technical / icing cause had be been identified from previous incidents and modification was in hand. The safety lessons stem from why this one accident differed from several previous incidents with the same trigger - go to previous threads for debate.

In the 737 Max accidents the aircraft did its own thing; crews were in recovery mode without explanation or guidance.

Even after modification, MCAS and the revised checklists could still lead to an AF447 type of incident. The checklist for AoA disagree requires action for unreliable airspeed; this biases the crew's mind to UAS, requiring pitch/power, bypassing wider situational aspects such as cross referring standby instruments which could clarify the situation, not requiring any manoeuvre.
This suggests that Boeing's operational approach to MCAS, alerting and drills, are still out of sync; perhaps not really appreciating if (why) MCAS is required - certification or training.
Old aircraft, even with new mods still require old style situational awareness to help crews understand, without ambiguity, and not presuming any failure, cause, or action. It is difficult to impose new technical philosophies on an old aircraft; similarly for operational aspects.

[gums]

Thanks, PEI.

My view is we are experiencing an epoch of old tech mixed with new tech, but still have to deal with basic, fundamental laws of physics and aerodynamics.

Many of the younger folks seem to believe we can do anything with sfwe, and a few older folks of the "macho, Yeager wannabes" revert to attitude, pitch, power solutions. I am a old fart, but matured during the transition of pure mechanical flight controls and actual feedback to zero feedback and eventually, electical commands to servoactuators that moved the rudder, ailerons, elevators, flaps, and the beat goes on.

My views are here and I shall check in on ocassion, but basically lurk.
======

The MCAS debacle represents an attempt to use technology to compensate for a basic design that did not satisfy the "rules" and the company wanted to sell the plane with no additional training for pilots flying the basic plane. So save a few bucks here, but then spend billions down the road, and then add the personal losses by a few hundred folks.

I sure hope all manufacturers look at this debacle and look in the mirror.

[zzuf]

Gums, F102, I think I have your pic!! High over Thailand 6Jul1964, probably 100 miles or so north of Korat.
Courtesy RAAF Avon Sabre and A4 radar gunsight. Concede a gun splash??? Ha Ha good old days.
Truly sorry about the thread drift, won't do it again.
Best regards.


https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/1160x2000/usaf_f102_d05c5afd4016e437145c6b6e63cac82c692b514f.jpg

[gums]

@ zzuf,

YOU SWINE!!!

[PAXboy]

I ask a question that may well not be for this thread or indeed any thread:

In the whole MCAS affair, Boeing has received (and will continue to) all the justifiable anger of humans and the law. However, South West Airlines who wrote the $1m per airframe penalty clause appear not to have received even a glancing blow?

Whilst it can be said that Boeing were big enough to make their own mistakes (and did) would they have been as likely to commit to MCAS if not for such a high penalty being set by their customer?

Of course, it might just have been 'good old capitalism' at work ...

[vilas]

I ask a question that may well not be for this thread or indeed any thread:

In the whole MCAS affair, Boeing has received (and will continue to) all the justifiable anger of humans and the law. However, South West Airlines who wrote the $1m per airframe penalty clause appear not to have received even a glancing blow?

Whilst it can be said that Boeing were big enough to make their own mistakes (and did) would they have been as likely to commit to MCAS if not for such a high penalty being set by their customer?

Of course, it might just have been 'good old capitalism' at work ...
Boeing was selling an aeroplane not cocaine. They are solely responsible for the product and it's aftermath. By this absurd logic why not blame the Airbus Neo or the bigger fan engines fitted on them? Without which the MAX would never have been made?

[john_tullamarine]

Truly sorry about the thread drift, won't do it again.

Unless it is appropriately infrequent ... in which case, it will not only be tolerated, but encouraged, aided, and abetted.

[PAXboy]

No vilas that is not a valid comparison but I shall let the matter go.

[RVF750]

Gums and TD thanks. The penalties of, and that they did indeed try to put alloy sticky-outs on to get what they wanted first is a relief. As to Airbus, yuk. I've tried my whole career to avoid flying one. I like feel and feedback, thank you very muchly.

I always thought the answer for FBW sidesticks was to mount the whole stick and force sensing assembly on a moving base that mimicked the actual movement of the control surfaces. That way you'd get both moving, and more softer felt motion at slower speeds, plus the benefit of feeling any interference from the computer limits. It's a Win-Win-Win option. Not sure if they do that at Gulfsteam or on the C17? It was certainly a trick Airbus missed.

[PAXboy]

Perhaps that level of sophistication was not available when they started out their FBW design. When it was - they already had so many machines in service, and pilots used to their side stick, that it would have caused more problems to uprate? Gosh they might even have had carriers specifying that the change must not compel any SIM time by force of financial penalty... :uhoh:

Seriously, if they had a working system making a fundamental change would be diffcult. Might be good for the longer term but Bus were still climbing the market at the time and such major changes could have been tricky.

[megan]

However, South West Airlines who wrote the $1m per airframe penalty clause appear not to have received even a glancing blow?Southwest was just a customer seeking a deal on a product, Boeing said yes we can do that, so the airline bought in. The longitudinal handling issues required them to do something to alleviate the problem and after trying aerodynamic fixes, which didn't work, Boeing came up with MCAS. SW are not in the aircraft design business, they just say as a customer what they would like, it's up to the manufacturer to tell them what's possible. SW made an offer, Boeing accepted, same as when you walk into a car dealer.

[blind pew]

What puzzles me is the difference in the stick force criteria and the real world!
My UK instructors Bible circa 1969 BLAC flight instructors manual has no mention of increasing back pressure or stick position in the stalling exercises nor theory.
Likewise my British Gliding Association instructor manual from 2005.
Never during heavy metal simulator stall exercises has any one mentioned stick pressure.
The only times I’ve had the death rattle go was on approach in turbulence on the Trident..whether incorrect load and genuine or the system I was never told but there wasn’t any “ohh the stick force warned me” moments.
I’ve flown several gliders where it doesn’t change although a few have rudimentary springs used for trimming which do have increased force purely due to the stretch.
Model aircraft controllers..the most difficult aircraft I’ve flown..have simple centring springs iirc with a parallel mechanism.
The only increasing force requirement in my real world is on low performance paragliders which is intended to stop low airtime pilots stalling inadvertently...say he who has accidentally stalled and spun them.
Off hand I can remember five occasions where colleagues got stall warnings or stalled.
Two were with incorrect droop selection, one at low speed which ended up in a field, the second extended at two high a Mach number and went through several levels in a holding stack before control was regained.
The third was a mate who was too busy talking during an intermediate level off having forgotten to engage auto throttle.
The final pair were both on visual approach into Nice on the then new Fokker 100 which supposedly had an all talking autothrottle and stall protection system which it didn’t.
Stick force didn’t come into it.
IMHO whoever drew up the requirements should have been an experienced pilot rather than a bean counter.

[Uplinker]

..............As to Airbus, yuk. I've tried my whole career to avoid theying one. I like feel and feedback, thank you very muchly.

I always thought the answer for FBW sidesticks was to mount the whole stick and force sensing assembly on a moving base............. It was certainly a trick Airbus missed.

I am interested to know if you have actually been type rated onto Airbus FBW? I have flown them for 13 years and personally don't think the FBW side-sticks need an "answer"; they work very well.

Having previously been type rated on four different makes of conventional aircraft; I took to the Airbus FBW like a duck to water. You either see and feel your control limits through a yoke the old fashioned way, or you feel that you are at neutral or have reached the limit of the side-stick quadrant on the Airbus. That and the PFD is all the feedback I need.

The Airbus side-stick and FBW relationship is very poorly taught, I grant you. No TREs I asked ever properly explained to me how to use the side-stick, and eventually I taught myself. Initial training is hampered by not having linked controls - I learned a lot in my early days on turbo-props when Captains would invite me to "follow them through on the controls.

[Checkboard]

The airbus sidestick is fine. The lack of feedback from the other side is a bit of a problem.

The non-moving thrust levers, compared to say the Boeing, are the thing that I would change. Having said that - it's the way of the world now.

