Dear forum members,

I don't want to start yet another B737MAX thread, but the recent terrible accidents in which the type was involved and the subsequent turmoil made me think about the transitions from earlier generations of the Boeing 737 to successive versions.

In the threads about the accidents and the grounding of the MAX, it is often said that the MCAS system was introduced to counteract the differences in center of gravity and aerodynamic properties that there are between the 737 NG and the 737 MAX. Because the MAX's LEAP engines are heavier than the NG's CFM56s and protrude further forward, the handling characteristics of the MAX would be much different from the previous NG versions and MCAS is said to be designed to compensate for that.

But when I compare the 'Classic' (300-400-500) series to the previous 'Jurassic' series (100-200), the differences look much bigger than from NG to MAX.
On the 100-200, the much smaller JT8Ds are litterally under the wing, but on the 300-400 series, the bigger CFM56's are for 90% in front of the wing.





Of course, devices like MCAS didn't exist in those days. How would this have been solved? I can image that a Classic will have had considerably different handling characteristics than a 100-200 series, with those larger engines much further forward. Why was this apparently not a problem, while it now is for the transition from NG to MAX? Or didn't the Classic have a common type rating with the Jurassic? Thanks!

Just speculating here, but the Jurassic was quite a different plane than the Classics. The Classics were probably designed with the engines in mind and their place/weight etc. The difference between the Next Generation and the Max are smaller, so I can imagine that this shift in weight will change the handling a bit. Don't think the Jurassic and Classic had the same type rating, the NG and Max do.

Ah well, all speculating on my part.

Dutchy wrote:

Just speculating here, but the Jurassic was quite a different plane than the Classics. The Classics were probably designed with the engines in mind and their place/weight etc. The difference between the Next Generation and the Max are smaller, so I can imagine that this shift in weight will change the handling a bit. Don't think the Jurassic and Classic had the same type rating, the NG and Max do.

Ah well, all speculating on my part.

The 737 type rating is a 737 type rating. You can still get a type rating to fly it using a 737-200 sim.

Great questions, and interesting thread. Hopefully this one stays on track and is civil. Looking forward to information on this.

DiamondFlyer wrote:

Dutchy wrote:

Just speculating here, but the Jurassic was quite a different plane than the Classics. The Classics were probably designed with the engines in mind and their place/weight etc. The difference between the Next Generation and the Max are smaller, so I can imagine that this shift in weight will change the handling a bit. Don't think the Jurassic and Classic had the same type rating, the NG and Max do.

Ah well, all speculating on my part.

The 737 type rating is a 737 type rating. You can still get a type rating to fly it using a 737-200 sim.

You can fly a Boeing 737NG with training on the 732?

How does this work? Reading in the press: that apparently the difference between the MAX and NG was so small that a two-hour tutorial was enough. How does that work with the difference between a Jurassic generation and a NG, the difference is quite substantial.

I thought there were different ratings for the Jurassics and the Classics? It seems strange to me if a Jurassic and Max have the same rating given they are very different in size and technology

The reason mcas wasn't required between the -200 and the classic is because the stab (in fact the entire empennage) was redesigned and had enough elevator authority to counteract the pitch up tendency with increased thrust.

A 737 type rating covers all models, but differences training is definitely required.

100-900 series of 737’s have one thing in common (among others) - no need for MCAS.
What bothers me most about the MAX is the need for MCAS to begin with.
Boeing has pushed the 737 through from the 100/200 series to a major redesign with the 300-600’s. And yet again with the NG.
All along making them more efficient, bigger and more powerful.
To compete with the gains of the NEO, Boeing has to push again with the 737’s engines to make them more powerful and therefore efficient.
The big problem with the same basic design that goes back to the 100 series from the mid-60’s is that low design compared to the Airbus A320.
Ever see the two parked next to each other? The 737 looks like a low-slung sports car compared to the Airbus.
And here is the problem. Those low wings require a lot of engineering to get more powerful and larger engines under them. Hence why the 300 series onwards had those flat nacelles.
We know Boeing can’t simply raise the landing gear to compensate. So what to do. By pushing those engines forward a little more AND making them more powerful at the same time you end up in a situation where the plane can become more easily unbalanced compared to all the previous 737’s
So now sensors and software compensate for this. MCAS wasn’t needed to compensate previously. And this bothers me somewhat - the need for MCAS to begin with.

