Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

wsj.com

Post reply on HN
Print view View original

11–20 of 43 posts

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#11

Post by droithomme »

chrisseaton wrote: post #7
jwildeboer wrote: post #6

Moderators: please add [paywalled] or [$] to paywalled content so I can ignore instead of wasting time. Thanks.

https://news.ycombinator.com/newsfaq.html > But please don't post complaints about paywalls. Those are off topic.

Please post the whole rule. You neglected this bit:

> It's ok to post stories from sites with paywalls that have workarounds.

Where's the workaround? I don't find workarounds for WSJ. WSJ is locked out. Please post the workaround, or kindly stop badgering people as it is not productive.

If there is no workaround that allows us to view WSJ articles, then WSJ article are NOT allowed here, per the rules you yourself selectively cited.

The rule about paywalls are that paywalled articles must come with a workaround, and that people should not post complaints about paywalls. His post did not complain about paywalls themselves nor does mine. He requests that paywalled articles be tagged as such, a much more relaxed rule than the official rules which are that paywalled articles without workarounds, such as WSJ articles (unless someone would like to post a legal workaround allowing us to view WSJ articles), are not allowed.

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#12

Post by msbarnett »

mlyle wrote: post #4
cjbprime wrote: post #3

Earlier quoted context omitted.

It's weird to see an article writing about this without mentioning the regulatory and training aspect. Previous MAX MCAS *couldn't" allow the pilot to override with the stick, because previous MCAS both needed to prevent a pilot-induced stall and needed to require no training or knowledge from the pilot in order to maintain the type rating. A better way to write the article would be "Boeing and the airlines have give…

> previous MCAS both needed to prevent a pilot-induced stall MCAS is there mostly because of certification requirements for hands-off stability. It is not a mechanism to prevent the pilot from stalling the aircraft.

> MCAS is there mostly because of certification requirements for hands-off stability

I don’t believe this is correct. During testing the MAX was discovered to have an inverted force curve on the stick approaching a stall — as the aircraft approaches stall angle, forces flip around and it becomes easier to pull the stick back (into the stall) than forward (out of the stall angle).

This violates a fundamental airworthiness requirement — commercial aircraft cannot be certified as airworthy if the stick forces invert.

MCAS “solves” this by commanding the stabilizers down as the airplane approaches stall — effectively using the stabilizer to put the forces on the stick that are “missing” due to the MAX’s aerodynamics, ensuring the force curve never inverts.

MCAS is entirely about generating force on the stick to meet airworthiness regs, not hands-off stability. It actually can’t disengage when the pilot pulls back on the stick, as that would defeat its entire purpose re: the airworthiness force-on-stick requirement.

The WSJ kind of muddled things here. The KC-46A does mid-air refueling, and its semi-similar MCAS system is about hands-off stability — compensating automatically as the weight and balance of the plane dynamically changes as fuel is offloaded. The pilot can override it with the stick because its purpose isn’t to provide stick force.

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#13

Post by kart23 »

tus88 wrote: post #8

But presumably the pilots of both downed MAXs were pulling back as hard as possible.

So scary. It's like driving a car, trying to slow down, slamming on the brake, but it just keeps accelerating. Cant imagine everyone's feelings on those flights.

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#14

Post by GhettoMaestro »

msbarnett wrote: post #12
mlyle wrote: post #4

Earlier quoted context omitted.

> previous MCAS both needed to prevent a pilot-induced stall MCAS is there mostly because of certification requirements for hands-off stability. It is not a mechanism to prevent the pilot from stalling the aircraft.

> MCAS is there mostly because of certification requirements for hands-off stability I don’t believe this is correct. During testing the MAX was discovered to have an inverted force curve on the stick approaching a stall — as the aircraft approaches stall angle, forces flip around and it becomes easier to pull the stick back (into the stall) than forward (out of the stall angle). This violates a fundamental airworthi…

Is there a summarized list somewhere of fundamental airworthiness requirements such as the one you listed?

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#15

Post by mlyle »

GhettoMaestro wrote: post #14
msbarnett wrote: post #12

Earlier quoted context omitted.

