class/class_basic_chapter.nut | 23 ++++++++++++++++++++++-
 class/class_chapter_04.nut    |  4 ++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/class/class_basic_chapter.nut b/class/class_basic_chapter.nut
index 301623e..ea1619f 100644
--- a/class/class_basic_chapter.nut
+++ b/class/class_basic_chapter.nut
@@ -3777,4 +3777,25 @@ function select_cube(tile_a, tile_b, obj = "") {
 
   return cube
 }
-// END OF FILE
\ No newline at end of file
+
+/**
+  * checks list entries for coord3d
+  *
+  * @param array tile list
+  *
+  * @return array tile list coord3d
+  */
+function check_coord3d(tile_list) {
+  local clist = []
+  for ( local i = 0; i < tile_list.len(); i++) {
+    try {
+      local t = tile_list[i].z
+      clist.append(tile_list[i])
+    } catch(ev) {
+      local c = square_x(tile_list[i].x, tile_list[i].y).get_ground_tile()
+      clist.append(coord3d(c.x, c.y, c.z))
+    }
+  }
+  return clist
+}
+// END OF FILE
diff --git a/class/class_chapter_04.nut b/class/class_chapter_04.nut
index 4f9fb39..98c725e 100644
--- a/class/class_chapter_04.nut
+++ b/class/class_chapter_04.nut
@@ -67,6 +67,10 @@ class tutorial.chapter_04 extends basic_chapter
     local fac_2 = factory_data.rawget("5")
     local fac_3 = factory_data.rawget("6")
 
+    local t = check_coord3d(ch4_schedule_line3)
+    ch4_schedule_line3.clear()
+    ch4_schedule_line3.extend(t)
+
     line1_name = get_good_data(3, 3) + " " + fac_1.name + " - " + fac_2.name
     line2_name = get_good_data(4, 3) + " " + fac_2.name + " - " + fac_3.name
     line3_name = "Passanger Ship"