[fdr]

gums, Detent, et al, caution with specific comparisons.
Following on from zzuf, good refs; - associating the A320 with feel and bob wts could be misleading.

Airbus chose the combination of electrical signalling, digital computation, and side stick as their FBW system. All of these challenged the certification status quo; this required adaptation, interpretation, and new regulations. Airbus designed the future, rewrote the regulations.
Conversely, Boeing, using the improved technologies where possible, chose to follow history. Moving sticks, trim based force-feel, fleet commonality.

The piloting differences matter little (avoiding endless opinionated debate); these aircraft meet the safety requirements, and are flown as any aircraft can be.

Airbus chose a manoeuvre demand algorithm C*, a combination of pitch rate and 'g', with rate dominating low speed, 'g' higher. The trim followup restores a stable condition and minimises drag. (Military systems may favour 'g' more than rate)

Boeing is similar except the trim followup had to maintain the speed-dependent force-feel; this is the basis of the C*U algorithm, where U is the speed aspect.

The 737 Max with MCAS extended previous trimming adjustments (STS), to compensate for aircraft weaknesses; in no way is this FBW (electrical signalling at best). Post modification, MCAS fails safe, no trim demand or incremental runaway (although separately, the stab still could).

Relating this to AF447; the A330 did exactly what the pilot demanded, for the situation, as the crew interpreted it - UAS - pitch/ power. The technical / icing cause had be been identified from previous incidents and modification was in hand. The safety lessons stem from why this one accident differed from several previous incidents with the same trigger - go to previous threads for debate.

In the 737 Max accidents the aircraft did its own thing; crews were in recovery mode without explanation or guidance.

Even after modification, MCAS and the revised checklists could still lead to an AF447 type of incident. The checklist for AoA disagree requires action for unreliable airspeed; this biases the crew's mind to UAS, requiring pitch/power, bypassing wider situational aspects such as cross referring standby instruments which could clarify the situation, not requiring any manoeuvre.
This suggests that Boeing's operational approach to MCAS, alerting and drills, are still out of sync; perhaps not really appreciating if (why) MCAS is required - certification or training.
Old aircraft, even with new mods still require old style situational awareness to help crews understand, without ambiguity, and not presuming any failure, cause, or action. It is difficult to impose new technical philosophies on an old aircraft; similarly for operational aspects.


C* works nicely however it leads to the atrophy of procedures in the event of a law change, and that has led to a few rapid dissemble events. It is nice to fly though when working rite/write/right... reversion needs practice.
C*U makes you appreciate C*.

The aerodynamic issues of MAX (incidentally a popular name for dogs, and cats) are able to be resolved aerodynamically. The fact that there is a lifty surface poking out before the wing is not a problem, the non-linearity in what it does though is. At the same time, the bits that are added to the BRT to cure previous non-linearities are kept.... and no one got out an angle grinder? On NTRS, there's about 1000 papers related to high alpha lifting body flow control, and, surprise, the bits on the pained side of the cowl work on those factors, and got rid of the exact opposite issue that existed which led to the implementation of the sticky-outy stuff, which ended up assisting the non-linearity that was then the needy bit for the guys to redo the "lets run the trim nose down" bit of MCAS... whew. one breff.

Getting out the hacksaw or angle grinder would affect one thing, however, it would increase VS1g by a bit. But putting a LET on the mid-span TE Flap would do more than compensate for that, and even the inner flap of the Yehudi area would function to increase CL, and drag the CP aft mitigating what otherwise would be a Cm reducing shift of spanwise lift distribution inwards and therefore forwards... it's a swept wing.

There are a few pretty neat papers with NTRS and with AIAA ARC, DLR, DTIC, Delft, TsAGI, RAeS etc on the matter of low aspect VGs on nacelles and flow interaction with a wing, they are easy reading, and how and why are well described. Slender body flow control gets to the same point, and John C Lin, Carranto, Bruce Storms, Li, and the rest of the mob of researchers covered the issues pretty well, following on Bob Liebecks works, however, the subject has always been missing a simple point, one group of researchers looked at low-speed stuff and just that area. in a cell next door, literally, was a bunch of guys looking at high-speed effects of another device, and apparently, there wasn't any time for two to compare notes over coffee, as the flow structures are the same... the effects are different the mechanisms are the same. The fringe benefit is you also get the real world supercritical flow outcomes that do not exist except on paper due to the point that details matter.

Anyway, a hacksaw or angle grinder would have removed the issues of stick force gradient and would have been readily offset by simple mods to the TE of the flap that would have reduced VS1g, and therefore retained or improved V speeds, while nicely reducing drag in transonic flight. There is a modest increase in trim drag in cruise due to the wing actually doing what it is supposed to do, but that is around 1% of the magnitude of the drag reduction on the wing (which is still only a little of the total lift, etc... ) some 16M USD later, we did prove to non-believers that, surprise, lift and drag are orthogonal, because they are, well, orthoganol. The negligible trim change was recorded, it was measurably less than the trim change resulting from shifting 1 x 67kg SLF from 18C to 1B. For the 737 particularly, the flap track design hates vibration, and the mods to the flap reduce that considerably because the reason for the vibration, instability of the Kutta condition at the TE, is resolved.

just sayin' MCAS was a hammer fix for a typo by a builder.

[mustafagander]

Sounds good fdr,
BUT MCAS does not operate with flaps extended as I understand things. So then, do what you like with the flappery, it matters not.
A simple old engineer like me sees the easiest and best fix as small strakes on the aft fuselage set to zero incidence in the CRZ case. Now they cost a bit of wetted area and maybe a bit of extra drag on CLB coz the strakes do not align with the streamlines. However it is a simple once for all fix with no failure case. Never mind this software stuff, KISS.

[PEI_3721]

fdr, thank you for the extensive background.

Re 'angle grinder' fixes. One of the first western public conferences where TsAGI presented a paper on high alpha aerodynamics. - In answer to a question on their approach to strakes re nose slice, why some aircraft could perform 'cobra' manoeuvres (SU27) vs those requiring extensive theoretical development (F18); 'if a particular aircraft had a problem then change the nose cone until one was found which did not roll off'. A lesson in practicality.

EASA neatly concludes the certification need for MCAS:-
"MCAS has been established to play only a limited role in augmenting the stability and stall characteristics of the aircraft in certain conditions. … needed to ensure the stability margins that make the aircraft fully compliant to the applicable regulations on stall demonstration and pitch control characteristics. This explains its inclusion in the original 737 MAX design.
These stability margins are required by regulation in order to support the flight crew handling of the aircraft during certain manoeuvres such as approach to stall …
MCAS was needed to provide full compliance but also that the loss of this function does not preclude the safe flight and landing of the aircraft; i.e. the 737 MAX remains stable following the loss of the MCAS function."
Boeing 737 MAX Return to Service Report
https://www.easa.europa.eu/sites/default/files/dfu/B737_Max_Return_to_Service_Report.pdf

[gums]

Salute!

Outstanding discussion and analysis by fdr. love it

Other than many posts concerning the aerodynamic solutions other than the kludge MCAS, I still need someone to explain how the 'bus got certified with no control feedback related to AoA or mach or....

I can unnerstan that a certain command from the yoke or stick should result in some aerodynamic response, but we have the gee command in the 'bus folks, then hybrid commands in the B777 and then the laws I flew with some of the systems years ago along with the Concorde.

My opinion is the FAA and other certification agencies need to revise the requirements. The MCAS was implemented to satisfy a relationship on a chart or graph that would be meaningless in the AB 320 and later. When I looked it up, it looked like something for the Aeronica Champ I flew in 1960.

Oh well, I hope we move forward and avoid a chain of decisions and implementations that resulted in the MAX tragedies.

Gums sends...

[Bergerie1]

Which, Gums, is why in the real world, I questions why it was ever required at all.

[gums]

TNX, Bergerie....

I would really like to have FAA or the European cert folks explain how the Airbus FBW was certified, but the 737 had to meet some formula about control force versus AoA or Gee or......

