Is the Boeing 737MAX Really Unstable?! The 737 Engine Saga.

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If you look at the original engines and engine nacelles of the 737, and compare them with those of the 737 MAX, the difference is… impressive.
So, WHY did the engines and their installation on the 737 evolve in this way? And is it really true that the placement of the 737 MAX engines make the aircraft unstable?
Stay tuned.
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Below you will find the links to videos and sources used in this episode.
• Shhh... Boeing's New 7...
• How Boeing Lost Its Way
• Boeing 737-100 - "Roll...
• Air California Boeing ...
• Martinair Douglas DC-9...
• Song of the Clouds - A...
• Delta Convair CV-880 P...
• Le Dassault Mercure 10...
• Southwest Boeing 737 &... v
• Air Inuit, the commitm...
• Richard Whitcomb's Dis...
• CFM, the journey conti...
• Boeing 707 re-engined ...
• Time-lapse CFM56-3C1 E...
• Canadian North, Boeing...
• Building Boeing’s Next...
• Rare Boeing 7J7 Mockup...
• {TrueSound}™ Airbus A3...
• Boeing seems to be foc...
• Boeing 707 Manufacturi...
• CFM56 3C
• Lufthansa Boeing 737 F...
• How the 737 MAX 10 lan...
• LEAP-1B First Engine T...

[@MentourNow]

Visit our sponsor betterhelp.com/mentournow today to receive 10% off your first month of therapy

[@anotherriddle]

Have you looked into the FTC fine/settlement that betterhelp had to pay last year? Did they clean up their act? Reading their privacy policy, knowing the information they shared with facebook, I still wouldn't feel comfortable in ever using their services. Too bad, really. I believe a service like betterhelp could do a lot of good, but this is really sensitive data and not a joke.

[@MeriaDuck]

Please do your research on the practices of better help. They aren't great to say the least.

[@etangdescygnes]

You are generally excellent, but here I must ask: "What are you talking about?!" I graduated in aeronautical engineering. Stability is determined for each axis of rotation by whether the total moment acting on the aircraft around that axis is such as to increase or decrease the angle of rotation, and it is defined for specific aircraft configurations (landing gear, flaps, spoilers, etc.) at specific flight speeds and density altitudes. When the Boeing 737 Max is flying within a certain part of its flight envelope and the pilots command pitch up, lift created by the engines beyond a certain alpha generates an unusual total net positive pitching moment that tends to lift the nose of the aircraft further. In this flight regime the Boeing 737 Max is by definition UNSTABLE IN PITCH. That's a mathematical fact. Boeing therefore introduced [faulty] software to correct this, so that pilots would not have to be retrained to cope with the instability. One reason for doing so was to prevent screw-ups where pilots would forget which model 737 they were flying and act inappropriately. Have you covered the Boeing 787 Dreamliner cockpit window cracking due to Boeing's abject failure to properly test the new curved panes for differential thermal expansion versus their frames before the aircraft entered service? That's a shocker!

[@stevenvaughn8431]

Betterhelp sponsorship makes me not even slightly trust you

[@KanalFrump]

Betterhelp are litigious scammers operating completely recklessly and sharing confidential patient data and identities with advertising networks. Please stop using these dishonest people as sponsors, it's very much to the detriment of your reputation.

[@unfixablegop]

Using a single sensor for MCAS even though two were available and it really should have been three was criminally stupid. And not mentioning MCAS to the pilots seems actually criminal to me. Why was nobody sentenced to prison?

[@Smart-Towel-RG-400]

Nope ..Boeing owns the government they probably would of gave Boeing a medal of bravery if they could of

[@roflchopter11]

It was a very poor implantation. It switched from left to right AoA sensor every flight. That said, it's effectively auto-trim, and pilots train to recover from runaway auto-trim, so its not like its a totally new system.

[@Hrafnskald]

Department of Justice announced today that it has opened a criminal investigation into Boeing regarding the door plug incident, and whether Boeing violated the terms of its settlement re: MCAS, by failing to document required safety work re: door plugs.

[@hakanevin8545]

@@roflchopter11 It is easy to talk from your warm armchair. They could recover only if they knew what the problem was.

[@hakanevin8545]

Search for "Boeing Charged with 737 Max Fraud Conspiracy and Agrees to Pay over $2.5 Billion" That is how American justice system works. You make a deal with the prosecutors to pay compensation and you are free to walk away.

[@f_pie]

RIP John Barnett, you will be remembered for standing up for what's right...

[@Jay-jb2vr]

And Boeing will be remembered for doing what's wrong

[@evogsr4807]

His "testimony" was complete BS. 80% of what I heard was nonsense

[@mbonje4948]

A singing canary and a bullet. That seems more like a mafia movie. The truth may never come out

[@prasenjittripura4691]

internet trollls😂😂

[@sasquatchman22]

​@@prasenjittripura4691how nice it must be to deny reality. People dissappear dude, it's a fact

[@koka3243]

I can't believe I am hearing the conclusions I am hearing from the Mentor Pilot 😮 The positions of the engines on NG were already enough of a problem during go-arounds (not some abstract "high angle of attack" scenarios mentioned in the video) as, depending on the configuration, the pitch up tendency was sometimes very difficult to handle, and this is part of the reason why pilots on 737 hate go-arounds, btw. And this is precisely the reason for the introduction of MCAS, as Boeing was sure that the number of incidents during go-arounds related to this issues will only increase with more powerful engines. As for choosing to rely on what the name of the system says -"augmentation" -rather than what it actually does - move the stabilizers - as Mentor Pilot does - well, this is reliance is exactly what killed those pilots on the two fatal flights. To repeat this now once we know all the facts is something unbelievable!

[@atlascruiser1456]

Yeah, I'm horrified by the campaign to downplay the serious issues. The wind tunnel tests in the very beginning told them this thing was going to be a handful at high angles of attack-- and the more you pitch up? The more Center of Life moves forward. It is a terrible trait.

[@samsharp8539]

I am surprised that Boeing did not place the engines above the wing like the Hondajet designers did. That would most certainly negate the pitch up problem (Bugs Bunny ‘he,he,he,he, laugh).

[@nagasako7]

Imagine an alternate world where Boeing didn't merge with Mcdonald Douglas. And instead just made a successor to 737 in 90s.

[@MentourNow]

They launched the 737NG in 1993, well before the merger with McDonnell Douglas, and it entered service in 1997. It is difficult to imagine the old Boeing making the MAX, but replacing the 737 in the 1990s would have been difficult.

[@godlugner5327]

Same world where the 757 was successful

[@idarpolden5913]

A better world

[@Dumbrarere]

@@MentourNow The old Boeing would have made the MAX. They just would have prioritized safety and reliability over profits. That in mind, old Boeing 737 Max would have been radically different from what we have now, being a better developed (or outright omission of) MCAS, more redundant systems, fly-by-wire, and other important upgrades.

[@cruisinguy6024]

If we ever invent time machines that merger should be high on the list of things to go back and stop from happening.

[@N82SV]

I am a retired aerospace engineer and a sport pilot. Your videos provide the absolute best explanations of these issues. Thank you so much for making them.

[@MentourNow]

Wow, thanks!

[@user-nt7sj5pz8i]

No your a liar

[@JohnSmith-dh3kx]

@@user-nt7sj5pz8iI think you mean "you are" or "you're"

[@MphAviation]

You’re*

[@joeschmoe21]

Aerospace engineer? May I ask what your education is? Given that you find these 'journalist' level videos best, I am curious. I have a PhD in Aerospace Engineers. My PhD was sponsored by GE Aircraft Engines. There is a lot of misinformation about the Max, which is understandable from the laymen. As for the Max itself, ... Lufthansa ordered 100 in Nov last year. One can assume Lufthansa, ordering 737s for the first time in 30 years, did their homework, and are more knowledgeable than KZbin specialists.

[@zzip0]

As a control engineer (we are the guys mostly obsessed with stability), I am horrified by how B737 was modified and the control system was augmented. The way this passed regulatory approval is scary. I will never willing fly B737 again.

[@luisurbina5115]

Actually, I would think the Max is probably much safer now, than it ever was.

[@18Ram]

thnx for the tip... i wont be telling my mother in law

[@allthatsheiz]

Honestly I have been following this since the first incidents since I am an engineer in aerospace and focus on design changes. I know they have improved things but I will still never willingly fly on that thing.

