737 MCAS clarifications:
1. MCAS does not override pilot column or stabilizer trim inputs. Column controls the elevator regardless of MCAS commands. Pilot's pitch trim electric switches override MCAS stabilizer commands.
2. Activating both stabilizer cutout switches disables all electric trim. That would leave just the flight crew's manual turning of trim wheel in cockpit as the only means of moving the stabilizer.
3. MCAS uses exactly the same control path as STS. The same motor (commanded by the FCCs for autopilot stabilizer control) is used to implement both MCAS and STS commands.