Plane: improve error messages on failed parachute release

ArduPlane/GCS_Mavlink.cpp

@@ -1486,7 +1486,17 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
                     break;
                 case PARACHUTE_RELEASE:
                     // treat as a manual release which performs some additional check of altitude
-                    plane.parachute_manual_release();
+                    if (plane.parachute.released()) {
+                        plane.gcs_send_text_fmt(PSTR("Parachute already released"));
+                        result = MAV_RESULT_FAILED;
+                    } else if (!plane.parachute.enabled()) {
+                        plane.gcs_send_text_fmt(PSTR("Parachute not enabled"));
+                        result = MAV_RESULT_FAILED;
+                    } else {
+                        if (!plane.parachute_manual_release()) {
+                            result = MAV_RESULT_FAILED;
+                        }
+                    }
                     break;
                 default:
                     result = MAV_RESULT_FAILED;

ArduPlane/Plane.h

@@ -979,7 +979,7 @@ private:
     void do_parachute(const AP_Mission::Mission_Command& cmd);
     void parachute_check();
     void parachute_release();
-    void parachute_manual_release();
+    bool parachute_manual_release();
 
 public:
     void mavlink_delay_cb();

ArduPlane/parachute.cpp

@@ -32,20 +32,27 @@ void Plane::parachute_release()
   after performing some checks for pilot error checks if the vehicle
   is landed
 */
-void Plane::parachute_manual_release()
+bool Plane::parachute_manual_release()
 {
     // exit immediately if parachute is not enabled
     if (!parachute.enabled() || parachute.released()) {
-        return;
+        return false;
     }
 
     // do not release if vehicle is not flying
     if (!is_flying()) {
         // warn user of reason for failure
         gcs_send_text_P(MAV_SEVERITY_WARNING,PSTR("Parachute: not flying"));
-        return;
+        return false;
+    }
+
+    if (relative_altitude() < parachute.alt_min()) {
+        gcs_send_text_fmt(PSTR("Parachute: too low"));
+        return false;
     }
 
     // if we get this far release parachute
     parachute_release();
+
+    return true;
 }