Author Topic: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'  (Read 77000 times)

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Online KL27x

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1150 on: October 21, 2019, 10:14:02 pm »
^That's another way of saying "unstable."
Unstable doesn't necessarily mean the plane can't be flown without electronic aid, requiring 50 corrections per second. Instability can be slow/gradual.

Quote
The airplane still has positive aerodynamic stability even with MCAS disabled.
The MAX is unstable at higher AOA. It will fly just fine, as long as the pilot keeps one eye on his pitch/AOA while doing w/e else he has to do. When things go wrong, you don't want to have to juggle so many things, and it's during takeoff and landing that you generally have things going wrong and are flying at a high AOA. It would also come into play in bad weather with shifting up/down drafts.

Test pilots complained for reasons. No matter how you want to word it, the plane doesn't behave as well after the modification. "Requiring more corrective force" sounds benign, but the plane can even run out of elevator range (no matter how hard he presses on the stick? Still not enough!) before the pilot realizes it, which is what MCAS is for. MCAS adjusts the stabilizer to get the elevators back into range for condition, but then the hydraulics can become the weak link. The elevator didn't need to do as much in the original design. It didn't have this additional nose up force that appears and gets even stronger at higher AOA.

Ideally, horizontal stabilizer adjustment would be for convenience. It was never meant to be a main maneuvering surface. Once adjusted, the plane should be able to fly to its limits without having to touch it, again. For the MAX, this is apparently not the case. 
« Last Edit: October 21, 2019, 10:37:08 pm by KL27x »
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1151 on: October 21, 2019, 10:59:03 pm »
"Instability" might be the wrong word for it - the nacelle's lift and mounting the engine in front of the wing, ahead of the plane's center of gravity -  a positive feedback loop leading to a stall. How bad is it?

Some team at Boeing was in charge of MCAS, identifying the need for it, flew the plane with those settings and changes, and put that behavior into the flight sim, as well as the transgressions.
 

Online sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1152 on: October 21, 2019, 11:17:13 pm »
The horizontal stab trim is not a “merely for convenience” flight control in an airliner, but is rather a control surface that is trimmed for each substantial airspeed change. (It’s the “raar-raar-raar” spinning crank sound that you hear periodically on every approach as the aircraft slows. You can also sometimes hear it on takeoff and climb out, but there other noises sometimes dominate.)
 

Online sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1153 on: October 21, 2019, 11:26:34 pm »
^That's another way of saying "unstable."
No, it’s not.

Aerodynamic stability has a defined meaning.

At most, it’s insufficiently positive stable, but it still exhibits positive stability (does not go neutral or negatively stable) throughout its flight envelope.

Quote
The airplane still has positive aerodynamic stability even with MCAS disabled.
The MAX is unstable at higher AOA.
No, it’s not. https://www.quora.com/Is-the-Boeing-737-MAX-aerodynamically-unstable-I-have-read-that-the-new-heavier-and-higher-mounted-engines-have-changed-its-center-of-gravity/answer/Alan-Dicey
 

Online KL27x

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1154 on: October 22, 2019, 12:27:10 am »
Apologies for stating opinion like fact. "Lower margin of stability," per the link. But still stable. And with the suggestion that it is perfectly airworthy, EXCEPT that it doesn't meet original cert? Ok, that sounds reasonable.

Per link, the higher the AOA, the more force the pilot has to exert in the original 737 (and is the goal in all planes). But in the MAX the force decreases. According to him, it doesn't increase less. It decreases from the force required at a more moderate AOA.

Unless the pilot has freak proprioception of large muscle groups, he can't tell the exact location of the yoke so much as how much force he is putting on it. In turbulence or extreme corrective maneuvering, it might even be hard to feel if/when the yoke is (net) moving. So while the plane might still be "aerodynamically stable," this is obviously undesirable for any plane, even if it were a new design. IMO.
« Last Edit: October 22, 2019, 12:55:06 am by KL27x »
 

Online BravoV

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1155 on: October 22, 2019, 08:46:03 am »
Imo, up to this stage, the only possible to fly is thru political maneuvers and backup by politicians, of course, compromises included ... nasty.  >:D

Unless Boeing turning into non profit organization.  :-DD

You have to factor in Trump's new tariffs on Airbus too, with it's consequential knock on effect on Scotch Whisky exports (Huh?).

https://www.bbc.co.uk/news/uk-scotland-scotland-business-49915034

Afraid those are just precursors, more are coming like a carpet bombing the whole Europe.

