No, it is not unstable without MCAS.
MCAS is only designed to change the trim if the airplane is hand flown in flaps-retracted, low-speed, nose-up flight.
This is something almost everyone is missing: A normal flight should not encounter this.
Plenty of normal flights fly manually for a significant portion of the climb-out after takeoff, which is exactly the portion of the flight when MCAS issues happened for the Lion Air and Ethiopian Air flights.
Also, you will have higher AoA in a bank, which can be encountered in manual flight on normal flights.
Nobody said there was anything abnormal about the two flights that crashed. It really doesn't matter since the root problem is the plane doing things without telling anyone and then doing it wrongly. Without MCAS these accidents would not have happened.
Without MCAS, wouldn't there be accidents caused by the nonlinear pitch though?
Not sure this is right. General aviation pilots often think of wing stalls as a consequence of low speed (their planes don't have AoA indicators!) but they can happen at any airspeed: they simply happen whenever the critical AoA is reached.
I think the idea is that the extra lift generated by the nacelles due to the engine position causes the plane to reach high AoA at e.g. full engine power, not just when flying slowly.
I think it's also the case that the plane does not actually become aerodynamically unstable, it just starts to handle differently (yoke pressure-wise) in a way that fails airworthiness requirements.
So it would only cause a stall if the pilots continued to pull back on the yoke into the stall while it's not fighting them as much as they're expecting it to.
What is your source? This is not what I have been reading. What I have been reading is that the MAX has a bigger engine and this engine has been positioned forward on the wing in order to preserve ground clearance. As a result of this unusual engine position, the MAX has a tendency to pitch up during acceleration. Nowhere did I read that this doesn't happen during normal flights.
Yes, but not what you may be thinking. The AoA is the angle of the wing vs relative wind (the angle the wing is attacking the air). You can have high relative pitch (attitude) to the horizon but a low AoA, such as during climb. That same attitude is a full stall at slower speeds/power.
The wing doesn't care where the nose points. All it cares about is its relative angle to the wind. Once it diverges past a critical angle the wing stalls.
What appears to have happened with these MCAS issues is that the MCAS senses that the AoA is too high when it's completely normal and safe, so it auto-trims down.
The nose can be pointed up with a low angle of attack (e.g. a climb during cruise) and conversely the aircraft can be pitched down with a high angle of attack (e.g. descent approach with flaps extended)
This is true for climb and cruise, but not necessarily true for a bank.
MCAS compensates this by trimming elevators. Without MCAS, it is up to the pilot to handle the unstable system.
It’s obvious that the code was executed during the regular flight conditions which means it has to be applied even then.
The motors simply push the plane nose up too much compared to the previous models, threating the plane to enter the stall. Once in the stall the plane is just not controllable. MCAS was there to hide that.
And now that the problem is known to the world either will Boeing provide the proper solution, no matter the cost, or there will be a third crash and that will be too much. Boring still tries to present all that as “business as usual.” It’s wrong.