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There's a difference between a new type-rating, which Max would have needed without MCAS, and being certified as a new type. You can have grandfathered-in certification as a derivative of an existing type, just certifying the changes, but still have those changes be extensive enough to need a new type certificate. Steam-gauge cockpits to glass cockpits as an example, the cockpit procedures are totally different, but you can still leverage the existing flying qualities parts of the certification.
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That's what every flight control system and stability augmentation system ever does. That's not a disaster, it's working as designed.
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It would actually make the instability problem worse. Moving it backwards a nudge and balancing that with a downforce from the tail would restore pitch stability but has other technical disadvantages such as loss of cruise efficiency, as well as needing significant mechanical redesign and re-certification.
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You'd want to go back if anything - move the centre of lift behind the centre of mass to generate a tail-up moment to counter the nose-up one from the engines, but that's the same amount of work as a new stretch, needs new aerodynamic and stress analyses, and might have other implications such as changing the behaviour of the aircraft in ground effect.
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And as we're discussing the F-16, let's remember its first flight was almost a disaster because of roll-instability/PIO caused by the FCS. The head of the flight controls team actually lost his job over that, at least until they realised they needed him to fix it. And what nearly happened to the F-16 did happen to the YF-22, and the Gripen (twice), yet a few software tweaks and all three types have been flying reliably for decades.
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This is interesting (linked from the other Times story), the head of the FAA feeling the need to publicly back his engineers against one of their managers over the speed of certification (even if he doesn't explicitly name him) doesn't give a good impression of the state of affairs in the agency.
https://www.nytimes.com/2019/11/15/business/boeing-faa-737-max.html?module=inline
OTOH what Boeing want to do isn't totally out there, it's just working in parallel. The issue is you would need to be explicit that any software or hardware change and the flight testing starts again. There's a difference between working in parallel during development, and working in parallel during certification.
https://www.nytimes.com/2019/11/15/business/boeing-faa-737-max.html?module=inline
OTOH what Boeing want to do isn't totally out there, it's just working in parallel. The issue is you would need to be explicit that any software or hardware change and the flight testing starts again. There's a difference between working in parallel during development, and working in parallel during certification.
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There are basically two issues here:
1) Are the flight qualities of the Max acceptable without MCAS? Obviously it must have been tested with MCAS disabled, but has it been assessed for suitability for low-end line pilots in day to day ops, versus a test pilot conducting a trial at altitude. I don't think I've seen an answer to that. No MCAS and a separate type rating doesn't fix the problem if line pilots can't handle the aircraft safely.
2) Does the change alter the behaviour of the aircraft systems in any way? Max without MCAS is not the same as Max with MCAS disabled. Are there any hidden dependencies that may only crop up from time to time? And some of the comments from the test programme suggest there may be, indeed that there may be problems completely separate from MCAS.
Everything else is politics and perception management (which are important, just not as important as actual safety).
I do have a lot of sympathy for his comment about code that's been changed and patched too many times, the logic flow becomes obscured, especially if people don't document their code adequately (BTDT, and cursed prior generations of coders to the outermost darkness).
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Yes, once the need for re-certification becomes inevitable, the main rationale for MCAS disappears. The main issue must be how the plane responds at high AoA. Is its instability manageable, or might some other system changes be needed, such as a more aggressive stick-pusher? Are there existing changes to the old system that will need to be rolled back? And there are at least three problems independent of MCAS, the inadequately polled dual AoA sensors, the hitherto unsuspected FCS nosedive failure mode and the forgotten jamming stabilizer trim jackscrews.
There must come a point when people say, "This dual-redundant system is 50 years old, designed to do just the basics for an inherently stable and manually flyable airframe. It is hopelessly inadequate for modern high-functionality, relaxed-stability requirements like the Max. Patching some kind of polling onto the umpteen existing patches and making MCAS take a back seat might sort of work but it's ridiculously high-risk. I mean, expecting a hasty software patch to arbitrate between two FCS which disagree and to decide which one gets to fly the plane, I ask you! It really does need to be triple-redundant with proper polling between the three. And now the AoA data has taken centre stage as flight-critical, we similarly need a third sensor. Now, what else needs triplicating?"
Right now, if I were head of the FAA, I'd be inviting Boeing's shareholders round for a friendly chat.
Thanks DWG & steelpillow for the clarification --
Another question, I used to work at Calgary International which is now almost totally surrounded by the city, and the airport was getting a lot of complaints from surrounding neighbourhoods about the noise. To counter that, the airport instructed the airlines when their aircraft were taking off, to have their aircraft at a 1000ft before the aircraft passed the airport property line at each end of the runways. I had noticed just how steep the aircraft flight path had to be to achieve that, and when this MCAS problem became apparent, I wondered how the Max operators were getting around it. Any ideas ?
