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FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

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Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#161

Post by Animats »

cyberferret wrote: post #75
th0ma5 wrote: post #51

Earlier quoted context omitted.

To be fair, ignoring user input could have potentially have saved Air France 447... I mean I actually can't think of an automated fool proof system that would've fixed 447, but incorrect input was a major factor.

Basic rudimentary 'stick and rudder' flying skills was a big factor in AF447's crash. All old school pilots know that when you aircraft is in a nose high stall condition, you never keep pulling back on the stick, but instead push it forwards to lower the nose and get the wings flying again. The fact that the co-pilot in question kept holding the stick to the back stops was the main reason that the aircraft wallowed i…

Basic rudimentary 'stick and rudder' flying skills was a big factor in AF447's crash. All old school pilots know that when you aircraft is in a nose high stall condition, you never keep pulling back on the stick, but instead push it forwards to lower the nose and get the wings flying again.

Except on an Airbus. If the plane is in "normal law", it won't go into a stall condition. Here's the Airbus training video.[1] Note, by the way, that the automatic recovery includes going to full throttle. The throttle levers don't move, though. Unlike Boeing, where the levers are moved by the computers and the pilot can overpower that. In the 737 Max, though, it's worse, because the engines are mounted too high and full thrust pushes the nose down. So "full power and back off on the stick" will not work.

[1] https://youtu.be/G161aMYCzbQ?t=100

Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#162

Post by snowwindwaves »

snovv_crash wrote: post #148
snowwindwaves wrote: post #130

Earlier quoted context omitted.

For anyone writing software controlling machines it is pretty much the status quo. It has to be darn near perfect, updating it later if it is even possible will be expensive and inconvenient As much as it is a shitty environment if you have 6 months to fix it and all of the company resources you can think of to ask for that is lots of time.

Having 6 months to fix it would have been fine. Instead what they've had is 2 weeks to fix it for 6 months, which is a very different kettle of fish.

Hopefully whoever is in the hot seat knows the name of the game. First you ask for 30 days, then you ask for 30 more.

Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#163

Post by blackflame7000 »

pvg wrote: post #101
blackflame7000 wrote: post #92

Earlier quoted context omitted.

By Original I meant the NG version

Both accidents attributed to rudder hardover took place before the 737 NG first flew in 1997.

There were a lot more than just 2 rudder incidents.

USAir Flight 427

United Airlines Flight 585

Eastwind Airlines Flight 517

Silkair Flight 185

Copa Airlines Flight 201

China Southern Airlines Flight 3943

MetroJet Flight 2710

Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#164

Post by firethief »

mikekchar wrote: post #158
lkrubner wrote: post #124

Earlier quoted context omitted.

Fukushima? That doesn't belong on the list. There is some limit to any engineering decision. Complaining about MCAS is totally reasonable, but it would be unreasonable to argue "The Air Max is not safe because if I hit it with enough Stingray missiles it won't fly anymore." Like, yeah? No kidding? Fukushima was designed to survive the earthquake, and it did, it just wasn't designed to survive the earthquake and also…

Fukushima survived the earthquake and even survived the tsunami. The generator got wiped out, but even that wasn't what ultimately led to the disaster. It was that the battery backup eventually ran out of power (not unexpected) and the connectors for recharging it were old and of a format that isn't used any more. There was no way of recharging the battery backup and so the pumps eventually failed. It's one of those…

> since the emergency system is not used normally, it's easy to overlook a critical problem.

This is a such an important antipattern when robustness is a goal.

Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#165

Post by jobigoud »

jbigelow76 wrote: post #119
chrisbolt wrote: post #108

Earlier quoted context omitted.

Like the European Aviation Safety Agency?

So the FAA says "this is fucked" and and the EASA says "they're all good bro"[1], who do you side with? [1] feel free to flip flop regulatory agencies if you so desire.

You side with the most conservative obviously. Your life is at stake. Only when there is a total consensus of safety you can feel confident.

Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#166

Post by hef19898 »

EdwardDiego wrote: post #125
halter73 wrote: post #103

Earlier quoted context omitted.

