During Apollo first stage flight on the Saturn IB and V, emergencies could happen far too quickly for a human to react in time to survive, so an automatic "emergency detection system" (EDS) operated during this time. Its primary sensor was the "Q-ball" at the tip of the launch escape tower; it monitored angle of attack and rotation rates in roll, pitch and yaw, automatically initiating an abort if any exceeded preset limits. The Commander could also initiate an abort manually but it's hard to think of a failure that would require him to do so very rapidly if the EDS were working properly.
The classic example of a failure that woud cause the angle of attack to suddenly increase would be an "engine hardover", a failure of an engine gimbal (or of its hydraulic actuator) that forced it all the way over to one side.
Anything that caused the angle of attack to increase suddenly was especially critical because, near the max-Q (maximum aerodynamic pressure) phase at about T+90 sec an excessive angle of attack could quickly rip the entire stack apart. An uncontrolled angle of attack -- not the disintegration of the external tank -- destroyed Challenger in 1986. I can cite numerous examples of angle-of-attack breakups in unmanned rocket launches, particularly the Delta failure that occurred a few months after Challenger.
Angle of attack has to be kept essentially at zero until the stack is outside the sensible atmosphere. A "gravity turn" maneuver is generally used to allow a gradual pitchover while keeping angle of attack at zero. Only above the atmosphere is "closed loop guidance" usually enabled, allowing the stack to take whatever angle is required to meet its target orbit with the least amount of propellant.
The Apollo Q-ball was jettisoned along with the escape tower shortly after staging. The Commander would inhibit the EDS manually just before staging, as depicted in the movie Apollo 13. Beyond that point the stack was outside the atmosphere so any failure, even one that caused the stack to turn around, would not rip it apart from aerodynamic forces and the automatic EDS abort capability was no longer needed. If a manual abort were needed, the launcher engines would be commanded to shut down and the Service Propulsion System engine would push the CSM away from the failed launcher to a safe distance. Then the CM would separate from the SM and come down as if after a normal entry.
