[webdevatlurk]

It's well documented in numerous reports that:

1. The position and size of the upgraded engines for the 737 MAX caused the plane to tend to pitch upwards, which could cause a stall. 2. Boeing was concerned designed MCAS to automatically push the plane's nose down to prevent stalls

Every single piece of reporting I've seen on the matter refers to MCAS as an anti-stall device.

Pilots of 737 who have talked to reporters refer to it as an anti-stall device.

I have a hard time believing that this information hasn't been fact checked to hell and back yet.

[VBprogrammer]

> Every single piece of reporting I've seen on the matter refers to MCAS as an anti-stall device.

Assuming you are a developer, have you ever seen some reporting of something technical in the news? Does it not make you cringe?

> Pilots of 737 who have talked to reporters refer to it as an anti-stall device.

Even Boeing themselves do; so who can blame them. The reason that the certification item exists is to prevent certification of aircraft which demonstrate increasingly lighter control forces as the aircraft approaches a stall. The reason being that it makes it easier for an inattentive pilot to accidentally fly the aircraft into a stall. So if you want to shorten that to anti-stall then I'm fine with that.

What I don't really like is the retoric about how these aircraft would fall out of the sky without MCAS "controlling" the plane. It isn't a closed loop control system implementing PID control to account for some crazy instability in the aircraft.

[AceyMan]

> Every single piece of reporting I've seen on the matter refers to MCAS as an anti-stall device.

"Anti-stall" has become a catchphrase wrt the 737 MAX. I wish everyone would stop using it, but the horse has left the barn it seems.

MCAS was cooked up to maintain the handling characteristics required by the FAA certification specifications.

Other commenters in other threads have explained why consistent response curves are vital in operating an aircraft, so I won't take on the why of the regulation other than to say it's well founded and some smart systems/human factors engineers have elucidated on this in earlier threads. Otherwise, wouldn't it have been easiest of all for Boeing to beg "let us have the airplane respond this way; all planes are different, right?" And even if the FAA allowed that, it'd force a new type rating, I suspect; the very thing they so badly wanted to avoid.

The standard (see below) requires stick resistance to increase as the critical (stall) angle of attack is approached. The MAX violated that requirement due to the aerodynamics of the new engine cowls. (So: why didn't they mess with the cowls? I suspect that wasn't possible without impacting efficiency, which is a key selling point of the MAX.)

Back to the spec: as noted, it exists to provide a consistent response curve to the pilot compliant with the regulation.

As borne out by these accidents, MCAS is Boeing's (quick & dirty) implementation of "artificial feel" to meet the spec. Big, transport planes with hydraulic flight controls have had artificial feel for many years to provide a consistent and properly scaled input response (not too heavy, not too light, etc.)

As far as the FAA specification in question, the critical section is in CFR 14 §25 Subpart B—Flight ¹, notably the sections on Controllability & Maneuverability and Stability. In these sections 'stick force' appears sixteen times; 'stick force curve' appears six times.

It's "stick force curve" that MCAS was created to tweak. There's no mention of "reduce the critical angle" or "change the stall onset speed" or anything about the aircraft performance. It's about how the plane handles in a particular part of the flight envelope².

> Every single piece of reporting I've seen on the matter refers to MCAS as an anti-stall device.

Because it was printed repeatedly doesn't make it true (see, Gell-Mann amnesia effect³).

+++

¹–https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#sp1...

²–I'm surprised that MCAS reacts fast enough to count as artifical feel. Electric trim doesn't move all that fast, AFAIK. Still an open question in my mind.

³–https://en.wikipedia.org/wiki/Gell-Mann_amnesia_effect?wprov...

NB: this comment is edited/recompiled from snips of earlier comments I posted.

(me: FAA licensed aircraft dispatcher in a previous life)