[@michaeledwards2251]

@@allthatsheiz 100% agree

[@henryposadas3309]

​​@@luisurbina5115how can it be when obviously they did not care about safety standards even after the 737 max crashes? Even if the design is theoretically good, who is to say everything was assembled right? Boeing is not safe.

[@craigenputtock]

"If it's Boeing, I'm not going."

[@benoithudson7235]

I’ve flown on a 737 with gravel kit. Canadian North retired them only after the pandemic. Air Inuit still has one.

[@benoithudson7235]

(Oh I just noticed you featured that very airframe in your video!)

[@MentourNow]

Awesome!

[@guenthersteiner8163]

Chrono aviation still flies one

[@shaunlaverty8898]

I thought Buffalo Airways was looking for a gravel kit for their 737?

[@Chris_at_Home]

For many years in the 1980s I commuted to Deadhorse, Alaska on 737s that had a gravel kit. I might have even been on ones that I helped assemble the engines because I worked at P&WA on the assembly floor in the late 1970s and saw that the customers of many JT-8s were for the airlines I flew on. 3 of those same 737s I flew on then ended up with a mining company in Indonesia that I also flew on over there. These ones had cargo doors.

[@helianocabral9832]

You are absolutely right when you say that using heavier engines or moving the engines forward increases static longitudinal stability, but may create longitudinal controlability problems. However, the main problem with the 73 max is an inversion of the static longiitudinal stability at high angles of attack, probably caused by altered airflow patterns aft of the engines toward the horizontal tail. It is a solvable broblem. However the way Boeing implemented a solution was a disaster, and we do not understand why the FAA did not catch it: 1) MCAS based on a single alpha vane. An alpha vane has a probability of failure somewhere around 1 failure in 40000h. But the MCAS in a way affects primary flight controls. Failure of primary controls are catastrophic and the requirement is that catastrophic failures can only happen once in 1000000000 hours. (10-9), as per FAA AC 25.1309. Had they used two alpha vanes (deactivating the system if there is a discrepancy between them) the probability of both failing at the same time would be once in 1600000000h, which would meet the safety requirement. 2) The MCAS actuated the stabilizer at a very high speed, turning the stabilizer into a kind of primary control. 3) PIlots were totally unaware of all those differences.

[@DennisMerwood-xk8wp]

How is it you know ALL this, but Boeing Engineer's and the FAA doesn't my friend?

[@pavlikkk101]

Could you describe in more details what is inversion of longitudinal stability and why this happens when engines are moved forward?

[@pcka12]

Moving the engines forward must change the centre of gravity, let alone all sorts of other considerations.

[@norlockv]

The MCAS system was designed with redundant sensors. This was later made optional as a way of generating upsell revenue. Designers also repurposed the MCAS from the special use case described by Petter to a larger role in flight, and the either failed to tell their test pilots or the pilots later denied knowing that they had. All of this is criminal neglect of their responsibility to the airlines and passengers.

[@pettread]

@@norlockv what do you mean MCAS was repurposed? Can you explain?

[@Hardts]

*You should drop BetterHelp as a sponsor as fast as possible*

[@JLo83]

Why is that? I haven't heard anything negative about them but it's possible I missed the story

[@Noksus]

​@@JLo83 they are sharing their customer's data, including non-anonymised mental health data to Facebook and other companies for advertising purposes and their therapists are far from competent...

[@castawayoloman]

He's already said he won't, he gave them a second chance. That's just how it is

[@Hardts]

That's too bad, really. When did he say this? Anyway.. I'll still watch his videos, it's not his fault. We need to punish these awful companies, so many people in this world have no moral standards.@@castawayoloman

[@castawayoloman]

@@Hardts don't have an exact video, but I'm pretty sure it was not long after the news broke, he put it in the comments section I think replying to someone asking him to drop the sponsorship

[@vexxedami7817]

My understanding is that the simulator test pilot for the max very pointedly made clear that the plane naturally pitches up way more than “slightly”. The MCAS was not there to simply make the plane more pre-Max-like, but to address a serious pitch up issue.

[@thewhitefalcon8539]

they thought they made it safe with MCAS?

[@terrymichael5821]

Because they are stupid civil servants with little aeronautical engineering expertise in aircraft flight controls on an unstable aeronautical airframe.

[@MrSarmad123]

Also, if MCAS is only to improve the handling, why would a wrong implementation lead to crashes?

[@RalphEllis]

Absolutely. Mentour does not seem to understand the problem. The forward engines generate so much lift, at high angles of attack, that they can pitch the nose up to such an extent that the aircraft can flip onto its back. It is called a ‘deep stall’. Check out what can happen to Rutan canard designs, where the foreplane can again flip the aircraft onto its back. THAT is the problem they were grappling with. R

[@umi3017]

Have you even watch the video? on 21:10 it shows you still need to pull a lot hall on the yoke to keep increase the AOA,. Have you ever tried to stall a 737 in simulator or IRL? I have tried to deep stall a max on Lv-D simulator and I can barely keep it at edge of stall with full yoke back and constant back trim input, the nose just want drop at high AOA, even without MCAS.

[@jamesthompson7282]

Your callout to Stefan Drury's channel & encouragement to help him out: that was kind & generous. Thank you for being a friend to him. That small gesture is infectious - encourages community amongst us all, is an example of how we can all help each other. We need more of that. I've occasionally enjoyed your channel's posts, but am now subscribed to yours & his.

[@Garythefireman66]

Agreed. Stef is a great creator, and wish him a speedy recovery

[@smithpauld1501]

Together with Jean-Claude Malroux of Snecma, my father was part of the original marketing team for the CFM-56. The big break was the DC-8, which was an obvious easy re-engine, followed by the KC-135 and other 707 military variants. My father always felt that the 737 re-engine program was a rush job as Boeing tried to keep small Airbus variants from eating their lunch. Still, the 737-300 broke the Pratt stranglehold with Boeing and proved to be a launching point for both CFM and GE. That clever engineering you mentioned paid off hugely. Although long-retired by the time that the MAX line came out, Dad was still connected enough to know that one of Boeing’s major pitches for the LEAP-engined planes was to that they were to require minimum pilot retraining. And therein lies the rub and at least some of the design errors.

[@tsuchan]

Not exactly to keep regulators happy, was it... it was to persuade regulators to keep the same type rating so that airlines didn't have to do more pilot training. Or am I wrong?

[@geraldrossouw4425]

Exactly, this is the crux of the problem, when is a 737 no longer a "737"? Of course planes should be allowed to change with advances in technology and requirements. But they also have to be classified as a different type when these changes are significant enough. Boeing tried to cheat on this latter part and it resulted in the deaths of 346 people.

[@toms1348]

It was both..but mostly your second point. Boeing would've been on the hook for the pilot training if a new type cert was required.

[@tonsssedell4318]

The latter is what mostly is meant by the former. Yes and yes. They also wanted to keep airlines happy.

[@Queenskid19]

Boeing was trying to keep the airlines happy by not having them spend money on training and sims i guess

[@hakanevin8545]

Contrary to what Petter says, EASA believes MAX is unstable, or at least can go into an unstable condition in certain flight envelopes. That is why there is a *third AOA sensor* requirement. Do not forget that Boeing's own staff says: "designed by clowns who in turn are supervised by monkeys" Also former Boeing Manager Ed Pierson says "He Won't Fly on a Boeing Max Plane".

[@glen6258]

I never finish a full video on KZbin or never watch a full tv show or movie. However with your videos I have never stopped it early and always watch it in its entirety. Thank you for the awesome consistent content.

[@escapetheratracenow9883]

If it’s a Boeing I ain’t going.

[@ajg617]

I never knew they extended the gear length. Every other source concentrated only on engine placement. Thank you.

[@Voyager.2]

Only on the 737 MAX 10.

[@ahndeux]

@@Voyager.2 On the 737 Max 8, they didn't extend the length, but they did beefed up the supporting structure, fuselage skins and other changes to accommodate the heavier engines. It was part of the reason why the MCAS was not given as much attention since the FAA was focused on the updated landing gear and fly by wire spoilers. This was all reported in the FAA report AV2020037.