Another question, I used to work at Calgary International which is now almost totally surrounded by the city, and the airport was getting a lot of complaints from surrounding neighbourhoods about the noise. To counter that, the airport instructed the airlines when their aircraft were taking off, to have their aircraft at a 1000ft before the aircraft passed the airport property line at each end of the runways. I had noticed just how steep the aircraft flight path had to be to achieve that, and when this MCAS problem became apparent, I wondered how the Max operators were getting around it. Any ideas ?
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Max can climb steeply enough without hitting the MCAS AoA threshold, one of the benefits of its more powerful engines. Things only went horribly wrong elsewhere when the AoA sensors got knocked about and gave false readings. It may seem counter-intuitive but a high rate of climb reduces the angle of attack as the air is effectively flowing down on the wing from above. For example if a plane is rising at a 5 deg angle and its nose is 7 deg in the air, the AoA is only 2 deg. But to stay in that state the plane needs powerful engines.
It happened here at London Heathrow, too. Set an airport down in open countryside. When urban developers come along, don't say "No, the planes make too much noise, go and build somewhere else", just grab the money. Then, when the new homebuyers complain about the noise, tell the airport it will have to make less noise. We do much the same thing on flood plains too, but the water is really bad at obeying regulations, not like airports at all.
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Yes. It seems that a visual check was not included in the routine maintenance schedule between flights. The plane swaps sensors for each flight. In both cases the unused one got damaged but the plane landed fine on the other one. Nobody noticed and when the plane took off again, it switched to the broken sensor.
In fact a similar thing had happened on an earlier LionAir flight, but by a stroke of luck an experienced Max pilot (who did know about MCAS) chanced to be a passenger, realised what was wrong and told the crew what to do. The fix for it was already being worked on when the fatal accidents happened.
thanks for the explanation.
Let me ask the following question...
The move from A320 to A320 Neo did just introduced a SECOND generation of A320 to a plane first flown in 1987.
The 737MAX by contrast was the FIFTH generation of 737 first flown in 1967 - from memory: 100/200, then 300-400-500, then 800NG, and then MAX.
So I ask the question, didn't simply the 737 basic airframe ran into its ultime limits ? Born in 1967, no shame, that was 42 years ago... the younger A320 just has more growth potential. No ?
for example, the 737 was born with JT8D, then in the 90's an engine change (on the 800 / NG - can't remember, CFM56 ?) led to a flattened bottom nacelle because the engines were already uncomfortably too large and close from the ground... and then that engine mount issue returned, with a vengeance, on the MAX, causing all the present horror.
And then it bring us back, to both aircraft eventual successors - a huge investment for both aircraft makers... they prefer stretching old designs, not a bad thing, but isn't the MAX a cautionary tale against stretching too much an old airframe ?
Just asking...
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I am not sure what you mean by "ultime". The 737 has undergone progressive modifications, with fuselage lengths (and therefore structural strength) varying widely. the NG introducing a new wing. The basic airframe design is as airworthy as it ever was. And airframes do live a lot longer than they used to. Once you have something optimal, you will not change it substantially unless major technology changes bring significant benefits. Yes an all-fibre replacement will probably follow some time, but the 787 Dreamliner is using up Boeing's capacity there and the airframe for the 737 replacement must wait in the queue.
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It's not solely the airframers. Both Boeing and Airbus were ready to go to next generation designs in the early part of this decade. The airlines said, "no, let's warm-over 737 and A320 one more time".
It's the civilian form of MRCA - Must Refurbish Canberra Again, but here it's Must Refurbish Commercial Aircraft Again
If I may... Indeed the 737 when through a lot of modifications with the successives generations, but apparently one important was not done : lengthening the LG.
As noted 737 started life with the JT8D which didn't needed a lot of ground clearance, so they could do with relatively short landing gear legs.
This is the main problem that caused the positioning of the big fan engine forward of wing LE as it is on the MAX, that in turn changed the way the plane flies in certain conditions ---> MCAS.
Now why wasn't it done ? Was it because a big modication of the LG geometry was considered too costly by Boeing , in term of manufacturing or because it would have changed the plane so much that again it would have needed another certification/pilot training to make it again too expensive to the airlines ?
Either ways, it just maybe shows that the basic 737 airframe as good as it is, may be too old to be modified again and again to be kept competitive with other airframes that were designed at the begining of the big fans engines era and thus with longer LG for more ground clearance.
As noted 737 started life with the JT8D which didn't needed a lot of ground clearance, so they could do with relatively short landing gear legs.
This is the main problem that caused the positioning of the big fan engine forward of wing LE as it is on the MAX, that in turn changed the way the plane flies in certain conditions ---> MCAS.
