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Comment by zaroth | Hacker News Reader

I made the prediction a month ago and I’ll make it again. MCAS won’t ever fly again.

I think the plane will fly without MCAS with a new type rating, and where pilots specifically train on the stick feel during a power on stall.

They needed the 737 with new engines to fly like the old 737 in order to maintain the type rating and avoid training. Now that they obviously have lost that and require substantial training, I don’t see any reason to keep the system.

Some people think the plane is unflyable / inherently unstable without MCAS. I’ve only flown about 15 hours in my life, and a Cessna at that so I’m not qualified to offer an expert opinion.

But my intuition is that if that were true, if MCAS was not just a bandaid to maintain a type rating, but rather a safety critical system essential for flightworthiness, it would never have shipped in its current form in the first place. Or rather, the 737 MAX would not have been viable to begin with.

If it is the case that 737 MAX is not actually airworthy without a functioning MCAS then Boeing has fucked up an order of magnitude worse than even they appear to have at this point.

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MCAS is not there because of maintaining pilot type rating.

The plane's airworthiness certificate depends on certain behavior while approaching stall and the new larger and more forward engines on the MAX changed the behavior of the machine in such way that would make it very difficult for the crew to bring the nose down at high angles of attack and high thrust.

The engines on the MAX are forward of the CoG, so they are pushing the nose up as you add thrust - exactly what you do not want when approach a stall. MCAS has been added to help with this - to help the crew push the nose down in such situation by using the stabilizer trim.

The older NG doesn't have this issue because the engines are both smaller and more to the back, so the pitch-up moment is smaller, even though it is still present. This is an inherent issue with underslung engines, all planes with engines mounted under and ahead of the CoG have this issue.

>If it is the case that 737 MAX is not actually airworthy without a functioning MCAS then Boeing has fucked up an order of magnitude worse than even they appear to have at this point.

That's BS. By that logic no Airbus or any fly-by-wire plane could ever be certified - they actually require the computer augmentations to fly. Even the 737 NG has a similar trim system that automatically trims the plane depending on speed, angle of attack and what not.

> The engines on the MAX are forward of the CoG

It doesn't make much difference, most of what you've said is accurate to the best of my knowledge, however the thrust can be as far forwards of the CoG as it likes, that doesn't increase the pitch up moment. Having them lower may increase that moment and them having more power too. But the main issue on the Max is airodynamic lift generated by the nacelles at high AoA.

> the main issue on the Max is airodynamic lift generated by the nacelles at high AoA.

This simplifies the physics so much that it's wrong. It is true that there are texts attributing everything just to the "nacelles", but the engineering doesn't work the way you argue:

First, you can't put the engines on the plane without some casing for them (you have to have nacelles).

Second, if you'd try to modify the casing of the engines (the said nacelles) to have other aerodynamic properties, you'd interfere with other design goals (e.g. you can increase the fuel consumption which was the most important design goal for the MAX).

Third, the position of the engines definitely does matter for the behavior like "nose up" as long as the rest of the plane has some already determined form, which in this case is what has to be kept to have the plane being 737 and not something completely different.

In short: the 737 MAX is Boeing's equivalent of VW's diesel cars. Its behavior was determined by the prescribed design goals (by those who sold the plane): Boeing simply directly lied, selling something that can't be achieved given the "sold" design characteristics.

Just like the diesel cars can reduce nitrogen oxides production, but then they are less "efficient" than as they were sold (they need more refills, or use more fuel, i.e. cost more than advertised). Likewise, the 737 MAX-like plane could have been safer, but then Boeing could have not sold it as a plane for which there's "no need for pilot's re-certification and retraining."

At the end, Feynman conclusion of his Shuttle investigation report holds:

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled."

Note also: https://www.theguardian.com/business/2019/apr/15/former-head...

("Former head of Volkswagen could face 10 years in prison -- Martin Winterkorn and other executives charged with fraud over emissions test cheating")

I'm quite sure Boeing's "heads" won't even be charged. And no, the "nacelles" aren't the main issue. It's the fraudulent selling of the planes which can't deliver what they were sold for. Fraud.

(P.S. It's "aerodynamic")

I wonder if thrust vectoring could be of use here? I know it's primarily a military technology now, but maybe the MAX can be saved by having engines that slightly divert their thrust in very specific situations to offset this undesirable effect?

For this to be stable it would seem very elegant if you could design this in such a way that it occurred in equilibrium with any undesirable lift generated by the nascelles.

