+ void updateAudio( double dt );
+
+ void updateReceiver(double dt);
+ void updateGlideSlope(double dt, const SGVec3d& aircraft, double signal_quality_norm);
+ void updateGPSSlaved();
+ void updateCDI(double dt);
+
+ void clearOutputs();
+
+ FGNavRecord* findPrimaryNavaid(const SGGeod& aPos, double aFreqMHz);
+
+ /// accessor for tied, read-only 'operable' property
+ bool isOperable() const
+ { return _operable; }
+
+ // implement SGPropertyChangeListener
+ virtual void valueChanged (SGPropertyNode * prop);