[@tanmayta9131]

@@Voyager.2 I believe they extended the nose strut on all MAX variants. However, the main landing gear that expands during rotation to increase tail clearance is restricted to the MAX 10. I'm not 100% sure about this, so take it with a grain of salt. :)

[@gergister]

Extended gear length you said.... kzbin.info/www/bejne/h2nSdJyijpmmsMU

[@StratMatt777]

@@ahndeux The MCAS wasn't given much attention by the FAA because Boeing intentionally hid the existence of the system, just as they hid it from pilots by choosing to remove it from the Aircraft Operating Manual to preserve the type rating.

[@ronaryel6445]

You are correct regarding the reuction of the fan diameter on the CFM-56 engines powering the 737NG, but your explanation was incomplete. In addition to lowering its efficiency, this lowered its power too. The engine was derated from 24,000 lb of thrust to 20,000 of thrust. Also, your explanation of the MCAS is great. I would like to add that MCAS is not new to the 737MAX. An MCAS was implemented on the KC-46 (767) air refueling tanker. This much more robust MCAS was needed because a tanker's center of gravity is frequently changing during flight as the tanker offloads fuel to recipient jets requiring it, and as such, MCAS is more active on the refueling tanker. The KC-135 tanker and KC-10 Extender tanker had a Second Officer (flight engineer) who was in charge of fuel transfers between tanks (to manage the center of gravity) but the 767 tanker does not, and requires more robust computer functions to fly safely. The 737's MCAS was less robust, lacking sensor redundancy, to reduce its cost, because Boeing calculated that airline 737s would not need it often, only in specific situations. Boeing's assumption, while correct, led to a problem which not only caused two crashes, but also caused some incidents on US airlines that could have resulted in crashes, but did not.

[@couespursuit7350]

In my 30 years at a US major I never heard our 737-300's called the "classic" that was a southwest term. Also the "Jurassic jet" was uniquely a term for the 727, never used for the 737-200. When I bid up from the 737-200 to the 737-300 I was trained on how at hi nose & low speed the addition of thrust does input a bit of nose up pitch unlike the 200, exactly was you have addressed. Also the NG series again had bigger more forward engines, higher mounted engines and would input some nose up pitch more so than the 300. Thank you so much for addressing this misinformation propagated by lax/sloppy media reports.

[@KelpieDog]

I'm a private pilot, (love the decathlon for the upside down silly stuff), and obviously never flown the big guys but I love hearing the technical stuff about how these huge metal boxes fly.

[@stevesr9037]

High, I’m a 737 veteran myself and quite familiar with the concept you are discussing. I flew most variants of the 73 and my flying came to a halt when the mcas mess came about a few years ago. I was in the middle of the type conversion in Singapore when it all happened. Anyways to the point, I firmly believe that it’s time for Boeing to say good bye to the 73 and maybe concentrate on the 75 comeback and making that model a better unit than the original was. I’m not an engineer but common sense tells us that shrinking an airframe is probably a little easier than trying to stretch it as in the max. The Russians have come up with an airframe around 210 pax and I think that’s a good size to have, which is why I think a redesign 75 makes a lot of sense. And knowing Boeing will do anything to screw this up, make it a totally new wing design instead of the bs job they did with the max which was the same airframe as the NG. A new design is a new aeroplane period.

[@roflchopter11]

Enjoy the joys of heterogenous fleets, expensive training to change airframes, etc.

[@slartybarfastb3648]

​@@roflchopter11Pilots take on new type ratings all the time. It isn't a big deal. A pilot will typically have three type ratings before they ever begin commercial training. Another one or two for mulri-engine. Probably another for instrument. Then one or two, or three at their first regional job. Then three or four more at the majors before retiring.

[@ACPilot]

Well what then do you out of Airbus making the A321XLR MTOW above 101 ton, the wing was never ment to lift that weight. An updated 757 isn’t really a suitable way instead of the MAX. Most 737’s are as you probably know the 400/800/MAX8 as it is the most popular size.

[@HaroldBrice]

Juan likes the 75. That is good enough for me. Dust it off. Fly it.

[@VicTor-gi7so]

​@@HaroldBrice so does Trump

[@martinfendt1305]

I believe that the ME262 was the aircraft that inspired the original B737's wing & engine layout!

[@davebollmann5292]

Tnx for great analysis. When you talked about the different noise of various engines. This brought back memories when i was a flight dispatcher at O,Hare working for Aeroflot and later Air Ukraine with Iluyshun 62M aircraft. While waiting for the aircraft to land the loud engine sound told me that that was my aircraft. This was in the mid ninetys. Later Aeroflot switched to Boeing 757.The Illuyshin 62M had a tail hydraulic post so it would not tip over.

[@ryanlittleton5615]

Fun fact: the 737-900ER needs a post too. I don't think it's hydraulic though.

[@gcorriveau6864]

"A little knowledge can be a dangerous thing." And lately, thanks be to internet - there are a ton of people running around repeating false/misunderstandings base on "a little knowledge." Thanks for seeking to counteract some of this with Quality Information, Mentour Now!

[@PrincessAngelaXOXO]

It's not that it made it unstable, it is that it made it a aircraft with a different type rating. The problem is, they tried to hide that fact so that aircrews did not need to get a different type rating

[@idarpolden5913]

Actually MCAS made the plane hopeless unstable.

[@danharold3087]

Start with did it need a different type rating?

[@idarpolden5913]

@@danharold3087 No, it needed a banning.

[@mariemccann5895]

You are clever.

[@ryanreedgibson]

@@idarpolden5913 Yes and no. MCAS was a "quick fix" to the plane being retrofitted with new engines.

[@jasoncamps77]

Actual aircraft designer and propulsion engineer here. Any change that results in a nose-up tendency at slow speeds is inherently less stable, and MCAS was intended to address it by inducing elevator deflections to keep the nose down. That's exactly what lead to the 737 Max 8 crashes. Additionally, the CFM56 redesigns also led to a greater risk of uncontained blade loss which also resulted in passenger injuries. Lastly, the worst problem is Boeing's repeated failure to report known safety issues, starting in the early 90s with a known issue with the rudder controls that eventually led to two fatal accidents, and ending up with unreported issues with the MCAS and it's single-point failure mode (which violates regulations for safety critical systems) and finally the recent quality escapes on the Max 9 and potentially other models. The 737 has become increasingly less safe with each generation and Boeing has repeatedly cut corners on safety.

[@gottfriedheumesser1994]

As I had to do with nuclear power plants, there should be no discussion that this plane needed three angle-of-attack sensors with a discrimination unit that indicates when one of these sensors differs too much from the others.

[@ShaunHensley]

Exactly. Very disappointed with Mentour here

[@michaelnacevski]

@@faceless360 Cos its fact maybe your not ready for it ...... Nothing wrong with the max.

[@michaelnacevski]

@@ShaunHensley Its fact...

[@michaelnacevski]

@@faceless360 Mcas did not cause those crashes read the reports and dont listern to the bullshit media, Cos its just all lies and misleading information.

[@robertsonmiller]

Thank you for showing the photograph of the Air California 737 (time 5:02 in the video). My father was vice president of Air California starting in 1968 for several years. As a child I loved flying on those 737-200 airplanes. The paint job was golden yellow (for the Golden State) as were the flight attendant's uniforms (then known as stewardesses). I loved the sunflower on the nose of the airplane. It was a great logo. Air California ceased to exist when American Airlines purchase the company in 1987. They had one crash at John Wayne Airport in 1981. Thankfully everybody survived.

[@mickboakes7023]

I was always under the impression that MCAS was there to readjust the C.G. which was impaired by moving the new engines forward and upward. I also did not realise they had lengthened the nose wheel leg. Thank you for explaining, so I even I, just an enthusiast understands. Really great content as usual. Stay safe. All the best. Mick🇬🇧

[@MansoorUmarkathab]

My son is passionate about pilot and aviation. So I started to search a good channel about aviation finally I found it. Sir, your are doing great work and your creating curiosity but you are explain about technical side. I am really impressed. Who wants become a pilot must follow this channel can learn lot. this channel should be dubbed in other languages also. (Consider)But English is the priority. I really appreciate your efforts. ❤

[@MentourNow]

Thank you! I’m so happy you find it helpful and send my best regards to your son.

[@craigmclane5610]

Good luck to your son. I think this channel will prove to be an excellent resource for him.