Not sure bout you Brits though, assuming once you're detached from EU as in Brexit, the bargaining power will not be as strong as EU as the whole, like below "opinionated" column ...

Read thoroughly here -> China tariff deal was easy compared to the EU’s bazooka-proof trade walls

Ok, enough off topics.  ::)
« Last Edit: October 22, 2019, 08:51:20 am by BravoV »
 

Offline dzseki

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Offline SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1157 on: October 22, 2019, 01:23:54 pm »
I won't discuss the merits of tariffs or lack thereof (another topic entirely), but I just think, given the whole context, that it actually won't help Boeing whatsoever. It just conveys the idea that the only way to save Boeing now is to artificially help it through State meddling. Not something most Americans are fond of, AFAIK.
 

Offline SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1158 on: October 22, 2019, 03:10:46 pm »
Actually the reason for the Airbus tariffs don't have to do anything with the 737Max, seriously, but with EU subsidies.

I beg to differ. It has everything to do with it IMO, on several levels.

First, it's obvious that it comes from Boeing difficulties, which ARE related (even though not only, I admit) to the 737 MAX debacle.
Second, the whole history of the 737 MAX itself mainly comes from the harsh competition with Airbus. Had Airbus not threatened Boeing as it does, the 737 MAX would never have seen the light.
What Boeing had done to counter Airbus on a significant market, namely the 737 MAX, has become a curse: worse than the previous state of things. So for the time being, and until things get ironed out, they are worse off than they were before.

The subsidies is just a pretext. As you just said, Boeing has been getting subsidies in various forms for decades. The US economic model may be a bit different, but the amounts, I'm not sure. I'd even venture that Boeing may have gotten more public money than Airbus from the start, but this is just a guess (don't have the figures). Just saying - this is all a pretext to try and save Boeing IMO. Sure it also comes from a general "economic war", but with a very concrete basis here.
« Last Edit: October 22, 2019, 03:14:26 pm by SiliconWizard »
 

Offline SilverSolder

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1159 on: October 22, 2019, 03:58:30 pm »

The elephant in the room (re. tariffs) is that the USA has an unsustainable trade deficit  -  and has only recently woken up to the need for import tariffs to help manage the problem.  Now that they have been implemented, we can be pretty confident that they are never going away again...
 

Offline SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1160 on: October 22, 2019, 04:15:26 pm »
Oh, yeah. But since I don't really buy the "recently woken up", the interesting part is understanding why the trade deficit is suddenly becoming a problem.
 

Offline SilverSolder

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1161 on: October 22, 2019, 05:12:38 pm »

USA probably hasn't "suddenly woken up" to the trade deficit,  it is more likely that (especially in the wake of the financial crisis of '07) the powers that be have given up on the previous model that economic growth would solve this problem, so a change of strategy was called for.  That which cannot possibly keep going on, won't...  eventually.

Most countries / trading blocs use tariffs to manage financial flows, the USA is a laggard here and is only really beginning to do what everyone else does (probably for pretty much the same reasons).

 

Offline Rick Law

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1162 on: October 22, 2019, 05:21:11 pm »
In terms of keeping 737Max in the air, or not...

One significant factor that had not been mentioned is pilot certification.  A pilot certified to fly on a certain variant needs to stay certified and to do so the pilot needs fly-time on the plane.  Not so long ago, there was a news item titled something like "737 Max flies again, but...".  It was an FAA authorized flight for pilot certification or to retain the pilot certification.  I don't recall exactly, but there were other special circumstances.  (If I recalled correctly) They needed to have at least some pilots capable of moving the grounded MAX around.

With 737-Max grounded for so long, I suspect many more pilots may need to fly a bit again to remain certified.  Whether there is an increasing pilot certification flights granted may be the indicator if 737-MAX is staying alive or heading to the grave yard.