When the MAX came out there was a fair amount of criticism here about another generation of 737’s instead of a clean and fresh design (797).
It seems Boeing was under pressure to compete with the NEO and therefore was forced to move ahead with the MAX.

Personally I think Boeing has made a few key mistakes-
1 - shutting down the 757 prematurely
2 - not getting a jump on a fresh design replacement for the 737. Had Boeing started this maybe 6 years ago, we’d have a 797 now instead of a 737 pushed to the max (haha) of its design abilities. Airlines could have picked from the 797 or the NG at this point.
3 - shutting down the 717 prematurely

Funny how airlines that have the 757 and 717 want to keep them as long as possible.

flybynight wrote:

Personally I think Boeing has made a few key mistakes-
1 - shutting down the 757 prematurely
2 - not getting a jump on a fresh design replacement for the 737. Had Boeing started this maybe 6 years ago, we’d have a 797 now instead of a 737 pushed to the max (haha) of its design abilities. Airlines could have picked from the 797 or the NG at this point.
3 - shutting down the 717 prematurely

If I remember correctly, Boeing was considering doing an all new narrowbody (797) as a response to A320NEO. But existing 737 airlines told Boeing they wanted an updated 737 sooner rather than a 797 later. So Boeing produced the 737MAX.

flybynight wrote:

Personally I think Boeing has made a few key mistakes-
1 - shutting down the 757 prematurely
2 - not getting a jump on a fresh design replacement for the 737. Had Boeing started this maybe 6 years ago, we’d have a 797 now instead of a 737 pushed to the max (haha) of its design abilities. Airlines could have picked from the 797 or the NG at this point.
3 - shutting down the 717 prematurely

Funny how airlines that have the 757 and 717 want to keep them as long as possible.

On Point 1. The market for the airplane had dried up, at the time of the decision to stop building it. Boeing made the right decision at the time.

Agree on Point 2. Boeing seems to have become an airplane assembly company, vs the development and engineering powerhouse they once were. Had they gotten on with the fresh narrow body product, maybe the A321N wouldn't be beating them so badly in that gauge.

Agree on Point 3. Boeing killed the MD-95/717 to protect the 736/737 matket share. The MD-95/717 was/is the more efficient product on routes and markets it's designed for. They wish they could have killed the CSeries/A220 for the same reasons.

Austin787 wrote:

flybynight wrote:

Personally I think Boeing has made a few key mistakes-
1 - shutting down the 757 prematurely
2 - not getting a jump on a fresh design replacement for the 737. Had Boeing started this maybe 6 years ago, we’d have a 797 now instead of a 737 pushed to the max (haha) of its design abilities. Airlines could have picked from the 797 or the NG at this point.
3 - shutting down the 717 prematurely

If I remember correctly, Boeing was considering doing an all new narrowbody (797) as a response to A320NEO. But existing 737 airlines told Boeing they wanted an updated 737 sooner rather than a 797 later. So Boeing produced the 737MAX.

That is fair enough, but the point being, Boeing should have started the 737 replacement 6+ years ago instead of being put into a defensive situation where they needed to produce the MAX in the first place.
After 50 years with 737 I think Boeing should have started the process a while back.

I enjoy flying on the 737 on a regular bases with AS, but at the end of the day it is still a 737 that can be tied back to a design from the same time Star Trek was originally on TV!
That’s before Neil Armstrong landed on the moon and Johnson was President of the US.

It's not clear to me whether the MAX flight control system modifications, including the MCAS, were driven by the desire to claim that there were no differences in the handling compared with the NG, or to address intrinsic problems of the aircraft. In other words, if Boeing had accepted the fact that the MAX would handle differently and some extra training was needed, would things have been different?

