Update ArduPlane/Plane.cpp

Co-authored-by: Peter Hall <[email protected]>

Author: Ryanf55

ArduPlane/Plane.cpp

@@ -1011,7 +1011,7 @@ bool Plane::is_taking_off() const
 
 bool Plane::start_takeoff(const float alt) {
 #if HAL_QUADPLANE_ENABLED
-    return quadplane.do_user_takeoff(alt);
+    return plane.quadplane.available() && quadplane.do_user_takeoff(alt);
 #else
     return false;
 #endif