We had older planes like the 727 that had a nasty problem if you got to a high AoA, just like the VooDoo I flew as a clueless yute. For some reason Boeing implemented the MCAS versus a pusher or some warning to meet the requirement of Part XXX of the rules. And then they screwed up the MCAS activation and repeated cycles and.... GASP.

Make no mistake. I would love to fly a new plane without any "help" from the electronics or even yaw and pitch dampeners we saw in early 60's. Their performance would not be economical nowadays for commercial use, and sadly lacking for military performance - we could be like that guy in early days of the "max" debacle that iterated the stick and rudder mantra. After UPT in USAF, I only flew one plane that had actual feedback from the moving control surfaces. And my first high preformance plane had zero feedback in the stick!! Did I adapt? Yep.

The Viper FBW was an amazing advance and helped improve range plus high performance maneuvering that did not require Chuck Yeager to yank and bank. Ditto for the first Bus planes with near- complete FBW versus cables, torque tubes, pulleys and such. We pilots adapted in a new minutes and did not need the "feel" from the elevator or aileron or rudder to do the task.

So I iterate the question to FAA and other agencies to look at and change the cert requirements.

[tdracer]

Gums, no first hand knowledge, but I believe the A320 (and subsequent brand 'A' FBW) were certified via an "Alternate Method of Compliance" - AMOC. AMOCs get used quite a bit when new technology allows the aircraft to meet the 'intent' of the rule without meeting the 'letter' of the rule. They are quite common when new technology basically makes the letter of the rule obsolete. A classic example on the Boeing side was the implementation of EICAS - the regulations say that you need full time indications for all sorts of things, with EICAS those full time indications were suppressed unless the were not doing what they were supposed to (e.g. fuel shutoff valve - on older aircraft there were indicator lights that indicated valve position - with EICAS those lights were replaced by an EICAS message if the valve wasn't in the commanded position).
So in the case of the side stick controller, I believe Airbus took the position that the FBW flight control algorithms eliminated the need for the physical feedback.

[PEI_3721]

Hi gums,
'… how the 'bus got certified with no control feedback …'

The simple answer is that they rewrote the rules. Airbus chose not to use stick force as a cue for speed, instead argued the then novel view that an artificially stabilised and well protected aircraft, available with 'FBW', would provide an equivalent level of safety.
This was no simple task, it took many years of proposals supported by extensive research, simulation and experimental flights; effectively having to re-educate the aviation world (regulators).

The step change to an electrically controlled aircraft with computed protections did not come with past 'baggage' from previous products. The A300 broke into the commercial market, it had three crew until modern avionics, EFIS, digital technology, resulted in the Forward Facing Crew Cockpit (FFCC) -600, thence A310. This change was at the time of great focus on workload and the 2 crew cockpit, where all new aircraft were subject to workload evaluation B737, MD80, F28, BAe146, thus opportunity for radical change.

Copy of Bernhard Ziegler's paper linked below; this is a very thoughtful and far reaching note, which provides the background and much more. Sorry you need to read the pages in reverse, last page first, so concentrate !
https://www.dropbox.com/s/8uzkoc47lmgeo4w/

Bernard Ziegler - much maligned at the time, but time writes history.

Also, many other contributions; including John Wilson (copilot on Comet first flight), with the Advanced Flight Deck simulator (ended up in the Smithsonian in DC).
https://www.dropbox.com/s/dte4j6oadegmot4/Advanced%20Flight%20Deck%20SKMBT_C25210092409410.pdf?dl=0

Some of the gems from Ziegler:-
"… very careful not to use guidelines which are too broad and subject to too many interpretations, like: 'The man shall be kept in the loop', which is obvious but of no practical use, which is too specific or may prove to be harmful constraints with the evolution of man and machine (at least of his evolution of his culture and habits)."

"Crews got use to automation much faster, but designers moved forward even faster. A lesson in modesty in front of the immense inventiveness of the human being, and the army experts in human science who are now descending on our community, and should well meditate on this lesson. … as Socrates said, the only thing we know is that we know nothing." - and then the last pages on "Protections …… ", human reasoning, culture, human machine interface, task, free flight;
… … are you listening Boeing, FAA.

[FlightDetent]

.. no first hand knowledge,
[..]
I believe Airbus took the position that the FBW flight control algorithms eliminated the need for the physical feedback. People who do have first hand and personal knowledge testify - that's about 40.000 brand A. rated pilots worldwide - there's non-linear, gradient force opposing a pilot's pull for a higher AoA with that F/CTL implementation. Not a feedback by far, but does what the regulation prescribes both in active FBW and "raw" direct control law.

One imagines it could have been enjoyable to implement. The stick is spring-loaded towards the neutral and thus provides closed haptic loop how much the pilot is demanding. All the engineers needed to do after flight testing the aerodynamic behaviour was to "gear" their algorithms properly so that the plane would respond to deflections on the control any particular way that may have been required.

Yet you can't take Chicago out of the girl.

[fdr]

Sounds good fdr,
BUT MCAS does not operate with flaps extended as I understand things. So then, do what you like with the flappery, it matters not.
A simple old engineer like me sees the easiest and best fix as small strakes on the aft fuselage set to zero incidence in the CRZ case. Now they cost a bit of wetted area and maybe a bit of extra drag on CLB coz the strakes do not align with the streamlines. However it is a simple once for all fix with no failure case. Never mind this software stuff, KISS.

Noted re flaps, however, the underlying issue is this. The flow from the engine nacelles of fans under almost all wings results in a loss of CL in the area of the wing behind the nacelle. The addition of the low aspect delta from VG's control the flow off the nacelle and result in coherent vortex structure streaming over the wing LE, and that happens to recover the CL for the section. Along comes the new blender, with "biggly" nacelles sticking out further, and the same VG is placed on the nacelle, and, oops, we have a surplus of goodness. So out with the angle grinder. As CL correlates to V1Sg which correlates to Vr, and V2, and Vref, The beancounters and hawkers of wares at the bazaar don't want higher V speeds, they want higher $$$$ per pound of plain. To get the Veezes back in harmony with the multiverse, just add. ... tabs. tabs increase CL, "biggly" but they move Cp rearwards on the section, which is what y'all driving Boeing's overly huffed n puffed toy need for happiness. The surprise of doing that is... you happen to also aft load the wing in transonic flight, which happens to put the shock and lambda foot of the SBLI back where the CFD models would predict they would be for a clever wing such as Bob Liebeck envisaged with SC-1 and similar foil types, the basic shapes which oddly go back to Herr Kawalki back in '44. The neat thing about your common variety supercritical foil is that they are not acting as advertised. (the 737 is aft loaded, and the LE radius makes it, and most TBC designs a hard ask for being supercritical in practice due to excessive LE suction. Airbus makes a really neat wing, since the 330/340 and the 380... I say through gritted teeth, cuz, damn! ) Take a DES, LES, RANS 2D or 3D preferably model of the wing and you get a different location of the shock to what you see when you look out the window. A schlieren image of the shock foot is observable as a shadow on the wing surface. The neat thing about that it is is in the wrong place, but it is the real world, and it is what the as-built vs the generic monolithic sections used in CFD are employed. as opposed to detail). The effect of a DTE is to aft load a section and the flow effect is the same in detail as a LET, so you get the chance to stop the wear n tear of the 737s odd flap tracks by stopping unstable separation points, reduce inflight vibration, (it aint from the engines... its from the flow over the TE of the wings being unstable, and making the shock location unstable... ) you reduce drag, and increase lift, and... for the MAX machine, you shift the CP rearwards in that section, and that mitigates the nacelle lift Cm effect. tail trim force is increased slightly but it is a fraction of the total forces. A Max runs out at about 70+ tons, more or less, with a L/D around... say 20:1, so the drag in cruise is around 3.5T, and the thrust is the same. 1% drag change is... a big deal, but it is 350kg, 2 x "400lb hackers" on their beds.

