Boeing altered key switches in 737 MAX cockpit limiting ability to shut off MCAS • Hacker News Board

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

#291

Post by usrusr » Sun, May 12, 2019, 5:44 PM UTC

jhayward wrote: post #87

old-gregg wrote: post #65

Earlier quoted context omitted.

> The bugs will be addressed and they'll still fly. The engines are mounted incorrectly, so much so that Boeing believed pilots need the assistance of MCAS on take-off now. The bug isn't with its algorithms, rather the need for MCAS to begin with. They can't "address" it. That's why I'll be very careful not to ever book a flight on a 737 Max, probably easier to simply stick to Airbus-only airlines: Jetblue, Alaska/Vi…

> The engines are mounted incorrectly, so much so that Boeing believed pilots need the assistance of MCAS on take-off now. This overstates the issue. The engine mounting changes the flight characteristics enough that the MAX 8 needs to be flown differently in certain corners of the flight envelope. The MCAS was added to avoid having to re-train pilots or trigger a new type certification. The engine mounting certainly…

> The engine mounting certainly does not make the plane unsafe.

Unless there is something about the magnitude of MCAS necessity that Boeing did not tell us yet.

Boeing's original stance of "stupid pilots should have followed runaway trim procedures" does not seem very consistent with actively removing a two-stage disable feature that already existed (and which, in hindsight, might have saved those lives). How desperate exactly were they to never ever let the pilots catch a glimpse off the real flight characteristics?

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

#292

Post by anticensor » Sun, May 12, 2019, 6:18 PM UTC

echelon wrote: post #273

pentae wrote: post #266

Earlier quoted context omitted.

You know the 737 and the 737 MAX are two completely different planes right?

I'm not going to fly on any 737, just in case the MAX bit gets truncated. Everyone I've talked to has expressed the same fear. I don't care if it's irrational or not - it's my life, and I'm not risking it on one of these stupid, cost-cutting planes.

Boeing 737-MAX is longer than previous iterations of 737.

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

#293

Post by anticensor » Sun, May 12, 2019, 6:19 PM UTC

the_mitsuhiko wrote: post #253

nicoburns wrote: post #248

Earlier quoted context omitted.

Why not?

Because it has grandfathered rules that new planes don’t have it depends on. For instance no new plane design us allowed to have 737 style emergency exits.

Just add more doors.

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

#294

Post by rpiguy » Sun, May 12, 2019, 6:34 PM UTC

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…

Conversely I don’t see how they can’t be returned to the sky. Boeing has deep pockets and the US government will push behind the scenes to make sure it happens, regardless of whatever public statements they make. There is no way regulators will be able to keep this plane grounded simply on the ground of politics.

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

#295

Post by anticensor » Sun, May 12, 2019, 6:41 PM UTC

mcsoft wrote: post #20

It strikes me how a seemingly insignificant decision at the time - to position fuselage slightly higher above the ground - gave Airbus a strategic advantage 50 years later. It forced the competitor into a services of unexplainable and reckless decisions that break basic principles of reliable engineering. Which in turn led to a very visible disastrous business consequences: Boeing had to silently reduce 737 MAX produ…

You mean genetic algorithms at work?

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

#296

Post by anticensor » Sun, May 12, 2019, 6:55 PM UTC

Majromax wrote: post #22

exabrial wrote: post #7

> As various warnings went off in the cockpit, they never reached the conclusion to use the runaway stabilizer procedure. We continue to put the microscope on Boeing but this is why there is a person in the cockpit: to oversee the planes automated systems. There were multiple failures, and while we pick apart Boeing, we have not done the same to the pilots.

> There were multiple failures, and while we pick apart Boeing, we have not done the same to the pilots. At the time of the crash, it appears that the established procedures were insufficient. In particular, the MCAS failure creates a qualitatively different 'runaway stabilizer' than the previously-imagined failure mode of a stuck-on motor. In turn, that seems to have created a situation where the pilots did accurate…

Checklist amendments would require far less retraining than creating a new type.

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

#297

Post by salawat » Sun, May 12, 2019, 7:12 PM UTC

rocqua wrote: post #227

_ph_ wrote: post #222

Earlier quoted context omitted.

Alternatively just train the pilots on the behavior in the domain where MCAS would activate. MCAS main purpose is to lower the training requirements.

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 c…

To clarify, since this seems to be a slight misreading of one of my comments.

The original one is https://news.ycombinator.com/item?id=19568158

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.

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

#298

Post by rurban » Sun, May 12, 2019, 7:13 PM UTC

presto8 wrote: post #280

rurban wrote: post #203

Earlier quoted context omitted.

They are heated now, after the Air France loss. This incident was also the reason for the MCAS system in the first hand: "Don't trust the pilot, regulate it into safety by your own".

Are you referring to AF447? According to the BEA incident report, the AF447 plane was already equipped with heating systems for the pitot probes and AoA sensors. "1.6.9.1 Probe heating The probes that are installed on the aircraft are heated electrically to remove water by vaporisation when the aeroplane is on the ground and to protect them from icing in flight." Reference: https://www.bea.aero/docspa/2009/f-cp090601…

Right, I mixed that up. With AF447 the initial problem was not the AOA but the very common pitot tube icing, which renders the airspeed indicator useless, thus leading to wrong stall warnings.

Even if the pitot tube is heated (mandatory), very often airframe icing leads to a blocked static port, rendering even more indicators useless.

https://en.wikipedia.org/wiki/Pitot-static_system

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

#299

Post by sean_the_geek » Sun, May 12, 2019, 7:14 PM UTC

pentae wrote: post #266

sean_the_geek wrote: post #263

Earlier quoted context omitted.

Count one more please. Searched for flight, saw Boing 737, no thank you! Paid premium for Airbus. That’s for three passengers.

You know the 737 and the 737 MAX are two completely different planes right?

Yes I do. But as the comment above says, I am not risking it, even though it is borderline irrational.

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

#300

Post by grumdan » Sun, May 12, 2019, 7:20 PM UTC

erentz wrote: post #43

djsumdog wrote: post #28

What is the endgame now for 737 MAX planes? Every airline using them has had several weeks to totally reorganize to deal with these huge missing parts of their fleets. Boeing keeps talking about fixing them and putting them back in the air, but I dunno. At this point, it should be agreed the fundamental design flaws are serious, and Boeing should have simply made a brand new plane, with much more modern controls and…

> 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…

> 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.

In a world that had actually severe consequences for corporate negligence, regulators would force Boeing to let airlines cancel/change all orders, and compensate them for the 737 Max models they already shipped to them, as they cannot be flown safely. Boeing's behavior does not indicate that they are interested in properly fixing this problem as opposed to getting it certified via corporatism / the FAA allowing them to perform a big part of their own checks.