[@user-nt7sj5pz8i]

No one cares about your son Shutup

[@tomedgar4375]

If you are in the US, check out the Civil Air Patrol and Young Eagles

[@zvartemax4832]

Great video again Petter! Don't know about the jurrasic 737 but the Classic already had the Speed Trim System which would act on the Stab position in Low speed, high AOA+High Thrust conditions, i.e. Take off and Climb phases. According to our course notes and instructors this was to counter the nose up tendency the aircraft would have in such conditions. This was a direct result of engine shape and placement. In other words, the issues with the Max were not exactly new ones. However, the course notes never went into depth about the exact characteristics of the systems (one in each FCC) and which inputs were actually used to control the Stab. Neither did the Aircraft Maintenance Manual. We just knew the system was there with a fault light on the overhead panel to prove it. To add a little more, the CFM56-7 wasn't the only upgrade on the NG, it too had a taller main gear (and re-designed wing) to accomodate the larger nacelle diameter compared to the CFM56-3 on the Classic. In other words, the issues with the Max were not exactly new ones.

[@bobandvirginiaravera4775]

Thank you for your excellent discussion of the technical (and piloting) issues surrounding the 737 MAX. (I worked at Grumman Aircraft over 60 year ago, on the A-6 Intruder and the Gulfstream 1 Turboprop). It is refereshing to hear a knowledgeable and dispassionate discusion of the issues, My early experiences as a 737-100 passenger is that the pilots loved it (especially former military) b/c it was one "hot" aircraft.

[@andrebello4191]

About placing the engines forward and under the wing. Some good points were mentioned. Throw in a few more. I think it causes the engine to aerodynamically interfere with the wing less. Which makes the wing more efficient and allows a smaller wing, less drag etc. Higher bypass engines also have different airflow characteristics than lower bypass engines, with the air going in, its got to be carefully designed so wing and engine don't interfere with each other too much. Placing the engine forward allows the weight of the engine to act as a mass balance which helps to reduce aerodynamic/aeroelastic flutter. Which helps to save structure weight. And the possibility of fire was mentioned. Also if theres a uncontained failure such as compressor or turbine blade it will be less likely to penetrate wing structure and damage crucial structure or fuel tank or system. So theres lots of benefits. As for the instability caused by larger engines. Yes its not because of the added weight forward of the wing I agree. It comes from a combination of things. Compared to previous 737 types. The engine has a larger diameter. Which means the thrust line tends to be further below the wing. It produces more thrust. The shape of the nacelle causes it to produce lift. And the engine is further forward. So all this means that the engine and nacelle are going to generate more pitch up moment. Thats means if you're in a high angle of attack situation with high thrust setting. It mite be harder to pitch the nose down. Hence taking away from the effect of natural longitudinal I think stability. Hence the need for all this MCAS crap to compensate. Not just to avoid potentially dangerous high angle of attack situations. But also to make the plane handle like previous 737s to please airlines and regulations and certification etc. etc. But ya the new engines do kinda make it unstable, but not because of weight and cg, because of thrust and aerodynamic effects and moments. Thanks for listening to my 2 cents good nite.

[@andrebello4191]

Correction maybe the engine thrust and aerodynamics doesn't actually make it unstable. Maybe just slightly interferes with the stability. Ok maybe there is no real danger for stall or difficulty in avoiding stall at lower speed higher pitch or higher angle of attack situations. Due to engines or otherwise. Maybe its just a relatively minor handling issue. It needed to handle similar to previous 737s so that discrepancy needed to be fixed, to meet regulations and what not. Also contributing to the pitch up moment is just the fact that the engine/nacelle is bigger, it has more area to produce lift. But also theres other aerodynamic reasons too it makes a big vortex something like that. Combination of a few things. I think the 737 MAX could have worked. They didn't need a all new design yet. But. I think they rushed it too fast, didn't take the time to develop it right.

[@jblyon2]

Another major issue with MCAS is that it was not implemented as designed. The engineers designed its ability to change trim to be very minor. In this way tying it to a single angle of attack sensor was not a big deal as if it went off the rails due to bad input MCAS' ability to endanger a flight was almost nonexistent. Later on however management dictated that MCAS needed to be much more aggressive in order to ensure that they could tell airlines that no simulator training would be required for pilots of earlier 737s. It was a perfect storm. A system that was not designed to be redundant because it wasn't seen as necessary due to the relatively minor fight inputs it was capable of making, which was then altered to be able to make extreme changes, and then pilots were not informed about the system.

[@timempson2146]

The original design did not link it to just to AoA sensor. It was much more for the higher speed manouver where the aerodynamic effect of the engine meant the stick pressure reduced - the regulatory requirement. Later it was found that to keep the handling feel the same it was needed at slower speeds. In this phase of flight the second sensor (I thick it was an accelerometer but I could be wrong there) would not be effective - so the use of a second sensor was removed - without adequate risk analysis of what would happen should the AoA sensor become defective. This is the root cause.

[@nafnaf0]

Hmm, I am not surprised based on Boeing's management structure. The entire line of management is non-technical and that has major consequences. They should not be making decisions, and not even be with the company. It needs to go to a unified engineering group, where the managers are still still leads or individual contributors and no on the other side of the union wall. This is the way many other engineering firms are

[@mikemines2931]

One thing comes to mind is flying down the north coast of New Guinea at midday listening to the Goon Show in a 707 and watching the engines contra rotating on their fairings.

[@caiocc12]

As a programmer, it baffles me that they didn't do simple saturation arithmetic to control the inputs. If the needed adjustment was very slight as said, it should've been capped, in order to not force the aircraft down even if the algorithm gets completely haywire.

[@PeteSty]

Going back in time, way back, I grew up in Chicago and remember some interesting sights. This was back in the early and mid+ 60s. I remember seeing a DC-8 fly over our house (going East) and one could hear it for 20 minutes or so but see the black exhaust for at least half an hour or so. Another thing was I saw a DC-3 painted with orange stripes or tips and Dad told me it was the FAA doing checks on the O'Hare landing radios. I did have a DC-3 right in front of me at Palwaukee, coming right at me but then turned and scared me to death. I was about 5. After that, I end up getting a license in a 152, and was in aviation for 45 years until retirement. Love you channels!

[@walterpleyer261]

The most amazing aspect about the 737 is that they still fly with the original ceretification

[@JackS425]

Is that true? I thought they were waiting on certification for the MAX7 and MAX10 variants?

[@MegaSunspark]

@@JackS425 I think he meant pre-max models, especially 737 classics.

[@ryanlittleton5615]

The -300 through the -900ER have the same type rating I believe.

[@craigmclane5610]

Your videos are always clear, fascinating, and watch-friendly. I have to compare the Max issues with my experience in military aircraft, where we were instructed that we would compensate for wild changes in handling characteristics in various routine flight regimes (not just takeoff and landing) simply by learning to anticipate that the plane would attempt to surprise, annoy, resist, or depart from controlled flight. We also had cutout switches for multiple automated systems in case we suspected the automation had somehow taken on a life of its own...including stab trim, anti-skid, stability augmentation, autopilot (of course) and others. Finally, we also had many, many restrictions on engine anti-icing, which became an onerous addition to workload when it was in use. I can really appreciate the comparatively modest enhancement that MCAS makes, and I hope more of your viewers come to understand that the terrible results stem from Boeing's corporate (Chicago) decisions regarding the profit implications of how they addressed transition training, rather than from the engines or the MCAS engineering (Everett).

[@berkeleyfuller-lewis3442]

EXACTLY CORRECT.

[@craigmclane5610]

@@berkeleyfuller-lewis3442 I'm struggling not to resort to ranting about the catastophic results of the merger with McDonnell-Douglas...to include their behavior in the next-generation fighter, tanker, and SAOC competitons! Reprehensible. Chicago is trying hard to singlehandedly destroy yet another pillar of the US economy.

