Ethiopian Airlines 737 MAX Investigation Preliminary Report • Hacker News Board

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#341

Post by toss1 » Fri, Apr 05, 2019, 3:36 PM UTC

darkpuma wrote: post #311

toss1 wrote: post #235

Earlier quoted context omitted.

They would be the set of assholes who: 1) decided to move the engines forward making the aircraft dynamically unstable, but improve performance and potential sales 2) decided to counter the instability with a software system (MCAS) based on a single sensor, with zero redundancy or fail-safe mode, AND make a second sensor an optional extra cost for the airlines, AND bury the whole thing in a poor UI, in short: cheapin…

> "decided to move the engines forward making the aircraft dynamically unstable," I don't believe that's true. Per Mentour Pilot, the 737 MAX and the 737 NG are both very stable aircraft that are not prone to stalling[0]. That there is a difference in performance characteristics that creates a difference in how an escape from stall maneuver is to be performed, and the MCAS is meant to paper over that difference. [0]…

I'll have to track it down but from what I'd read, the change in handling characteristics was that once the airplane started to pitch up, the pitch-up forces would increase, making a stall much more likely if you didn't keep on top of it.

So, yes, if you;re actively flying the plane and staying on top of your trim & pitch, keeping it in the middle of the range is just a bit different. But, if it gets out of hand, it gets progressively worse at an increasing rate, which is what MCAS was apparently designed to prevent.

Of course, if they'd designed the MCAS with multiple redundant sensors, as well as integrating other data (thrust, accel, GPS trajectory, pilot inputs, etc.) into a complete image, or at least a solid series of sanity checks on then applied it, it could have been a great advance.

Instead, they cheaped out, with the result that they added to the design a single point of failure.

The result, within a year of its rollout, is 346 people dead.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#342

Post by godson_drafty » Fri, Apr 05, 2019, 4:13 PM UTC

To avoid FAA scrutiny, Boeing developed and deployed MCAS covertly. This was done because they feared scrutiny would have led to huge losses in the face of competition from Airbus. Had Boeing management just laid all their cards on the table, potentially the FAA could have still approved the design, with small but crucial improvements. These changes might have included: using both AOA sensors, using a 3rd AOA sensor, not switching between left and right sensors each flight. Instead, the covert nature of the development and deployment of this feature allowed flaws in its design to go unchecked.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#343

Post by unionemployee » Fri, Apr 05, 2019, 4:41 PM UTC

mhandley wrote: post #3

Indeed looks like they did disable MCAS using the stabilizer trim cutout switches, but the aircraft was trimmed nose down when they did so. Aerodynamic loading prevented manual trimming using the trim wheels. They eventually turned electric trim back on, as they didn't really have any other options, but didn't trim back enough, and left it turned on. At this point the right airspeed indicator (which should be more re…

Had they paid closer attention to their airspeed. The aircraft could have been saved. By reactivating the system at such high speed, adding further nose down trim, there was no way to keep the aircraft level. Tunnel vision.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#344

Post by cjbprime » Fri, Apr 05, 2019, 5:55 PM UTC

djmips wrote: post #328

cjbprime wrote: post #327

Earlier quoted context omitted.

You can't have an AoA disagreement when stationary on the ground. It is a wind vane.

You don't know that. If it's malfunctioning it could be in the electronics and nothing to do with how it operates.

And if it's reporting a difference, it could just be because there's no airflow and the vanes aren't at identical positions. You can't rely on the difference meaning anything.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#345

Post by pdonis » Fri, Apr 05, 2019, 7:55 PM UTC

cjbprime wrote: post #323

pdonis wrote: post #126

Earlier quoted context omitted.

> That's the first I've heard that it's only for edge cases. It's only supposed to activate in a specific edge case (high angle of attack, manual flight, no flaps, low airspeed). That's been discussed plenty online (including previous threads here at HN). But that assumes that the angle of attack sensors are accurate. If the AoA sensors are inaccurate, as they were on this flight (more specifically the left one), MCA…

I don't agree with "low airspeed". You can exceed critical AoA (and therefore stall) at any airspeed.

> You can exceed critical AoA (and therefore stall) at any airspeed.

I wasn't talking about at what airspeeds a stall is possible. I was talking about at what airspeeds MCAS is designed to activate (assuming correct AoA sensor input).

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#346

Post by teh_klev » Fri, Apr 05, 2019, 9:16 PM UTC

bronco21016 wrote: post #307

teh_klev wrote: post #306

I usually enjoy HN discussions, but this is a pitiful and sad thread. I couldn't be bothered trawling past the responses to the top comment with back seat drivers, and "ooh but I read the 737's flight manual, they fucked up". Likely 99% of the commentariate here are neither 737 Max pilots, let alone even licensed to fly commercial passenger jets, or even have a pilots license. And no, as much as I love the guy, watch…

Can’t upvote enough. As someone who actually does fly airplanes for a living it’s disturbing to me the amount of ‘expert’ arm chair quarterbacks that have come out on HN in the wake of these two incidents. Immediately after the Ethiopian crash there were 200+ comment threads every few hours full of experts speculating about all the things that went wrong. People who were flat out wrong could not be told otherwise. I…

Thanks for the supportive comment. I thought I was going to get a polite but firm message from dang asking me not to drink-and-hackernews :)

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#347

Post by MisterTea » Sat, Apr 06, 2019, 11:47 AM UTC

toufiqbarhamov wrote: post #292

MisterTea wrote: post #249

Earlier quoted context omitted.

http://n-gate.com Enjoy! :-)

Mother of god, that’s equal parts funny and just plain accurate. Dell wonders if maybe their hiring process can be improved. Hackernews debates whether this is a cynical attempt to mine talent from previously-overlooked seams or a genuine attempt to treat human resources as human beings. Some Hackernews consider labeling such personnel so their specific status is on display at all times, an idea that nobody got from…

Wow both of us downvoted. Looks like no one likes a mirror being held up mixed with humor.