As supposed to an active measure controlled by electronics based on a separate AoA sensor, if somehow the lift caused the engine the thrust vector in opposition to the lift as a matter of physics.

I mean, in theory there’s nothing to say inherently such a design would be more reliable than triple redundant sensors and a bunch of code, but that would be pretty neat.

>But the main issue on the Max is airodynamic lift generated by the nacelles at high AoA.

I agree.

I did not find the original article I read about it but e.g. this article ( https://moneymaven.io/mishtalk/economics/boeing-737-max-unsa... ) contains a statement similar to what I read - a bit more aggressive and I did not actually read the article and I do not know the website (so yeah, it might be a bad and unconfirmed source). Anyway, just focusing only on the nacelles and AoA here is the statement:

>>because the engine nacelles were so far in front of the wing and so large, a power increase will cause them to actually produce lift, particularly at high angles of attack. So the nacelles make a bad problem worse.

>>I’ll say it again: In the 737 Max, the engine nacelles themselves can, at high angles of attack, work as a wing and produce lift. And the lift they produce is well ahead of the wing’s center of lift, meaning the nacelles will cause the 737 Max at a high angle of attack to go to a higher angle of attack.

Summarized, I understand this as a looping chain reaction: the higher the AoA the higher the lift produced by the nacelles, which in turn (without auto-trim by MCAS or active pilot correction) will increase the AoA which in turn will increase the lift, etc... .

I admit of not being able to understand this:

>>>because the engine nacelles were so far in front of the wing and so large, a power increase will cause them to actually produce lift,

I thought that it would make the plane "tilt" upwards, but the quote mentions "lift".

Does this happen because the engines, being in front of the wing and as well very near to it are "sucking" air that would otherwise flow as well >>over<< the wing, therefore creating a lower-than-usual pressure above the wing, therefore making the airplane climb/generate lift?

It has nothing to do with power. Even cylindrical bodies produce some lift when their axis is not aligned with the airflow, and all engine nacelles do this. If they are forward of the CofG, this produces a pitch-up moment that increases with increasing angle of attack, and therefore reduces stability. The further forward they are, the more the leverage and the stronger the effect. With rear mounted engines, the effect produces a nose-down moment, which contributes to the longitudinal stability. See the links in my other post: https://news.ycombinator.com/item?id=19904685

A good way to visualize it, I've found, is imagine the low pressure area created by the wing as a bubble attached to the aircraft, "sucking" the aircraft up. Imagine the air going under the wing as analogous to the surface of a lake.

The more the plane diverges from parallel to the airstream, the stronger the tendency for the bubble to suck through the "shadow" created in the airstream, and the plane to "skip" on the surface (the air getting pushed under the airfoil).

In reality, these are two different ways of illustrating the same force. This visualization though, let's you pick out two different aspects.

Air is a fluid. Just like water will follow the edge of a pan when you pour it, the curvature of an airfoil does the same thing with air flowing by.

Those nacelles basically enhance the surface area across which that pressure differential acts through. In short, generating extra lift, "pulling" the plane up more, (or pushing, if you prefer looking at it from the skipping stone aspect) creating more lift, all the way into a stall condition.

Thx!

The engines on the MAX are forward of the CoG, so they are pushing the nose up as you add thrust - exactly what you do not want when approach a stall. MCAS has been added to help with this - to help the crew push the nose down in such situation by using the stabilizer trim.

The forward-backward position of the engines have nothing to do with their resultand pitch torque. What matters is that they are below the CG.

The engines being forward matters because it shifts the center of pressure forward, giving an inherent pitch-up tendency that becomes more pronounced at high angles of attack.

And like you say, all planes with underslung engines have this issue to some degree. Maybe the issue with the MAX is severe enough to cause certification problems but the stall recovery procedures for the NG apparently already call for reducing pitch angle before going to full power or you may not be able to get it down.

The fore/aft position has a lot to do with the AofA-dependent effect, as it results from the approximately cylindrical engine nacelles producing some lift when their axis is at a positive angle of attack (fuselages have a similar effect [1].) On airplanes with rear-mounted engines, this effect on their nacelles increases the longitudinal stability [2].

The high/low position matters for the power-dependent effect, and furthermore, what matters in steady-state is the pitch moment created by misalignment of thrust and drag (when accelerating, the moment around the CofG also matters.) A modest tendency to pitch down when the power is reduced is preferable to the opposite.