For example, I understand the issue of the aerodynamic effects of the larger and more forward nacelle at high AoA. But a nacelle in the end is an annular airfoil, and at least in principle it should not be impossible to design it so that it stalls a little earlier and does not contribute as much to a nose-up pitching moment of the entire aircraft. One could add the equivalent of a tiny spoiler on the outside of the nacelle to trip the boundary layer and promote separation.

flybynight wrote:

Austin787 wrote:

flybynight wrote:

Personally I think Boeing has made a few key mistakes-
1 - shutting down the 757 prematurely
2 - not getting a jump on a fresh design replacement for the 737. Had Boeing started this maybe 6 years ago, we’d have a 797 now instead of a 737 pushed to the max (haha) of its design abilities. Airlines could have picked from the 797 or the NG at this point.
3 - shutting down the 717 prematurely

If I remember correctly, Boeing was considering doing an all new narrowbody (797) as a response to A320NEO. But existing 737 airlines told Boeing they wanted an updated 737 sooner rather than a 797 later. So Boeing produced the 737MAX.

That is fair enough, but the point being, Boeing should have started the 737 replacement 6+ years ago instead of being put into a defensive situation where they needed to produce the MAX in the first place.
After 50 years with 737 I think Boeing should have started the process a while back.

I enjoy flying on the 737 on a regular bases with AS, but at the end of the day it is still a 737 that can be tied back to a design from the same time Star Trek was originally on TV!
That’s before Neil Armstrong landed on the moon and Johnson was President of the US.

If I remember correctly, Boeing thought a clean sheet design would not gain that much efficiency over a re-engined one, only 4% if I remember correctly. That was not as much as needed to warrant a 10bn investment and subsequently bigger pricetag to recoup the investment.

flybynight wrote:

Personally I think Boeing has made a few key mistakes-
1 - shutting down the 757 prematurely

They didn't shut it down prematurely. There was no market for the type once the A321-200 and 737-900ER entered service and could do most of the missions far more efficiently. By closing the 757 when the last orders stopped, they freed-up space to make thousands more 737NGs.

flybynight wrote:

2 - not getting a jump on a fresh design replacement for the 737. Had Boeing started this maybe 6 years ago, we’d have a 797 now instead of a 737 pushed to the max (haha) of its design abilities. Airlines could have picked from the 797 or the NG at this point.

Boeing was working on a 737 replacement at the same time they were working on a 747, 767 and 777 replacement. Market forces pushed the 767 replacement to the front and that became the 787.

Also, the biggest driver of a new narrowbody was a new engine and that was not available until the middle of the decade. Boeing pushed the 737 replacement as an option against the A320neo, but it really would have just been a Boeing version of the A320neo arriving years later and costing millions more a copy. So airlines went with the A320neo and Boeing created the MAX because they could bring it to market much sooner and much cheaper (for both them and the airlines).

flybynight wrote:

3 - shutting down the 717 prematurely

Like the 757, the market for the 717 had effectively dried-up. The 717-300 concept had minimal interest from airlines: not enough to justify bringing it to market.

flybynight wrote:

Funny how airlines that have the 757 and 717 want to keep them as long as possible.

The only airlines that still have large 757 fleets are the US3, And they still have them only because they are fully-amortized (so all they pay is operating costs) and they used them mostly on missions where the LCCs could not follow (US-Hawaii and TATL) so they could command high fares to cover the higher operating costs.

Now the LCCs have access to long-range 737MAX and A320neo and they're putting them on US-Hawaii and TATL markets and the US3 are rapidly doing the same to replace those non-competitive 757s. Within a decade the US3 757 fleet should all be flying for FedEx and UPS.

Same with the 717-200. Soon enough those will be replaced with A200s.

TurboJet707 wrote:

[...]Of course, devices like MCAS didn't exist in those days. How would this have been solved?[...]

The problem itself did not exist because it had been avoided in an old school way: mechanically. Undesired shiftings of the center of gravity to a critical point had often been avoided by adding a certain number of frames forward the wing and another certeain number after it when stretching the fuselage. Maybe the most spectacular mechanical solution had been Boeing's Queen of the Air: at a time, her tails contained super-heavy depreciated uranium. Those were the days when gasoline was a few pennies per gallon...