[@addamochs]

A part in this video reminded me of a flight when I was a kid. Then that reminded me of another part of that flight or another flight. I remember seeing the bucket reversers, as you just called them, deploy on landing and I thought the plane was falling apart. On a flight from DTW to San Diego when I was somewhere around 5 years old I think, I was afraid to use the toilet because I thought it was going to suck me out of the plane. Since then, I have been on many flights, including a single engine 4 seater prop plane around 3rd grade and one commercial flight in a puddle jumper flight. It was a VERY loud twin engine prop plane that I think were turbo props. I couldn't even stand up in it and they told us where to sit for weight distribution. Another commercial flight was in a more modern twin engine turbo prop that I could stand up in. It had just one seat on either side of the aisle and a curtain to the cockpit that was left open for the night flight. That was cool seeing into and through the cockpit while flying. And one memorable flight was Alaskan. It was a flight from California to Oregon and it had a capacity of around 50-100. It had top mounted wings and there was only 4 passengers on board. We got to drink for free. I remember getting a Craft Beer that was an Alaskan Brewery. I still have that can, empty of course. But with all the problems Boeing is having now and the whistle-blower taking his own life, allegedly, during his deposition, I will NEVER fly on a Boeing ever again. I just can't trust them anymore.

[@38whitcomb]

As a retired aeronautical engineer and airline pilot I found this video to be an excellent explanation for the average person. Great job

[@nigelclinning2448]

MCAS is all about one small paragraph in 14CFR25. The real problem was the single point of failure of the AoA vane. “25.203 Stall characteristics. (a) It must be possible to produce and to correct roll and yaw by unreversed use of the aileron and rudder controls, up to the time the airplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall. In addition, it must be possible to promptly prevent stalling and to recover from a stall by normal use of the controls.”

[@luislongoria6621]

Faulty pitch sensor? Why did it indicate Unreliable Airspeed? If the AoA stuck at a high angle, there would have been a stall warning condition for BOTH landing and takeoff

[@luislongoria6621]

Now if MCAS was integrated into the autopilot sensor suite, engaging the autopilot, would automatically trigger the MCAS even if it had previously been turned off

[@ryanlittleton5615]

@@luislongoria6621 There was. On takeoff roll in both crashes the captains AoA vain deviated, so when the plane rotated the stick shaker immediately activated.

[@Mavfly1967]

I have flown most 737 models except the 200 and the MAX and have thousands and thousands of hours on the type. For the last 15 years I have been flying the Airbus A320 series and the NEO. From being an absolute Boeing fan, after changing to the Airbus, as I see it, the 737 is a totally outdated product, and should’ve been scrapped years ago. (Sorry Petter). In my opinion, the A321 NEO is the best plane you can buy in the narrow buddy segment. Flying with 240 passengers, it burns less fuel than an old A319 with 156 passengers, on the same route. So quiet and so powerful. What a machine. Petter, work on one of these for a while and you would never want put your feet in a Boeing again, I promise, from experience. 😊

[@Angel33Demon666]

Wouldn’t the E195 E2 or A220 be more modern designs?

[@Mavfly1967]

Probably. But they are much smaller and can only compete with the A319 NEO . The A220 if for sure better, the E2 is again an old plain with new engines and wings, and I think is less appealing in this market segment.

[@dcxplant]

Excellent video as usual! You mentioned the "speed trim system" very briefly, however a little more information about the Mach/Speed Trim features on the 737-300 would be useful. The Mach and Speed Trim system along with the Elevator Feel system operating through the trim system were all designed to 'augment' the feel of the pitch during manual flight. I flew the Jurassics, and Classics. When I first flew the -300 after years on the -100 and -200 Basic and -200 Advanced, the Mach/Speed Trim and Elevator Feel system were very prominent during hand flying. While pitching up in manual flight, the trim wheel would actually trim nose down while pulling the yoke nose up. A curious thing for the a pilot new to the 737-300. The very light feeling of the yoke in pitch is not new and began with the -300. The trim system was used to augment the pitch feeling from the very first installation of the CFM-56 onto the airframe.

[@machdaddy6451]

If the engine upgrade didn't make the plane unstable, then why did they have to use a computer band-aid to make the plane stable and why were there two fatal crashes directly attributable to computer band-aid?

[@StephaneCalabrese]

It didn't make it unstable. It made it different. So came the MCAS, which nobody knew about. The FAA didn't know about it, the pilots didn't know about it. Never mentioned in the Max manuals. THIS is the outrageous part. Profits were put above safety. Boeing should have worked on a new 737 since the 80s, or at least early 90s, to take full advantage of composite materials, more efficient engines, fly by wire technology... They're at least 30 years late.

[@roflchopter11]

Its functionality equivalent to auto-trim, which pilots and the FAA did known about. In fact, pilots have a memory procedure for handling runaway trim. The procedure works, as other pilots used it to recover from MCAS anomalies on the same aircraft that later crashed. Those airlines failed to record and repair the AoA sensors that caused the anomaly. The implementation was very sloppy, but the pilots were trained in recovering and failed to do so.

[@Milkmans_Son]

System differences manual, page 734. Go look for yourself.

[@RoelandJansen]

Mcas isn't the problem with such crashes I believe. Lack of being able to understand flying was more the case.

[@RoelandJansen]

@@daftvader4218 I do have a clie actually. You should listen to the flight safety detectives and also familiarize yourself with stab trim cut-out switches that may only on the ground may be placed back as well as memory items, the fact that the two crashes aren't exactly for companies that do well. Also, the most of the a/c flew with MCAS w/o any problems. both totally were avoidable. yes there were maintenance issues at one of the planes but with capable pilots it would never have happened. Also, when it comes to news: even if a maintenance guy forgets to install a wheel correctly, it's still in the news of being Boeing's fault. Ayways, I do have clue. Good moment for you to dive in what really happened on two flights and ask a few people who actually fly a/c with MCAS. The grounding is due to people that -indeed- have no clue.

[@robvoyles1985]

@@RoelandJansenyou are insane if you said the system that killed over 500 people is not the problem smh……

[@221340]

Thorough as usual Mentour. I flew all versions of the 737 from the 200 thru the 800. With each new variant, Boeing increased the size of the horizontal tail surface. The result was a jet that was fun to fly. After the McDonnell Douglas merger, Boeing broke with tradition. No longer were engineering decisions made be engineers. The Bean Counters had taken over. They thought the flight characteristics could be "smoothed out" with software and refused to mod the tail. Yes, the MAX can be flown without MCAS, but MCAS caused the two accidents.

[@Tom-tk3du]

As I recall, the only engineer on the Boeing Board of Directors was the CEO. If it can be flown "safely" without MCAS, it should have been taken out or better yet not installed in the first place. Concerns about wanting to avoid pilot type-training sounds exactly like something a bean counter would come up with. All this reminds me of the Challenger Space Shuttle disaster.

[@DerekJohnson-us7vy]

@@Tom-tk3du Silly.

[@Tom-tk3du]

@@DerekJohnson-us7vy Up yours.

[@nathanaligizakis760]

Obviously, the MAX had a longitudinal stability problem in some parts of the flight envelope. Yes, increasing the tail size is the logical solution. A trim workaround like MCAS as a concept is a questionable solution. As originally Implemented with a single point failure mode, it violates the most fundamental principle of transport category aircraft design, which you would think any Boeing engineer should know very well.

[@Tom-tk3du]

@@nathanaligizakis760 It looked to me to be a hurried last minute modification where corners were cut in terms of safety analysis and engineering supervision. According to FAA regs, yoke pullback force has to continuously increase up to the point of stall. Should be easy to verify with MCAS deactivated. I’d imagine it might also be detectable with the wind tunnel model.

[@jeremypearson6852]

I love the way you make your explanation as simple as possible for the average layman. I also like that you aren’t afraid to admit that you maybe wrong on something.

[@jamiecheslo]

Continue to love your work!! An interesting tidbit of information for you: The very first jet aircraft in the world (while definitely NOT a commercial airliner) the Messchershmidt ME-262 fighter/interceptor had its engines mounted directly underneath the wings without pylons. They extended both fore and aft of the wings. Hope this helps! Looking forward to your next instalment. Cheers from Canada!

[@gayakola3]

Even in aircraft conceptual design stage, a commercial aircraft is always designed for inherent static and dynamic stability. It means the design itself tends to return to stable equilibrium in air. Then comes controllability - where we size stabilizers, control effectors, to be able to takeoff and land properly; and non-ideal cases. So, they're never designed to be unstable under any scenario. Even the wings are slightly angled upward to stabilize in roll. The way I understand it, the new larger engines created a larger thrust force that caused the aircraft to pitch up slightly from the OG design. Now I'm intrigued to look more into it. Thank you for the informative video, loved it!