The issue MCAS was supposed to solve was due to the AofA-dependent effect. That's why it has AofA as an input, and not any measurement or proxy for thrust.

[1] https://leehamnews.com/2018/11/30/bjorns-corner-pitch-stabil...

[2] https://leehamnews.com/2018/12/07/bjorns-corner-pitch-stabil...

Isn't that exactly what I said? Edit: not quite, good point about center of drag in steady state conditions.

"The forward-backward position of the engines have nothing to do with their resultand pitch torque. What matters is that they are below the CG.

"The engines being forward matters because..."

Janoc repeated a mistake that has been made several times, attributing the problematic pitch-up to the thrust of low-slung engines, and also made some mistakes about how that effect works. I am sure you did not intend it, but by combining corrections to both the former and the latter, and not differentiating between the two, you ended up with something quite confusing, so I felt some clarification would help. The key points are that the engines do produce lift at high AofA, and it is this, not thrust, that creates the problem MCAS was intended to fix.

The key points are that the engines do produce lift at high AofA, and it is this, not thrust, that creates the problem MCAS was intended to fix.

Is that really true? I agree that the pitch-up torque from engine thrust does not vary based on AoA, but the elevator deflection needed to counteract said torque definitely depends on airspeed and hence on AoA. Even if there was no aerodynamic effect of the engines at all, the pilot would be required to trim nose-down as airspeed goes down relative to an airplane with centerline thrust.

If the thrust gets high enough, at some point this pitch torque would overwhelm the natural tendency of the airplane to pitch down as airspeed goes down and result in negative longitudinal stability.

My impression is that MCAS was intended to counteract the decreasing stick force with decreasing airspeed. Both effects, offcenter thrust and aerodynamics, combine to produce the same effect.

First you said I was repeating what you said, now you are saying the opposite?

Various good sources [1],[2] state that the issue is lift, not thrust. The article I linked to from my earlier post shows that this lift is not unique to 737 Maxes, and that it contributes to the stability of the DC-9, on account of being behind the CofG on that airplane.

The LEAP-1B engines of the Max variants are not significantly more powerful than those on NGs (they are more efficient and somewhat quieter.) As the whole problem arises from the fact that they cannot be mounted lower, it seems unlikely that an increased thrust moment is what is making the Max handling unacceptable.

> If the thrust gets high enough, at some point this pitch torque would overwhelm the natural tendency of the airplane to pitch down as airspeed goes down and result in negative longitudinal stability.

There seems to be some confusion here over what longitudinal static stability is: it a matter of the rate of change of pitching moment with respect to AofA (take a look at the links in my first post for data from real airliners, where a negative slope indicates stability.) Thrust is not a function of AofA, and consequently is not factor in the relationship that gives longitudinal stability of ordinary airplanes - and, as I said before, neither thrust nor any proxy for it is an input to MCAS (while AofA is.)

[1] http://www.b737.org.uk/mcas.htm

[2] https://leehamnews.com/2018/11/14/boeings-automatic-trim-for...

Sorry for making unclear references. My question was referring to "it is [lift], not thrust, that creates the problem MCAS was intended to fix", which I never addressed before.

The article you linked has some nice cross-sectional illustrations that makes clear that the thrust line of the MAX engine actually is higher than on the NG. I hadn't realized this but it makes sense given their larger diameter and needed ground clearance. That would indicate that the thrust dependent pitch up is likely smaller on the MAX than the NG so, if the MAX behaves worse, it stands to reason that the aerodynamic effect must dominate.

I guess the issue is that lift overall is just so much larger that a small shift in the center of lift has a large effect on pitch moment?

As for your comment about longitudinal stability, I agree that the pitch moment due to thrust is independent of AoA and hence can't change the shape of the pitch moment curve. I gotta think about this some more.

Yes, I should have been clearer about that as well. There are indeed two issues there - the lift of the nacelles and the thrust pitch-up effect.

Thanks. Your post is the first time I've read a physically plausible explanation of this.

The Boeing whistleblower in the recent 60 Minutes Australia exposé said that's exactly why it was designed. Not only was a new type rating unacceptable, engineers were not permitted to make any design changes which would require simulator training.

Fly by wire systems are classified as safety critical and require much more redundancy. The Boeing 777 has three flight control computers, four sets of low-level controllers, and a fault-tolerant air data sensor system.

