Originally Posted by dera

That's just for takeoff. I'm thinking 25.671(c)
.
"to be capable of continued safe flight and landing after any of the following failures or jamming in the flight control system and surfaces (including trim, lift, drag, and feel systems)"

(c)(1)

"(1) Any single failure, excluding jamming (for example, disconnection or failure of mechanical elements, or structural failure of hydraulic components, such as actuators, control spool housing, and valves)."

Also 25.671(c)(3)
"A runaway of a flight control to an adverse position and jam must be accounted for if such runaway and subsequent jamming is not extremely improbable."

Extremely improbable is defined in 25.1309. "they are not anticipated to occur during the entire operational life of all airplanes of one type".

So - airplane must be controllable if a control surface can runaway to a mechanical stop.

Boeing is in a world of hurt if the MCAS is shown to be Part 25 uncompliant.