> MCAS is there mostly because of certification requirements for hands-off stability I don’t believe this is correct. During testing the MAX was discovered to have an inverted force curve on the stick approaching a stall — as the aircraft approaches stall angle, forces flip around and it becomes easier to pull the stick back (into the stall) than forward (out of the stall angle). This violates a fundamental airworthi…

Is there a summarized list somewhere of fundamental airworthiness requirements such as the one you listed?

It's 14 CFR 25.173 and 14 CFR 25.175.

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#16

Post by mlyle »

cjbprime wrote: post #9
mlyle wrote: post #4

Earlier quoted context omitted.

> previous MCAS both needed to prevent a pilot-induced stall MCAS is there mostly because of certification requirements for hands-off stability. It is not a mechanism to prevent the pilot from stalling the aircraft.

I don't agree. I think the lift from the nacelles results in decreasing stick backpressure while the nose is being raised in some circumstances, which is both a handling issue and an airworthiness violation. It's an airworthiness violation because it exacerbates rather than discourages stalls. If the pilot continues pulling back on the stick with reduced backpressure the plane would stall, therefore MCAS is (indirect…

I think it's odd that you describe a failing of 14 CFR 25.173-- the stability airworthiness requirement-- as not being "fundamentally aerodynamically unstable".

The stick force inversions you describe are just a symptom of divergent longitudinal stability. If you are trimmed stick-neutral for climb, deceleration doesn't cause sufficient nose drop, which in turn causes further deceleration and the aircraft does not return to the trim speed.

Both test methods are described in 25.175 and were problematic for the 737 MAX.

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#17

Post by [deleted] »

droithomme wrote: post #11
chrisseaton wrote: post #7

Earlier quoted context omitted.

https://news.ycombinator.com/newsfaq.html > But please don't post complaints about paywalls. Those are off topic.

Please post the whole rule. You neglected this bit: > It's ok to post stories from sites with paywalls that have workarounds. Where's the workaround? I don't find workarounds for WSJ. WSJ is locked out. Please post the workaround, or kindly stop badgering people as it is not productive. If there is no workaround that allows us to view WSJ articles, then WSJ article are NOT allowed here, per the rules you yourself sel…

[deleted]

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#18

Post by blattimwind »

kart23 wrote: post #13
tus88 wrote: post #8

But presumably the pilots of both downed MAXs were pulling back as hard as possible.

So scary. It's like driving a car, trying to slow down, slamming on the brake, but it just keeps accelerating. Cant imagine everyone's feelings on those flights.

The good thing with cars is that the time to avert a crash is generally very low (<1 second - <10 seconds), so while you're bending the supports of your seat pushing down on the brake pedal in panic, that state is not going to last very long.

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#19

Post by trimbo »

droithomme wrote: post #11
chrisseaton wrote: post #7

Earlier quoted context omitted.

https://news.ycombinator.com/newsfaq.html > But please don't post complaints about paywalls. Those are off topic.

Please post the whole rule. You neglected this bit: > It's ok to post stories from sites with paywalls that have workarounds. Where's the workaround? I don't find workarounds for WSJ. WSJ is locked out. Please post the workaround, or kindly stop badgering people as it is not productive. If there is no workaround that allows us to view WSJ articles, then WSJ article are NOT allowed here, per the rules you yourself sel…

The 'web' link hacker news supplies worked for me (in incognito)

Re: Before 737 Max, Boeing’s Flight-Control System Included Key Safeguards

#20

Post by chrisseaton »

droithomme wrote: post #11
chrisseaton wrote: post #7

Earlier quoted context omitted.

https://news.ycombinator.com/newsfaq.html > But please don't post complaints about paywalls. Those are off topic.

Please post the whole rule. You neglected this bit: > It's ok to post stories from sites with paywalls that have workarounds. Where's the workaround? I don't find workarounds for WSJ. WSJ is locked out. Please post the workaround, or kindly stop badgering people as it is not productive. If there is no workaround that allows us to view WSJ articles, then WSJ article are NOT allowed here, per the rules you yourself sel…

If you don’t know how to workaround WSJ paywalls then ask someone - the rules allow for that. They didn't ask - they just complained. Or pay up and subscribe to the WSJ!
Post reply on HN