> The engine mounting certainly does not make the plane unsafe.
I don't think this is a very...'precise' statement. what is "safe" in the context of aviation? If you had no MCAS, then this plane has a very bad propensity to stall. I hope we can both agree that's an unsafe airplane. You can't just say "don't do that [pull up too much] and then you're fine". The aircraft "wants" to pitch up too high and stall, which predicated the MCAS system itself. So to me, yeah the engine mounting (in and of itself) makes this plane quite unsafe.
Now, with a properly functioning MCAS it may be "safe", but when the MCAS is itself another point of failure, my opinion is that the aircraft is only safe on paper, while in practice it's just got too many hacks and kludges for it to be practically safe for the millions of safe flight hours that these things are expect to deliver.
No, it did not “have a bad propensity to stall”. That’s a very imprecise statement in the first place but if you take it to mean, it would try to stall during normal flight conditions, it’s definitely false.
Airbus aircraft are “safe” despite the fact that dual conflicting pilot input is averaged without stick feedback (see the Airfrance flight from Brazil). If electronics being used to fly the aircraft upsets you, you’re going to be in for a real shocker on any airbus.
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 that it handles like any other 737 despite the pitch-up characteristic.
Go ask any commercial pilot, go watch any of the commercial pilots on youtube who have commented on this, go look on stackexchange. The notion that the MAX 8 is inherently unstable, or unsound, or dangerous, is a laughable myth to anyone in the industry. I get that the news cycle is financially rewarded for fearmongering, but I really expected people who frequent HN to know better and do some cursory research into the topic rather than posting comments that perpetuate bullshit.
There are several major issues with what boeing has done, such as the alleged failure to reclassify MCAS as a critical system after flight testing. But instead of discussing these legitimate issues, public debate seems to have been directed towards a bullshit myth about the airframe being inherently unstable. This has been eye-opening and dispelled my notion that HN had above-average quality of discussion on technical topics.
That's not quite correct.
When the aerodynamics of a plane was not designed to push forward the mounting of the engines, you have more reinforcement. That alone causes an uneven distribution for lift not accounted in the design itself. THIS is what causes the plane to nose up. But that doesn't mean stress is not put on the frame itself and mechanical parts that will be, on a daily basis, "abused" to the point of metal fatigue.
You see, when it comes to aerodynamics, it's easy to test it on a simulator. And it seems boeing's 737 max passed with flying colors. Then, it had to fly. That's the moment when test pilots came to a conclusion that the design will not work. Boeing's solution was a software "fix" and it needed to relay on 1 sensor to pass certification.
So, what do you have? NO TRAINING on this airplane, a bugged software system, poor aerodynamics, poor design choice, stress on elevator, etc. The ethiopian airlines plane had such force that pilots were not able to manually turn the trim control wheel. Do you know how much force that plane had to have that the jack screw couldn't be operated manually? THAT is a severe design flaw. THAT is what is being investigated. Who is investigating Boeing? Boeing is investigating Boeing. Boeing on 5/7/19 admits it knew they had a severe problem but it can still be fixed. Who certified the fix? Boeing. But now the FAA is investigating that fix which was promised by April. Again, this is a severe design flaw with still many unknowns yet to be found.
you're concerned about "comments that perpetuate bullshit". To me, the real bullshit is that a computer drove 2 aircraft into the earth. If we're so mistaken about what happened here, maybe the boeing engineers are similarly mistaken about how flight control systems work. I think they're the ones who have "ignorance and misinformation", like how many AoA sensors are required. Or whether a vigorous elevator UP position from the stick should be ignored and in fact counteracted by an opposite stabilizer position. Tell me what perpetuates the arrogance in the software departments at boeing that the computer knows better than the human. Unlike the pilots, the computer has nothing to lose. Yet the computer won the final decision. But calling this out is just the "news cycle financially rewarding" ... something ?
Nobody who isn't an engineer wants is terribly interested in the argument that a model of plane that has killed 2 planes full of people recently is in anyone's opinion safe.