[@tomellingham8627]

Yes, this is what I understand. The Max is never at a stable equilibrium. It wants to pitch up. MCAS moves the control surfaces to pitch it down. It's still flyable without MCAS, but battling physics somewhat, instead of just being naturally balanced.

[@737MaxPilot]

@@tomellingham8627false statement

[@XPLAlN]

@@tomellingham8627….the MAX is inherently stable as are all Part 25 airplanes. That is what this guy is saying here. However, it seemingly did not reach the degree of longitudinal stability across the speed range required by 14CFR 25.255 and the chosen method of compliance was MCAS. According to the NTSB, this was expected from early in the design phase. Then things became murky after flight testing began and the authority of MCAS was expanded, perhaps partly in their quest to assure level B difference training (ie no sim) for 737 NG type rated pilots, but also to address pitch up characteristics in the stall. MCAS does not move the elevator control surface, it moves the stabiliser in the contra elevator sense in order to increase stick force required to pitch the airplane, thereby reaching the arbitrary rate mandated by part 25. With or without MCAS, upon release of elevator pressure, the airplane has to return to within 7.5% of initial trimmed speed, and is thus defined to be stable.

[@oswaldoramosferrusola5235]

Not true for Airbus. The A320 family is unstable by design

[@737MaxPilot]

@@oswaldoramosferrusola5235 oh, please explain how that got by the regulatory agencies!😂🍿

[@amanthaesports3228]

This video is probably more in-depth than the official iPad conversion training. Very good work Mentour

[@paulis7319]

Very well put-together explanation of what most of us aviation enthusiasts have been wondering! I think it would be a great idea for you to clip some of your more popular videos into "shorts" so it doesn't take as long to get to the point. As Tom Petty sang in the 1990's "Let's get...to the point...let's roll..."

[@hollowman6282]

Your videos have really helped with my previous fear of flying. I am no longer gripping the seats like a madman with sweat pumping from my cold forehead

[@aeraxe]

if u used to be scared of flying then your should be having a heart attack in a car lol there wasn't a single passenger plane crash in 2023, but there is over 5,000 car crashes a day in the country that i live in. the chance ur flight crashes is essentially impossible

[@generaliserad]

Very swenglish centimeters, but i love the work going in to the channels. Firm knuten näve i bröstet, and the Robert Redford nod meme

[@idanceforpennies281]

If the 737-MAX had a fly by wire system (which it doesn't it only has FADEC which is just engine control)), the pitch up tendency at low speed high thrust setting could have been simply dialled out. But it still uses a 1960s mechanical direct link control system which needs a supplementary control device (MCAS) to prevent a pitch up under those conditions. Airbus also have a system which prevents over-rotation/pitch up situations. But the key thing is its fully integrated into the electronic FBW system. Not only that, but the Airbus' always run two AoA sensors at the same time, and if there is a disagreement between them, the system disconnects automatically. It's just a smarter plane, not a Frankenstein 1967 design.

[@Riogrande1964]

Thanks for this. Have to fly on these and your clear explanation is helpful, anxiety-wise

[@mburland]

Classy to give Stephen a shout-out, well done!

[@MungaiStiivo]

Mentour Pilot's students must be the luckiest to have such an instructor. They get to learn History, Engineering and Navigation all at the same time. There's never a boring class when he's the tutor.

[@HarryDunlopClark]

Right!? I often think about this whenever I watch one of his videos.

[@RuminatingWizard]

He's not an instructor. He's a check pilot.

[@adamsvette]

I would love to see you make a video on the History of pilot training. Who was the first pilot that the wright brothers trained? How did they train early pilots? When was the first flight simulator used? What was it like? How has pilot training evolved? Sure someone else might be able to read the Wikipedia article on it but you have the insider insight into this specific topic that I think would be extremely interesting to have that viewpoint.

[@joefin5900]

Another great, informative performance. Wondering when you, Kelsey, Juan, and others will get together and collaborate.

[@OskarHartmannsson]

I seem to remember that when the NG came out it had a elevator tap working apposing the movement of the elevator to keep it from starting to rotate by it self during takeoff, this was the consequence of the new engine (more thrust and further in front of center of gravity) and this is the problem with moving engines too far in front of the wing as it will increasingly make the plane pitch up as you apply thrust(moving center of thrust changes the behaviour)

[@dersebbler9452]

Just to add to the points made: the mcas worked by moving the trim leadscrew in the horizontal stabilizer. This system would be way to slow to actually correct any aerodynamic instability.

[@Hans-gb4mv]

I'd say a clean design is long overdue ;) and I always understood what MCAS was designed for. The 737 Max would have been a safe aircraft to fly on even if MCAS was never installed. But the system was designed to prevent the requirement of simulator training for pilots, which was also the reason why it also was using the input of a single AOA sensor because to be dependable, it requires all AOA sensors which would have made it a safety critical system which would have brought back the simulator training even though Boeing was selling the aircraft to airlines with the promise of not needing sim training. At the end of the day, the problem with the entire thing is that Boeing sold an aircraft with a promise that it couldn't keep. What many people also don't know is that the 737 Max was not the first aircraft to get an MCAS system. A variation has been used on the KC-46 refueling aircraft as the balance of the aircraft shifts during refueling. While the system is also called MCAS, it does serve a different, but similar function.

[@danharold3087]

As much as people would like to, and have, dump this on Boeing I see a systemic problem that caused all these issues to line up and crash not one but 2 airplanes. Is a system that favors less simulator time is broken. If the difference is so minor pilots can turn off MCAS, did a 737 MAX w/o it need a unique type certificate? This needs to be looked at from the top level.

[@ahndeux]

You actually think that Boeing would have LESS problems with a clean sheet design than one that is almost 20+ years old and had stellar safety record up to the redesign? I would argue their problems would increase by 10 fold or more with more design changes. The engineers that work on the redesign are not the same as the ones who did the previous generations. I think your assessment is completely flawed. What it might have done with a total redesign is to force the FAA to pay more attention to the entire design than with the update from the 737NG generation. Boeing flagged the fly by wire spoiler update and the landing gear reinforcement as a high risk change and that was where the FAA spent most of their focus on. There is an old saying in engineering. The issues that you spent the most time on due being assessed as a high risk are usually not the ones end up biting you in the rear. Its the "low risk" items which fell through the cracks. A lot of bad assumptions were made to determine it to be low risk and that's what bites you in the end. It always has and always will be.

[@matthewhall5571]

Nobody ever blames the irresponsible airlines like Southwest that hammered and hammered and hammered on Boeing to avoid requiring the flight simulator time until Boeing relented. There's plenty of blame to go around.

[@ahndeux]

@@matthewhall5571 "The customer is always right."

[@irideaduck939]

@@ahndeux finally some common sense here in the comments! Frankly nothing scares me more than the phrase "All new!" ... I'd rather prefer a refinement of the previous version. Boeing know knows the weakness of the 737 airframe due to its history, hopefully it has address the issues with each version/iteration.

[@tsnovak20]

I flew on one yesterday, it was really nice flight but neos are just more comfortable

[@ryanlittleton5615]

I've never flown on either the MAX or NEO but the NG and CEO I've never noticed much of a difference.

[@Andystinker]

Stumbled across you channel and I love your content! Do you do anything on military jets or keep it aimed at commercial airliners?

[@docnele]

I remember that I read that tendency of the aircraft to increase the input of desired maneuver without increasing control input is also called "instability". Instability in yaw, pitch, roll, etc. Now, there is no perfect airframe and those instabilities exist almost in any airplane, and such non-linear characteristic are carefully implemented in flight controls, speeds placarded, pilot trained for such regimes etc. This way or another, those are dealt with in almost any airplane. The problem of MCAS was that discovered "instability" (because by the upper definition, it is THE instability), one that was acceptable by itself IF pilots got warned and trained, got to get "smoothed out" to approximate previous behaviour by totally inappropriate methods from the standpoint of safety and relability.

[@CmdrKien]

Max is not unstable. You let go of the controls while it is still pre stall, and the plane will return to level flight. The force on the stick always remains positive. It just fails to increase linearly as required by regulation.

[@karlp8484]

The bottom line is because the MAX hasn't got a FBW system, there needs to be this supplementary MCAS system. Airbus' have FBW and also has this over rotation/ stall prevention but the key thing is that it's built into the control laws and isn't some add on. The other thing is that all the AoA sensors are working all the time...

