diff --git a/conf/flight_plans/EMAV2008.xml b/conf/flight_plans/EMAV2008.xml
index 1d81947daf..57fa34c38a 100644
--- a/conf/flight_plans/EMAV2008.xml
+++ b/conf/flight_plans/EMAV2008.xml
@@ -47,7 +47,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+40" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+40" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <go wp="CLIMB"/>
     </block>
@@ -86,11 +86,11 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 15 > fabs(GetPosAlt() - WaypointAlt(WP_BASELEG))" wp="BASELEG"/>
     </block>
     <block name="final">
-<!--      <exception cond="ground_alt + 6 > GetPosAlt()" deroute="flare"/> -->
+<!--      <exception cond="GetAltRef() + 6 > GetPosAlt()" deroute="flare"/> -->
       <go approaching_time="0" from="AF" hmode="route" wp="SF"/>
     </block>
     <block name="shortfinal">
-<!--      <exception cond="ground_alt + 6 > GetPosAlt()" deroute="flare"/> -->
+<!--      <exception cond="GetAltRef() + 6 > GetPosAlt()" deroute="flare"/> -->
       <go approaching_time="0" from="SF" hmode="route" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/EMAV2009.xml b/conf/flight_plans/EMAV2009.xml
index 28c86bd6f1..e9f4de4d36 100644
--- a/conf/flight_plans/EMAV2009.xml
+++ b/conf/flight_plans/EMAV2009.xml
@@ -26,7 +26,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" pitch="15" throttle="1.0" vmode="throttle" wp="CLIMB"/>
diff --git a/conf/flight_plans/EMAV2009_safety.xml b/conf/flight_plans/EMAV2009_safety.xml
index 9982b628ca..5e2dca0b32 100644
--- a/conf/flight_plans/EMAV2009_safety.xml
+++ b/conf/flight_plans/EMAV2009_safety.xml
@@ -2,7 +2,7 @@
 
 <procedure>
   <exceptions>
-    <exception cond="Or(! InsideGreen(GetPosX(), GetPosY()), GetPosAlt() > ground_alt + 150)" deroute="Center"/>
+    <exception cond="Or(! InsideGreen(GetPosX(), GetPosY()), GetPosAlt() > GetAltRef() + 150)" deroute="Center"/>
   </exceptions>
 
   <blocks>
diff --git a/conf/flight_plans/IS.xml b/conf/flight_plans/IS.xml
index 6d636cb7b1..598371aed5 100644
--- a/conf/flight_plans/IS.xml
+++ b/conf/flight_plans/IS.xml
@@ -101,15 +101,15 @@
     </block>
 
     <block name="climb 75">
-      <circle radius="50+(GetPosAlt()-ground_alt)/2" wp="1" throttle="0.75" pitch="15" vmode="throttle" until="10 > PowerVoltage()"/>
+      <circle radius="50+(GetPosAlt()-GetAltRef())/2" wp="1" throttle="0.75" pitch="15" vmode="throttle" until="10 > PowerVoltage()"/>
     </block>
 
     <block name="climb 1">
-      <circle radius="50+(GetPosAlt()-ground_alt)/2" wp="1" climb="1" pitch="5" vmode="climb" until="10 > PowerVoltage()"/>
+      <circle radius="50+(GetPosAlt()-GetAltRef())/2" wp="1" climb="1" pitch="5" vmode="climb" until="10 > PowerVoltage()"/>
     </block>
 
     <block name="descent 0">
-      <circle radius="50+(GetPosAlt()-ground_alt)/2" wp="1" throttle="0.0" pitch="-15" vmode="throttle" until="ground_alt+50 > GetPosAlt()"/>
+      <circle radius="50+(GetPosAlt()-GetAltRef())/2" wp="1" throttle="0.0" pitch="-15" vmode="throttle" until="GetAltRef()+50 > GetPosAlt()"/>
       <deroute block="wait"/>
     </block>
 