The SFC is around 0:35 for the older blenders at SL, going to about 0.65 at cruise, and the new biggly built versions of the TFE731, the GENX etc are about 20% better. but, still, drop off at altitude. Why? cuz, the fan is a fixed pitch prop. yes, it changes the inflow velocity, but it is fixed pitch, and so the faster y'all go, the more turbojet you end up relying on (residual thrust) you still get the pleasure of the blade drag. If only there was a way of altering Cl vs Cd at static and high-speed conditions. And indeed there is. How that can be done is in a dumpster load of papers at ARC, NTRS, DLR etc, but as far as I am aware, it has only been tested once, on a really daggy JT15D-1A which was less than enjoyable to work on, and we only got around to doing the static runs. The prop mod stuff though we have flown since 1994, and that was fun in its own rights. turns out there is a philosophical question on the simple calculation of efficiency, otherwise, it is hard to get a 20% improvement in thrust output from a prop that is P=po/Pi= 85%. The static test of the JT15 got a marginal increase in efficiency for the thrust output, but it did put out 30% more thrust at 100% N1, while remarkably remaining within T5 limits. It put out the normal thrust at 94% so that wasn't a bad thing. I digress.

Miller time...

wiggles

An angle grinder and some velcro would have removed the requirement for MCAS.

[fdr]

fdr, thank you for the extensive background.

Re 'angle grinder' fixes. One of the first western public conferences where TsAGI presented a paper on high alpha aerodynamics. - In answer to a question on their approach to strakes re nose slice, why some aircraft could perform 'cobra' manoeuvres (SU27) vs those requiring extensive theoretical development (F18); 'if a particular aircraft had a problem then change the nose cone until one was found which did not roll off'. A lesson in practicality.

EASA neatly concludes the certification need for MCAS:-
"MCAS has been established to play only a limited role in augmenting the stability and stall characteristics of the aircraft in certain conditions. … needed to ensure the stability margins that make the aircraft fully compliant to the applicable regulations on stall demonstration and pitch control characteristics. This explains its inclusion in the original 737 MAX design.
These stability margins are required by regulation in order to support the flight crew handling of the aircraft during certain manoeuvres such as approach to stall …
MCAS was needed to provide full compliance but also that the loss of this function does not preclude the safe flight and landing of the aircraft; i.e. the 737 MAX remains stable following the loss of the MCAS function."
Boeing 737 MAX Return to Service Report
https://www.easa.europa.eu/sites/default/files/dfu/B737_Max_Return_to_Service_Report.pdf

AIAA's JoA had every 2nd article in the early 90s being CFD of the snout of the F/A-18, working on the flow instability at high alpha, about 1:10 of the remainder were dealing with the vortex interaction with the verticals tab... and the subsequent structural loads issues. Back to basics, fluids don't like having to make up their collective minds as to where to separate from a body. a crossflow over a pretty cigar nose is going to give instability in shedding, and shedding is bad on jumpers from cats and dogs, and from noses of aircraft at high alpha, as in the latter case, it generates random force vectors. In the former case, it affects allergies and makes for a messy wash.

The 16 was more stablerer, the nose is not as near to circular. The F-35 nose is much more stable, but even there, it could have done away with the short radius upper curve of the cross-section, which would have given more lift at the nose which could be an issue for the pitching moment but would be extremely stable at high alpha. Pyotr Ufimtsev's work may have led to a preference for roundy upper shoulders when run through better supercomputers, otherwise, the 117 style edge would work well, upside down. fluids don't care that much about the front bits they are very interested in the rear area. That point which is pretty basic seems to be lost in almost all car design, up through F-1, and to an extent in lots of light aircraft design,

[Funny thing is we have smart design of stealth structures and we use dumb designs of anechoics]

PS: F-15 nose slicing was also an issue identified in flight, similar deal to -18, 16 was a little better, flow control on the 16 was related to advanced manoeuvering more than stopping an instability, but they are similar in nature and the cures are similar too. jet blowing avoids the impact on target RCS but is a pain to maintain.

PPS: the fact that NASA has an F18 as the HARV probably added some emphasis to it being the poster child for CFD in the early 90s, and the cracking of the vertical stabs that started to become expensive, along with the tail bits from the vortex interaction from the LEX. neat fix for the classic F18s, cleaner with the E/Fs, but it took away the charm of the design.

[Bergerie1]

Thank you fdr, Gums, PEI 3721 and tdracer.

I started this thread because, having read the EASA report, I really did wonder why Boeing decided to use MCAS. I can see its advantages for Boeing as 'a simple extension of the STS', but as we know, without triple AoA sensors it was vulnerable to a failure. Surely simpler solutions would have been a stick nudger as required by the UK CAA on the 747 (had that been fitted to the MAX it would not have required any extra crew training) or some aerodynamic device like the 'angle grinder' devices you have mentioned.

But I guess Boeing decided that the MCAS was cheaper.

And, as hinted to by EASA and by some of you, was it really necessary to meet a regulatory requirement on stick force gradient when the aircraft may have been perfectly safe without any of these fixes?

[mustafagander]

Hey fdr,
Thanks for the learned explanations of this stuff.
I'll work through it tomorrow before beer o'clock and after I revise some old aero notes. Been a long time since I had to think much about this stuff!!

[CaptainSandL]

FDR
Re An angle grinder and some velcro would have removed the requirement for MCAS.

They did try that - or at least they tried revising the leading edge stall strip. They also tried modifying the leading edge vortilons and a revised wing vortex generator pattern but none could be made to work so they borrowed MCAS from the 767 tanker.

[fdr]

LE stall strips generally act to give a reliable buffet signal to the driver from vortex impingement on the stabilizer, while that is nice to have, they generally don't act on altering the stall event. They can, but if you look where they are located, they are not used for that purpose.

Vortilons are great at stopping the spanwise flow, which has it's benefits but not to the issue of the nacelle Cm effect. The NG adopted them and they were great, along with the revised aileron design in stopping the 737's aileron vibration at high Mach (relatively...) Wing VGs are not going to do a whole lot to alter the Cm issue either, not if the flow is already happily attached, and the Cm non-linearity starts before there is separation on the outboard sections. The 737 aileron effectiveness in high AOA is not too bad, so long as the slats are rigged symmetrically. The suto-slat function could have avoided the MCAS, it is scheduled at an AOA however, so would have needed to have some reliability, I can't recall if it has dual sensing or not, its a few years since I last stalled a 737.

Have a look at where the stall strips are located and where that is relative to the outboard tips of the stab.(other than the early 737s which had a strip on the Krueger which was a curious thing to have) The neat thing about fluid flow is that almost everything you do will work to some extent. A B52's stunning cheese grater array, like the Gloster Javelin, The Lear's various forms except for John Raisbecks beautiful MK II wing... The Avanti's wing... lots of fluid getting pushed around there... the B707, B757, B767, the 737 tail area, a fence on the 727, hawker vortilon & VGs...... , the outboard wing on the classics, the mid-wing on the classic, and NG, the 787... the MD80 vortilon, the Hunter and F4s dog tooth, notches, MiG15, 17, 19, 21 fences, (not great help on the 15, good on the 21 though) etc and pretty much everything else out there. The EFA Typhoid drools a notch inboard.... a bit like a 330. The A-10 has some stuff going on out there, looks suspiciously like aileron effectiveness related. Gee whizzes have lots of cheese slicers on the wing outboard... which is aileron buzz related I guess. Of all of those, the P168 is curious, the cuff on a beautiful little rocket seems out of place, about like a Ferrari with a bull bar. I digress. Pretty clean wings came out on the 747, and on the A330-340-350-380. Boeing excelled with the 747, but Airbus really did well on their wing design (making up for the A300Bs wing/aileron... woof).

[FlightDetent]

And, as hinted to by EASA and by some of you, was it really necessary to meet a regulatory requirement on stick force gradient when the aircraft may have been perfectly safe without any of these fixes?Counter question: If the gradient requirement was not met only formally but the true effect is not relevant handling wise, why did Boeing go through with MCAS and not just simply declaring the behaviour and asking for relief?