I am in the school of thinking 737-MAX will stay alive rather than left dead.
 

Online KL27x

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1163 on: October 22, 2019, 05:44:40 pm »
Seems like if the plane is stable and perfectly safe (just different) without MCAS, then the worst case would be remove MCAS and recertify as a new airframe?

I think it costs less than 8 billion dollars, but maybe I'm wrong. With all the grounded planes and customer recompensation accumulating, you would think recert would be peanuts. Unless MCAS is necessary to make the plane safe.
« Last Edit: October 22, 2019, 05:59:09 pm by KL27x »
 

Offline Rick Law

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1164 on: October 22, 2019, 05:49:01 pm »

USA probably hasn't "suddenly woken up" to the trade deficit,  it is more likely that (especially in the wake of the financial crisis of '07) the powers that be have given up on the previous model that economic growth would solve this problem, so a change of strategy was called for.  That which cannot possibly keep going on, won't...  eventually.

Most countries / trading blocs use tariffs to manage financial flows, the USA is a laggard here and is only really beginning to do what everyone else does (probably for pretty much the same reasons).

In my view, "Suddenly woken up" is an appropriate description.  Bush II was preoccupied with 9/11 and the military actions after.  Obama was preoccupied with "fundamentally changing America".  So no one was caring about the trade deficit or the resulting joblessness.  Most in the political world or journalism world did not expect a Trump victory.  The pressure that was building up was missed by folks.   So it appears sudden to many or even most.

Frankly, it is not surprising that those with a job would not see the trade deficit and the resulting joblessness being an issue.  They go on with their lives thinking all is well, and I am sure it was for them.  The ones in affected occupations would be largely invisible to the job-holders.  Exception is the mail-delivery guys.  About mid-way into Obama's second term, I was friendly with my former mail-delivery guy who is also former US Marine.  He told me one in four households (on his route) were receiving unemployment benefit checks.
« Last Edit: October 22, 2019, 06:02:20 pm by Rick Law »
 

Online sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1165 on: October 22, 2019, 06:28:22 pm »
Seems like if the plane is stable and perfectly safe (just different) without MCAS, then the worst case would be remove MCAS and recertify as a new airframe?

I think it costs less than 8 billion dollars, but maybe I'm wrong. With all the grounded planes and customer recompensation accumulating, you would think recert would be peanuts. Unless MCAS is necessary to make the plane safe.
MCAS is necessary to meet the certification requirements under Part 25. I provided the link to the specific law above.

I don't think it's "perfectly safe" without MCAS; I do think that MCAS is an appropriate fix to ensure compliance with Part 25 rules.
 

Offline SilverSolder

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1166 on: October 22, 2019, 06:32:23 pm »

USA probably hasn't "suddenly woken up" to the trade deficit,  it is more likely that (especially in the wake of the financial crisis of '07) the powers that be have given up on the previous model that economic growth would solve this problem, so a change of strategy was called for.  That which cannot possibly keep going on, won't...  eventually.

Most countries / trading blocs use tariffs to manage financial flows, the USA is a laggard here and is only really beginning to do what everyone else does (probably for pretty much the same reasons).

In my view, "Suddenly woken up" is an appropriate description.  Bush II was preoccupied with 9/11 and the military actions after.  Obama was preoccupied with "fundamentally changing America".  So no one was caring about the trade deficit or the resulting joblessness.  Most in the political world or journalism world did not expect a Trump victory.  The pressure that was building up was missed by folks.   So it appears sudden to many or even most.

Frankly, it is not surprising that those with a job would not see the trade deficit and the resulting joblessness being an issue.  They go on with their lives thinking all is well, and I am sure it was for them.  The ones in affected occupations would be largely invisible to the job-holders.  Exception is the mail-delivery guys.  About mid-way into Obama's second term, I was friendly with my former mail-delivery guy who is also former US Marine.  He told me one in four households (on his route) were receiving unemployment benefit checks.

Before the 2007 financial crisis, the growth model in the USA (and to a significant extent, also the UK) was based on selling houses to each other at ever increasing prices, while taking out loans based on property valuations to spend on consumption / import.  That whole house of cards collapsed, as we know, and there is much less money to go round today as a result.  This gave us Trump in the USA, and Brexit in the UK.

