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Boeing MAX production cut signals long grounding

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Re: Boeing MAX production cut signals long grounding

#111

Post by thefounder »

hodgesrm wrote: post #106
thefounder wrote: post #101

Would you still fly with Boeing Max after all this? I understand that the "issue" can be fixed with software but it looks like a hardware/design issue in the first place. If your highest priority is safety the software should be used only when the hardware fails not to support a flawed design.

Sure, assuming it's just MCAS. The B737 program has had previous problems most notably uncommanded rudder movement that caused two US crashes in the 1990s with loss of all on board. [1] From what's visible so far in the investigations Boeing (a) botched the MCAS implementation and (b) failed to train pilots on differences between the Max and previous models. Cure those two and the problem seems to be solved. [1] http…

As far as I understand without MCAS software the aircraft is impossible to fly manually. I'm not sure I'm comfortable with that. Like turning off self driving just to find out that the car still changes direction by itself to compensate for a twisted wheel.

Re: Boeing MAX production cut signals long grounding

#112

Post by AnssiH »

bronco21016 wrote: post #74
joshbaptiste wrote: post #73

The 737MAX was designed to compete with A320NEO .. why Did Boeing have to move the engines forward while Airbus did not ? AFAIK the NEOs weren’t a complete redesign either

The 737 rides significantly lower. Check out the 737-700/800/900 series and you’ll notice the engine cowl (inlet) is not perfectly round at bottom because of ground clearance. This is likely a design choice leftover from the original 737 series that used JT8D engines which are turbojet engines rather than high bypass turbo fans that make modern airliners efficient. Because Boeing has been so set on retaining the orig…

JT8D are low-bypass turbofans, not turbojets. But yes, their diameter is smaller than modern engines, thus the issue.

Re: Boeing MAX production cut signals long grounding

#113

Post by darkpuma »

jarym wrote: post #108
darkpuma wrote: post #103

Earlier quoted context omitted.

Right, but the MCAS system as it was implemented during those two crashes did not disable itself when the two sensors disagreed. It could have, but didn't. Boeing is apparently changing that, and I believe that change to be sufficient. MCAS being automatically disabled when the sensors agree but leaving the pilots with electronic trim control seems like a perfectly adequate solution. The MCAS system was never even ne…

I think your maths is sound but the question is what are the odds that multiple sensors fail on the same flight (and I don't know the answer)? Because as soon as one sensor fails that aircraft will go in for maintenance.

That was kind of my point..

MCAS should turn off as soon as a single sensor fails, and three sensors are therefore unnecessary. Two sensors are sufficient to detect when a single sensor fails. If you only have two sensors and two fail, then MCAS remains active and your plane crashes. But that's not likely to happen. However that's more likely to happen if you have three sensors and try to use two sensors to vote out a third, in order to keep MCAS active when a sensor fails. In that configuration, a double failure (causing a crash) is three times more likely.

My conclusion is turn off MCAS as soon as even one sensor disagrees with the others. And if that's how MCAS is configured, then three sensors is unnecessary overkill. If you want overkill, you may as well double up the sensors on both sides and have four instead of three; all the better right?

Re: Boeing MAX production cut signals long grounding

#114

Post by Someone1234 »

Innominate wrote: post #105
thefounder wrote: post #101

Would you still fly with Boeing Max after all this? I understand that the "issue" can be fixed with software but it looks like a hardware/design issue in the first place. If your highest priority is safety the software should be used only when the hardware fails not to support a flawed design.

I would be perfectly comfortable flying on the 737 Max right now even without the software fixes.

That's an irrational position. After the Ethiopian Airlines initial report was released pilots were discussing refusing to fly them even for ferry flights (i.e. no passengers).

The Ethiopian airlines crew followed Boeing's post-Lion Air safety bulletin and still crashed. There's no safe way to operate a 737 Max in its current state. The hypothetical recovery techniques (e.g. point nose down to release pressure on the horizontal stabilizer) only work at high altitude, which is notable if Ethiopian airline's AOA sensor was damaged by a bird strike right after take-off.

Nobody who understands the current state of this investigation should be saying they'd be comfortable on a 737 Max without changes. The "pilot training" narrative isn't just dead, but dead, buried, with a tomb stone.

Sure, pilots should have received training on MCAS existing, but MCAS was commanding trim changes that aren't easily recoverable under any circumstances and certainly not if you follow procedure and disable electronic trim. Nobody should fly on the 737 Max until an update completed, I'd go so far as to suggest that the US/EU should ban ferry flights.

Re: Boeing MAX production cut signals long grounding

#115

Post by weaksauce »

MuffinFlavored wrote: post #18
tibbydudeza wrote: post #9

Like the Toyota unintended acceleration issue we need third parties to look at the flight control software and engineering decisions taken for the MAX line and give a an independent report. Certainly not the FAA who delegated their oversight to Boeing. 346 people died because of their ineptitude.

> 346 people died because of their ineptitude. This might be too hot of a take for HackerNews, but... look at how many people the FAA has kept safe over the past 30 years. I'm pretty sure the number of people who travel without dying is very, very high. I don't disagree that their might have been some ineptitude (I'm sure you could find that anywhere for anything since it's opinion driven), but to say the FAA is all…

I think it was not the FAA's fault but rather the fault of the shrinking budgets and deregulation in parts that offload the safety checks to the manufacturer. blame congress over the past 20 years or so. the greed of boeing to shoehorn the MCAS into the aging airframe is the issue. they didn't want to have to get a new type rating and wanted to prevent needing to retrain pilots.

