What happened
While cruising at flight level 290, the Fokker F.28 MK 1000 experienced an uncommanded climb of approximately 3,000 feet. The crew attempted to arrest the ascent by applying full forward pressure on the control column, but this action failed to stop the climb. When the pilot attempted to use the alternate stabilizer trim switch, the circuit breaker repeatedly popped.
To regain pitch control of the aircraft, the pilot moved passengers toward the front of the cabin and utilized the physical assistance of a flight attendant. By adjusting power settings and flap configurations, the crew was eventually able to complete a successful landing.
The investigation
The investigation determined that the rod end bearing on the stabilizer servo spool valve had been overtorqued. This mechanical error caused the failure of the spool, which led to the slow nose-up stabilizer runaway.