insert missing arcs from source to target for each aircraft

aviation_planning/airlineplanning.ipynb

@@ -687,7 +687,12 @@
     "            if f1!=f2 and flight_end_time[f1] < flight_start_time[f2] and flight_dest[f1] == flight_origin[f2]: \n",
     "                flight_arcs_for_each_aircraft[a].append((f1,f2))\n",
     "                deltaplus_flightarcs[a][f1].append(f2)\n",
-    "                deltaminus_flightarcs[a][f2].append(f1) \n"
+    "                deltaminus_flightarcs[a][f2].append(f1) \n",
+    "            # allow to connect source and target directly for the case that aircraft is not used at all    \n",
+    "            elif str(f1).startswith('source') and str(f2).startswith('sink'):\n",
+    "                flight_arcs_for_each_aircraft[a].append((f1,f2))\n",
+    "                deltaplus_flightarcs[a][f1].append(f2)\n",
+    "                deltaminus_flightarcs[a][f2].append(f1)"
    ]
   },
   {