Getting Boeing "fixed" is a part of the cure, in my view.  Getting back to a strong focus on "making real things" and "making them good" is a time honoured principle that beats financial voodoo in the long run.  (See Japan/Germany today, and US/UK in the past)
 
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Online KL27x

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1167 on: October 22, 2019, 07:10:52 pm »
Sokoloff:
So the Boeing is aerodynamically stable, but it does not demonstrate longitudinal stability?

And it is allowed to be fixed through electronic chicanery? Maybe if they put some rubber bands on the stick in just the right spots, it would also pass? :)
Quote
14 CFR § 25.175 - Demonstration of static longitudinal stability.
CFR

Everything I had read, prior, suggested that the Beoing needed MCAS ONLY so it would be "grandfathered in" under the original 737 cert. This sounds like it might be way more serious (which is what I suspect?).
« Last Edit: October 22, 2019, 07:45:11 pm by KL27x »
 

Online sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1168 on: October 22, 2019, 07:23:39 pm »
 :palm: It is aerodynamically stable (which, when unqualified, typically means "longitudinally stable", being one of three axes of stability and roll and yaw stability are rarely the concern), in the sense that it exhibits positive stability (as contrasted with the alternative adjectives: neutral or negative).

It does not demonstrate longitudinal stability consistent with that required by that certification part, which requires specific performance in order to demonstrate safe, predictable control forces. The fix is electronic control of a (slow-moving) mechanical control surface to meet certification requirements.

I'm not sure what's confusing. The airplane is stable. It's not stable "enough" for certification. Properly implemented MCAS is a perfectly good fix.
 

Online sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1169 on: October 22, 2019, 07:30:48 pm »
The identically designed Max would have required MCAS (or another fix) to meet certification requirements.

MCAS may have been designed the precise way that it was in order to qualify on the existing A16WE type certificate, but some fix (almost surely an aerodynamic one, whether MCAS or other) would be required to be certified under part 25 in any event.
 

Online KL27x

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1170 on: October 22, 2019, 07:39:19 pm »
^Thanks, really. Your post is covering concepts that are hard to convey in the readers digest or popular news.

So the MAX, even if it were certified as a new plane not connected to the 737-100, would not pass (without MCAS).

So as long as a plane is slightly positively stable, the airframe is ok? We can then use electronics to make it feel/behave MORE stable, longitudinally or otherwise, to the pilot, in order to meet the more stringent stability requirements. But we can't (with passenger planes) cross into neutral or negative  aerodynamic stability and go fixing that with computers?

BTW, I edited my previous post while you were posting yours. I'll go back and put it back to how it was. Just added a few words.
« Last Edit: October 22, 2019, 07:44:48 pm by KL27x »
 

Offline Kleinstein

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1171 on: October 22, 2019, 07:51:46 pm »
Seems like if the plane is stable and perfectly safe (just different) without MCAS, then the worst case would be remove MCAS and recertify as a new airframe?

I think it costs less than 8 billion dollars, but maybe I'm wrong. With all the grounded planes and customer recompensation accumulating, you would think recert would be peanuts. Unless MCAS is necessary to make the plane safe.

Besides the MCAS problem, they found other problems with the control software. So they will have to do a fix if the system anyway. Fixing MCAS may very well be the easier part.  Getting a complete new certification would need it to meat newer standards and also a lot of time. It is the delays that make the process expensive. Not the maybe 10 man-years for the specialists to rewrite the code - that is peanuts.

The usual planes are stable only for a limited AOA range. The changes to the airframe reduced the stable range - not sure if too much, but at least too much to get the same flight certificate. 

If turning off MCAS would be the remedy to handle a single faulty sensor - the plane should be safe without and the pilots must be able to fly it without MCAS.  So I can't follow the argument that an unreliable MCAS could bring the plane to the same type class.  It is more like making the system more complicated needing extra training.
 