Now why wasn't it done ? Was it because a big modication of the LG geometry was considered too costly by Boeing , in term of manufacturing or because it would have changed the plane so much that again it would have needed another certification/pilot training to make it again too expensive to the airlines ?
Either ways, it just maybe shows that the basic 737 airframe as good as it is, may be too old to be modified again and again to be kept competitive with other airframes that were designed at the begining of the big fans engines era and thus with longer LG for more ground clearance.
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We can assume reasonably that if FAA had seen anything that would have pushed the 737 design pass its limit, they would not have certified it. And very probably Boeing won't have submitted it.
Then free to each blogger to make their point on something highly improbable...
Then free to each blogger to make their point on something highly improbable...
Do we ? I have no doubt about you, but who is "we" ?. Yet the MAX was submitted as it was and certified by the FAA despite the MCAS problem we now know of, and we have 346 victims.
And note, The 737 airframe is a good airframe, what I say is that keeping it completely aerodynamically sound by having a less problematic engine position would most likely have cost too much to be cost competitive.
it would have cost either too much to Boeing to redesign and manufacture that it would have impacted the price, or to the airlines due to the changes that would have needed new certification and pilots training/type cert to be made that would have impacted service cost, or both.
Thus the MAX problematic engine position and the resulting MCAS stuff that caused this mess.
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The nose gear on the Max is 8" longer, and even that caused a reworking of the forward avionics bay. Going bigger still would have meant relocating the entire bay IIRC.
There were further issues with the nose-gear for the Max 10, and that's another case of Boeing going for a more complex design to avoid introducing a different type rating.
https://www.geekwire.com/2018/boeing-737-max-10-landing-gear/
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I've been on a project going through FAA certification, and the FAA were basically making it up as they went along/taking guidance from other people as to what was significant. Now 777 was a bit special that way as the FAA hadn't certified an FBW FCS before, so were being guided by EASA as on the job training, but there was significant input from industry as well. There's room there for FAA to be manipulated, potentially even inadvertently, around less obvious problems.
We know we have a real life example of this with Max certification because we now know Boeing's Mark Forkner convinced FAA there was no reason to mention MCAS in the Max pilot's notes.
Thanks for the link and info Galgot and others.
Second quote is what I had in mind when typing my post, indeed.
Yes by "ultimate" I meant exactly that - that the 737 is getting a bit long on the tooth and the MAX might have been a bridge too far. That undercarriage issue with the MAX 10 is an interesting case in point. And the difficulty integrating a third generation of engine after the JT8D and CFM56 is interesting too.
And don't you think Airbus had an easier time refurbishing an A320 born with FBW and large fans CFM56 in 1987 - while Boeing had to struggle updating the 737, born in 1967, for the fifth time and third engine change ? I think Galgot made some good points, both 737 wing pylons and undercarriage reached their limits and indirectly this caused the MAX hassles - since the MCAS trick to make this 737 flies like the earlier 4 generations... ended in catastrophe.
Basically this fifth generation 737 was a little too different from the four earlier ones, and in order to avoid recertification of a "new" aicraft Boeing tried the MCAS trick that backfired catastrophically.
A case could be make that the 737 MAX was halfway between the older 737s and a truly new aircraft... and Boeing tried to get the best of both worlds, and the MCAS trick was born, and it backfired catastrophically.
But of course. With the "business model" trend of trying to make as much profit as possible with as less investment as possible, you'll sure have airlines cutting on costly maintenance. Like you'll have airlines asking for new models not requiring costly new certification/Pilots training.
Now if you are really serious about safety as a plane maker knowing that, you install that third AOA vane cause miss maintenance on one of just two installed could wreck your genius MCAS device that makes your new 737 fly exactly like an old 737 as clients demanded.
And knowing that as a regulator too, you should also impose a third AOA vane as a minimum.
For sure it's also airlines faults. Like big Boeing clients as SouthWest asking for as less possible changes on a new model yet more performance.
it's like if a guy has a 2cv, he goes to the manufacturer and ask "I would like you to install a 300cv engine in my 2cv, but I would like it to behave exactly like with the 2cv engine, cause learning to drive a 300cv car would cost me an arm".
So the manufacturer would either laugh, or he has that "economic culture" we talked about earlier, fully "understands" the client "business model" and tries to do it. And one day...
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Maybe worth clarifying that the Max was never to be a "new plane" in the sense of full type certification, the bare-bones version (without MCAS) would have been just a new variant with only the changed bits re-certified. This is no different to many variants of many production aircraft, the 737 included.
Even larger bays for longer legs), a shift in wing position, larger tailplane, triplex FCS and so on would not have needed a new type certificate, just another amendment.
However they would also have required a new type rating for the pilots. MCAS avoided both mechanical redesign and pilot re-rating.