The 757 was definitely shut down prematurely


A NG version would be selling today and completely solve Boeing’s dilemma with the 797

Max Q wrote:

The 757 was definitely shut down prematurely. A NG version would be selling today and completely solve Boeing’s dilemma with the 797

I can't see it selling at all considering it would have been - and still be - stuck with RB211s and PW2000s hanging off the wings.

I mean Rolls is not willing to offer an engine for NMA so there was no way they would have made a bespoke 40-45K Trent for the 757NG. Pratt has been having issues with the GTF at 35K, much less the 45K a 757NG would have needed. And the most powerful CFM56 model (the -5C) would have needed another 10K of thrust.

Stitch wrote:

Max Q wrote:

The 757 was definitely shut down prematurely. A NG version would be selling today and completely solve Boeing’s dilemma with the 797

I can't see it selling at all considering it would have been - and still be - stuck with RB211s and PW2000s hanging off the wings.

I mean Rolls is not willing to offer an engine for NMA so there was no way they would have made a bespoke 40-45K Trent for the 757NG. Pratt has been having issues with the GTF at 35K, much less the 45K a 757NG would have needed. And the most powerful CFM56 model (the -5C) would have needed another 10K of thrust.

RR had plans for an updated lower burn engine If Boeing had launched the 757ERX, the design called for a cockpit update based on the 767-400 (which was tested and proven) a 2000 gallon stabilizer fuel tank, further use of composites and a revamped cabin


Conservative performance estimates had the range over 4500NM with further improvements planned to take it to 5000NM



Shutting down the 757 line was Boeing’s biggest commercial blunder in the history of the company



A NG or Max version would be extremely popular these days and more importantly completely eliminate the billions of dollars required to develop the NMA


Which I’m not convinced will work, no matter what technology you use a widebody, even a ‘small one’ will always cost more to operate than a narrowbody aircraft


Because Boeing gave up on the 757 Airbus is going to own this segment with
the perfectly placed A321LR

Thanks all for your responses!

Kilopond wrote:

The problem itself did not exist because it had been avoided in an old school way: mechanically. Undesired shiftings of the center of gravity to a critical point had often been avoided by adding a certain number of frames forward the wing and another certeain number after it when stretching the fuselage (...)

Stitch wrote:

Boeing was working on a 737 replacement at the same time they were working on a 747, 767 and 777 replacement. Market forces pushed the 767 replacement to the front and that became the 787.

Also, the biggest driver of a new narrowbody was a new engine and that was not available until the middle of the decade. Boeing pushed the 737 replacement as an option against the A320neo, but it really would have just been a Boeing version of the A320neo arriving years later and costing millions more a copy. So airlines went with the A320neo and Boeing created the MAX because they could bring it to market much sooner and much cheaper (for both them and the airlines).

If the Jurassic could 'smoothly' be changed into the Classic, with its new engines and their totally different placement, by redesigning the empennage and/or stretching the fuselage to get the CoG right again, one can wonder why Boeing didn't follow that route again when they decided to modernise the NG into the MAX?
Could we say that, due to pressure from the market and from the competition, Boeing didn't have time to develop a more structural solution to the MAX's changed CoG and aerodynamics? Like adding one or two more frames behind the wing and perhaps some aerodynamic improvement around the engine nacelles? Or am I thinking too simplistically here?

Maybe, if Boeing had got it right first time with the 787 and 748, we might have had a 797 around the corner now, or a MAX with more structural changes, rather than a correction system that is entirely in the software domain.

I am absolutely not trying to blame or flame Boeing, I'm just puzzled with hindsight by the apparently smooth transition from the first to the second generation 737, which involved some very important structural changes at the time, but resulted in a very reliable and safe plane. I think they did a great job back then.

