diff --git a/libraries/AP_SpdHgtControl/AP_SpdHgtControl.h b/libraries/AP_SpdHgtControl/AP_SpdHgtControl.h
index e9c3e3e74a..a58092ca63 100644
--- a/libraries/AP_SpdHgtControl/AP_SpdHgtControl.h
+++ b/libraries/AP_SpdHgtControl/AP_SpdHgtControl.h
@@ -50,6 +50,9 @@ public:
 	// return maximum climb rate
 	virtual float get_max_climbrate(void) const = 0;
 
+    // return maximum sink rate (+ve number)
+    virtual float get_max_sinkrate(void) const = 0;
+
     // added to let SoaringController reset pitch integrator to zero
     virtual void reset_pitch_I(void) = 0;