Index: src/disaster_cmd.cpp
===================================================================
--- src/disaster_cmd.cpp	(Revision 20904)
+++ src/disaster_cmd.cpp	(Arbeitskopie)
@@ -43,6 +43,7 @@
 #include "company_base.h"
 #include "core/random_func.hpp"
 #include "core/backup_type.hpp"
+#include "aircraft.h"
 
 #include "table/strings.h"
 
@@ -120,6 +121,50 @@
 	_disaster_images_4, _disaster_images_5,                     ///< small and big submarine sprites
 };
 
+static inline uint GetTileHeightBelowFlyingDisasterVehicle(int x_pos, int y_pos)
+{
+	TileIndex tile = TileVirtXY(x_pos, y_pos);
+	uint tile_height;
+
+	/* Check for being inside the map. If not call TileHeightOutsideMap() instead of TileHeight(). */
+	if (x_pos >= 0 && x_pos <= (int)MapSizeX() * (int)TILE_SIZE - 1
+			&& y_pos >= 0 && y_pos <= (int)MapSizeY() * (int)TILE_SIZE - 1) {
+		tile_height = TileHeight(tile) * TILE_HEIGHT;
+	} else {
+		tile_height = TileHeightOutsideMap(x_pos, y_pos) * TILE_HEIGHT;
+	}
+
+	return tile_height;
+}
+
+static inline int GetFlyingDisasterVehicleMinHeight(int x_pos, int y_pos)
+{
+	return GetTileHeightBelowFlyingDisasterVehicle(x_pos, y_pos) + AIRCRAFT_MIN_FLYING_ALTITUDE;
+}
+
+static inline int GetFlyingDisasterVehicleMaxHeight(int x_pos, int y_pos)
+{
+	return GetTileHeightBelowFlyingDisasterVehicle(x_pos, y_pos) + AIRCRAFT_MAX_FLYING_ALTITUDE;
+}
+
+static inline void AdjustFlyingDisasterVehicleHeight(DisasterVehicle *v)
+{
+	int min_altitude = GetFlyingDisasterVehicleMinHeight(v->x_pos, v->y_pos);
+	int max_altitude = GetFlyingDisasterVehicleMaxHeight(v->x_pos, v->y_pos);
+	int middle_altitude = min_altitude + ((uint)(max_altitude - min_altitude)) / 2;
+	if (v->z_pos < min_altitude || (v->is_in_min_height_correction && v->z_pos < middle_altitude)) {
+		v->is_in_min_height_correction = true;
+		v->z_pos += 2;
+	} else if (v->z_pos > max_altitude || (v->is_in_max_height_correction && v->z_pos > middle_altitude)) {
+		v->is_in_max_height_correction = true;
+		v->z_pos -= 2;
+	} else if (v->is_in_min_height_correction && v->z_pos >= middle_altitude) {
+		v->is_in_min_height_correction = false;
+	} else if (v->is_in_max_height_correction && v->z_pos <= middle_altitude) {
+		v->is_in_max_height_correction = false;
+	}
+}
+
 static void DisasterVehicleUpdateImage(DisasterVehicle *v)
 {
 	SpriteID img = v->image_override;
@@ -131,7 +176,7 @@
  * Initialize a disaster vehicle. These vehicles are of type VEH_DISASTER, are unclickable
  * and owned by nobody
  */
-static void InitializeDisasterVehicle(DisasterVehicle *v, int x, int y, byte z, Direction direction, byte subtype)
+static void InitializeDisasterVehicle(DisasterVehicle *v, int x, int y, int z, Direction direction, byte subtype)
 {
 	v->x_pos = x;
 	v->y_pos = y;
@@ -144,13 +189,15 @@
 	v->vehstatus = VS_UNCLICKABLE;
 	v->image_override = 0;
 	v->current_order.Free();
+	v->is_in_min_height_correction = false;
+	v->is_in_max_height_correction = false;
 
 	DisasterVehicleUpdateImage(v);
 	VehicleMove(v, false);
 	MarkSingleVehicleDirty(v);
 }
 
-static void SetDisasterVehiclePos(DisasterVehicle *v, int x, int y, byte z)
+static void SetDisasterVehiclePos(DisasterVehicle *v, int x, int y, int z)
 {
 	v->x_pos = x;
 	v->y_pos = y;
@@ -199,7 +246,7 @@
 		if (HasBit(v->tick_counter, 0)) return true;
 