[@d.jensen5153]

I got to land on a gravel runway in a 737 in the Canadian high arctic several years ago. The plane's low stance did indeed facilitate cargo removal via forklift from the large cargo door aft of the port wing. (Resolute Bay, Cornwallis Island, iirc.)

[@PeteG143]

Thank you for your reference to your colleague Stefan’s plight. And thank you for your great video work.

[@utoob7361]

You are wrong about the reasons for the engine placement. A wing in flight creates two forces - lift and drag. But it also creates a torque or twist. By placing the engines forward of the leading edge, they act as counterweights to the aerodynamic torque on the wing, allowing for a lighter structure. Boeing did this first on the B-47. It's a very clever thing to do, using the weight of the engines for something positive. Airbus copied it. The engine placement of the 'Jurassic' 737 is simply a matter of the engine being longer than the wing chord. They couldn't put it anywhere else. Also, placing the engine forward without a pylon would lead to heat issues on the wing - you don't want anything touching that hot exhaust. So the 737 wing was designed to handle the aerodynamic torque by itself, without counterweights. The plane is small and the weight penalty was probably not much. Fuel was cheap back then. The reason for the engine placement on the newer 737s is that the entire design is a kludge. By lining up the top of the cowling with the wing and squashing the lower part, they barely got the fan to fit, almost scraping on the runway. The only way to do this is to move the engine forward. Together with the shortness of modern fanjets, this places almost the entire engine forward of the wing, but not for the reason it was originally done. Boeing may have been able to lighten the wing structure a bit, I don't know. The alternative would have been to lengthen the undercarriage, but on the 737, that would amount to a complete redesign, might as start over clean. Incidentally, Boeing had an aircraft just like this, the wonderful 757, but the bean-counters killed it. Boeing is now reaping the rewards of decades of short-sighted accounting decisions. I wouldn't worry about them though, the military division can carry the wayward airliner group for a long time. Boeing didn't buy McD for their airliners. Every time I look at a 'fat-engine' 737 plowing down a runway, I wince. FOD must be a major problem that gets swept under the rug. How Boeing got away with such a mess is beyond me. They obviously have the FAA and NTSB in their pocket. As for the old thrust reversers being pointed at the fuselage, I can't imagine a good reason. I may have mis-remembered the part about the torque on the wing, or 'aerodynamic pitch moment'. It's been a long time. The discussions I find online only talk about straight wings, not swept. There are other reasons to hang the engines out front, the most important being to get clean undisturbed airflow, but also for flutter. And mounting the engines directly on the wings results in an overall lighter airframe. This gets pretty technical: agodemar.github.io/FlightMechanics4Pilots/mypages/pitching-moment/ At any rate, Boeing had good reasons for mounting the engines the way they did, even if my old brain is addled by covid. Engines are typically mounted below the wing for maintenance reasons. It was easier for ground crews, although modern engines are so huge that it is much less help today. The HondaJet mounts its tiny engines on pylons above the wing.

[@Tacobeo]

Where could I find materials to learn all of the 73’s wing stuff in the your comment, Sir? So fascinating

[@pythagorasaurusrex9853]

To answer your question at the end: Did Boeing have any problems with its new LEAP engine mounting (aka MAX)? Yes. A lot! Did Airbus have any problems with its new LEAP engine mounting (aka NEO)? No. Not that I know of any. That says it all.

[@tedstriker6743]

All current MAX aircraft have an ongoing and known issue with the engine anti-ice system! Left on too long in excess of five minutes the engine could fail and blow apart. The FAA has now required to redesign of the systems on the MAX 7 and 10 aircraft. Clearly, this says the FAA does not think the aircraft that are currently flying are safe however, they continue to allow them to fly. It’s only a matter of time before there is a major and accident involving them. The MAX needs to be grounded until they can redesign and fix all of these aircraft!

[@Dirk-van-den-Berg]

I am very glad you pointed out the differences in the engines that Airbus and Boeing put under their wings. The plane you fly (and I live directly under the approachroute to Schiphol runway 06) is one of the noisiest, the 737-8. The newer models are already quieter, but the difference in noiselevel is remarkable. The lowpitched noise that the engines on the 737-8 or 737-9 make is thunderous. Where as the newer engines are highpitched and less noisy, mostly on Airbus neo-planes. I love the RR Trent engines, with their high bypass high pitched sound. Especially on the 350 and the 380.

[@vasileracasan8767]

"It wasn't dangerous, it just needed MCAS to bring it into full regulatory compliance[....] to keep the authorities happy" So the plane without MCAS wasn't dangerous, it just wasn't compliant with the safety regulations. You might be contradicting yourself just a tad.

[@srccde]

It wasn't about safety regulations but about the common type rating. The aircraft would fly perfectly fine without MCAS but behave just slightly differently enough for pilots to require expensive retraining.

[@zanemumford8699]

I have followed you for some time now and have watched nearly all of your videos regarding the 737 and still I learned a few things from this video that were new to me. Thank you so much for continuing to produce high quality and informative content!!!

[@MentourNow]

Great to hear, thank you!

[@roberthenry9319]

Absolutely no one on the internet gives us aircraft and commercial information as detailed, informative, understandable and fun than Mentour. Cannot thank you enough.

[@Gavin-zp6nk]

To me, the Max is equivalent to a lifted Monte Carlo with 22’ spinning rims, so it’s no wonder there are design issues related to it.

[@TheN1Chris]

I am of the belief that the 737 MAX should have its own type rating. When a plane doesn’t behave like its predecessors, it needs to be treated a new design entirely with pilots specifically trained for it, not using a system as a crutch for poor design. It may not be “unstable” if we really want to split hairs here, but it behaves differently in the most critical stages of flight: Takeoff and Landing.

[@jb8331]

In a perfect world that's exactly what would happen, but the 737 Max was designed specifically for airlines who wanted to effortlessly transition their pilots from the older NG models to a newer, more fuel efficient plane. Creating a new type rating was unacceptable for low carrier airlines whose entire fleet consisted only of 737s, as well as other airlines who weren't interested in adding a new type to their existing fleet. Basically they wanted the same plane with lower costs, which is technically impossible due to the low profile of the 737. MCAS was basically a compromise allowing the FAA to certify the Max as a 737 despite the engines causing it to handle differently from a traditional 737.

[@vaggosm4232]

@@jb8331Yeah, Boeing wanted to skip 10 or more years of making, testing and certifying a new aeroplane. The cost would be gigantic. Human lives one the other hand, are expendable 🤔

[@ACPilot]

Well it doesn’t fly very differently, actially i hardly notice any difference when flying the MAX, compared to the NG, i also fly.

[@TheN1Chris]

@@ACPilot I feel like that's literally the whole point of MCAS. But we shouldn't be relying on crutches for poor design choices.

[@ACPilot]

@@TheN1Chris It is not a cruch. Other aircraft have something similar, just called something else, or embedet in another system.

[@dimitri1946]

Just flew in one of the 737 Max8's and really loved how the engines just barely clear the ground if the plane has any lateral rocking when landing.

[@WhystudySculpture]

Great job. Having spent practically all my life involved in airlines, flying, and aviation the misinformation passed thru reputable news sources is quite depressing. Keep up the good work !Set the record straight.

[@Ronlawhouston]

You should create a copy of the INOP shirt that says "Anti-ice 5 minutes"

[@TinLeadHammer]

When 737 MAX returned to service after being grounded for two years, its stab trim cutoff switches were not rewired to the NG configuration. As a consequence, in case of runaway trim, it is not possible to turn autopilot/STS/MCAS off and still use servos controlled with the buttons on the control wheel. It is much harder to recover the MAX compared to the NG if runaway trim happens.

[@roflchopter11]

The NG also fully disables the trim servos with the switches. The solution is to turn the cutout switched back to normal and yhr use the trim control. One of the 737 MAX incident pilots did that, but failed to set them back to cut out, resulting in the crash.

[@TinLeadHammer]

@@roflchopter11 No, and you would know it if you looked at the switches instead of recalling the runaway trim checklist, which instructs to turn both switches off. But on the NG the switches are different: one turns off autopilot/STS, another turns off electric trim servos. On the MAX both switches do the same thing and each of them turns off everything.

[@hakanevin8545]

That is why Ethiopian crash happened, right? Contrary to Lion Air pilots, they knew about MCAS, but still they could not recover the aircraft.

