As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: CABIN PRESSURIZATION V/S ERRATIC DURING CLIMB TO 1200 FPM TO 600FPM WITH 1000 FPM CLOSING IN 6 SECONDS. OUTFLOW VALVE OSCILLATING, AT SAME RATE OPEN & CLOSED 4500 CAB ALT NORMAL OPERATION IN CLIMB. REPLACED #1 CABIN PRESSURE CONTROLLER AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 21-31-34.