 		GetNewVehiclePosResult gp = GetNewVehiclePos(v);
-
+		AdjustFlyingDisasterVehicleHeight(v);
 		SetDisasterVehiclePos(v, gp.x, gp.y, v->z_pos);
 
 		if (v->current_order.GetDestination() == 1) {
@@ -247,7 +294,7 @@
 
 	int x = v->x_pos;
 	int y = v->y_pos;
-	byte z = GetSlopeZ(x, y);
+	int z = GetSlopeZ(x, y);
 	if (z < v->z_pos) z = v->z_pos - 1;
 	SetDisasterVehiclePos(v, x, y, z);
 
@@ -296,6 +343,7 @@
 		if (Delta(x, v->x_pos) + Delta(y, v->y_pos) >= (int)TILE_SIZE) {
 			v->direction = GetDirectionTowards(v, x, y);
 			GetNewVehiclePosResult gp = GetNewVehiclePos(v);
+			AdjustFlyingDisasterVehicleHeight(v);
 			SetDisasterVehiclePos(v, gp.x, gp.y, v->z_pos);
 			return true;
 		}
@@ -331,7 +379,7 @@
 		v->direction = GetDirectionTowards(v, u->x_pos, u->y_pos);
 		GetNewVehiclePosResult gp = GetNewVehiclePos(v);
 
-		byte z = v->z_pos;
+		int z = v->z_pos;
 		if (dist <= TILE_SIZE && z > u->z_pos) z--;
 		SetDisasterVehiclePos(v, gp.x, gp.y, z);
 
@@ -389,6 +437,7 @@
 	v->image_override = (v->current_order.GetDestination() == 1 && HasBit(v->tick_counter, 2)) ? image_override : 0;
 
 	GetNewVehiclePosResult gp = GetNewVehiclePos(v);
+	AdjustFlyingDisasterVehicleHeight(v);
 	SetDisasterVehiclePos(v, gp.x, gp.y, v->z_pos);
 
 	if ((leave_at_top && gp.x < (-10 * (int)TILE_SIZE)) || (!leave_at_top && gp.x > (int)(MapSizeX() * TILE_SIZE + 9 * TILE_SIZE) - 1)) {
@@ -486,6 +535,7 @@
 			v->direction = GetDirectionTowards(v, x, y);
 
 			GetNewVehiclePosResult gp = GetNewVehiclePos(v);
+			AdjustFlyingDisasterVehicleHeight(v);
 			SetDisasterVehiclePos(v, gp.x, gp.y, v->z_pos);
 			return true;
 		}
@@ -496,7 +546,7 @@
 			return false;
 		}
 
-		byte z = GetSlopeZ(v->x_pos, v->y_pos);
+		int z = GetSlopeZ(v->x_pos, v->y_pos);
 		if (z < v->z_pos) {
 			SetDisasterVehiclePos(v, v->x_pos, v->y_pos, v->z_pos - 1);
 			return true;
@@ -541,6 +591,7 @@
 		if (Delta(x, v->x_pos) + Delta(y, v->y_pos) >= (int)TILE_SIZE) {
 			v->direction = GetDirectionTowards(v, x, y);
 			GetNewVehiclePosResult gp = GetNewVehiclePos(v);
+			AdjustFlyingDisasterVehicleHeight(v);
 			SetDisasterVehiclePos(v, gp.x, gp.y, v->z_pos);
 			return true;
 		}
@@ -576,6 +627,7 @@
 	v->tick_counter++;
 
 	GetNewVehiclePosResult gp = GetNewVehiclePos(v);
+	AdjustFlyingDisasterVehicleHeight(v);
 	SetDisasterVehiclePos(v, gp.x, gp.y, v->z_pos);
 
 	if (gp.x > (int)(MapSizeX() * TILE_SIZE + 9 * TILE_SIZE) - 1) {
@@ -691,7 +743,8 @@
 	}
 
 	DisasterVehicle *v = new DisasterVehicle();
-	InitializeDisasterVehicle(v, x, 0, 135, DIR_SE, ST_ZEPPELINER);
+	int z = GetFlyingDisasterVehicleMinHeight(x, 0);
+	InitializeDisasterVehicle(v, x, 0, z, DIR_SE, ST_ZEPPELINER);
 
 	/* Allocate shadow */
 	DisasterVehicle *u = new DisasterVehicle();
@@ -712,7 +765,8 @@
 	DisasterVehicle *v = new DisasterVehicle();
 	int x = TileX(Random()) * TILE_SIZE + TILE_SIZE / 2;
 