Even larger bays for longer legs), a shift in wing position, larger tailplane, triplex FCS and so on would not have needed a new type certificate, just another amendment.
However they would also have required a new type rating for the pilots. MCAS avoided both mechanical redesign and pilot re-rating.
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Actually, neither of us used the right words (according to Wikipedia).
The type certificate applies to an aircraft type throughout its manufacturing life. If a significant variant is introduced it may require an associated amendment to the type certificate.
It is the pilot who is granted a type rating before he is allowed to operate that particular type. An amendment to a type certificate may or may not require the pilot to be re-rated for the new variant.
Thanks for the precisions. Indeed I meant changes in the certification that would have required new type rating for the pilots.
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Not really that significant in the run of things, it's basically delivery paperwork, but probably indicates the FAA is going to be going out of its way to be seen to be controlling Boeing on Max, not vice versa.
https://www.flightglobal.com/news/a...ax-airworthiness-certificate-issuance-462555/
https://www.flightglobal.com/news/a...ax-airworthiness-certificate-issuance-462555/
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"The Max 10 will be capable of seating up to 230 passengers and, with an auxiliary fuel tank, have range of 3,300nm (6,100km). That is 10 more seats and about 250nm less range than 737 Max 9, according to Boeing's figures.
Boeing holds orders for 531 Max 10s ... But those orders are a fraction of the 3,142 A321neos sold by Airbus. That aircraft can carry 244 passengers and has range of 4,000nm, according to Airbus. Further complicating Boeing's position, Airbus is developing a 4,700nm variant, the A321XLR.
"Boeing is being beaten by a factor of five," Teal Group analyst Richard Aboulafia says of the sales divergence. "This has become a serious problem [for Boeing]."
"
The article says Aboulafia speculates Boeing may abandon the New Mid-Market Airplane (NMA, 757 replacement) intended to compete in this sector and jump straight to the 737 replacement Future Single Aisle.
https://www.flightglobal.com/news/articles/picture-muted-boeing-unveils-737-max-10-462495/
Boeing holds orders for 531 Max 10s ... But those orders are a fraction of the 3,142 A321neos sold by Airbus. That aircraft can carry 244 passengers and has range of 4,000nm, according to Airbus. Further complicating Boeing's position, Airbus is developing a 4,700nm variant, the A321XLR.
"Boeing is being beaten by a factor of five," Teal Group analyst Richard Aboulafia says of the sales divergence. "This has become a serious problem [for Boeing]."
"
The article says Aboulafia speculates Boeing may abandon the New Mid-Market Airplane (NMA, 757 replacement) intended to compete in this sector and jump straight to the 737 replacement Future Single Aisle.
https://www.flightglobal.com/news/articles/picture-muted-boeing-unveils-737-max-10-462495/
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That's actually quite a draconian "We don't trust you any more" step. The FAA will be issuing a modified type certificate once the design changes are agreed, but it no longer trusts Boeing to administer that approval safely. It wants to personally check that each and every new plane has been modified to meet that new certification. Or at least, as you say, it wants to be seen to have withdrawn trust and to be controlling that process.
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Ironically for Boeing, the extra 9 inches ( ca 23 cm) ground clearance added by the new extending u/c could have been substituted for the upwards-and-forwards repositioning of the MAX engines in the first place, negating the need for MCAS. If all MAX models had had this u/c from Day One, the whole MCAS fiasco would never have happened! As it is, the MAX 10 must fly with a complicated and expensive millstone round its neck that it really does not need.
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It would make a ton of sense, really. The 737 airframe has run its course, 1967 is too far away in time even with 5 generations of improvements.
THIS
The A320 born in 1987 only has two generations so far. At some point a brand new airframe is needed. Boeing should trunk the 737MAX career and create as fast as possible a brand new replacement. Ideally designed to make the A320Neo looking like... the present 737Max.
"Thus passes the glory of the world"
Sic transit gloria mundi !
Presently applies to the 737, but works both ways: could apply to the A320Neo facing a 737 successor.
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To be honest, I'd rather see general speculation on future airliner developments being given their own topic elsewhere. This is about the 737 MAX.
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The 737 and A320 are inextricably linked, each development in one sparks a development in the other. You can't really understand the drivers in the development of one without looking at what's happening in parallel on the other. The Max 10 and A321 Neo being a very obvious case. Boeing keeps saying the Max has better economics than the Neo, but the airlines don't seem to agree, and that's going to drive a Boeing response at some time.
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Up to a point yes, but dragging in other variants of other models does get a bit off-topic. The MAX futures being verifiably checked out by Boeing, or being equally verifiably laid out for it by the competition, are quite enough here. Sorry, maybe I'm just getting a bit touchy over the various distractions that have happened on this thread in the past.
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