Re: Boeing MAX production cut signals long grounding

#116

Post by Obi_Juan_Kenobi »

HarryHirsch wrote: post #96
noncoml wrote: post #51

Earlier quoted context omitted.

The problem is not the missing extra angle of attack sensor, but incompetence at every step. If I understood correctly, MCAS trimmed it so much that the pilots were unable to bring it back manually. This sounds like Boeing engineers didn’t even put a limit on the maximum trimming that MCAS can do, not even to the maximum theoretical limit for the plane/engines.

MCAS trimmed it so much that the pilots were unable to bring it back manually. Not only that, MCAS controlled an electric motor which turned the trim wheel and which could apply more torque than a human turning it manually. The only way to disable MCAS was to cut power to that motor. MCAS pointed the aircraft at the ground, and it was impossible to trim the aircraft to achieve level flight again. Mind, MCAS was suppo…

The electric trim adjustment is obviously going to be more powerful, that's just the reality of large planes. That's not the issue.

The issue from the Ethiopian crash was that, in the extreme trim angle, there was simply too much force on the screw to turn manually. This condition is trained for, and the solution is to let the plan angle down to relieve the aerodynamic pressure on the control surface. That gives you an opportunity to manually control the trim wheels.

The pilots did not have the benefit of altitude to perform this maneuver, so (likely) instead re-enabled the electric trim in a bid to use it to reduce the nose-down trim before the MCAS would re-engage. This proved fatal.

Re: Boeing MAX production cut signals long grounding

#117

Post by TheSpiceIsLife »

Baeocystin wrote: post #70
TheSpiceIsLife wrote: post #50

Earlier quoted context omitted.

if you were to accelerate a Toyota sedan (any of them) to 70mph, then stomp on the brakes while holding the accelerator to the floor, the car will absolutely come to a complete halt in about the same distance as if you didn’t have your foot on the accelerator. Are you saying the additional, let’s say, what?, 60kW of power being applied to the wheels will require no additional effort at the brake pedal to overcome. Co…

Assuming a properly-maintained braking system, it makes very little difference. >And despite dramatic horsepower increases since C/D’s 1987 unintended-acceleration test of an Audi 5000, brakes by and large can still overpower and rein in an engine roaring under full throttle. With the Camry’s throttle pinned while going 70 mph, the brakes easily overcame all 268 horsepower straining against them and stopped the car i…

Hmmm, interesting. Colour me convinced.

Re: Boeing MAX production cut signals long grounding

#118

Post by Obi_Juan_Kenobi »

thefounder wrote: post #111
hodgesrm wrote: post #106

Earlier quoted context omitted.

Sure, assuming it's just MCAS. The B737 program has had previous problems most notably uncommanded rudder movement that caused two US crashes in the 1990s with loss of all on board. [1] From what's visible so far in the investigations Boeing (a) botched the MCAS implementation and (b) failed to train pilots on differences between the Max and previous models. Cure those two and the problem seems to be solved. [1] http…

As far as I understand without MCAS software the aircraft is impossible to fly manually. I'm not sure I'm comfortable with that. Like turning off self driving just to find out that the car still changes direction by itself to compensate for a twisted wheel.

> As far as I understand without MCAS software the aircraft is impossible to fly manually.

Why does anyone think this? The MCAS system rarely engages.

The issue is simply to make the stick behavior similar to the older 737s at high AoA. For an older 737, when you're pitching way up, you really have to pull on the yoke to keep that high AoA. The plane naturally wants to return to a neutral AoA, so you have to fight it. With the new design, the engine position keeps the plane from wanting to return to the neutral AoA, at least to the degree it did before. Hence, the 'stick feel' at high AoA is lighter. You don't get the same tactile feedback about being near a stall. (you still have the stick shaker)

The MCAS is simply there to bring back that resistance to extreme AoA, and thus make it less likely to accidentally stall. MCAS isn't even active with flaps down (i.e. around takeoff and landing) so can't possibly affect those aspects of flight.

It's a questionable design for a number of reasons, but it's not at all necessary for flight, let alone 'basically impossible' without it.

Re: Boeing MAX production cut signals long grounding

#119

Post by Gibbon1 »

mrpippy wrote: post #40
rasz wrote: post #16

Earlier quoted context omitted.

I agree, we need someone like Michael Barr to comb thru supposedly clean safety certified Ada codebase (in reality most likely full of C++ garbage).

The problem here is not a software bug—-the software performed as designed, the design was just bad.

Yeah there was exactly one single point probably mechanical failure, the AOA sensor.

I'm coming down on the side of the cause of these accidents was due to the failure to properly type certify the aircraft. Because they were trying to avoid that they failed to do the system analysis and testing including simulator testing that would have easily found this.

Re: Boeing MAX production cut signals long grounding

#120

Post by the_fonz »

This doesn't go far enough. As reported by Al Jazeera in 2010, critical structural elements of the 737 NG that were supposed to be CNC'ed were handmade and grossly out-of-spec, leading to at least three deaths when 737 NG's broke apart in several sections on runway overruns, while in the past airframes held together intact in such events, protecting passengers. Boeing then covered up and scuttled its own investigation panel after management didn't like its conclusions.

tl;dr: 737 NG and MAX aircraft are fundamentally unsafe because of systemic lapses in regulatory oversight. These aircraft cannot be made safe economically due to Boeing's regulatory capture of the FAA, so it's best to never fly on them.

In my mind, Boeing as a passenger transport company is, or should be, finished. How they acted regarding the 737 NG and MAX are criminally-unforgivable.

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