-	InitializeDisasterVehicle(v, x, 0, 135, DIR_SE, ST_SMALL_UFO);
+	int z = GetFlyingDisasterVehicleMinHeight(x, 0);
+	InitializeDisasterVehicle(v, x, 0, z, DIR_SE, ST_SMALL_UFO);
 	v->dest_tile = TileXY(MapSizeX() / 2, MapSizeY() / 2);
 	v->age = 0;
 
@@ -746,7 +800,8 @@
 	int x = (MapSizeX() + 9) * TILE_SIZE - 1;
 	int y = TileY(found->location.tile) * TILE_SIZE + 37;
 
-	InitializeDisasterVehicle(v, x, y, 135, DIR_NE, ST_AIRPLANE);
+	int z = GetFlyingDisasterVehicleMinHeight(x, y);
+	InitializeDisasterVehicle(v, x, y, z, DIR_NE, ST_AIRPLANE);
 
 	DisasterVehicle *u = new DisasterVehicle();
 	v->SetNext(u);
@@ -776,7 +831,8 @@
 	int x = -16 * (int)TILE_SIZE;
 	int y = TileY(found->location.tile) * TILE_SIZE + 37;
 
-	InitializeDisasterVehicle(v, x, y, 135, DIR_SW, ST_HELICOPTER);
+	int z = GetFlyingDisasterVehicleMinHeight(x, y);
+	InitializeDisasterVehicle(v, x, y, z, DIR_SW, ST_HELICOPTER);
 
 	DisasterVehicle *u = new DisasterVehicle();
 	v->SetNext(u);
@@ -785,7 +841,7 @@
 
 	DisasterVehicle *w = new DisasterVehicle();
 	u->SetNext(w);
-	InitializeDisasterVehicle(w, x, y, 140, DIR_SW, ST_HELICOPTER_ROTORS);
+	InitializeDisasterVehicle(w, x, y, z + 5, DIR_SW, ST_HELICOPTER_ROTORS);
 }
 
 
@@ -799,7 +855,8 @@
 	int x = TileX(Random()) * TILE_SIZE + TILE_SIZE / 2;
 	int y = MapMaxX() * TILE_SIZE - 1;
 
-	InitializeDisasterVehicle(v, x, y, 135, DIR_NW, ST_BIG_UFO);
+	int z = GetFlyingDisasterVehicleMinHeight(x, y);
+	InitializeDisasterVehicle(v, x, y, z, DIR_NW, ST_BIG_UFO);
 	v->dest_tile = TileXY(MapSizeX() / 2, MapSizeY() / 2);
 	v->age = 0;
 
Index: src/saveload/vehicle_sl.cpp
===================================================================
--- src/saveload/vehicle_sl.cpp	(Revision 20904)
+++ src/saveload/vehicle_sl.cpp	(Arbeitskopie)
@@ -664,6 +664,8 @@
 
 		     SLE_VAR(DisasterVehicle, image_override,            SLE_UINT16),
 		     SLE_VAR(DisasterVehicle, big_ufo_destroyer_target,  SLE_UINT16),
+		 SLE_CONDVAR(DisasterVehicle, is_in_max_height_correction, SLE_UINT8,     MORE_HEIGHTLEVEL_SAVEGAME_VERSION, SL_MAX_VERSION),
+		 SLE_CONDVAR(DisasterVehicle, is_in_min_height_correction, SLE_UINT8,     MORE_HEIGHTLEVEL_SAVEGAME_VERSION, SL_MAX_VERSION),
 
 		SLE_CONDNULL(16,                                                           2, 143), // old reserved space
 
Index: src/vehicle_base.h
===================================================================
--- src/vehicle_base.h	(Revision 20904)
+++ src/vehicle_base.h	(Arbeitskopie)
@@ -733,6 +733,10 @@
 	uint16 image_override;
 	VehicleID big_ufo_destroyer_target;
 
+	// see aircraft_is_in_min/max_height_correction in aircraft.h
+    bool is_in_max_height_correction;
+    bool is_in_min_height_correction;
+
 	/** We don't want GCC to zero our struct! It already is zeroed and has an index! */
 	DisasterVehicle() : SpecializedVehicle<DisasterVehicle, VEH_DISASTER>() {}
 	/** We want to 'destruct' the right class. */