Bad air data (airspeed, altitude, angle of attack) has been a big problem in the past. Each of those involves a sensor that sticks out through the skin, and can potentially be damaged or plugged. Remember Air France 447, where the airspeed sensors iced up. Those things need redundancy.

The Boeing 777 has three flight control computers

And still only two alpha vanes.

>The engines on the MAX are forward of the CoG, so they are pushing the nose up as you add thrust - exactly what you do not want when approach a stall. MCAS has been added to help with this - to help the crew push the nose down in such situation by using the stabilizer trim.

And the pilots canot push the nose down in such a situation by actuating the stabilizers?

I've never flown an airplane, but as far as I know, MCAS doesn't have unique access to controls that the pilot does not. (eg, it's different from ABS in a car where the driver does NOT have 4 individual brake levers).

It seems to me if the pilots are trained and certified on the Max, they'll do a better job flying it than a poorly designed system.

OTOH, the system is also fixable, but it is becoming a matter of trust.

> That's BS. By that logic no Airbus or any fly-by-wire plane could ever be certified - they actually require the computer augmentations to fly.

I would imagine that, to be certified, the Airbus planes had to demonstrate that:

a) The computer augmentation was unlikely to fail,

b) when failed, the plane was still flyable enough, and

c) the pilots were trained to fly the plane when the augmentation failed. (I believe this is called “direct law”, and I would be utterly shocked if pilots are not trained to fly the plane in direct law mode.)

They are so trained, and the airplane is still considered airworthy in that mode, including in particular as it related to this conversation, the FAR 25 positive static stability and stall behavior requirements.

Is the 737 MAX’s proposed behavior with one AoA sensor broken also compliant?

This is completely wrong. An Airbus is not made conformant with FAR 25 airworthiness standard by software protections. It conforms to all of FAR 25 requirements without any of the safeguards in place, whereby stick inputs are directly translated to control surfaces. The airworthiness standards are predicated on aerodynamics, not software abstraction of an otherwise unairworthy design.

The idea there are switches in the airplane I can use to make the airplane unairworthy is absurd. And it is equally absurd that the aircraft flight manual and an emergency airworthiness directive would so direct a pilot to make the plane less airworthy than it already is, let alone unairworthy, as a corrective action. It's just absurd. You're welcome to provide a citation, however.

I submit FAR 25. I've read the entire thing and there's nothing in there that permits software to paper over an otherwise unairthworthy aircraft design.

>I think the plane will fly without MCAS with a new type rating, and where pilots specifically train on the stick feel during a power on stall.

Maybe. Keep in mind MCAS was a system put in place to mitigate a catastrophic risk. If you remove it, you no longer have that mitigation - meaning you either have to argue that increased training can be a substitute (I would be skeptical of that if I was a regulator) or come up with something else. It's a shitshow.

I think it all comes down to certifying bodies other than the FAA. FAA seems happy to go along with whatever Boeing wants (as evidenced by the 'self certification' efforts of the agency); it remains to be seen if the EU or another major market airspace will capitulate.

>FAA seems happy to go along with whatever Boeing wants (as evidenced by the 'self certification' efforts of the agency)

I strongly suspect this is way overstated.

I think there's a misinformed view of what a regulator is and the role they play. Regulations and regulators don't work within a system where there's a preponderance of cheating. This is why you can't go do a corrupt country and simply legislate corruption away (all corrupt countries have very good laws on the books). Regulators necessarily exist within a largely honest system. The FAA, and FDA and other regulatory agencies do not go around testing every claim made by every manufacturer - though they reserve the right to. If that was the case the economy would grind to a halt and no product would be released. This would be akin to the IRS auditing every tax return every year.

The second point about regulations is that like security or marketing, there is no end-game. You can always have more regulations, just as you can invest in more security and more marketing - but at some point, you will have diminishing resulting leading to negative outcomes. In the specific case, Boeing put themselves under a certification process meant for certifying non-trivial but also non-major incremental upgrades (i.e. no fuselage and wing redesigns). The process is less onerous because the aircraft upgrades don't introduce new significant risks. This process does not apply to the 737Max8. Boeing was wrong to put the plane in that category and they will pay dearly for this and will serve as a cautionary tale moving forward, but let's not throw out the regulatory regime that resulted in making the airline industry incredibly safe, and the safest it has ever been in history.

> This process does not apply to the 737Max8. Boeing was wrong to put the plane in that category...

