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I have a little question concerning MCAS from Boeing and Alpha Protection from Airbus.

I think these two systems are the same, if I'm wrong please tell me.

If the two 737 MAX crashed because of the pilots not knowing how to behave when the MCAS behaves wrong, isn't it possible that the same could happen to A321 pilots?

I remember a Lufthansa flight (Airbus) in which the sensors froze and the pilots also didn't know how to behave. They turned the sensor off after talking with the technicians.

Jimy
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  • Could it happen to Airbus Pilots? Yes! Could it happen to Bombardier Pilots? Yes! Pilots of other manufacturers? Yes! While during the takeoff, pilots have a huge workload and little time to evaluate any problems, this appears to me to be more of a training problem rather then piloting skills. – Maverick283 Mar 14 '19 at 07:53

1 Answers1

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No, the two systems are completely different.

The MCAS of the new Boeing 737 MAX was introduced to help the pilots lower the nose in high angle of attack situations by applying down stabilator trim. This was necessary because the engines are mounted further forwards compared to the previous NG models.

Note: We do not know whether or not MCAS caused the recent crash in Ethiopia yet, it is a bit premature to jump to conclusions now!

The Alpha Protection on Airbus aircraft is part of the fly-by-wire control (What is the Alpha protection?) and will limit control inputs from the pilots instead of applying trim. This is very different from how MCAS works.

Bianfable
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    Also, and kind of importantly, based on what I read so far, the design features regarding e.g. redundancy of input sensors are very different (Boeing: one (or two?) sensors operative at a time, meaning pilot must identify whether system works correctly; Airbus: three sensors operative at a time, meaning the system can determine whether it receives correct data (by comparing all three parameters) and can declare itself inoperative in case it doesn’t). – Cpt Reynolds Mar 13 '19 at 18:36
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    Also, on Airbus, it is not overriding control inputs, it limits control inputs. For example, on MMO/VMO protection if you push down your nose, and you reach VMo or MMO, you will still be able to pushdown but the pitch angle you will be able to reach will be limited by the EFCS. During a stall approach it is quite different since you also have the Alpha floor protection from the engine. – Chris Lau Mar 13 '19 at 20:31
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    @ChrisLau you're right, override was a wrong choice of words, I fixed it to limit. – Bianfable Mar 14 '19 at 07:22
  • re "We do not know whether or not MCAS caused the recent crash in Ethiopia". What about Lion Air? If I understood correctly, you can handle "nose down" by MCAS as a runaways stabilizers problem, even without knowing the existence of MCAS; the stab trim cutoff avoids the MCAS to be able to do anything, but in the same time makes it necessary to trim manually (if you are not at high altitude and realized the problem too late, the stabilizers could be all "nose down" and maybe there will be no time to trim those back up). My point: put in certain ways, MCAS alone never will be the cause. – ShinTakezou Mar 31 '19 at 13:18
  • @ChrisLau this answer says somewhat differently, stating the Alpha protection will act to lower the nose of the aircraft. Although I think its a somewhat academic distinction... if flight conditions change and suddenly alpha prot is limiting your control input to a lot less than it was a second ago, I think most people would call that being "overridden". – mbrig Apr 02 '19 at 18:58
  • @mbrig I understand your point. I was more pointing on the technical point of view. Because if we go from the perspective that if it is limiting, it is overriding then since you have a flight control computer giving you all the time a domain of work, it is always overriding your input when you are flying Normal or Alternate law. Same applies for other protection from other OEMs. – Chris Lau Apr 11 '19 at 12:33
  • @Chris Lau You got it backwards… Boeing limits pilot input when the edge of the flight envelope is encountered—actually, not a hard limit, makes it very, very difficult to move the control further, but if desperation should bestow superhuman strength on the pilot Boeing knows better than to stand in the way. Boeing doesn't allow primary control input with no control surface movement. Airbus allows the pilots to move the controls any way they please… and ignores any input that would result in ops outside the flight envelope. That is an override. – Pete P. Dec 16 '22 at 04:09