diff --git a/ArduCopter/GCS_Mavlink.pde b/ArduCopter/GCS_Mavlink.pde
index 5f37973ddc..1e43b7dd3e 100644
--- a/ArduCopter/GCS_Mavlink.pde
+++ b/ArduCopter/GCS_Mavlink.pde
@@ -1045,6 +1045,7 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
         switch(packet.command) {
 
         case MAV_CMD_NAV_TAKEOFF: {
+            // param3 : horizontal navigation by pilot acceptable
             // param4 : yaw angle   (not supported)
             // param5 : latitude    (not supported)
             // param6 : longitude   (not supported)