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

#111

Post by JudgeWapner » Sun, May 12, 2019, 1:15 AM 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.

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.

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

#112

Post by bushido » Sun, May 12, 2019, 1:16 AM UTC

skellera wrote: post #76

davewasthere wrote: post #66

Earlier quoted context omitted.

Yeah, but who is going to want to fly in one again? Even working in aviation in the past and knowing that they've probably nailed the issue, I'd still be less than keen.

Most people don’t even think about the plane they’re flying in. It will not be that big of an issue to continue using them unless some group actively tries to warn passengers about flying in those specific planes.

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.

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

#113

Post by salawat » Sun, May 12, 2019, 1:21 AM UTC

stingraycharles wrote: post #41

salawat wrote: post #5

>A cynical man could be inclined to think that with this change, they casually removed a possibility of pilots/airlines realizing the existence of MCAS: "we have thrown off the right switch to unlink the autopilot from the trim motor and there is still something making automated stabilizer inputs, what could it be?" It's worse actually. They've taken a procedure, and are raising it on a pedestal as if to say "See, th…

It's fair to recognize this is not entirely Boeing's fault either: it was the airline industries that don't want to re-train their pilots and wanted this type of plane (American Airlines was specifically keen on getting Boeing to manufacture this plane [1]), so they were kind of told "we want you to make exactly $this, otherwise we switch to Airbus". [1] https://www.vox.com/2019/4/5/18296646/boeing-737-max-mcas-so...

Given. However, in Engineering, it is totally expected that when you start getting into areas that sketchy, you say "No. The best I can do is this. I'm sorry."

Instead, Boeing saw dollar signs, and threw caution and people's lives, and years of good will to the winds.

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

#114

Post by CydeWeys » Sun, May 12, 2019, 1:21 AM UTC

jsjohnst wrote: post #75

peteradio wrote: post #60

Earlier quoted context omitted.

What was the reasoning?

The linked article says why, but to paraphrase, the training has always said to flip both switches. Previously the only time you’d need to flip the switches was due to an electric motor being stuck-on. It’s only with the MAX that there was an actual useful reason to flip one vs the other, but the training was always to flip both and Boeing decided to simplify it. My personal guess is that it was internally totally di…

> The linked article says why, but to paraphrase, the training has always said to flip both switches.

And the root cause reason for that is Boeing was hiding changes in order to make the same type certification. Many decisions were made not in the interest of maximizing safety but in minimizing visible changes. This is one of those.

It would have been safer overall to have a new type, and then they could've had a cut-out switch just for the MCAS and trained pilots on how to use it.

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

#115

Post by CydeWeys » Sun, May 12, 2019, 1:24 AM UTC

nwallin wrote: post #83

deskamess wrote: post #57

Earlier quoted context omitted.

Why would they not have gone with a, say, 757 MAX - it seems to fit the bill spec wise. Is it that global pilot pool is not as great for the 757 as 737?

The 757 "max" is a 767. 757s and 767s share a common type rating. It's not so much that the pilot pool is lacking, it's that a lot of airlines have a pool of existing 737 pilots already on their payroll. If you need to lay off half your employees, and replace them with an entire new pool of people, half of them are going to be terrible employees, and it will take you years to weed out the bad ones. For better or wors…

Huh? There's no such thing as a "737 pilot", there is a "pilot with 737 type rating". It's the whole "becoming a pilot in the first place" part that's hard, not certifying a new type. Plenty of pilots are certified to fly multiple types. The fundamentals of flight are the same across all planes.

The airlines would've just had to retrain their existing pilots to fly the new type. It's not nothing, but it's a lot less worse than massive lay-offs and rehiring.

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

#116

Post by [deleted] » Sun, May 12, 2019, 1:26 AM UTC

skybrian wrote: post #104

hirowan wrote: post #101

Earlier quoted context omitted.

You're putting the safety record into chauvinist context, to be exact. An AoA failure is sufficiently rare for it to have only occured in a couple of occasions in - shockingly - only a couple of countries.

Okay, I probably should have calculated the number of successful flights to avoid this. But, nowhere did I say any country is better than any other. That's your inference.

[deleted]

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

#117

Post by AnimalMuppet » Sun, May 12, 2019, 1:26 AM UTC

davidkuhta wrote: post #107

an_account_name wrote: post #93

Earlier quoted context omitted.

Some of these applications have been withdrawn, but there are in fact some in flight. https://www.nrc.gov/reactors/new-reactors/col/new-reactor-ma...

> In flight Hopefully, their planes don't need MCAS ;)

I don't know - a lot of those nuclear plant applications seem to stall ;)

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

#118

Post by cletus » Sun, May 12, 2019, 1:27 AM UTC

So a lot is known at this point:

1. The A320neo caught Boeing completely off-guard;

2. The threat of the likes of American Airlines (already a mixed Airbus/Boeing customer and the largest airline in the world) placing a large A320neo order for regional aircraft operations scared the bejesus out of Boeing management;

3. For airlines like Southwest that are pure 737, the prospect of adding a plane that didn't share a common type rating with their existing fleet would complicate their lives and make them vulnerable to a sales pitch from Airbus; and

4. The development cycle for a completely new body was too long for many customers as it would arrive several years after the A320neo.

I don't think any of this is in dispute so the constraints for Boeing were to design a more fuel-efficient plane that shared a common type rating with the 737. To get there:

- They added newer, more fuel efficient engines. These changed the flight characteristics so they had to be moved;

- These engines moving made the plane more vulnerable to a stall situation. To counter this, they added MCAS, which would point the nose down when the AoA sensor told it the nose was too high;

- Standard configuration had 2 AoA sensors but MCAS only ever read from one;

- There was a safer configuration as an optional extra purchase;

- Telling airlines and pilots about this and providing overrides risked the common type rating.

I don't believe any of this is in dispute. It is widely believed, but not yet proven, that the primary cause of both fatal crashes was a runaway MCAS that drove the planes into the ground. It's also believed that with proper training a pilot may have been able to counter this (as happened the day before the Lion Air crash with a pilot in the jump seat).

Now what I find interesting is the response people have to all this. Some claim this is a fundamental design flaw that puts a shadow over the plane. Others believe it will be corrected and everything will be fine.

I'm firmly in the first camp: the plane CLEARLY flies differently to a 737. An automatic system, with no triple redundancy, was required to correct the flight characteristics of the plane.

I'm no expert but it seems to me the plane is fundamentally flawed at this point.

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

#119

Post by jordache » Sun, May 12, 2019, 1:27 AM UTC

fack man, this is some crappy vendor releasing un-documented APIs.. Except this is a machine that is carrying hundreds of lives.

Regulations needs to ensure every little detail about these planes are articulated to the end-user.

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

#120

Post by CydeWeys » Sun, May 12, 2019, 1:28 AM UTC

zb wrote: post #108

rootusrootus wrote: post #19

Earlier quoted context omitted.

It would not be invalid to observe that the first Lion Air crew dealt successfully with the malfunction, and ask why the second crew did not. Every aspect of these accidents should be investigated.

If I recall correctly, the first crew encountered the issue during cruise, at which point which you have both (a) time, and (b) sufficient altitude that you can afford to push the stick forward in order to reduce the aerodynamic force on the horizontal stabiliser to the point where it will be physically possible to correct the trim without powered assistance. Pilots encountering the issue during takeoff have neither…

This is probably it, but even if not, there's a large amount of randomness in these kinds of situations, so it's not clear you'd be able to derive anything meaningful at all. Disasters are a highly complex, multi-factor, chaotic phenomenon.