I think it links to your conclusion on the (lack of) other fixes apart from MCAS. They seem to have honestly chosen a solution that was readily available, required less R&D and cost as little as necessary, all that without penalizing performance As much as the internet likes to ridicule that decision, showboating and all [this thread is a great exception!!], what's being called clearly obvious in the laymen media sphere was for sure well known and thoroughly considered by the dedicated professionals yet AFTERWARDS they chose MCAS. No matter the pathetic killer gremlin MCAS 1.0 which was born later, the initial choice of picking the MCAS tool was a fair one. If it would be done again, there's absolutely no presentable evidence to deny that particular path. And as matter of fact that's what happened: The proper and agreed solution to control forces is MCAS 2.0 which is all that 1.0 wasn't and at the same time the exact thing they originally planned for.

Without getting carried away too far: Imagine the trailing edge modification had been chosen resulting in all the super critical geeky cool effects fdr explains. BUT THEN during the actual design and implementation aviation reality would be abused same as with MCAS 1.0. Such as failing to do ice contamination test and the additional load stress calculations. Resulting in flaps detaching a few years down the road - with crew performance same as on the second crash day, the death toll would have been identical.

Trying to say that selecting what is now disclosed and known as MCAS as a tool cannot be faulted. With extreme probability, it was well-reviewed against all the other options and chosen maybe even as a win-win.

Cons of the other suggestions, as picked up over the forums here1:

strakes
- Very badly predictable in the design stage. You do not know what it does unless you flight test it. Single engine, side slipped flight at high AoA with ice on them and only one gets a hot air blast the exhaust,? A/C departs controlled flight to the side. Unpredictable risk on the development scope and amount of effort. fdr's stories on fast jet nose section design speak volumes.
- Adding weight and drag penalties, no matter how small amounts, does count (for some). The largest customers do care, rightfully or not their Excels are sharp and furious.
- Extra maintenance requirement for inspections over the lifetime of the airframe. Cost, costs, costs... customer choice, customer choice, customer choice
- Increased risk of ramp collisions. IDK but any object with mass has its own gravity and on the ramp EVERYTHING gets hit eventually. New repair schedule, new DDG items... oh.

trailing edge mod on the wing or elevators
- Completely out of scope, design frozen, signed and dusted for. The simple little issue needs a simple little solution. Constant re-tweaking kills projects like nothing else. And why touch the wing unless you absolutely have to? You don't. Sure, for the MAX+ at 2028 it will be done.

stick pusher AS WELL AS artificial feel unit mod
- certification review of the F/CTL system
- training required, commonality tanked
- extra weight
- messing with what works never goes without problems. Probably best they did not - geez these guys failed to connect the AoA light and could not see MCAS acting on the sole most powerful aerodynamic control is class A critical item like no other.

MCAS
- a software routine, simple to model and dry test
- easy to update and change later across the global fleet
- does what needs to be done
- does not involve touching any of the existing systems that have been time-tested to perfection
- no extra hardware
- no additional training as it really is just an additional spinning mode for what the STS actually is - an autonomous THS compensator.


Yet, after all, the very same teams who understandably chose the proper way out is with MCAS against the hard options, could not avail themselves to just doing anything but simply admit a less than perfect force characteristics on the control column. The EASA boss statement is inconclusive. Various otherwise dangerous aeroplanes (not the case of MAX) can be flown safely if you know how to do it.

[fdr]

Copy of Bernhard Ziegler's paper linked below; this is a very thoughtful and far reaching note, which provides the background and much more. Sorry you need to read the pages in reverse, last page first, so concentrate !
https://www.dropbox.com/s/8uzkoc47lmgeo4w/

Bernard Ziegler - much maligned at the time, but time writes history.

Also, many other contributions; including John Wilson (copilot on Comet first flight), with the Advanced Flight Deck simulator (ended up in the Smithsonian in DC).
https://www.dropbox.com/s/dte4j6oadegmot4/Advanced%20Flight%20Deck%20SKMBT_C25210092409410.pdf?dl=0

Some of the gems from Ziegler:-
"… very careful not to use guidelines which are too broad and subject to too many interpretations, like: 'The man shall be kept in the loop', which is obvious but of no practical use, which is too specific or may prove to be harmful constraints with the evolution of man and machine (at least of his evolution of his culture and habits)."

"Crews got use to automation much faster, but designers moved forward even faster. A lesson in modesty in front of the immense inventiveness of the human being, and the army experts in human science who are now descending on our community, and should well meditate on this lesson. … as Socrates said, the only thing we know is that we know nothing." - and then the last pages on "Protections …… ", human reasoning, culture, human machine interface, task, free flight;
… … are you listening Boeing, FAA.

Page 10 is worth the read of Ziegler's paper, particularly for those who were dismissive of the complexity of the task confronting the ET and Lion drivers. (I have the paper formatted in order if you want... it is a worthwhile read from the beginning.

[PEI_3721]

'… why did Boeing go through with MCAS and not just simply declaring the behaviour and asking for relief? '
This is likely to be the financial 'dazzle' of commonality with previous versions.
The MAX might have met the requirements, but it may not have been sufficiently similar to a 737' for the minimum-change training objective (valued at $1M / SW aircraft).

'Angle Grinder devices, or strakes'
An example; https://www.rafmuseum.org.uk/research/collections/sepecat-jaguar-act-demonstrator/
The the leading edge extensions and mass location deliberately destabilised the aircraft.
The experimental control system provided the basis of a quadruplex 'FBW' poof of design and certification (*) for future military aircraft - Typhoon, and for the B777 flight controls, but with a Boeing (stick-force) algorithm.

The 737 Max may not have warranted this level of design, but did require equivalent certification. The dominating bias was commerce - simple low cost, quick, time = money, and 'the same as previous 737s'.
Conversely, all to often we seek to use the latest technology; e.g. use Artificial Intelligence, but not always understanding the need for it.
Instead of AI we need 'IA', Intelligent Assistance.
With hindsight, MCAS was designed to assist, but it wasn't intelligent.

* for the technophobes - https://apps.dtic.mil/dtic/tr/fulltext/u2/p002713.pdf

fdr, yes please - see pm.
Clean wing - you overlook the 146/RJ. Not a VG in sight; a stall breaker to ensure that the inboard wing stalled before the tip. Same aero team as the early Airbus wings.

[gums]

Thanks to Bergerie for hosting this thread on the subject. I was disappointed when the Mods froze all the 737 threads, as I am a curious type and wanted to learn about the development of the MCAS. I unnerstan freezing the main forum stuff when discussion got away from the technical and factual aspects of the two crashes. But I sought refuge here on Tech Log. My AF447 education in the Tech Log was a joy, and I hope I contributed just a bit to folks' understanding of FBW.

I especially appreciate the contributions here by FDR, PEI and Detent. Then we got an occasional input from Tdracer, that offered inside looks at Big B. At the outset it seems we had a "mole" in Boeing that contributed to our technical discussions and may still be around or was found out by the company and silenced.

As with some here, my academic aero study was from the 60's, then I learned new stuff flying brand new planes until the mid-80's. Who thot of relaxed static stability back then, or vortex contributions we see with strakes and LEX and.....

So I salute all of you and will try to lurk more.

[fdr]

Counter question: If the gradient requirement was not met only formally but the true effect is not relevant handling wise, why did Boeing go through with MCAS and not just simply declaring the behaviour and asking for relief?
.

Fair point. TBC was caught off guard by the A320 NEO, and having been led down the path of common type by the large fleet users, such as SWA etc, they were reticent in their planning to put out a greenfield design, which the big fleet customers would object to. To that end, TBC was a victim of their own success. The 737 design was in itself an outgrowth of the fuse sections that existed off the shelf, and plonking the JT8 underwing was a great idea at the time, but did come with complications for future large diameter engine use. Forget about the fact that they are miserable for cargo carriage underfloor, they were a great compromise in the 60s for a domestic short to medium haul jet. A shrink of the 757 was not a great option, it had relatively poor structural weight for its size. Pity, as it is still one of the fun jets to drive. Those that reminisce on the 727 remember the performance which was brilliant, but forget about the awful ailerons, the dutch roll, and the rest of the fun stuff). Stuck with the basic design of the gear/engine pylon, putting bigger blenders on was always an issue, have a look at the -3 engine cowl shape, the -7’s are slightly better but from raising the shaft height… and the top of the cowl v the wing LE. The MAX took that a step further, and the stability issue started to come out.