Personally I won't fly on one in my lifetime.
I'll leave the analysis of why to others to figure out why I fly on other airplanes.
Incidentally I have seen pilots argue that the max is inherently unsafe on this forum which is probably why people are reiterating it.
What is your area of expertise and what is your opinion?
You're missing the point of the post you're responding to. The poster is saying that the 737 MAX isn't inherently unsafe due to its aerodynamic configuration. The safety issue arose from the bungled MCAS system. This could be fixed without changing the airframe.
Actual engineers do care about the "why" since that's what matters. Otherwise don't bother flying on any aircraft since all models have crashed at some point.
Your second sentence is too glib. By just about any statistic you want to look at, the MAX-8 has an abysmal safety record. Probably worse than any other aircraft in revenue flight.
It's perfectly rational to look at the results, regardless of "why", and decide that the risk is just too great.
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.
Troubling to me is the footnote in the manual which there are times where the manual wheels for the trim require 80 lbs or 100 lbs or more of force. This amount of force would potentially preclude female pilots on these planes to handle these sorts of emergencies.
>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.
Okay, how's: you can use thrust to pitch up a 737 beyond the authority of the elevator.
Airbus aircraft are “safe” despite the fact that dual conflicting pilot input is averaged without stick feedback (see the Airfrance flight from Brazil).
There is an aural warning (DUAL INPUT) on Airbuses with conflicting input.
> That’s a very imprecise statement in the first place but if you take it to mean, it would try to stall during normal flight conditions, it’s definitely false.
The precise wording would be that it is dynamically unstable, and the ball is with Boeing now to prove it's not the case. Also after all we discovered on the last weeks, Boeing better make a good case, or they won't convince anyone.
The US aviation industry is about to change. I don't know into what, but it's not in a stable situation.
The aircraft flies fine. MCAS is a stability control system that applies in certain cases (full power, high angle of attack) where the nose pitches up. It may lead to a stall but that's not what it's correcting for and it doesn't just happen during level flight. If the MCAS system was disabled then pilots handle it manually. Trim is not an exotic concept and just takes training and understanding of the operating characteristics.
Airliners are very safe. They're not in dynamic stability like jet fighters and don't need active measures at all times to stay airborne. Having sensors and systems that coordinate to keep the aircraft flying optimally to remove pilot load and increase safety margins is a good thing and has been in use for decades.
The problem here was a badly implemented system without redundancies and without enough training so that pilots were actually aware of the flight profile and MCAS. Also aircraft do not have millions of flight hours, they wouldn't reach a million even if they flew 24 hours a day for 100 years.
To me MCAS looks like an ugly software hack implemented to save money on redesigning a plane and re-training pilots. It brings several problems:
- it is difficult for pilots to understand how MCAS works, and how to diagnose failures. They are not programmers or engineers. And MCAS doesn't provide any debugging information about its work anyway. And pilots don't have time to analyze it.
- it adds new points of failure
- sometimes there are situations when automatic systems shut down and pilots have to control everything manually. With MCAS, they would have more things to look after. Pilots who got used to flying with autopilot are usually not comfortable with manual flight, and systems like MCAS only make things more complicated for them. An example is a recent crash of SSJ100 in Moscow where experienced pilots failed to land a plane manually after autopilot has turned off.
So I think that plane designers should be very careful with adding more automatic controls. Especially if their purpose is only to save money at cost of making place less safer.
Yes, that's what I said. The artificial behavior would be fine if the pilots actually knew it was artificial and how it was being done. That lack of understanding and training is the critical error, made worse by a poorly designed system that failed too easily.
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.
The aircraft flies fine in most flight profiles, yes.
At high angle of attack, the MAX-8 is more unstable than pilots were trained to expect. And the MCAS has done an absolutely miserable job of fixing this. Worst case scenario bad: it caused the loss of two airplanes that, if the MCAS had never been added to the MAX-8, would have reached their destinations just fine.