If you, the layperson, can make this statement, then why wouldn't the regulators make this obvious determination? Regulators should have said "No, Boeing, you're not eligble for this process because of XYZ"

So, if they can't make such a high-level determination, what exactly are they doing? Not much, it seems.

>If you, the layperson, can make this statement, then why wouldn't the regulators make this obvious determination?

No doubt FAA will re-evaluate their process moving forward, but it depends on what Boeing wrote in their submission.

If they didn't put in pertinent details for the FAA to make this determination, then it would only get caught if the FAA did a deeper audit (which they reserve the right to but it may not be something that happens with every submission of this type).

On the other hand, it may have been the case that Boeing did put in the pertinent details and FAA was negligent.

So neither FAA nor Boeing are in the clear. Boeing is in trouble no matter what - they fucked up real good and they are ultimately responsible for the safety of their airplanes - but it remains to be seen how negligent the FAA is.

I don't have experience with aviation and the FAA, but I do work on a regulated product and deal with the FDA quite a bit.

I strongly suspect this is way overstated.

I don't.

https://www.seattletimes.com/business/boeing-aerospace/engin...

It is a critical system. Part of the problem is that AOA sensors and MCAS were never considered critical before the software changes made for the 737 MAX and uprating them to critical was overlooked (which would have forced a lot more testing of them).

There is no established requirement that says software can't be used to correct for pitch up on acceleration. The software just has to work properly.

> uprating them to critical was overlooked (which would have forced a lot more testing of them).

Was this "overlooking" accidental or designed specifically to ignore the forced testing? This is the question that might be hardest to answer, but would justify criminal charges for the deaths in my mind.

True. Would be impossible to prove without a whistle blower. Boeing hasn't been charged with a crime so there won't be any subpoenas of e-mail records, etc. It is within the realm of possibility, but I certainly hope that was not the case. I lean very slightly toward thinking it was an accident as the whole program was rushed and give the engineers the benefit of the doubt (innocent until proven guilty) - however, it would not take much evidence to sway my mind.

I’m not sure a type rating works that way. A Boeing 717 has the same type rating as a Douglas DC-9. The two aircraft have similar airframes and some common systems but are quite different as one was built decades later. What the FAA does in these cases is requires more training. A DC-9 rated pilot who has only flown DC-9s will not fly a B717 without several hours in a simulator. The MAX will certainly fly again. I suspect some form of a redesigned MCAS in addition to more training for pilots will be the end result. The airlines may have to spend some money training but they’ll still be left with B737 type rates pilots who can fly B737NG and B737MAX which is where the cost savings is derived.

Is there any indication that MCAS is a problem when it is provided with accurate AOA data? I don't think so, but I'm willing to be educated.

My understanding is that MCAS only goes haywire when it gets haywire sensor data--specifically, data that indicate an AOA that is much higher than reality.

So much depends on the investigations, which are currently in progress. But it seems possible that the technical solution could simply be: require 3 AOA sensors and require agreement between 2 out of 3 to activate MCAS. Of course, there are probably significant business and regulatory issues to consider/fix as well.

It might be. I suppose the flight testing program tested MCAS on the situations where it would trigger and it has performed accordingly.

Unfortunately the way things are, my supposition is anything but certain

I'm not sure how easy it is to just bolt a third AoA sensor onto an existing airframe. OTOH, the MCAS system could at least be redesigned to take BOTH AoA sensors into account.

Yes, but there's also the problem of just how haywire it goes --- forcing the horizontal stabilizer in an unflyable position from which it can't be moved (the subject of this article).

> I think the plane will fly without MCAS with a new type rating

Without the 737 type rating, the value prop of the 737 MAX is lost. There would be no point in continuing the program (at least at anywhere near its current scale).

There's billions in capital sunk in the already existing 737 MAXs. They will fly again.

Type ratings don't really work like that. 90% of the type rating is systems knowledge, emergency procedures etc. If a new type rating was needed there would be a conversion course from the existing type rating.

That's a red herring, the MCAS issue has nothing to do with the type rating. MCAS is not something the crew was even supposed to be aware of, even less trained on, so no effect on type rating at all there.

What it may cause problem with is the certification of the plane as such - MCAS was required to correct the behavior of the plane in high speeds/high thrust and high angle of attack situation where the new larger engines made it difficult to bring the nose down (and avoid stalling).

