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Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

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Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#331

Post by mannykannot »

roelschroeven wrote: post #330
mannykannot wrote: post #177

Earlier quoted context omitted.

While the effect of pushing the nose down is an all-too observable effect, that its purpose is stall prevention is not directly observable. According to this article[1], the intended purpose was to restore the back-force needed to put the airplane in a stall, as the effect of the new engines was to make the control feel lighter at high AofA. The article also discusses the certification requirements with regard to acc…

One of the requirements for an airplane to receive a certification is that the pilot needs to put more and more pressure on the stick to achieve higher and higher angle of attack. If at some point the airplane starts to pitch to higher AoA without extra pressure from the pilot, that's a big no. Reason: otherwise it would be all too easy to inadvertently enter a stall condition. Boeing 737 MAX without MCAS violates th…

You have a point, though, from what I have read, I do not think the airplane would become unstable prior to the stall, merely less statically stable than its predecessors.

Boeing may be denying that MCAS has a stall prevention purpose only because to say so might put it in the critical systems category, requiring additional training. If so, this would apply as much to the fix as it does to the original version. To acknowledge that it has a stall prevention function might require an additional AofA sensor as well as additional training.

Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#332

Post by acqq »

manigandham wrote: post #317
acqq wrote: post #313

Earlier quoted context omitted.

> If it’s prohibited then how was it certified? Without the active MCAS the plane would have not been certified because the behavior of controls is then not inside of the prescribed limits.

I was talking about the the artificial behavior, so if it was certified then it was deemed allowable to have a stability control system maintain the necessary behavior. If the plane must have natural behavior, then MCAS would not allow it to be certified because it's artificial control.

Then I misunderstood your point, sorry.

Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#333

Post by rtkwe »

CaptainZapp wrote: post #233
erentz wrote: post #43

Earlier quoted context omitted.

> What is the endgame now for 737 MAX planes? The bugs will be addressed and they'll still fly. Airlines have no choice, there's a limited capacity in the world for airplane construction, several thousands of orders on the books for the 737 and 320 waiting to be filled. What can an airline do? They can cut back some orders but not all orders. > I'd honestly like to see the 737 MAX taken out of service and Boeing simp…

The bugs will be addressed and they'll still fly. Airlines have no choice, there's a limited capacity in the world for airplane construction, several thousands of orders on the books for the 737 and 320 waiting to be filled While true I don't think that airlines and regulators will go for it, if there's even the slightest risk of an additional accident. No matter what. And Boeing's "communcation strategy" after the i…

The simple solution would be to just remove MCAS and take the certification as a new plane. Boeing might have to eat the retraining costs but it's got to be better than eating the cost of the planes should they be deemed unfit for purpose and Boeing sued by every airline to recoup the costs of the now useless planes.

There's also the possible hardware fix to add an additional AoA sensor and change the software to limit the total deflection allowed + add a way to disable the MCAS only while keeping the electronic trim. The plane itself isn't irredeemable by a long shot though.

Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#334

Post by rtkwe »

7952 wrote: post #258
CydeWeys wrote: post #102

Earlier quoted context omitted.

You need three redundant sensors for safety-critical systems, so that if one fails you know which one is failing. Airbus has three AoA sensors (and three of others as well) on their planes for this reason. And it's worth pointing out that 737s already have two of these sensors, but don't use them both for MCAS (?!?!).

It is not certain that the 737 AOA ectually needs to be safety critical. You could just ignore the AOA data completely and divert. The pilot should still have sufficient instruments and training to land safely.

The problem is without MCAS and the AoA sensors that power it the 737MAX8 handles differently enough that it would be categorized as a different aircraft and require recertification of pilots. This happened because the 737 frame is relatively low to the ground and to increase fuel efficiency the only real option is a larger engine so Boeing pushed the engines up and forward. This changes the relation between the Center of Thrust and the Center of Mass on the plane causing it to have a tendency to pitch further up towards a stall when climbing so Boeing added the MCAS to make the new plane behave like the old plane by automatically performing the pitch down maneuver for the pilot.

This system is critical to the Max 8 remaining classified to 'fly the same' as the 50+ year old 737 air frame design so it's critical to pilots being certified to fly the plane at all. Ergo it is a critical system and needs more redundancy or the Max 8 needs to just have a new type certificate and pilots certified to fly it as well.

Boeing REALLY REALLY doesn't want to do this because it would require airlines to retrain their pilots to use it in their fleets making them less attractive to airlines. The whole fiasco is a confluence of 1) Cost of retraining pilots on a new air frame 2) need from airlines for a more efficient plane 3) the old 737 design not having any more room below the wing for a bigger engine (which is pretty much the main way we get more efficiency these days).

Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#335

Post by echelon »

anticensor wrote: post #329
na85 wrote: post #321

Earlier quoted context omitted.

The physical characteristics are not presented to you when booking your flight. By the time you've arrived at the airport and see the MAX at your gate, it's too late and you've already paid your fare.