Until the it flies predictably in every flight profile (including high AOA), it's demonstrably wrong to say "the aircraft flies fine." Maybe it will eventually "fly fine" but Boeing's got quite a bit of work to do first.
Not quite if I am to believe other HN comments. The thing MCAS compensates for is that, in certain cases, as you pitch up more, the pressure on the stick decreases. This feels to pilots like leveling out, which is dangerous. MCAS was designed to counter this.
The specific design of MCAS and not adding any new procedures, was to lower the training requirements. Specifically, anyone certified on the old 737 was still certified on the max.
If they had improved the interface of MCAS and changed the procedure for runaway trim, it would have required more training. However, without MCAS or another remedy for the 'decreasing stick pressure at increasing pitch' problem, the plane would not have been allowed to fly at all.
and was written at night, so there's some loopy phrasing in there I never corrected. Let me unpack some of it to fit the context here.
The pressure applied on the stick itself does not change. Rather, the function of how much deflection you get out of the plane per unit force applied to the stick changes.
Design regulations state an airframe for which this curve at any point goes negative cannot be certified as a civil transport airplane.
That means, there should be no point in the flight envelope where the sensitivity of the controls drastically changes. It should be a predictable increase in force required to get more deflection, all the way to stall.
With the MAX without MCAS, this rule is broken at high AoA when the engine nacelles start making lift.
MCAS is meant to compensate for this necessary breakage by inducing some mistrim.
The effect of mistrim in that case is to cause the controls to require more force to induce those last few degrees of deflection, using the AoA sensor as the primary indicator as to whether the system should activate, in order to bring the curve into compliance.
The problem, as hinted by the response to my post in that thread, is that an honest to god stick-pusher would be more akin to the system you'd want for that. Adding the AoA sensor as a single point of failure is insane, due to the consequences should that sensor start spewing garbage data in normal flight.
Most of those are realizations I came to after stumbling across a Royal Aeronautics Society interview of D.P. Davies, a British test pilot for the ARB, the aircraft certification authority for the U.K., which I believe I linked in the comment.
At the time I wrote it I was in the midst of a deep dive into the more arcane aspects of control systems. I have some literature tucked away somewhere that I was referencing, bit I'd need to dig rather deep in my browsing history to recover all the context.
An interesting historical note: MCAS is similar to a system McDonnell Douglas implemented in MD-11's (LSAS, Longitudinal Stability Augmentation System) for the same reasons as Boeing eventually implemented MCAS: to be able to claim that the new aircraft flew just like the old MD-10.
Makes one wonder if someone brushed the dust off something that really shouldn't have been emulated again after the merger.
> This feels to pilots like leveling out, which is dangerous. MCAS was designed to counter this.
Pilots are trained extensively not to trust what motion feels like, and to use the horizon and instruments. An adjustment in stick pressure is not a notable new threat, they just need to be trained for the plane's behavior.
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. (?)
There are already lot of things that pilots have to keep in mind and look after. Learning how MCAS changes the behaviour of the plane makes everything more complicated.
> Also aircraft do not have millions of flight hours, they wouldn't reach a million even if they flew 24 hours a day for 100 years.
Most commercial planrs fly 3000 hours a year. There are about 400 787-Max planes built - that's a million flight hours per year already (if they weren't grounded...)
I don't think this is a very...'precise' statement. what is "safe" in the context of aviation? If you had no MCAS, then this plane has a very bad propensity to stall. I hope we can both agree that's an unsafe airplane. You can't just say "don't do that [pull up too much] and then you're fine". The aircraft "wants" to pitch up too high and stall, which predicated the MCAS system itself. So to me, yeah the engine mounting (in and of itself) makes this plane quite unsafe.
Now, with a properly functioning MCAS it may be "safe", but when the MCAS is itself another point of failure, my opinion is that the aircraft is only safe on paper, while in practice it's just got too many hacks and kludges for it to be practically safe for the millions of safe flight hours that these things are expect to deliver.