Stitch wrote:

flybynight wrote:

Personally I think Boeing has made a few key mistakes-
1 - shutting down the 757 prematurely

They didn't shut it down prematurely. There was no market for the type once the A321-200 and 737-900ER entered service and could do most of the missions far more efficiently. By closing the 757 when the last orders stopped, they freed-up space to make thousands more 737NGs.

flybynight wrote:

2 - not getting a jump on a fresh design replacement for the 737. Had Boeing started this maybe 6 years ago, we’d have a 797 now instead of a 737 pushed to the max (haha) of its design abilities. Airlines could have picked from the 797 or the NG at this point.

Boeing was working on a 737 replacement at the same time they were working on a 747, 767 and 777 replacement. Market forces pushed the 767 replacement to the front and that became the 787.

Also, the biggest driver of a new narrowbody was a new engine and that was not available until the middle of the decade. Boeing pushed the 737 replacement as an option against the A320neo, but it really would have just been a Boeing version of the A320neo arriving years later and costing millions more a copy. So airlines went with the A320neo and Boeing created the MAX because they could bring it to market much sooner and much cheaper (for both them and the airlines).

flybynight wrote:

3 - shutting down the 717 prematurely

Like the 757, the market for the 717 had effectively dried-up. The 717-300 concept had minimal interest from airlines: not enough to justify bringing it to market.

flybynight wrote:

Funny how airlines that have the 757 and 717 want to keep them as long as possible.

The only airlines that still have large 757 fleets are the US3, And they still have them only because they are fully-amortized (so all they pay is operating costs) and they used them mostly on missions where the LCCs could not follow (US-Hawaii and TATL) so they could command high fares to cover the higher operating costs.

Now the LCCs have access to long-range 737MAX and A320neo and they're putting them on US-Hawaii and TATL markets and the US3 are rapidly doing the same to replace those non-competitive 757s. Within a decade the US3 757 fleet should all be flying for FedEx and UPS.

Same with the 717-200. Soon enough those will be replaced with A200s.

Your statement about the new Boeing NB being their version of the A320 NEO indicates that there hasn't been much progress in the NB segment since 1988 - something I keep harping about here but most seem to not understand.

Guess I'm not alone anymore...

Somehow, the fact nobody was ordering 757s is beyond comprehension. Great airplane, but in today’s world, too expensive.

Max Q wrote:

RR had plans for an updated lower burn engine If Boeing had launched the 757ERX, the design called for a cockpit update based on the 767-400 (which was tested and proven) a 2000 gallon stabilizer fuel tank, further use of composites and a revamped cabin. Conservative performance estimates had the range over 4500NM with further improvements planned to take it to 5000NM.

Never heard of it, so I did some digging. Boeing first started floating the idea in 1996 and it appears to have only drawn interest from US operators of the 757, Condor and British Airways. By the new decade, the Europeans had all dropped out so it was only being pitched to the US carriers (in parallel with the 767-400ERX) and of those, only Continental were willing to consider ordering it - and then only 10.

Of course, 9/11 happened and it was killed, but even if 9/11 had not happened, interest looked to be very luke-warm and therefore Boeing would have killed it, anyway, due to lack of interest. And that's a good thing because even with a slightly-better engine, it would not have survived the A321-200neoLR with the LEAP-X and GTF.

Max Q wrote:

Shutting down the 757 line was Boeing’s biggest commercial blunder in the history of the company.

It was one of their best. It allowed them to significantly increase 737 family production - a family that was very much in demand - and made them scores of billions.

Max Q wrote:

A NG or Max version would be extremely popular these days and more importantly completely eliminate the billions of dollars required to develop the NMA.

There is no LEAP-X or PW1000 series engine powerful enough for a 757MAX and even if Boeing had somehow been able to sell another 1000 757NG during the last 15 years (and they would not have gotten anywhere near close to that), the market would not have been large enough to justify the engineering to push the engine that far so neither company would have done it.

Max Q wrote:

Because Boeing gave up on the 757 Airbus is going to own this segment with the perfectly placed A321LR

Yes they will. But as of this time last year the frame had around 130 orders and all of them were from lessors - none of the carriers had ordered direct. I believe this will be a niche frame that will either see only a few hundred orders maximum, or if it does see a lot of orders, the majority of them will not be used on true "LR" missions where they are flying it at or near it's 4000nm design range (so they did not have to order an LR model).