The system (10) has two electronic control units (32, 34) for redundant controlling of an engine (12) of an aircraft. A selection unit (38) selects one of the electronic control units for controlling the engine of the aircraft. The selection unit comprises a monitoring module (56) that determines a measure of rotation speed of the engine from an output signal of speed sensors (18, 20). The monitoring module compares the speed measure determined by the monitoring module with a rotation speed measure determined by the control units to determine an operating condition of the control units.
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