However, that's not something that cannot be fixed. Airbuses fly full of similar augmentation systems and there is no problem with them, so it is certainly doable.

Yes but the 737 is not fly by wire, you don't have the same ways of "inserting yourself" into the loop as in a fbw plane

How do you "insert yourself in the loop" on a FBW plane when the computers conk out? There is manual reversion on an Airbus but it is very minimal - if you ever end up in a situation where that is needed you are having a very very bad day.

On the other hand, 737 is actually fly-by-wire - literally, because actual steel wires are still connected between the cockpit controls and the control surfaces. So if the electronics dies and the hydraulics isn't working neither for whatever reason, the plane can still be controlled.

These "magic boxes" are there to augment the control characteristics, such as the "feel" of the control column (which is normally lost due to the hydraulics driving the control surfaces). Or, in the case of MCAS, to help with an aerodynamic issue. Both are hardly unprecedented - the last large transport plane that didn't rely on any computers/electronics for controls was maybe the 707.

The problem is the poor design of the MCAS software/system, not that it exists as such.

> MCAS is not something the crew was even supposed to be aware of, even less trained on, so no effect on type rating at all there.

Exactly this is the argument for a type rating problem. If pilots would have to undergo heavy training for the MAX there would probably have been a new type rating. There are some experts out there who argue that this is why Boeing tried to hide the existence of MCAS. Pilots should have been informed about MCAS and the reason it is there before all this started.

Yes but the point is that it was thought this isn't something that was to be required - and had the system been correctly implemented (and handled by the crews), there wouldn't have been a problem.

I don't think Boeing was intentionally "hiding" the existence of such a system, they just didn't consider it critical enough to bother the crews with it because it was supposed to come into play only in a very unusual flight regime - manual flight, flaps up and high angle of attack. There was no special "MCAS training" needed because any failures fall into the "runaway stabilizer" emergency procedure.

It just didn't work out exactly that way, unfortunately.

If I recall correctly, the system has been mentioned in the documentation - not prominently and not something the crews would have been forcibly made aware of, but given that the plane certification depended on it and it had to be certified, they couldn't exactly "hide" it from the regulators.

Keep in mind that the procedure for the stabilizer problem is the same since 737 has been first introduced in the late 60s. Had it been correctly followed, likely neither of the crashes would have happened, MCAS or no MCAS.

The Lion Air crew didn't identify the problem as a possible runaway in the first place for whatever reason and the Ethiopian crew made several (understandable, but still) mistakes, such as cutting the trim system out while heavily out of trim, not reducing the excessive speed and then finally re-activating the electric trim (which is against the procedure) when they couldn't re-trim the plane manually due to the resulting excessive forces. Which has directly caused the crash once the MCAS has re-activated.

That's a red herring, the MCAS issue has nothing to do with the type rating.

In the 60 Minutes Australia piece a Boeing employee explains that MCAS was set up to only use one alpha vane specifically to avoid being classed as a difference that required simulator time for pilots transitioning. Whether or not that's true (or how that even works), I couldn't tell you.

Unflyable or unstable isn't nearly the same thing as uncertifiable. People have flown a whole lot of time in uncertifiable aircraft (see the whole experimental aircraft sector) but transport category aircraft are supposed to exhibit as full proof as possible behaviour.

I bet you it flies again with MCAS. I'll also bet it flies with barely a few hours of conversion training and that there aren't any accidents directly related to the updated MCAS system.

This isn't true though, it seems perfectly possible to certificate transport-category airplanes with sketchy stall characteristics, since T-tail planes can end up in unrecoverable situations by blanketing the tail in a stall.

Twin-engine planes also are not required to be recoverable from an engine failure at speeds below Vmc.

I don't know what the certification requirements are, but it seems they rely on being able to guarantee that you never get below a certain speed since in multi-engine airplanes there's always a low power/high thrust regime that's potentially uncontrollable.

While the FAA has allowed it, not all aircraft have been certified to fly in all airspace without safety systems to prevent stalls. Give the D. P. Davies Interview, recorded by the Royal Aeronautics Society a listen, and you'll learn how the 727 was not allowed to be certified in the U.K. without a stick pusher equipped.

I think it's this one. https://www.aerosociety.com/news/audio-the-d-p-davies-interv...

If not that one then this one. https://www.aerosociety.com/news/audio-the-d-p-davies-interv...

Edit: 2nd one I think is the one I'm remembering. Pumping the first one, because...well, it's just damn interesting.

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