Going to the feds with a waiver request would have been embarrassing, but probably not pushed back by the feds, maybe. There are some good guys in the ACO/ transport office, but that horse has bolted. The aircraft still has to be acceptable within the guidelines of 25.173 by methods per 25.175 AC25.07 (Rev D at present) has a couple of interesting graphs on that matter. EASA and the associated comments suggest that the non-linearities were not substantial, but without the flight data and force measurements how close that was to being waivable is not quantified. The manner by which vortex interaction occurs would suggest that it was not a severe non linearity. IMHO.

https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/1808x964/screen_shot_2021_02_02_at_9_21_45_pm_83f078806334a37d9773158 f5ce4424606b9a360.png

https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/1784x1172/screen_shot_2021_02_02_at_9_21_12_pm_d139afe8a490c3d3c953713 6b2196765b0af6c63.png







I think it links to your conclusion on the (lack of) other fixes apart from MCAS. They seem to have honestly chosen a solution that was readily available, required less R&D and cost as little as necessary, all that without penalizing performance As much as the internet likes to ridicule that decision, showboating and all [this thread is a great exception!!], what's being called clearly obvious in the laymen media sphere was for sure well known and thoroughly considered by the dedicated professionals yet AFTERWARDS they chose MCAS. No matter the pathetic killer gremlin MCAS 1.0 which was born later, the initial choice of picking the MCAS tool was a fair one. If it would be done again, there's absolutely no presentable evidence to deny that particular path. And as matter of fact that's what happened: The proper and agreed solution to control forces is MCAS 2.0 which is all that 1.0 wasn't and at the same time the exact thing they originally planned for.

Without getting carried away too far: Imagine the trailing edge modification had been chosen resulting in all the super critical geeky cool effects fdr explains. BUT THEN during the actual design and implementation aviation reality would be abused same as with MCAS 1.0. Such as failing to do ice contamination test and the additional load stress calculations. Resulting in flaps detaching a few years down the road - with crew performance same as on the second crash day, the death toll would have been identical.

Trying to say that selecting what is now disclosed and known as MCAS as a tool cannot be faulted. With extreme probability, it was well-reviewed against all the other options and chosen maybe even as a win-win.

.


Mmmm’kay,



Nothing ever goes wrong with software changes.



- Like the PIO of the JAS 39 Gripen,

- Like the Mars climate orbiter,

- Like Ariane V,

- Bitcoins hack,

- Soviet Gas line explosion,

- The Patriot Missile in KSA,

- Airbus OEB 117

- Nissans airbags

- HSBC, and others customer lockouts.

And,

- just for stamps the near start of WW III on 26 SEP 1983, avoided by the actions of a single, fallible human, Stanislav Yevgrafovich Petrov. We can chat about software, facebook, twitter and the rest of the inane stuff of this century because one man was smart enough to avoid Armageddon. On that day, at that time, I was sitting above a Yankee I, in the middle of nowhere.



Yup, computers, to mess up spectacularly and end the world takes software code.


​​​​​​​

[fdr]

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/2000x1149/screen_shot_2021_02_02_at_11_17_27_pm_5db2b71153364dadb7a892 21f95a3692ee75a9a4.png



https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/2000x1227/screen_shot_2021_02_02_at_11_17_14_pm_f2db6be6eb5b3c7b8f129e 49ff51befb55cf0d2c.png




I think it links to your conclusion on the (lack of) other fixes apart from MCAS. They seem to have honestly chosen a solution that was readily available, required less R&D and cost as little as necessary, all that without penalizing performance As much as the internet likes to ridicule that decision, showboating and all [this thread is a great exception!!], what's being called clearly obvious in the laymen media sphere was for sure well known and thoroughly considered by the dedicated professionals yet AFTERWARDS they chose MCAS. No matter the pathetic killer gremlin MCAS 1.0 which was born later, the initial choice of picking the MCAS tool was a fair one. If it would be done again, there's absolutely no presentable evidence to deny that particular path. And as matter of fact that's what happened: The proper and agreed solution to control forces is MCAS 2.0 which is all that 1.0 wasn't and at the same time the exact thing they originally planned for.

Without getting carried away too far: Imagine the trailing edge modification had been chosen resulting in all the super critical geeky cool effects fdr explains. BUT THEN during the actual design and implementation aviation reality would be abused same as with MCAS 1.0. Such as failing to do ice contamination test and the additional load stress calculations. Resulting in flaps detaching a few years down the road - with crew performance same as on the second crash day, the death toll would have been identical.

Trying to say that selecting what is now disclosed and known as MCAS as a tool cannot be faulted. With extreme probability, it was well-reviewed against all the other options and chosen maybe even as a win-win.

.


As first envisaged, for the high-speed case, MCAS has some redundancy, and was not a bad option. The problem came when the concerns on low-speed stability resulted in a repurposing of the system by expediently removing what was the safety. That’s what humans do. We learn better from mistakes, and the systems that are employed to catch such errors are dependent on the individuals own characteristics to give assurance that the safeties work.







Without getting carried away too far: Imagine the trailing edge modification had been chosen resulting in all the super critical geeky cool effects fdr explains. BUT THEN during the actual design and implementation aviation reality would be abused same as with MCAS 1.0. Such as failing to do ice contamination test and the additional load stress calculations. Resulting in flaps detaching a few years down the road - with crew performance same as on the second crash day, the death toll would have been identical.

Trying to say that selecting what is now disclosed and known as MCAS as a tool cannot be faulted. With extreme probability, it was well-reviewed against all the other options and chosen maybe even as a win-win.

.


The strakes on the nacelles mitigate the reduction of section CL at higher AOA, by controlling the flow over the LE of the wing, and they do that well, They sit happily on the MAX, an aircraft that has a problem exactly from the fact that there is a surfeit of CL, coming off the surface in front of the wing, so that happy characteristic is able to be amended by reducing the size and effectiveness of the VG strakes on the nacelle. The downside is that would result in flight test increase of VS1G, and that gives a runway/payload penalty. Putting a trailing edge tab on the elevator is something that you do when you want more CL per angle of deflection, the same effect comes from having a thicker TE, which is nice enough, but it is not the problem that the MAX has, authority is not the issue, non -linear response is the issue. And to linearise that, either get rid of the offending force, nacelle dCL + vs nacelle/LE CL – from reducing the strake size. Nothing magical in that. To offset the runway performance, add a tab to the TE of the flaps, either inboard (improves wing bending moment, or both inboard and outboard to balance wing bending moment. Tabs increase CL/AOA, total, by a bucket load, but do add to a suppression of the stall AOA, which is oddly exactly what the doctor is ordering here… inboard reduction in CL at high AOA gives a nose down pitching moment on the swept wing, and makes the stall much nicer, and… happens at a lower speed, as total CL of the wing is higher, and that is for flaps down, flaps up and in fact at all times of the day or night. The additional benefits of tabbing a section is, you move the Cp aft on the associated section, so that is good too, it ensures that there is a solid moment to counter at all times. On Flaps, having paid for the recurrent AD on the maggots flap tracks, they are less than stellar in their design, per Peter Rudolphs comprehensive review of Transport Aircraft high lift devices, (High-Lift Systems on Commercial Subsonic Airliners, NASA Contractor Report 4746, contract A46374D(LAS) September 1996)



“This mechanism had its drawbacks because of the complexity in manufacturing and inherent problems with track and roller wear and reliability. Roller and track wear is caused by the load magnification that results from the flap loads that create a fairly short roller couple on the flap carriage”.



