As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AUTO PILOT ALT HOLD MODE ON, HOLDS ALT FOR SHORT TIME. ALT DEVIATION OCCURS, INITIALLY USES YOKE TO COMPENSATE, THEN USES EXCESSIVE TRIM INPUTS. REMOVED AND REPLACED AUTO PILOT PITCH CONTROL CHANNEL. TESTED IAW B727 M/M CHAPTER 22-11-01. OPS CHECKS NORMAL ON GROUND.