IIRC, the cockpit voice recording included a comment from one of the co-pilots about how pulling back on the yoke couldn't cause a stall. The assumption was that the Airbus's fly-by-wire system would prevent it and ensure the aircraft still climbed as long as the pilot held back on the stick. The co-pilot apparently didn't realize that the sensor issue that disabled the autopilot also disabled the stall prevention. A…

Exactly - the computer had switched contexts, but the pilot hadn't. And expecting pilots to switch their mental map of expected behaviour when the computer does (and did so with, from the accounts I read, very minimal indication that it had done so) during a high stress situation, is asking for trouble.

One of the best explanations I have read on that issue. Short and accurately summing it up.

Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#167

Post by kunday »

bjourne wrote: post #133

Since this thread is already full of armchair airplane engineers opinions about the root cause, I'll add mine too: Never ever write new software under the condition that it must work EXACTLY as old software. It can't be done and you'll always miss something. Case in point: Wine. They've been at it for years and the emulation layer is still far from perfect. It works 99% of the time which is good enough for games, but…

Fair point. Compaq in 1980's is probably the best case for reverse engineering and building a robust system. In some cases it out performed IBM PC's.

However, I have to admit, reverse engineering a home desktop is different from a airline software, considering that bugs can instantly kill people.

Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#168

Post by jamesharding »

Animats wrote: post #161
cyberferret wrote: post #75

Earlier quoted context omitted.

Basic rudimentary 'stick and rudder' flying skills was a big factor in AF447's crash. All old school pilots know that when you aircraft is in a nose high stall condition, you never keep pulling back on the stick, but instead push it forwards to lower the nose and get the wings flying again. The fact that the co-pilot in question kept holding the stick to the back stops was the main reason that the aircraft wallowed i…

Basic rudimentary 'stick and rudder' flying skills was a big factor in AF447's crash. All old school pilots know that when you aircraft is in a nose high stall condition, you never keep pulling back on the stick, but instead push it forwards to lower the nose and get the wings flying again. Except on an Airbus. If the plane is in "normal law", it won't go into a stall condition. Here's the Airbus training video.[1] N…

The engines in the MAX are still producing thrust below the centre of mass of the plane...how would this produce a nose down pitch at TOGA thrust?

Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#169

Post by yread »

rjvehn wrote: post #27

There are a myriad of issues that put the planes at risk, but I think that the fact that when the control system (MCAS) is engaged causes it to ignore feedback is the biggest issue of all. "But with the MCAS activated, said Fehrm, those breakout switches wouldn’t work. MCAS assumes the yoke is already aggressively pulled back and won’t allow further pullback to counter its action, which is to hold the nose down. Fehr…

It was designed to trim down when the pilot is pulling up. Of course pulling up is not going inhibit it. That's the point of the system!

Re: FAA Finds New Risk on 737 Max, Orders Boeing to Make Changes

#170

Post by afthonos »

mikekchar wrote: post #160
afthonos wrote: post #149

Earlier quoted context omitted.

I refrain from using “simply” or “just” unless I am the person expected to design or fix the problem. Ahead of time. Saying after a disaster caused by the most powerful earthquake ever recorded in Japan[0] that the solution was “simply” to do some coincidentally simple-sounding thing is not credible. [0] https://en.m.wikipedia.org/wiki/2011_Tōhoku_earthquake_and_t...

Yeah, this is something that I think doesn't really resonate with people well. The reactor site is 25 meters above sea level. I'm not exactly sure how high the generators were, but they were well above the level that experts thought was safe at the time. The earthquake was a 1 in 1000 year event and so there was no data on record to help them model the resultant tsunami. In the years following the tsunami, the way pe…

Agreed. I think the background you shared shows one of the big problems in design: it's always easy to see the tsunami markers after the fact and say "the information was there all along". It's a lot harder to pick them out from a thousand information sources that are, a priori, just as compelling. Looking for those markers before design would have required looking at every bit of evidence at least as compelling as those markers, which would likely be cost-prohibitive.
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