Comment by SomeHacker44 | Hacker News Reader

Comment by SomeHacker44 | Hacker News Reader

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The point is that all legally licensed 737-type-rated pilots are currently legal to fly the 737 MAX line, no questions asked, no training needed. (As far as I know.) The plane should be moved to a new type certificate and all its attendant requirements, seems to me.

I can’t legally be the PIC (pilot in command) in a Citation 525 (“CitationJet” or CJ) despite it being nearly identical to the 550 (Citation II or Bravo) I can, in most ways that I can tell matters. I have copilot time in both and PIC in the 550 (and related models). The newer plane is even easier to fly, frankly, and has some nice safety features for engine failures. I have to get the training and certification (and recertification every two years) to legally be PIC in the newer Citation, though.

My limited understanding is that the aerodynamics and flight characteristics of the 737 MAX are quite different than the older 737-800 - let alone the even older second (or even first) generation 737s. The memory items may be different. That alone should have mandated a new type certificate in my non-regulatory expert perspective.

Flight characteristics are reported to be the same in the normal flight envelope except at high angles of attack where the new engine nacelle actually produces lift which translates into a further pitch up - but I have no idea how aggressive this is. But it's enough that this is why MCAS exists.

I'm certainly concerned whether MCAS is both working as intended, and also failing safe. But my more immediate concern is like yours: when MCAS is effectively disabled in the normal course of troubleshooting runway trim by setting stab trim to cutoff, now you have a plane that has different stall behavior than you're type rated for! Flip those switches, now you need a different type rating! Of course pilots can learn different stall behaviors and avoidance for a new type, we don't need abstraction to do that for us when we know about it and have trained for it. Stall avoidance is fundamental make+model knowledge, but it can be non-obvious and making it obvious and deliberate is what the type rating is about.

So yeah we might actually end up in the very curious case where either Boeing, or FAA or NTSB are all: this is going to require a type rating afterall. The very thing the airlines in particular want to avoid.

It seems to me the in-cockpit "aoa disagree" option needs to become standard by AD. MCAS only takes input from one of the two alpha vanes, so if it gets bogus data it has no backup source. Meanwhile the pilots have no indication the two vanes disagree unless they (apparently) bought that indication feature. Which I think is pretty fucked up if that turns out to be true and relevant as to either cause or solution in all of this.

The solution here is going to be to have MCAS automatically disengage when the two sensors disagree, which will change the stall behavior automatically. Airbus has the same problem, and so will any manufacturer that introduces computer augmented flight characteristics in their aircraft. If a component of the computerized flight control system fails, the flight characteristics of the aircraft will change. In fact, Airbus has had a similar crash: in that instance, a pilot was pulling full back on the stick thinking that the aircraft was unstallable, but one of the sensors (airspeed, maybe? can't remember) was disabled (by icing, if I remember) and the aircraft had changed to a different flight control law that didn't have the anti-stall function. Splash.

Eh, I googled it for you people. It was air france 447: https://en.wikipedia.org/wiki/Air_France_Flight_447

I don't think the AF crash was a case of that pilot "thinking it was unstallable" so much as not thinking, in the mental state he was in at that point. Even if the plane were "unstallable", pulling full back on the stick like that would not have been the right course.

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