4 ms·

> but shouldn't planes always be controllable by the column so long as the plane is mechanically OK? The problem is that you can easily exceed the aircraft fli

by Shank 8y ago

> but shouldn't planes always be controllable by the column so long as the plane is mechanically OK? The problem is that you can easily exceed the aircraft flight specifications if you enable unlimited control. If you pull the stick back at max power you can seriously risk the creation of a stall, which is why MCAS exists in the first place. The whole goal Boeing had was to create a safe plane by letting software ensure it was always flying within the safe envelope for mechanical stress. > That is: a pilot in panic at low altitude should never be required to do anything more than he basically can with hands on throttle and stick, to avoid disaster? You would hope this, but what makes the determination that the pilot is at a low altitude? The altimeter tells you where you are in relation to sea level, not the nearest distance to terrain. You could be 10,000 feet above sea level but only 1,000 above a mountain. There's a lot of sensor data you'd have to take into account if you were to try to enable a higher degree of control based on how safe/dangerous it is to give that control.

hammock 8y ago
>what makes the determination that the pilot is at a low altitude? Give the pilot an emergency override button and let him make the judgment call. The whole point of parent comment is that too many sensors and software have removed the pilot's final discretion over the aircraft.
drunken-serval 8y ago
> You would hope this, but what makes the determination that the pilot is at a low altitude Radar altimeter. Any aircraft with autoland capability should have three of them.
CaptainZapp 8y ago
The problem is that you can easily exceed the aircraft flight specifications if you enable unlimited control. If you pull the stick back at max power you can seriously risk the creation of a stall, which is why MCAS exists in the first place. That's manifestly wrong. MCAS was introduced because of the design decision to place the larger and more powerfull power plants further in front and higher up. The reason for this was that Boeing wanted to grandfather the 737 certification into this model and wanted to avoid pilot retraining in the simulator, which was an important sales argument. The problem with this redesign was that the airframe tended to point the nose up, since its aerodynamical characteristics changed due to the redesign. MCAS was introduced in order to simulate the same behavioral characteristics of the older 737s. This is proven by the fact that the system was neither documented nor was it part of the scenarios in the 737 MAX simulator. The idea was that the functionality is completely transparent to the pilots so that the could fly the new plane after a minimal presentation on an iPad, which was less thank one hour if they were already 737 certified. The problem was not pilots pulling the nose too high. The problem, which MCAS tried to correct was the tendency of the plane to pull the nose high and correct for it. Boeing tried to cram a 50 year old airframe into a new plane with engines too big to fit that airframe and wanted to avoid recertification and retraining. That's the whole issue we're discussing here. edit: clarification
- Shank 8y ago
  > The problem with this redesign was that the airframe tended to point the nose up, since its aerodynamical characteristics changed due to the redesign. Alas, I do appreciate your comment. This is what I was attempting (but failing) to say.
- cmurf 8y ago
  >MCAS was introduced in order to simulate the same behavioral characteristics of the older 737s. Sounds plausible, but something with the story is still super screwy because a nose down "push" every 15 seconds is nothing like older 737 approach to stall behavior. If the idea is you want the same stick forces at approach to stall as 737NG, then you need some kind of motor or brake in the yoke mechanics to simulate it on a MAX. If it were really simulating the 737NG stick forces, and this were erroneously triggered in an appropriate angle of attack state, the pilot would simply be getting weird/unexpected control stick forces - rather than a fight to the death, possibly at low altitude. And if that simulation were to fail when needed (real high angle of attack), well yeah you're fucked if it's a necessary simulation to help the pilot avoid a developed stall. But at least in that case I would expect even slightly delayed recovery from stall is a better scenario than forcing the nose down. I just don't like this feature pretty much as designed when working, when it's disabled, and when it's confused. It all smells like bullshit. Now I could easily be wrong and it's actually duck farts. But something stinks. I don't see how it gets around either FAR 25 airworthiness certification requirements, because it can be disabled. Or around FAR 61.31 type rating requirement, because it can be disabled. Disable it, and now your airplane is not airworthy and your pilot possibly not suitably type rated? Come on.
  - CaptainZapp 8y ago
    But something stinks. I don't see how it gets around either FAR 25 airworthiness certification requirements, because it can be disabled. That's easy. When the manufacturer rubberstamps his own ariworthyness certification this is not really a problem. Disable it, and now your airplane is not airworthy and your pilot possibly not suitably type rated? That's the exact crux of the issue. Boeing panically wanted to avoid recertification of the plane and the pilots in order to be competitive with Airbus' A320 NEO.

