On April 25, 2001, about 1815 eastern daylight time, an Embraer EMB-145, N29917, was not damaged during an elevator trim malfunction, while in cruise flight near Norfolk International Airport (ORF), Norfolk, Virginia. The airplane was operated by Continental Express Airlines Inc. as flight 3365. There were no injuries to the 3 crewmembers and 50 passengers. Visual meteorological conditions prevailed for the flight that originated from Newark International Airport (EWR), Newark, New Jersey; destined for ORF. An instrument flight rules flight plan was filed for the air carrier flight conducted under 14 CFR part 121. The flight crew reported that they departed EWR about 1700. About 1815, at 5,000 feet, the horizontal stabilizer jammed in the (-1)-degree trim position. The flight crew completed the emergency checklist items, but the primary and secondary trim actuation systems did not respond. The flight crew then declared an emergency and landed uneventfully at ORF, at 1833. Examination of the airplane by a Federal Aviation Administration inspector revealed that the elevator trim actuator had failed. The unit was forwarded to the manufacturer's facility in Irvine, California, and examined under the supervision of a Safety Board investigator. The unit contained a primary and back-up clutch gear, and each gear had a respective torque nut and lock washer. The examination revealed that that the tabs on the lock washers were not bent over into the locked position. Additionally, there was no evidence that the tabs had ever been bent into the locked position. The back-up clutch torque nut had backed off and down the shaft, coming to rest against the clutch gear cluster bearing outer race. The backed-off nut exhibited a scratch around the outer edge of the face, consistent with fouling against the clutch gear cluster bearing outer race, subsequently jamming the unit. The manufacturer identified the error in the production process. After the examination, the manufacturer inspected all new production units in-house, and reviewed repair records on over 200 units. No discrepancies were detected during the in-house inspection or record review. The manufacturer also issued service bulletins and added quality control information and steps to the production process.