If you model the track system, the manner by which the track and carriages function can be seen, and that shows a system that is not going to like vibration, and that is what comes from all of the conventional flap systems that exist as the flow is separated at the TE, and so oscillatory loads are applied. Steady loads are easy, alternating loads mess stuff up. Stopping oscillation is a good thing, and that comes within the load capability of the flap tracks without mods.



To ascertain the wing bending moment changes on the aircraft in real time takes 2 flights, been there, done that, got the photos. That provides both bending and torsion changes for comparison. Calibration takes some rat cunning but is simple to accomplish. Someone wrote a nice paper on that technique; they were from the right side of the pond. TE modification was done on the MD11, as Divergent Trailing Edge, DTE. Airbus also flight trialled the same on the A330. TBC did a quiet trial on the B742, and that was an interesting outcome, Joe Sutter was a force behind doing that test, may he rest in peace.



Ice testing. The best software for doing that is out of Canada, and is approved by TC, as well as EASA. Lewice had its day, but as soon as computation went past as Tandy Trash-80, it went out of being that ground-breaking. Last I heard, it was no longer being supported, but the FAA still was cautious about a software that had a French flavor. A former national icing SME for the FAA did some spectacular work for us with that particular software, so, apart from the amount of drink vouchers that it cost to get the CFD imagery and the forces, I remain ardently supportive of the capability that the Canucks developed. As to whether the competency of analysis exists, the following is an excerpt of the relevant DERs background: Project Manager for natural icing testing of Chinese ARJ21-700 in Canada during March and April 2014. DER in icing for 14 CFR Part 23 & 25. Constructed 3D CAD models of airplanes for CFD analysis using laser and photogrammetry. Consultant to Accident Investigation Board of Norway for takeoff icing incident of CRJ-200. Managed icing certification and noise testing project of C-26B STC. Lecturer on use of CFD in icing certification for airplanes, rotorcraft and engines. Icing consultant for transport airplane ice protection systems and rotorcraft engine inlet icing testing and other STC projects. Expert witness in FAA certification and icing issues. Author of technical articles and SAE papers. 2007 to present
The most recent resource for icing for the FAA, Tom Bond is also highly competent, and anyone doing certification in EASA or the FAA would have their concerns assuaged by the skill and competency of the people in the offices, and for my money, of the capabilities of the north of the border approved icing software. FWIW, we did validations of the software up at Bethpage, and also in-flight natural icing conditions. Amazing how hard it is to get icing when you want it.



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[fdr]

Cons of the other suggestions, as picked up over the forums here1:

strakes
- Very badly predictable in the design stage. You do not know what it does unless you flight test it. Single engine, side slipped flight at high AoA with ice on them and only one gets a hot air blast the exhaust,? A/C departs controlled flight to the side. Unpredictable risk on the development scope and amount of effort. fdr's stories on fast jet nose section design speak volumes.
- Adding weight and drag penalties, no matter how small amounts, does count (for some). The largest customers do care, rightfully or not their Excels are sharp and furious.
- Extra maintenance requirement for inspections over the lifetime of the airframe. Cost, costs, costs... customer choice, customer choice, customer choice
- Increased risk of ramp collisions. IDK but any object with mass has its own gravity and on the ramp EVERYTHING gets hit eventually. New repair schedule, new DDG items... oh.

.

Strake flow effects are very predictable, with respect to core, rotational moment and stability. Additionally, interaction of a vortex flow with flow around an arbitrary body is quite accurately projected. It’s not that hard, I do it freehand, and get the same output as the Cray would over a couple of months of DES runs… can’t agree with your assertion, but I’ve only been doing flow visualisation since 1970, as a kid.



The drag of a single TBC VG is by recollection 0.0002 units, so, yes, they do add drag. They also can reduce drag by about 100 times their own drag count where there is a flow control benefit, so, not sure I concur.



Funny thing about aero mods, apparently it is assumed that they need to be of iron or steel or at least aluminium. That is in spite of the certain knowledge that an air jet with modify a flow field, and oddly for the last 30 odd years, I worked with elastomeric materials and other soft structures as I was both cheap, and having a desire to play with blades, didn’t have a death wish. In 2007 I flew elastomeric materials as a tab on a helicopter rotor, having done the same on propellers for 13 years previously. The argument on ramp rash doesn’t end up having validity when the devices are able to be squishy stuff. Just my opinion though. The materials required are high tech, you have to be able to find an Ace Hardware at least, or an Auto One, so, yes, there are technical hurdles.





trailing edge mod on the wing or elevators
- Completely out of scope, design frozen, signed and dusted for. The simple little issue needs a simple little solution. Constant re-tweaking kills projects like nothing else. And why touch the wing unless you absolutely have to? You don't. Sure, for the MAX+ at 2028 it will be done.

.

? have you heard of Part 21?






stick pusher AS WELL AS artificial feel unit mod
- certification review of the F/CTL system
- training required, commonality tanked
- extra weight
- messing with what works never goes without problems. Probably best they did not - geez these guys failed to connect the AoA light and could not see MCAS acting on the sole most powerful aerodynamic control is class A critical item like no other.

.


The stick pusher is actually not a cure for the issue, it avoids one of the undesirable states, but does not affect the stick force gradient that is the underlying irritant. If one was employed, refer to the bean counters lament re runway/payload loss. The B747 never required a stick pusher, putting an extraneous safety device on an aircraft due to ignorance is not the hallmark of excellence. 747s stall very nicely.






MCAS
- a software routine, simple to model and dry test
- easy to update and change later across the global fleet
- does what needs to be done
- does not involve touching any of the existing systems that have been time-tested to perfection
- no extra hardware
- no additional training as it really is just an additional spinning mode for what the STS actually is - an autonomous THS compensator.




Yet, after all, the very same teams who understandably chose the proper way out is with MCAS against the hard options, could not avail themselves to just doing anything but simply admit a less than perfect force characteristics on the control column. The EASA boss statement is inconclusive. Various otherwise dangerous aeroplanes (not the case of MAX) can be flown safely if you know how to do it.




I think Peter Ladkin and the gang at the RVS Group (AG RVS - Arbeitsgruppe Rechnernetze und Verteilte Systeme) at U Bielefeld may disagree. Would be an interesting conversation though.

A thought in passing: We live in a world that we establish heuristics that are functionally linear as that is what we can comprehend as analogs of complexity. The world however is stochastic, and we are set up by our very nature to have bad days as a consequence. Our own behavior is anywhere from logical to emotional, and the complete spectrum in between. We do not think linearly at all, yet we attempt to model the world in that way. The variability and non-linear manner that the human conducts cognitive functions gives the ability to achieve creativity, which helps when we get situations that give divide by zero outcomes. More often than not, it is the human's ability to cognitively function in conditions of uncertainty, using our innate fuzzy logic, that permits a solution, a save, or creativity to occur. It was the human variability in September 83 that saved the planet from a , man-made destruction, Stanislav Yevgrafovich Petrov (Станисла́в Евгра́фович Петро́в) saved the whole damn planet, and he passed away in near anonymity in 2017, "I was made a scapegoat". He stands alongside Captain Vasily Arkhipov (Василий Александрович Архипов) who refused to fire a nuke torpedo during the Cuban missile crisis. Arkhipov had been on the Hotel I K-19 previously during the reactor casualty event, under the command of Captain Nikolai Zateyev (Николай Владимирович Затеев). A couple of years later, on a Foxtrot DE SS, B-59.

Arkhipov and Zateyev both died of cancer, 10 days apart; the Hiroshima class was an apt name for the Hotel, Echo, and November boats of the USSR.

Perfect systems... like Chernobyl, 3 Mile Island, Fukushima...

[safetypee]

With due acknowledgement and apologies to the editor and chairman of UK Flight Safety Committee (UKFSC) Focus magazine.