by Shank 8y ago

hammock 8y ago

>what makes the determination that the pilot is at a low altitude? Give the pilot an emergency override button and let him make the judgment call. The whole point of parent comment is that too many sensors and software have removed the pilot's final discretion over the aircraft.

drunken-serval 8y ago

> You would hope this, but what makes the determination that the pilot is at a low altitude Radar altimeter. Any aircraft with autoland capability should have three of them.

CaptainZapp 8y ago

The problem is that you can easily exceed the aircraft flight specifications if you enable unlimited control. If you pull the stick back at max power you can seriously risk the creation of a stall, which is why MCAS exists in the first place. That's manifestly wrong. MCAS was introduced because of the design decision to place the larger and more powerfull power plants further in front and higher up. The reason for this was that Boeing wanted to grandfather the 737 certification into this model and wanted to avoid pilot retraining in the simulator, which was an important sales argument. The problem with this redesign was that the airframe tended to point the nose up, since its aerodynamical characteristics changed due to the redesign. MCAS was introduced in order to simulate the same behavioral characteristics of the older 737s. This is proven by the fact that the system was neither documented nor was it part of the scenarios in the 737 MAX simulator. The idea was that the functionality is completely transparent to the pilots so that the could fly the new plane after a minimal presentation on an iPad, which was less thank one hour if they were already 737 certified. The problem was not pilots pulling the nose too high. The problem, which MCAS tried to correct was the tendency of the plane to pull the nose high and correct for it. Boeing tried to cram a 50 year old airframe into a new plane with engines too big to fit that airframe and wanted to avoid recertification and retraining. That's the whole issue we're discussing here. edit: clarification

Shank 8y ago
> The problem with this redesign was that the airframe tended to point the nose up, since its aerodynamical characteristics changed due to the redesign. Alas, I do appreciate your comment. This is what I was attempting (but failing) to say.
cmurf 8y ago
>MCAS was introduced in order to simulate the same behavioral characteristics of the older 737s. Sounds plausible, but something with the story is still super screwy because a nose down "push" every 15 seconds is nothing like older 737 approach to stall behavior. If the idea is you want the same stick forces at approach to stall as 737NG, then you need some kind of motor or brake in the yoke mechanics to simulate it on a MAX. If it were really simulating the 737NG stick forces, and this were erroneously triggered in an appropriate angle of attack state, the pilot would simply be getting weird/unexpected control stick forces - rather than a fight to the death, possibly at low altitude. And if that simulation were to fail when needed (real high angle of attack), well yeah you're fucked if it's a necessary simulation to help the pilot avoid a developed stall. But at least in that case I would expect even slightly delayed recovery from stall is a better scenario than forcing the nose down. I just don't like this feature pretty much as designed when working, when it's disabled, and when it's confused. It all smells like bullshit. Now I could easily be wrong and it's actually duck farts. But something stinks. I don't see how it gets around either FAR 25 airworthiness certification requirements, because it can be disabled. Or around FAR 61.31 type rating requirement, because it can be disabled. Disable it, and now your airplane is not airworthy and your pilot possibly not suitably type rated? Come on.
- CaptainZapp 8y ago
  But something stinks. I don't see how it gets around either FAR 25 airworthiness certification requirements, because it can be disabled. That's easy. When the manufacturer rubberstamps his own ariworthyness certification this is not really a problem. Disable it, and now your airplane is not airworthy and your pilot possibly not suitably type rated? That's the exact crux of the issue. Boeing panically wanted to avoid recertification of the plane and the pilots in order to be competitive with Airbus' A320 NEO.