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This is entirely false. Stop spreading disinformation. Myth: the 737 MAX 8 is not inherently stable, has relaxed stability, etc. Fact: it's very much inherentl

This is entirely false. Stop spreading disinformation. Myth: the 737 MAX 8 is not inherently stable, has relaxed stability, etc. Fact: it's very much inherently stable. Myth: the 737 MAX 8 is easier to stall than other planes. Fact: no it isn't. The pitch-up characteristic of the MAX 8 is less strong than of e.g. the 757 and that plane flies just fine. The actual problem with the MAX 8 is that Boeing added MCAS to allow it to share a type rating with the rest of the 737 family (allowing existing 737 pilots to fly the MAX 8 without additional training), and they fucked up MCAS. There's a number of solutions on the table, including removing rather than fixing MCAS and giving up the 737 type rating. I am continuously astounded that even on HN people are focusing on news cycle bullshit about inherent instability instead of the actual issues with Boeing/FAA that caused this situation. Evidence so far suggests that MCAS was originally a non-critical system that was found to be too weak during flight testing, and given significantly more pitch authority. For whatever reasons, this didn't trigger the reclassification of MCAS as a critical system and it all went downhill from there. Here's a pair of sources slightly more credible than the bullshit news cycle: https://www.youtube.com/channel/UCphqjYZxxzjNbONVmY-0J7Q https://www.youtube.com/channel/UCphqjYZxxzjNbONVmY-0J7Q https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow

thefounder 7y ago
The engines are too BIG for the airframe! Why people don't get it?
usrusr 7y ago
> I am continuously astounded that even on HN people are focusing on news cycle bullshit about inherent instability instead of the actual issues with Boeing/FAA that caused this situation. How is it surprising that people are sceptical of claimed native flight characteristics after the way Boeing has handled communications after the crashes? I don't think that there are any independent facts around, even airline pilots who had been flying MAX from day one would not have much (if any) experience at the edges of the flight envelope. One data point we do know is that some people at Boeing were apparently very concerned about MCAS ever being off.
- tjoff 7y ago
  Skeptical, absolutely! But it doesn't help to make up new facts.
neuronic 7y ago
If a software system has to be designed to make up for aircraft design problems, namely the too large engines that break the limits for ground clearance in the normal 737NG config, then the mentioned issues are not "entirely false" and "disinformation". Boeing needed to counter the A320neo and they needed to take shortcuts that ended up killing people. I wouldn't be surprised if this were management failure and the actual engineers at Boeing have always been throwing around copious WTFs when building the 737 MAX 8. "Hey engineers, improve the 737 to be X% more fuel efficient and make sure it doesn't need to be reclassified as new type. Have fun!"
- rbanffy 7y ago
  > they needed to take shortcuts that ended up killing people. No. They chose to take shortcuts.
  - neuronic 7y ago
    I stand corrected.
mgsouth 7y ago
Ironically, I believe that your information is also inaccurate. MCAS is required in order to meet federal airworthiness requirements. Without it, in certain flight conditions the back-pressure on the control yoke gets less as the yoke is pulled further back. It's like over-steer in a car, and is simply not allowed. Yes, the plane is dynamically stable; if you leave the yoke in one position it won't pitch up even more. However, the forces must be corrected somehow, regardless of type rating concerns. "The 737 MAX was a bit too easy to pull into a stall when flying with high AoA and making abrupt maneuvers. The larger engines for the MAX hung further forward from the wing, added a destabilizing aerodynamic area ahead of the center of gravity, destabilizing the pitch moment curve at high AoA. Boeing and the certification authority, FAA, decided added margins was called for. Boeing added a pitch augmentation at high AoA called Maneuvering Characteristics Augmentation System, MCAS. The aircraft should trim nose down to increase the stick force needed once it passed into the light grey area where the base aircraft had a region of less stability. Before the augmentation, the pilot felt if the aircraft wanted to fly into the stall, it got easier to increase the AoA after 12°AoA. With the augmentation the felt extra force was the same for the first and last part of the curve before the maximum lift was achieved at stall (and stall warning kicked in)." [0] The manner of the fix (MCAS transparently pushing the nose down) was designed to avoid pilot retraining and thus keep the same type rating. Edit: The fact that the 737-Max needs a handling tweak is not a failure. Modern planes have all kinds of these tweaks, whether aerodynamic (such as strakes), mechanical (stick shakers) or enabled in software. As the cited article continues: "So far so good. It's common an aircraft’s flight control system has fixes to stability margin changes in different parts of the flight envelope." The problem is that Boeing had a pretty severe collapse of its systems engineering regime. "The implementation for the 737 MAX had two problems, however: - The fault checking of the triggering AoA signal was not rigorous enough. This problem has been discussed a lot. No need to add anything. - The judgment the pilots would identify a problem with the augmentation as a trim runaway and shut the trim off was wrong. Why the pilots didn’t see MCAS rouge actions as a trim runaway is poorly understood." (The article was published in February. Since then lots of information has come to light about how MCAS determinedly fought correction, and the huge mental and physical loads imposed on the pilots.) Edit 2: FAA regulation mandating increasing elevator forces for all transport aircraft: FAR §25.253 High-speed characteristics, (a) Speed increase and recovery characteristics, (3): With the airplane trimmed at any speed up to VMO/MMO [maximum operating airspeed], there must be no reversal of the response to control input about any axis at any speed up to VDF/MDF [maximum airspeed demonstrated in testing]. Any tendency to pitch, roll, or yaw must be mild and readily controllable, using normal piloting techniques. When the airplane is trimmed at VMO/MMO, the slope of the elevator control force versus speed curve need not be stable at speeds greater than VFC/MFC [maximum control airspeed], but there must be a push force at all speeds up to VDF/MDF and there must be no sudden or excessive reduction of elevator control force as VDF/MDF is reached. [1] [0] https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stability-part-9/ https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stabil... [1] https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se14.1.25_1203 https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se1...
dingaling 7y ago
> The pitch-up characteristic of the MAX 8 is less strong than of e.g. the 757 and that plane flies just fine. The 757 ( and 737NG etc ) has constant pitch rate. The Max does not, which is the root of the problem. The actual forces involved aren't pertinent.