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[Bergerie1]

fdr,

Thank you (and all you other knowledgeable posters here too). As you say fdr, the 747 stalls very nicely, I did many on the -100s and -200s during CofA check flights. When the 747 was put on the British register, D. P Davies required a stick nudger (not a pusher) to restore longitudinal stability shortly before the clean stall at aft CG. I quote his words from his book, Handlng the Big Jets:-

"With trim speed of 1.3Vs, after a small elevator force to start the speed reduction, the stick force falls to zero while the aeroplane quietly progresses all the way to the stall on its own .... It is common knowledge that the UK attitude to stalling is quite firm and this degree of instability, although slight, was declared unacceptable. The fix was the nudger. This is a gentle stick force augmentor of about 16lbs in the nose down sense which operates when the stick shaker starts to operate and remains effective until the stick shake cancels. In a fairly rough and rudimentary manner it restores pre-stall longitudinal stability and satisfies the requirement at little cost and with no snags. It is similar to the nudger fitted to 707-320B/C aircraft certificated in the UK which, while not taking out all the pre-stall pitch up at full flap aft CG, at least restores a positive stick force gradient down to a point very close to the stall."

Here was a simple cheap and reliable fix which had already been used on Boeing aircraft. It would have required no training with only a mention in the manuals. Would this not have been a better solution?

[FlightDetent]

Guess all left here is saying thanks for setting me straight? I do, appreciated. Happy and excited to read your contributions, fdr.

[PEI_3721]

Bergerie, '… a better solution'
We might assume that a STS type of fix was considered / tested.
STS as I understand is only a single trim input, also like the 747 example it uses speed as the sensor; loss of sensor was not critical.
MCAS 'downfall' involved the dynamics of the situations; the need of AoA as a sensor and more than one trim input. Introducing these was critical to the MAX deficiency (type similarity / certification), which enabled the opportunity, with corporate pressures, to poorly engineer MCAS where loss of sensor was critical.

[fdr]

fdr,

Thank you (and all you other knowledgeable posters here too). As you say fdr, the 747 stalls very nicely, I did many on the -100s and -200s during CofA check flights. When the 747 was put on the British register, D. P Davies required a stick nudger (not a pusher) to restore longitudinal stability shortly before the clean stall at aft CG. I quote his words from his book, Handlng the Big Jets:-

"With trim speed of 1.3Vs, after a small elevator force to start the speed reduction, the stick force falls to zero while the aeroplane quietly progresses all the way to the stall on its own .... It is common knowledge that the UK attitude to stalling is quite firm and this degree of instability, although slight, was declared unacceptable..... ."

Here was a simple cheap and reliable fix which had already been used on Boeing aircraft. It would have required no training with only a mention in the manuals. Would this not have been a better solution?

K, for those wanting to stall any of these aircraft, a note first up, there is a maintenance procedure for inspections after stall buffet encounter on most if not all of these aircraft. The amount of buffet that occurs varies from type to type and with configuration. Clean is usually quite light buffet and associated loads on the tail, but heavy buffet entry in the MD11 in the cruise, at high Mach pretty mush shredded the elevators on both sides, and came close to two ripples on the pond. A fully configured stall buffet can be quite impressive, as are the loads to the tail and flap tracks.

25.173 requires 1lb/6kts average gradient over the desired window being assessed, which is within the flight envelope from stall to upper limits. There are two main methods of determining compliance, but basically, taking the load on the control, coming off the trimmed speed, (1.23 or 1.3 depending on the rules applied earlier in the Part, the year etc... ) and slowing down as well as speeding up around that datum. For a stall speed around 100kts, the minimum trim point is Vref... so the loads being measured total are around 4lbs to 6 lbs of elevator force, which is quite light. The requirement is for the average to be that, and the guidance material in AC25.07 shows clearly that a reduction in force can occur towards an extreme of the test points, and still be acceptable. That is open to interpretation in so far as a zero gradient for the last 10kts could be fully compliant, but considered objectionable from an HQ view by the testing driver. My recollection is that the stick gradient in the mid-trim condition was way higher than that, and never encountered reversal, which is where a rationale for a SAS system would arise. D.P. Davies did good work, and perhaps at aft CG limit -0.5% at light weight, high thrust, he encountered an undesirable that Boeing didn't. It is possible. Is it likely? TBC did a comprehensive testing program on the 747 under the gaze of Joe Sutter and coming in the wake of the Trident, and some 727 funnies, they were not without awareness of what was needed. A spring balance to the controls could detect that level of force in the day, today, some of the FBW systems record the forces applied, or force sensing gloves can be applied and calibrated to give the info. (make your own, go grab some Phidgets... ).

[tdracer]

Gums, I joined this forum about 3 years before I retired (basically right after the Asiana 777 crash-landing at SFO). Several co-workers knew of my presence, but I was very, very careful about what I posted to avoid anything that might be considered sensitive, proprietary, or anything that would otherwise get me crossed up with management. More than once, someone posted something that I knew was total BS, but couldn't respond because my knowledge was considered to be Boeing proprietary (one example that comes to mind was a discussion regarding 747-8 fuel burn - of which I had first hand knowledge but couldn't talk about).
Since retirement, I don't need to worry as much but still need to be careful about posting info that could still be considered sensitive. Much of what I know about MCAS is based on an off-the-record discussion I had with a Boeing test pilot friend shortly after the Ethiopian crash. I felt obligated not to post any of that information as not to betray his trust. Most of it has since been reported in the Seattle Times, so I'm confident discussing it - but a few things I still need to keep under wraps...

[osborne]

"Most of it has since been reported in the Seattle Times"

I knew people who worked for Airbus who greatly enjoyed Byron Acohido's pieces in the Seattle Times.
I often wonder whether Boeing would have preferred to have him silenced (in a friendly, painlesss, way).

[Jhieminga]

Lecture on the 737 MCAS story by Chris Brady kicks off in just over 10 mins: https://www.solent-raes.org.uk/lectures
Free to join (I'm just another listener, nothing to do with it so I hope it's allright to post this).

[Less Hair]

Thanks the harp plays already.

[Jhieminga]

PPRuNe got mentioned! :ok:

[Less Hair]

It was worth it. Thanks for telling us right on time.
Thanks to RAeS for sharing this event. Most appreciated.

[DaveReidUK]

Lecture on the 737 MCAS story by Chris Brady kicks off in just over 10 mins: https://www.solent-raes.org.uk/lectures
Free to join (I'm just another listener, nothing to do with it so I hope it's allright to post this).

Recording still available on the above link. Lecture starts at around the 15:55 mark.

[CaptainSandL]

Re Recording still available on the above link That link will disappear soon (if not already) but it will remain available at this link: https://youtu.be/JApoVC6iIIE

[vilas]

https://leehamnews.com/2021/02/02/the-737-max-a-tragedy-60-years-in-the-making/

[Uplinker]

Great presentation by Chris Brady. Many thanks to him for an informative, comprehensive and unbiased lecture.

Most particularly, how MCAS can look like normal THS operation and therefore not necessarily lead the pilots to Runaway Stab Trim.

[CaptainSandL]

Follow-up presentation just posted by Chris taking a more detailed technical look at MCAS.
https://youtu.be/bljlduBx1TE

[B-767 fan]

it was legally required AFAIK, Airbus ran into similar problems when desigining the A321 through of course its esier when you have FBW

[fdr]

As suggested previously, when encountering the longitudinal stability issue, Boeing could have completed aerodynamic mods to the design to remove the anomaly, which resulted from the nacelle adding lift to the wing/nacelle structure that was more than anticipated. That alone would have suggested that an angle grinder should be taken to the strakes to trim their nose hair a shade. Instead, they came up with a neat trick to change a high speed design that had questionable redundancy on trigger events to being low speed too by removing one of the two trigger conditions which gave a single point of failure as a matter of certainty. As AOA probes have a fairly modest MTBF in use, that wasn't a great concept.

Here is a set of charts that show the effect of having strakes or not, which would have been a relatively minor change to the aircraft. As the engines are inboard, it is a matter of certainty that reducing the section CLmax proximate to the nacelle would have ended up in an improvement in the stick force/g. Being judicious, the effect to Vs1g would have been quite modest, and surely, please surely the OEM noted that the stall speed was curiously lower with their design than expected, otherwise, they need a serious boot in the bottom of their trousers for being myopic.


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