diff --git a/nasal/aerotow.nas b/nasal/aerotow.nas
index 7be1f51..65aae0e 100644
--- a/nasal/aerotow.nas
+++ b/nasal/aerotow.nas
@@ -42,6 +42,7 @@ var Aerotow = {
     #
     del: func () {
         me.thermal.del();
+        me.scenario.del();
 
         foreach (var listener; me.listeners) {
             removelistener(listener);
diff --git a/nasal/dialogs/route.nas b/nasal/dialogs/route.nas
index 6150658..7adb169 100644
--- a/nasal/dialogs/route.nas
+++ b/nasal/dialogs/route.nas
@@ -17,11 +17,13 @@ var RouteDialog = {
     # Constants
     #
     ROUTE_SAVES_DIR: "route-saves",
+    MAX_ROUTE_WAYPOINTS: 10,
 
     #
     # Constructor
     #
     # addon - Addon object
+    # message - Message object
     #
     new: func (addon, message) {
         var obj = { parents: [RouteDialog] };
@@ -31,7 +33,6 @@ var RouteDialog = {
         obj.addonNodePath = addon.node.getPath();
 
         obj.savePath = addon.storagePath ~ "/" ~ RouteDialog.ROUTE_SAVES_DIR;
-        obj.maxRouteWaypoints = 10;
         obj.listeners = [];
 
         # Set listener for aerotow combo box value in route dialog for recalculate altitude change
@@ -45,7 +46,7 @@ var RouteDialog = {
         }));
 
         # Set listeners for distance fields for calculate altitude change
-        for (var i = 0; i < obj.maxRouteWaypoints; i += 1) {
+        for (var i = 0; i < RouteDialog.MAX_ROUTE_WAYPOINTS; i += 1) {
             append(obj.listeners, setlistener(obj.addonNodePath ~ "/addon-devel/route/wpts/wpt[" ~ i ~ "]/distance-m", func () {
                 obj.calculateAltChangeAndTotals();
             }));
@@ -78,7 +79,7 @@ var RouteDialog = {
         # 0 means without altitude limits
         var maxAltAgl = getprop(me.addonNodePath ~ "/addon-devel/route/wpts/max-alt-agl") or 0;
 
-        for (var i = 0; i < me.maxRouteWaypoints; i += 1) {
+        for (var i = 0; i < RouteDialog.MAX_ROUTE_WAYPOINTS; i += 1) {
             var distance = getprop(me.addonNodePath ~ "/addon-devel/route/wpts/wpt[" ~ i ~ "]/distance-m") or 0;
 
             # If we have reached the altitude limit, the altitude no longer changes (0)
diff --git a/nasal/flight-plan.nas b/nasal/flight-plan.nas
index b7329e7..85e9017 100644
--- a/nasal/flight-plan.nas
+++ b/nasal/flight-plan.nas
@@ -43,6 +43,13 @@ var FlightPlan = {
         return obj;
     },
 
+    #
+    # Destructor
+    #
+    del: func () {
+        me.flightPlanWriter.del();
+    },
+
     #
     # Get inital location of glider.
     #
diff --git a/nasal/io/flight-plan-writer.nas b/nasal/io/flight-plan-writer.nas
index 9578572..f6941ec 100644
--- a/nasal/io/flight-plan-writer.nas
+++ b/nasal/io/flight-plan-writer.nas
@@ -21,19 +21,30 @@ var FlightPlanWriter = {
     new: func (addon) {
         var obj = { parents: [FlightPlanWriter] };
 
-        obj.fpFileHandler = nil; # Handler for wrire flight plan to file
+        obj.fpFileHandler = nil; # Handler for wrire flight plan to the file
         obj.flightPlanPath = addon.storagePath ~ "/AI/FlightPlans/" ~ FlightPlan.FILENAME_FLIGHTPLAN;
         obj.wptCount = 1;
 
         return obj;
     },
 
+    #
+    # Destructor
+    #
+    del: func () {
+        me.close();
+    },
+
     #
     # Open XML file to wrire flight plan
     #
     open: func () {
         me.wptCount = 1;
 
+        if (me.fpFileHandler) {
+            io.close(me.fpFileHandler);
+        }
+
         me.fpFileHandler = io.open(me.flightPlanPath, "w");
 
         if (me.fpFileHandler) {
diff --git a/nasal/scenario.nas b/nasal/scenario.nas
index 788bf0d..8c514e8 100644
--- a/nasal/scenario.nas
+++ b/nasal/scenario.nas
@@ -56,6 +56,7 @@ var Scenario = {
     #
     del: func () {
         me.routeDialog.del();
+        me.flightPlan.del();
 
         foreach (var listener; me.listeners) {
             removelistener(listener);