thefounder 7y ago

The engines are too BIG for the airframe! Why people don't get it?

usrusr 7y ago

> I am continuously astounded that even on HN people are focusing on news cycle bullshit about inherent instability instead of the actual issues with Boeing/FAA that caused this situation. How is it surprising that people are sceptical of claimed native flight characteristics after the way Boeing has handled communications after the crashes? I don't think that there are any independent facts around, even airline pilots who had been flying MAX from day one would not have much (if any) experience at the edges of the flight envelope. One data point we do know is that some people at Boeing were apparently very concerned about MCAS ever being off.

tjoff 7y ago
Skeptical, absolutely! But it doesn't help to make up new facts.

neuronic 7y ago

If a software system has to be designed to make up for aircraft design problems, namely the too large engines that break the limits for ground clearance in the normal 737NG config, then the mentioned issues are not "entirely false" and "disinformation". Boeing needed to counter the A320neo and they needed to take shortcuts that ended up killing people. I wouldn't be surprised if this were management failure and the actual engineers at Boeing have always been throwing around copious WTFs when building the 737 MAX 8. "Hey engineers, improve the 737 to be X% more fuel efficient and make sure it doesn't need to be reclassified as new type. Have fun!"

rbanffy 7y ago
> they needed to take shortcuts that ended up killing people. No. They chose to take shortcuts.
- neuronic 7y ago
  I stand corrected.

mgsouth 7y ago

Ironically, I believe that your information is also inaccurate. MCAS is required in order to meet federal airworthiness requirements. Without it, in certain flight conditions the back-pressure on the control yoke gets less as the yoke is pulled further back. It's like over-steer in a car, and is simply not allowed. Yes, the plane is dynamically stable; if you leave the yoke in one position it won't pitch up even more. However, the forces must be corrected somehow, regardless of type rating concerns. "The 737 MAX was a bit too easy to pull into a stall when flying with high AoA and making abrupt maneuvers. The larger engines for the MAX hung further forward from the wing, added a destabilizing aerodynamic area ahead of the center of gravity, destabilizing the pitch moment curve at high AoA. Boeing and the certification authority, FAA, decided added margins was called for. Boeing added a pitch augmentation at high AoA called Maneuvering Characteristics Augmentation System, MCAS. The aircraft should trim nose down to increase the stick force needed once it passed into the light grey area where the base aircraft had a region of less stability. Before the augmentation, the pilot felt if the aircraft wanted to fly into the stall, it got easier to increase the AoA after 12°AoA. With the augmentation the felt extra force was the same for the first and last part of the curve before the maximum lift was achieved at stall (and stall warning kicked in)." [0] The manner of the fix (MCAS transparently pushing the nose down) was designed to avoid pilot retraining and thus keep the same type rating. Edit: The fact that the 737-Max needs a handling tweak is not a failure. Modern planes have all kinds of these tweaks, whether aerodynamic (such as strakes), mechanical (stick shakers) or enabled in software. As the cited article continues: "So far so good. It's common an aircraft’s flight control system has fixes to stability margin changes in different parts of the flight envelope." The problem is that Boeing had a pretty severe collapse of its systems engineering regime. "The implementation for the 737 MAX had two problems, however: - The fault checking of the triggering AoA signal was not rigorous enough. This problem has been discussed a lot. No need to add anything. - The judgment the pilots would identify a problem with the augmentation as a trim runaway and shut the trim off was wrong. Why the pilots didn’t see MCAS rouge actions as a trim runaway is poorly understood." (The article was published in February. Since then lots of information has come to light about how MCAS determinedly fought correction, and the huge mental and physical loads imposed on the pilots.) Edit 2: FAA regulation mandating increasing elevator forces for all transport aircraft: FAR §25.253 High-speed characteristics, (a) Speed increase and recovery characteristics, (3): With the airplane trimmed at any speed up to VMO/MMO [maximum operating airspeed], there must be no reversal of the response to control input about any axis at any speed up to VDF/MDF [maximum airspeed demonstrated in testing]. Any tendency to pitch, roll, or yaw must be mild and readily controllable, using normal piloting techniques. When the airplane is trimmed at VMO/MMO, the slope of the elevator control force versus speed curve need not be stable at speeds greater than VFC/MFC [maximum control airspeed], but there must be a push force at all speeds up to VDF/MDF and there must be no sudden or excessive reduction of elevator control force as VDF/MDF is reached. [1] [0] https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stability-part-9/ https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stabil... [1] https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se14.1.25_1203 https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se1...

dingaling 7y ago

> The pitch-up characteristic of the MAX 8 is less strong than of e.g. the 757 and that plane flies just fine. The 757 ( and 737NG etc ) has constant pitch rate. The Max does not, which is the root of the problem. The actual forces involved aren't pertinent.