6
$\begingroup$

We read that MCAS on the Boeing 737 MAX was needed because of the new, bigger, heavier engines of the MAX compared to the previous 737 versions.

The closest equivalent to MCAS on the Airbus A320 NEO is the alpha protection even if they are not the same.

But what have been the adaptations to the A320 due to heavier, larger engines? Can we be sure that A320 does not suffer from issues comparable to those the 737 MAX has, due to their similarities (bigger engines on same airplane)?

$\endgroup$
  • 3
    $\begingroup$ You're going to get shot down here due to having 6 questions in one request. $\endgroup$ – CrossRoads Apr 2 at 13:02
  • $\begingroup$ And your premise is not correct. It wasn't just "new, bigger, heavier engines", it is their change in location "The new Maneuvering Characteristics Augmentation System mitigates the pitch-up tendency of the new flight geometry due to the heavier engines being located further forward and higher than the previous ones." $\endgroup$ – CrossRoads Apr 2 at 13:06
  • $\begingroup$ Given that MCAS was a hidden feature, I don't think the question(s) can be answered factually. More so because the A320/neo is fly-by-wire, the 737/Max is not. $\endgroup$ – ymb1 Apr 2 at 14:16
  • 1
    $\begingroup$ "Can we be sure that A320 does not suffer from issues comparable to those the 737 MAX has, due to their similarities" looks awfully close to accident speculation, which is off topic here. $\endgroup$ – a CVn Apr 2 at 15:34
15
$\begingroup$

The A320 and 737 have very different flight control architectures.

The 737 has physical cables that transmit pilot (or autopilot) input directly to the hydraulic actuators. This was common in the 1960's when the airplane was first designed. This means that the airplane handling comes down to the aerodynamics and the pilot input.

The 737 MAX presented an issue when it was found that certain situations approaching stall could cause the airplane to pitch up, exacerbating the stall, rather than naturally pitching down and recovering as expected. This was due to the larger engine nacelles, which are located ahead of the center of gravity. An aerodynamic change would have taken lots of time and money and had its own drawbacks. Instead, Boeing created MCAS. This applies trim to help to pitch the airplane down when it reaches high angles of attack.

The A320, on the other hand, was designed as a fly-by-wire aircraft. This means that a computer is using sensor inputs to control the airplane all the time, and pilot or autopilot inputs only provide a guide to that computer control.

Fly-by-wire allows some helpful safety features, such as not allowing the airplane to exceed the design envelope, including stall. This means that any A320 in normal conditions will allow the airplane to reach a maximum angle of attack and no higher. Any aerodynamic differences such as a different fuselage length, larger engines, etc, are countered by the flight computer. Other than some possible fine tuning of the control laws of the fly-by-wire system, the A320 neo would not need any special new system to control angle of attack.

$\endgroup$
  • $\begingroup$ [1] Neither this, nor the answer posted by @Barath are not actual answers. There are several issues: (1) Is the 320 ceo inherently less aerodynamically stable than the 737 NG? (2) Do bigger engines introduce similar pitch-up issues on the Neo - aerodynamically, not in piloting - as they did on the Max? (3) Does neo mitigate these issues using existing fly-by-wire system without affecting piloting? (4) How many computers the neo has? (I believe the ceo has 3 independent 286-based computers. The Max has two computers). (5) Can the Neo switch between computers in-flight? (The Max cannot). $\endgroup$ – Rusty Core May 1 at 17:33
  • $\begingroup$ [2] (6) How many sensors does each Neo computer reads from? (The Max reads from a single AOA and a single airspeed sensor on one side of the aircraft; sensors on the other side are connected to the second computer, that is turned off in flight). (7) What is the design and positioning of the sensors on the Neo compared to the Max, are they better protected from impact or more durable? (8) When the fly-by-wire system activates on the 320, how much freedom does it give to a human pilot? (The MCAS is explicitly designed to overpower the pilot). $\endgroup$ – Rusty Core May 1 at 17:33
  • 1
    $\begingroup$ @RustyCore Welcome to Aviation.SE! I would suggest you ask new questions, at least splitting the architecture (how many computers, how many sensors, location of sensors) and the functionality (FBW effect on handling, pilot input) into separate questions. We also have some related questions already, such as this and this, feel free to look around and reference existing questions if there's something more you'd like to know. $\endgroup$ – fooot May 1 at 18:03
4
$\begingroup$

The 737 Max had short landing gear. Since the engines need to have a minimum ground clearance, this meant that the new larger engines had to be repositioned further forwrd and higher on the wing.

The repositioned engine along with the new engine nacelle shape meant it had different flying characteristics at high angles of attack (eg due to airflow). Thus Boeing introduced the MCAS system to reduce chances of stall in manual mode and try to make the plane behaviour the same as before.

The A320 has larger "legs". It could accommodate the larger heavier engines of the A320neo without requiring re-positioning from the A320ceo. In fact, the LEAP 1A of the A320neo is marginally larger and heavier than the LEAP 1B of the 737Max. Even the PW1100G option for the A320neo is marginally larger than the LEAP1B (737MAX). [All the newer gen engines are larger and heavier than the previous gen engines of the 737NG/320ceo]

Plus Airbus just has a completely different design approach and architecture for flight control. Airbus A320 was designed as a fly by wire aircraft, from the get-go, the Boeing 737 was designed in a different era,and manual mode had no real computer control (except automatic trims & MCAS). Plus there may be differences in the sensor/computer architecture etc.

Bottom line, the 737Max needed a new system, while the A320neo probably needed change in configurations but no new system for control...

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.