Incident Overview
During final approach, the first officer encountered difficulty trimming the airplane. The captain attempted to trim using both the yoke switch and manual trim handle, but neither method succeeded. The crew initiated a go-around and ran the applicable checklist, but control of the stabilizer trim was not regained.
Troubleshooting and Resolution
The crew pulled circuit breakers H11 and H20, then reset them, but the stabilizer trim remained inoperative. They then reset the trim cutout switches twice, after which normal operation of the stabilizer trim was reestablished.
Post-Event Inspection Findings
Subsequent inspection revealed that the left and right stabilizer position transmitters were out of calibration. Additionally, the left stabilizer trim control module (STCM) exhibited higher than normal leakage, and the connector for its corresponding shut-off valve was shorting across several pins due to Skydrol fluid incursion. No faults were identified for the right system except the out-of-calibration right stabilizer position transmitter.
Operator Commentary
According to the operator, the system should have operated at half rate given the discrepancies found, but it did not. No reports of further difficulties with the airplane's stabilizer trim system have been received since this event.