Originally posted by Black Ram
View Post
Announcement
Collapse
No announcement yet.
Lion Air 737-Max missing, presumed down in the sea near CGK (Jakarta)
Collapse
X
-
-
Originally posted by Evan View PostThe odds of an A320 having a bad ‘final AoA’ are extremely remote, and this was the standard used to certify it. I don’t recall the actual odds used, but they were considered, for all intents and purposes, impossible (barring any maintenance stoogery, of course). Even so, there are procedures to quickly degrade to alternate law without losing controllability or FBW methodology (whether those procedures are widely known is another story). But the point is, every REASONABLE precaution was taken to ensure that envelope protections required to certify the aircraft would be fail-operational following the failure of a single air-data source.
As I understand it, MCAS will now be inop following the failure of a single air-data source. It is now fail-safe but not fail-operational. That means the airplane, by certification criteria, is potentially unsafe (and we have learned many times over that aviation disasters often are the result of a rare but still foreseeable combination of failures and pilot error).
So the question I would like answered is: why is requiring triple modular redundancy for MCAS unreasonable in an age where it is the standard for critical systems?
In your own words:
The A320 needed three AoA sensors to achieve certification. Why? Because AoA data can override pilot inputs.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
Comment
-
Originally posted by Gabriel View PostEvan, I am not stating that it is unreasonable to require triple redundancy for the MCAS. What I am saying is that using the A320 certification as a basis for claiming so is not reasonable.
In your own words:
That's not the case with Boeing, with ANY Boeing, even with the previous version of the MCAS which was horrible and unacceptable for other reasons.
From everything I’ve learned about MCAS this far, it seems that it was also REQUIRED to compensate for a serious safety concern at the limits of the safe envelope and the -MAX cannot be dispatched for revenue service with MCAS inop. Yet MCAS was designed (and certified) without redundancy and now redesigned to be fail-safe, not fail-operational, after a single-point failure.
That seems a lot like a double standard to me. And I still would like to know why they didn’t require it to be fail-operational.
Comment
-
Originally posted by Schwartz View PostThe Airbus control design is fundamentally different and a loose comparison is not valid. Remember, MCAS may have only been necessary to make the MAX feel exactly like the old 737, so no new training was required. I would not be surprised, if they mandate new training for the MAX now. On it's own, the MCAS may not have been required as a safety issue. To be fair, I'm not certain of that, but again, I don't think your comparison is valid. It seems to me, the plane is entirely flyable without MCAS and the override if properly programmed is something the pilots train for.
Comment
-
Originally posted by Evan View PostYou need to read up more on MCAS. There were pitch behaviors created by the aerodynamic effects of the repositioned nacelles that resulted in serious concerns during approach to stall. The aircraft in this state was considered unsafe.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
Comment
-
Originally posted by Evan View PostOk, let me be more clear on this: certifying the A320 without trim force feedback REQUIRED envelope protections
From everything I’ve learned about MCAS this far, it seems that it was also REQUIRED to compensate for a serious safety concern at the limits of the safe envelope
All airplanes with underslung engines have a strong tendency to pitch up when power is added from very low thrust to very high thrust especially at low airspeed and high AoAs. There were even serious incidents with different airplanes where control was lost due to this combined with improper pilot handling of the situation. The fact that the MAX has a stronger effect than the NG doesn't per se make it a more serious safety concern than it is in other types. However, it may imply specific training that Boeing was trying to avoid.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
Comment
-
-
From everything I’ve learned about MCAS this far, it seems that it was also REQUIRED to compensate for a serious safety concern at the limits of the safe envelope
There may be SOME validity, but conversely, I question whether a slow trim response is really appropriate for an unrecoverable stall...
If unrecoverable stalls are an issue, I'd think a mega stick pusher might be more called for.
As Gabbieee has repeatedly stated, the goal to not have special training requirements was very big too.
I can see where special training to shove HARDER could be avoided with something MCASISH.
Also, if it's UNRECOVERABLE stall, I'd speculate they would have done double AOA instead of single AOA reading for MCAS...
If you just want to make it FEEL nicer, then what the heck, only one AOA vane is good enough.Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.
Comment
-
Originally posted by ATLcrew View PostThen why, in Saint Agatha's name, did you let him anywhere near the sim?
Comment
-
Originally posted by ATLcrew View PostOh aviation matters? I don't think so, Tim.
Comment
-
Originally posted by Evan View PostYou still don’t get it. This isn’t an aviation matter. It’s a matter of reckless management serving investor relations at the expense of safety. It’s a sort of industrial epidemic lately. And yes, the Times is a good place to find those truths.
Comment
-
Originally posted by Evan View PostYou still don’t get it. This isn’t an aviation matter. It’s a matter of reckless management serving investor relations at the expense of safety. It’s a sort of industrial epidemic lately. And yes, the Times is a good place to find those truths.
Comment
-
Even the NTSC's report on Lion AIr's accident (which is being praised by the industry at great) is ambiguous on the matter:
During the preliminary design stage of the Boeing 737-8 (MAX), Boeing tests and analysis revealed that the addition of the LEAP-1B engine and associated nacelle changes was deemed likely to negatively affect the stick force per g (FS/g) characteristics required by 14 FAR 25.255 and the controllability and maneuverability requirements of 14 FAR 25.143(f). After the study of various options for addressing this issue, Boeing implemented aerodynamic changes as well as a stability augmentation function called the Maneuvering Characteristics Augmentation System (MCAS), as an extension of the existing Speed Trim System (STS), to improve aircraft handling characteristics at elevated angles of attack. The MCAS was needed in order to make the Boeing 737-8 (MAX) handling characteristics so similar to the NG versions that no simulator training was needed for type rating. It was also required so that the 737 MAX passed the certification that the pitch controls could not get lighter on the approach to stall. If the aircraft had substantially different pitch behavior, then there would be a simulator training requirement for the pilots.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
Comment
-
Comment