@@ -147,7 +147,7 @@
     </block>
 
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
 
diff --git a/conf/flight_plans/basic.xml b/conf/flight_plans/basic.xml
index e404260c69..e690348416 100644
--- a/conf/flight_plans/basic.xml
+++ b/conf/flight_plans/basic.xml
@@ -35,7 +35,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block key="t" name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png" group="home">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" throttle="1.0" vmode="throttle" wp="CLIMB" pitch="15"/>
@@ -76,7 +76,7 @@
       <circle radius="nav_radius" until="And(NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10), 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG)))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/ccc_gl.xml b/conf/flight_plans/ccc_gl.xml
index cfec2305c6..a8e3ef5838 100644
--- a/conf/flight_plans/ccc_gl.xml
+++ b/conf/flight_plans/ccc_gl.xml
@@ -45,7 +45,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_icon="takeoff.png" strip_button="Takeoff (wp CLIMB)">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <go wp="CLIMB"/>
     </block>
@@ -66,19 +66,19 @@
       <circle pitch="auto" radius="75" throttle="0.7" wp="1"/>
     </block>
     <block name="Climb 75% throttle">
-      <circle pitch="10" radius="50+(GetPosAlt()-ground_alt)/2" throttle="0.75" until="(10 > PowerVoltage()) || (GetPosAlt() > ground_alt+ 1350)" vmode="throttle" wp="1"/>
+      <circle pitch="10" radius="50+(GetPosAlt()-GetAltRef())/2" throttle="0.75" until="(10 > PowerVoltage()) || (GetPosAlt() > GetAltRef()+ 1350)" vmode="throttle" wp="1"/>
     </block>
     <block name="Climb 0m/s">
       <circle climb="0" radius="nav_radius" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
     </block>
     <block name="Climb 1m/s">
-      <circle climb="1" pitch="5" radius="50+(GetPosAlt()-ground_alt)/2" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
+      <circle climb="1" pitch="5" radius="50+(GetPosAlt()-GetAltRef())/2" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
     </block>
     <block name="Climb nav_climb m/s">
-      <circle climb="nav_climb" radius="nav_radius" until="(10 > PowerVoltage()) || (GetPosAlt() > ground_alt+ 1350)" vmode="climb" wp="1"/>
+      <circle climb="nav_climb" radius="nav_radius" until="(10 > PowerVoltage()) || (GetPosAlt() > GetAltRef()+ 1350)" vmode="climb" wp="1"/>
     </block>
     <block name="Descent 0% throttle">
-      <circle pitch="-5" radius="50+(GetPosAlt()-ground_alt)/2" throttle="0.0" until="ground_alt+50 > GetPosAlt()" vmode="throttle" wp="1"/>
+      <circle pitch="-5" radius="50+(GetPosAlt()-GetAltRef())/2" throttle="0.0" until="GetAltRef()+50 > GetPosAlt()" vmode="throttle" wp="1"/>
       <deroute block="Standby"/>
     </block>
     <block name="Route 1-2">
@@ -115,7 +115,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 10 > fabs(GetPosAlt() - WaypointAlt(WP_BASELEG))" wp="BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
@@ -141,7 +141,7 @@
       </while>
     </block>
     <block name="Heading 30">
-      <heading alt="ground_alt+50" course="30" until="FALSE"/>
+      <heading alt="GetAltRef()+50" course="30" until="FALSE"/>
     </block>
     <block name="For loop (circles wp 1)">
       <for from="0" to="3" var="i">
@@ -156,7 +156,7 @@
     </block>
     <block name="Fly in Square">
       <exception cond="! InsideSquare(GetPosX(), GetPosY())" deroute="Come back wp 1"/>
-      <attitude alt="ground_alt+75" roll="0" vmode="alt"/>
+      <attitude alt="GetAltRef()+75" roll="0" vmode="alt"/>
     </block>
     <block name="Come back wp 1">
       <exception cond="InsideSquare(GetPosX(), GetPosY())" deroute="Fly in Square"/>
diff --git a/conf/flight_plans/corsica.xml b/conf/flight_plans/corsica.xml
index 02db9b1e70..7b96b5ad8f 100644
--- a/conf/flight_plans/corsica.xml
+++ b/conf/flight_plans/corsica.xml
@@ -21,7 +21,7 @@
   </includes>
 
