To ensure a reliable operation of a trim control system for a fully hydraulic horizontal stabilizer in a fixed wing type aircraft.

The control system uses hydraulic power only in controlling a trim control surface 8 of the horizontal stabilizer without any electric controllers except a three-position spring-centered toggle trim switch initiated by a pilot, a backup electric motor 22 and a standard electronic logic pilot interface, The control system controls rotational angular displacement by means of a mechanical feedback link between a spool of a flow control valve and the trim control surface 8 of the horizontal stabilizer. A sleeve of the flow valve has a variable outflow area for controlling a hydraulic flow rate to a motor port of a hydraulic motor. If the mechanical feedback link fails, the flow control valve automatically reverts to a default fixed flow rate.