[@TinLeadHammer]

@@hakanevin8545 Yes, they could not recover, because the moment they turned electric trim back, MCAS would work against them, fast and relentless. And when they turned the switches off, they could not re-trim it manually, the other pilot pulling up did not help, but if he did not pull up, they would not have the altitude anyway to complete the "rollercoaster" maneuver, if they knew about it at all, because it was removed from the NG and MAX FCOM.

[@737MaxPilot]

@@TinLeadHammerno, because the captain failed to retard thrust after he followed the procedure, leading to a rapid and extreme over speed, and therefore the inability to manually change the stab trim. Poor airmanship caused that crash.

[@joesantora8855]

I'll try to dive in here. I build and fly competition R/C sailplanes and spend a lot of time setting up the CG and decalage. Moving the CG forward increased stability at the cost of efficiency. The tail (V or crux) must counter the forward load with downforce and that causes drag. It also increases the effective wing (the aerodynamic pivot) loading making the wing more likely to stall. I had initially thought that the Max thought it was about to stall and decided to gain speed by going nose down.

[@Tacobeo]

More in-depth technical videos like this, please, Petter

[@miokujou]

It's probably in Boeing's best interest to make the Max their final variant and make an all new aircraft to replace it. They can design it in a way where they can retrofit taller landing gears on it in the future to accomodate bigger more efficient engines and also to minimize the risk of tail strikes when they eventually stretch it out again for the 2nd and 3rd generation of the aircraft

[@wild_lee_coyote]

Boeing has anchored itself to the 737 and it is now pulling them under. Especially since management is more interested in stock buybacks and profit margins. They needed to bite the bullet and completely redesign the 737.

[@shanemshort]

I have never heard someone say centimeters like that and it makes me laugh.. keep it up

[@AsteroSSB]

Very sad to hear about Stefan's tumor, but Peter to you personally i send many thanks for introducing Stefan's channel to me. I found his persona instantly very pleasant and i am sure to enjoy his videos as i enjoy yours.

[@warriorson7979]

This is what happens when you gradually replace all the engineers in your management structures with financial people....😑😒😔

[@big_steve_o5129]

Maybe I'm the odd one out here, but I really enjoyed flying the DC-9/MD-8X/MD-9X/717 family of aircraft. I always found them to be smoother in flight and less affected by turbulence, the major negative being the noise level if you were seated in the rear, adjacent to the engines.

[@EfficientRVer]

I was fine with flying in the "A" seat of those, but I found the pressurization system to be kind of herky jerky, more often causing ear problems than any other airliner I flew often. And I did fly into Detroit in one, looking down at the wreckage of another one. It also had the least desirable seat on a commercial flight, the one in the rear which is a window seat without a window, because if the engine flies apart, that's where it is aimed. The only takeoff roll I experienced being rejected at high speed, was also on one. One engine wasn't developing full power, which is a pretty rare thing to take that long to figure out. For a year or two after the DC-9 Super 80 came out, every time I was on one, I hoped it didn't buckle and almost fold in half if we had a hard landing, like the one did when they were testing minimum landing distance over a 50ft obstacle. Having said all that, it seemed like a super solid plane for what it was, a real workhorse. And it was the only airliner I got to sit in the co-pilot's seat of during a flight delay. Ahhh, aviation before 9/11.

[@BriGuy1974]

The knocks against MD were really on the DC/MD-10 and MD-11, which had major problems that got ironed-out too late. MD had overpromised and underdelivered on those jets. But the DC-9 series (MD-80s, 90s, now 717s) were super high quality builds. The 2+3 seating configuration was my absolute favorite in the air. The rides on the MD-90/95 just couldn't be beat for quietness and power. Fortunately, the X-66A seems to be bringing a lot of these possibilities back to us. I hope it is a success.

[@grumpy3543]

Fun fact. The 737-100/200 and the DC-9 had the same engines and reversers. The DC-9 engines were mounted quite a bit higher on the tail and the reverser buckets didn’t need to be canted. Thereby saving the tail of the DC9 a lot of unsightly soot on the fuselage. They both would hit the ground though if you deployed them with the nose wheel off the ground. 9:31

[@teakettle100]

@mentournow Your thorough approach is appreciated (with so much other information by other sources about Max/MCAS being wrong). You’re correct that the airplane is NOT unstable. In pitch there’s 4 types of stability…2 static and 2 dynamic. Big airplanes don’t typically have any issues with dynamic stability (short and long period) and the 737 is no exception. The two types of STATIC stability are speed stability (typically expressed as pilot pitch force vs speed) and maneuvering stability (typically expressed as pilot pitch force vs g) . Your video talks a lot about speed stability and kinda mixes it up with maneuvering stability. But you’re close enough for most non-aero engineering viewers. You mix the “see-saw” (which is speed stab) with Fs/g (man stab) and then you throw in stall characteristics (which is a totally different topic). Anyway, you’re close. Fs/g was predicted (from wind tunnel studies prior to the max ever flying) to not clearly meeting regulatory requirements (worst case aft cg) and this resulted in MCAS being implemented into the design (with fairly limited authority). Once the test airplanes started flying is when the stall identification characteristics (a wholly different regulation in part 25) were found to not clearly meet the regs and this is when MCAS was expanded to include the low speed (stall) region, and the authority was essentially multiplied by a factor of about 4. Add in the fact that a fail-safe feature incorporated in the prior generations of 737’s (column cutout) was bypassed for MCAS activations (necessiststed by the fact that MCAS works when the column is way aft) and the setup for disaster was sealed. The real miss (and it was missed not by anyone rushing, or being pressured or any of the other populist reasons offered by the media) was in evaluating the design against another regulation…25.1309(b) which concerns failure case analysis. In this case a failure which produced a single erroneous high angle of attack input into all the systems which use AOA information.

[@NJBaars]

The Max responded to this video by dropping a wheel when this one aired….

[@TomekSw]

Better help gives away your personal data, they got fined millions for doing that

[@Xuzyy]

Geat video, correctly explaining the story without taking sides

[@OregonBacon]

Keep doing what you do, you should actually be a consultant to the airlines and manufacturers. Everything you mention is super solid and you have a dream team as well as a tone of other pilot paying attention. Perhaps they should buy a mug and listen up.

[@SimonWallwork]

During certification, to stall an a/c, the pilot has to keep pulling on the yoke. This is mandatory. Otherwise a pilot might stall the thing inadvertantly. In the MAX (without MCAS) it became 'stick light' during the stall- so not acceptable. MCAS was the fix-trimming the a/c nose down, so the pilot still had to pull. MCAS augmented the manoevering characteristics during the stall, thus the name.

[@MentourNow]

Exactly

[@737MaxPilot]

Pilots still have to pull. Even when MCAS activates, it’s a very subtle change in column force required. Coming from repeated, frequent experience.

[@user-md2cb8qc9s]

Yes, retire them because consumer confidence is on a downward spiral on the plane and is affecting the company too. Consider the Hindenburg. One horrible crash pretty much stopped LTA transport for a hundred years. Now even though airships are made that can not go up in a ball of flame, the collective memory has deemed them unsafe, so the industry remains sidelined. Perception is everything.

[@ExaltedDuck]

To help visualize/conceptualize the mass balance effect, think of darts or badminton... those projectiles have forward mass and far back drag/lift. They tend to fly very straight because that heavy nose pulls along the draggy tail. The more extreme the separation, the more a plane will resist changes in pitch. A plane with its center of lift/drag right at the center of mass will be the most maneuverable as possible since any applied pitch torque would align to the center of rotation (think of a socket directly on a ratchet vs. turning a crow's foot that's not in line with the ratchet). But when the center of mass is behind the center of lift/drag, the plane becomes inherently unstable. Any happenstance drift of the airframe off the prograde direction will be met with positive feedback from drag. That is, if noses up or down, aerodynamics will cause increasing force to continue further off vector. It would fly like a leaf or a flat sheet of paper.

[@joeking22]

Boeing Engineer 1: Hey I think I fixed the problems with the Max's engine displacement. Boeing Engineer 2: WOW, how did you fix it? Boeing Engineer 1: I added extra bolts to each engine. Boeing Engineer 2: Nice, where did you get the extra bolts from? Boeing Engineer 1: Ummmmmm!!!!

[@user-lf1su7ql6i]

Someone trying to wash something out