Online sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1172 on: October 22, 2019, 08:56:26 pm »
^Thanks, really. Your post is covering concepts that are hard to convey in the readers digest or popular news.
Thanks; that line means a lot. I have to admit I was getting a little frustrated at times during our exchange, but I tried to keep it civil and factual, because there's an awful lot of misinformation out there and decoding aviation speak isn't always easy (especially if the goal of many journalists is fomenting outrages and harvesting clicks). Boeing's not blameless here for sure, but neither do I think they acted like total idiots.
So the MAX, even if it were certified as a new plane not connected to the 737-100, would not pass (without MCAS).
100% right if they are constrained to keep the landing gear and wing of the 737.
But, if you look at it differently, if they were willing to go for a from-scratch certification, they would likely have created taller landing gear, providing for more underwing space to hang the larger engines farther back, moving the center of thrust rearward and center of pressure slightly rearward. It's possible that they might have managed to get the pilot type rating to crossover even without the airplane being built on the same type certificate. (The 757 and 767 are built on A2NM and A1NM TCDS, respectively, but share a common type rating: "B-757, B-767".)
All of that is fairly academic though as the 757 and 767 are the only airplanes to share a common type rating, it's not very likely that Southwest and the like would buy a 737-Max class airplane that wasn't on the A16WE TCDS, and such a 737 would probably look an awful lot like the 757, which Boeing already has...
So as long as a plane is slightly positively stable, the airframe is ok? We can then use electronics to make it feel/behave MORE stable, longitudinally or otherwise, to the pilot, in order to meet the more stringent stability requirements. But we can't (with passenger planes) cross into neutral or negative  aerodynamic stability and go fixing that with computers?
I don't think there's anything to directly prevent the certification of an inherently unstable airplane with sufficient fly-by-wire mods to make it behave stably. Such fly-by-wire mods (and the associated power sources) would then become subject to mitigation against Catastrophic event severity, meaning you'd have to reduce the projected frequency of occurrence of such a failure to lower than 1 in 109 (1 [US] billion) flight hours. In practice, because there's no great advantage to making a passenger airliner unstable, airliners are stable inherently and have minor mods here and there to tweak performance and handling. Military aircraft which are inherently unstable rely on electronic controls and ejection seats as the ultimate backstop. They're also accepting of some amount of fatalities if that prevents greater fatalities in usage.

The airplane is certified as a system. That system must pass all certification requirements while everything is working as designed.

It must also have analysis done to consider the effects of degraded operation as various systems are inoperative. The effect of an MCAS system failure was judged (IMO reasonably) to be "hazardous", one level lower than catastrophic. This requires failure modes to exhibit themselves fewer than 1 in 10,000,000 flight hours (1 in 107 hours). Hazardous is characterized by a "Large reduction in safety margin or functional capability."

Boeing is going to wear a lot of this. It turns out that their analysis of frequency of failure was very likely wrong. It turns out that crews didn't react quickly and appropriately to the presentation of the MCAS fault. (NB: the guidance document provides a reminder: "Crew physical distress/excessive workload such that operators cannot be relied upon to perform required tasks accurately or completely") It turns out that the system was delivered with a higher control authority than originally contemplated (however that would still likely only result in a "hazardous" categorization). It turns out that crews could trigger multiple cyclic activations of MCAS, further increasing the authority of the stabilizer.

I have a certain amount of sympathy for Boeing engineers here. They screwed up, but I'm not nearly as convinced it was part of a diabolical scheme to separate airlines from their money and ship an unsafe product, but rather a drive to push a longer-range, more economical aircraft into a crowded market.

Ref - https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/risk_management/ss_handbook/media/chap3_1200.pdf
 
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Offline SilverSolder

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1173 on: October 22, 2019, 11:04:06 pm »

[the Max fail was the result of...] a drive to push a longer-range, more economical aircraft into a crowded market.


It seems plausible that this is the reason, when all is said and done.   But it is not a good reason...  are there ever any commercial projects that are not under time pressure?

 

Online sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1174 on: October 22, 2019, 11:21:25 pm »
They're under economic pressure to compete. It's not like stretching type certificates for derivative models is a novel thing or Boeing-specific.
The 737-900 is leagues different from the 737-100.
The Airbus A318, A319, A320, and A321 are all built on a common type certificate (EASA.A.064) and I count 47 individual models/variants of airplanes built on that type certificate.
 
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