diff --git a/src/AIModel/AIBase.hxx b/src/AIModel/AIBase.hxx
index daf0caedb..941ac87fa 100644
--- a/src/AIModel/AIBase.hxx
+++ b/src/AIModel/AIBase.hxx
@@ -57,6 +57,7 @@ typedef struct {
    double rudder;             // used by ship objects
    double strength;           // used by thermal objects
    double diameter;           // used by thermal objects
+   double height_msl;         // used by thermal objects
    double eda;                // used by ballistic objects
    double life;               // life span in seconds
    double buoyancy;           // acceleration in ft per sec2
diff --git a/src/AIModel/AIScenario.cxx b/src/AIModel/AIScenario.cxx
index 9742db92c..b4db6abfd 100644
--- a/src/AIModel/AIScenario.cxx
+++ b/src/AIModel/AIScenario.cxx
@@ -74,6 +74,7 @@ FGAIScenario::FGAIScenario(string &filename)
      en->rudder         = entry_node->getDoubleValue("rudder", 0.0);
      en->strength       = entry_node->getDoubleValue("strength-fps", 0.0);
      en->diameter       = entry_node->getDoubleValue("diameter-ft", 0.0);
+     en->height_msl     = entry_node->getDoubleValue("height-msl", 5000.0);
      en->eda            = entry_node->getDoubleValue("eda", 0.007);
      en->life           = entry_node->getDoubleValue("life", 900.0);
      en->buoyancy       = entry_node->getDoubleValue("buoyancy", 0);
diff --git a/src/AIModel/AIThermal.cxx b/src/AIModel/AIThermal.cxx
index a8fd777b2..c3d2def1c 100644
--- a/src/AIModel/AIThermal.cxx
+++ b/src/AIModel/AIThermal.cxx
@@ -80,7 +80,7 @@ void FGAIThermal::Run(double dt) {
    // copy values from the AIManager
    double user_latitude  = manager->get_user_latitude();
    double user_longitude = manager->get_user_longitude();
-   // double user_altitude  = manager->get_user_altitude();
+   double user_altitude  = manager->get_user_altitude();
 
    // calculate range to target in feet and nautical miles
    double lat_range = fabs(pos.lat() - user_latitude) * ft_per_deg_lat;
@@ -96,5 +96,16 @@ void FGAIThermal::Run(double dt) {
    } else {
      strength = 0.0;
    }
+
+   // Stop lift at the top of the thermal (smoothly)
+   if (user_altitude > (height + 100.0)) {
+     strength = 0.0;
+   }
+   else if (user_altitude < height) {
+     // do nothing
+   }
+   else {
+     strength -= (strength * (user_altitude - height) * 0.01);
+   }
 }
 
diff --git a/src/AIModel/AIThermal.hxx b/src/AIModel/AIThermal.hxx
index be772c733..b3fee71bc 100644
--- a/src/AIModel/AIThermal.hxx
+++ b/src/AIModel/AIThermal.hxx
@@ -42,8 +42,10 @@ public:
 
         inline void setMaxStrength( double s ) { max_strength = s; };
         inline void setDiameter( double d ) { diameter = d; };
+        inline void setHeight( double h ) { height = h; };
         inline double getStrength() const { return strength; };
         inline double getDiameter() const { return diameter; };
+        inline double getHeight() const { return height; };
 
 private:
 
@@ -52,6 +54,7 @@ private:
         double max_strength;
         double strength;
         double diameter;
+        double height;
         double factor;
 };
 
diff --git a/src/AIModel/submodel.cxx b/src/AIModel/submodel.cxx
index e11e0b7c8..0e2dd4299 100644
--- a/src/AIModel/submodel.cxx
+++ b/src/AIModel/submodel.cxx
@@ -26,6 +26,7 @@ FGSubmodelMgr::FGSubmodelMgr ()
   out[0] = out[1] = out[2] = 0;
   in[3] = out[3] = 1;
   string contents_node;
+  contrail_altitude = 30000.0;
 }
 
 FGSubmodelMgr::~FGSubmodelMgr ()
@@ -57,8 +58,12 @@ FGSubmodelMgr::init ()
     _user_speed_east_fps_node   = fgGetNode("/velocities/speed-east-fps",true);
     _user_speed_north_fps_node  = fgGetNode("/velocities/speed-north-fps",true);
 
-    ai = (FGAIManager*)globals->get_subsystem("ai_model");
+    _contrail_altitude_node = fgGetNode("/environment/params/contrail-altitude", true);
+    contrail_altitude = _contrail_altitude_node->getDoubleValue();
+    _contrail_trigger = fgGetNode("ai/submodels/contrails", true);
+    _contrail_trigger->setBoolValue(false);
 
+    ai = (FGAIManager*)globals->get_subsystem("ai_model");
 
 }
 
@@ -82,6 +87,11 @@ FGSubmodelMgr::update (double dt)
 {
   if (!(_serviceable_node->getBoolValue())) return;
   int i=-1;
+
+  if (_user_alt_node->getDoubleValue() > contrail_altitude) {
+     _contrail_trigger->setBoolValue(true);
+  }   
+
   submodel_iterator = submodels.begin();
   while(submodel_iterator != submodels.end()) {
     i++;
diff --git a/src/AIModel/submodel.hxx b/src/AIModel/submodel.hxx
index e02233a0a..7c733d48e 100644
--- a/src/AIModel/submodel.hxx
+++ b/src/AIModel/submodel.hxx
@@ -114,6 +114,8 @@ private:
 
     static const double lbs_to_slugs; //conversion factor
 
+    double contrail_altitude;
+
     SGPropertyNode* _serviceable_node;
     SGPropertyNode* _user_lat_node;
     SGPropertyNode* _user_lon_node;
@@ -129,6 +131,8 @@ private:
     SGPropertyNode* _user_speed_down_fps_node;
     SGPropertyNode* _user_speed_east_fps_node;
     SGPropertyNode* _user_speed_north_fps_node;
+    SGPropertyNode* _contrail_altitude_node;
+    SGPropertyNode* _contrail_trigger;
 
     FGAIManager* ai;
     IC_struct  IC;