You can DDG specifications of your plane by model number and nay, they have to be unique per revision.

I'm choosing

1. to make certain I don't board one of these machines by mistake. I will not risk my life over this egregious comedy.

2. to vote with my dollars and punish Boeing and businesses that do business with Boeing, especially if they refuse to remove these planes from their fleet.

What Boeing committed here is leagues beyond the recent emissions scandals. It's criminal and the perpetrators should be afraid of the coming justice. This should honestly be as close to a company-ending event as one could imagine. We shouldn't treat this lightly, slap on the wrist, business as usual. This must never happen again.

Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#336

Post by robben1234 »

TomVDB wrote: post #168
bushido wrote: post #112

Earlier quoted context omitted.

It seems like this is becoming a concern now - per: https://www.cnbc.com/2019/05/07/barclays-downgrades-boeing-s... The primary reason for the downgrade being: Barclays’ survey of airline passengers says many people will avoid the 737 Max “for an extended period” once the aircraft is flying again.

Here’s my thought experiment on that: if I booked a flight to my vacation destination and, at the last moment, I discovered that I’d be flying in a 737 MAX, would I cancel my trip or pay a considerable amount of moment to get all our tickets changed? I very likely would not. Would you? Would others? It’s one thing to answer a question of a pollster, it’s another to take concrete action.

there's a lot of services to look up what aircraft is typically flying the route for the airline you're buying tickets for. Or even simpler route: look up the fleet page before booking.

Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#337

Post by robben1234 »

bushido wrote: post #276
gmueckl wrote: post #250

Earlier quoted context omitted.

You are not guaranteed to fly on the model of airplane stated when you buy the ticket. This guarantee would be highly impractical because the airline would only have a limited ability to supply a replacement plane when the scheduled one is unavailable. So if push comes to shove, airlines will stop telling you what model of airplane they plan to use at all.

And we – those of us concerned and those who like voting with our feet – will stop using airlines with 737 max aircrafts in their fleet.

Considering how many airlines have max in their fleet it's not a viable tactic

Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#338

Post by foldr »

davidf18 wrote: post #287
kuzehanka wrote: post #182

Earlier quoted context omitted.

So much ignorance and misinformation about this issue even on HN. The parent comment and entire thread is 100% correct. There is nothing inherently unstable or unsafe about the MAX 8. It has a pitch-up characteristic that's mild compared to some other commercial jets like the 757. The only reason MCAS was put on that plane was to allow the MAX 8 to share a type rating with the rest of the 737 family, to make it so th…

The 737-MAX with the larger engines turned the statically stable airframe into one that must use computers (eg MCAS) to make it dynamically stable which is a technique used on modern fighter jets but to my knowledge has never been applied to a passenger aircraft. In this plane which is not "fly-by-wire" the pilots are part of the safety loop and are given a certain short amount of time to respond to an emergency. Tro…

>The 737-MAX with the larger engines turned the statically stable airframe into one that must use computers (eg MCAS) to make it dynamically stable which is a technique used on modern fighter jets but to my knowledge has never been applied to a passenger aircraft.

This is completely false. The 737 MAX does not have relaxed static stability in the manner of a fighter jet. It just has different handling characteristics than earlier 737s at high angles of attack -- a region of the flight envelope that the pilot should never take the plane into in the first place.

Fighter jets of the kind you're referring to require continuous and precise adjustments of the flight control surfaces merely to avoid departing from controlled flight. This is absolutely not the case for the 737 MAX.

Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#339

Post by bronson »

mveety wrote: post #285
bronson wrote: post #281

Earlier quoted context omitted.

That’s the whole point: the MCAS was supposed to be cheaper/easier for the airlines than new training.

You wouldn’t be retrained to ignore cues from your senses and trust your instruments. That training happens when you’re young and getting your IFR ticket.

I'm just pointing out that "they just need to be trained for the plane's behavior" isn't on the table for the MAX-8. The contracts said it would have the same type rating, and therefore the MCAS, for better or for worse.

I'm not quite sure how that is related to beginner flight lessons. (?)

Re: Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS

#340

Post by CydeWeys »

skybrian wrote: post #320
CydeWeys wrote: post #133

Earlier quoted context omitted.

There were "only" two instances (which killed >300 people) before the plane was yanked from the air entirely. That means that, roughly speaking, it was only going to happen in two countries at all, or one really unlucky country. So there's no use in pointing out that it didn't happen in many more countries, because that would have required dozens more accidents with tens of thousands of deaths, which was simply never…

You're explaining my own reasoning and then telling me how I'm wrong. Talking about countries is just another way of saying that the plane was flying in many places all over the world and the risk of accident, despite these horrible accidents, was never very high. As you say, would never happen.

The risk of accident was very high relative to other airliners, by more than an entire order of magnitude. I'm still not sure what point you're trying to make here.
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