MCAS is not a system at all - it is just a few lines of code in the flight control computer - other than that it does not exist in any form, part or shape. This code was supposed to give one single and small movement of the horizontal stab leading edge upwards when the aircraft enters one corner of the flight envelope and move the neutral point slightly back in order to satisfy the static stability regulation requirement.
Then during certification testing code was changed and instead of one activation new code allowed stabilizer to move more than once.
That effectively created a never ending loop - most common cause od any computer program gets stuck and only way to clear it is to reset the computer. It was a begginer's mistake. Only this time it was the aircrafts crashed not just code.
I do not know how deep the FAA can go into the code but they should have not ever ever approve this change.