   <exceptions>
-    <exception cond="Or(! InsideZRT(GetPosX(), GetPosY()), GetPosAlt() > ground_alt + 300)" deroute="Kill"/>
+    <exception cond="Or(! InsideZRT(GetPosX(), GetPosY()), GetPosAlt() > GetAltRef() + 300)" deroute="Kill"/>
   </exceptions>
   <blocks>
     <block name="Wait GPS">
@@ -33,7 +33,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby Menton"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby Menton"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go throttle="1.0" vmode="throttle" wp="CLIMB" pitch="15"/>
@@ -66,7 +66,7 @@
       <circle radius="nav_radius" until="And(NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-10), 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG)))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
@@ -74,7 +74,7 @@
       <attitude roll="0.0" throttle="0.0" until="FALSE" vmode="throttle"/>
     </block>
     <block name="Kill">
-      <exception cond="And(InsideZRT(GetPosX(), GetPosY()), ground_alt + 300 > GetPosAlt())" deroute="Resume Mission"/>
+      <exception cond="And(InsideZRT(GetPosX(), GetPosY()), GetAltRef() + 300 > GetPosAlt())" deroute="Resume Mission"/>
       <attitude roll="0" vmode="throttle" throttle="0.2"/>
     </block>
     <block name="Resume Mission">
diff --git a/conf/flight_plans/creidlitz.xml b/conf/flight_plans/creidlitz.xml
index d4b34b0250..58bfa754c3 100644
--- a/conf/flight_plans/creidlitz.xml
+++ b/conf/flight_plans/creidlitz.xml
@@ -33,7 +33,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" throttle="1.0" vmode="throttle" wp="CLIMB"/>
@@ -45,7 +45,7 @@
       <circle radius="nav_radius" wp="PROFILE"/>
     </block>
     <block name="profile_down" strip_button="Profile Down" strip_icon="down_profile.png">
-      <circle pitch="RadOfDeg(-10)" radius="nav_radius" throttle="0" until="(ground_alt+150 > GetPosAlt())" vmode="throttle" wp="PROFILE"/>
+      <circle pitch="RadOfDeg(-10)" radius="nav_radius" throttle="0" until="(GetAltRef()+150 > GetPosAlt())" vmode="throttle" wp="PROFILE"/>
       <deroute block="Standby"/>
     </block>
     <block name="MOB" strip_button="Circle around here" strip_icon="mob.png">
diff --git a/conf/flight_plans/fp_tp_auto.xml b/conf/flight_plans/fp_tp_auto.xml
index 444a7fc7c3..1c91224cc7 100644
--- a/conf/flight_plans/fp_tp_auto.xml
+++ b/conf/flight_plans/fp_tp_auto.xml
@@ -44,7 +44,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_icon="takeoff.png" strip_button="Takeoff (wp CLIMB)">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <go wp="CLIMB"/>
     </block>
@@ -65,19 +65,19 @@
       <circle pitch="auto" radius="75" throttle="0.7" wp="1"/>
     </block>
     <block name="Climb 75% throttle">
-      <circle pitch="10" radius="50+(GetPosAlt()-ground_alt)/2" throttle="0.75" until="(10 > PowerVoltage()) || (GetPosAlt() > ground_alt+ 1350)" vmode="throttle" wp="1"/>
+      <circle pitch="10" radius="50+(GetPosAlt()-GetAltRef())/2" throttle="0.75" until="(10 > PowerVoltage()) || (GetPosAlt() > GetAltRef()+ 1350)" vmode="throttle" wp="1"/>
     </block>
     <block name="Climb 0m/s">
       <circle climb="0" radius="nav_radius" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
     </block>
     <block name="Climb 1m/s">
-      <circle climb="1" radius="50+(GetPosAlt()-ground_alt)/2" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
+      <circle climb="1" radius="50+(GetPosAlt()-GetAltRef())/2" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
     </block>
     <block name="Climb nav_climb m/s">
-      <circle climb="nav_climb" radius="nav_radius" until="(10 > PowerVoltage()) || (GetPosAlt() > ground_alt+ 1350)" vmode="climb" wp="1"/>
+      <circle climb="nav_climb" radius="nav_radius" until="(10 > PowerVoltage()) || (GetPosAlt() > GetAltRef()+ 1350)" vmode="climb" wp="1"/>
     </block>
     <block name="Descent 0% throttle">
-      <circle pitch="-5" radius="50+(GetPosAlt()-ground_alt)/2" throttle="0.0" until="ground_alt+50 > GetPosAlt()" vmode="throttle" wp="1"/>
+      <circle pitch="-5" radius="50+(GetPosAlt()-GetAltRef())/2" throttle="0.0" until="GetAltRef()+50 > GetPosAlt()" vmode="throttle" wp="1"/>
       <deroute block="Standby"/>
     </block>
     <block name="Route 1-2">
@@ -114,7 +114,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 10 > fabs(GetPosAlt() - WaypointAlt(WP_BASELEG))" wp="BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
@@ -140,7 +140,7 @@
       </while>
     </block>
     <block name="Heading 30">
-      <heading alt="ground_alt+50" course="30" until="FALSE"/>
+      <heading alt="GetAltRef()+50" course="30" until="FALSE"/>
     </block>
   </blocks>
 </flight_plan>
diff --git a/conf/flight_plans/generic.xml b/conf/flight_plans/generic.xml
index b1fc8ab8ea..5cdf61eefc 100644
--- a/conf/flight_plans/generic.xml
+++ b/conf/flight_plans/generic.xml
@@ -24,7 +24,7 @@
       <circle radius="-75" wp="HOME"/>
     </block>
     <block name="climb 75">
-      <circle radius="50+(GetPosAlt()-ground_alt)/2" wp="1" throttle="0.75" pitch="15" vmode="throttle" until="10>PowerVoltage()"/>
+      <circle radius="50+(GetPosAlt()-GetAltRef())/2" wp="1" throttle="0.75" pitch="15" vmode="throttle" until="10>PowerVoltage()"/>
     </block>
     <block name="stack 1">
       <circle radius="GetPosAlt()/2" wp="1"/>
diff --git a/conf/flight_plans/grosslobke_demo.xml b/conf/flight_plans/grosslobke_demo.xml
index 6cdcaa5866..80343d88f0 100644
--- a/conf/flight_plans/grosslobke_demo.xml
+++ b/conf/flight_plans/grosslobke_demo.xml
@@ -53,7 +53,7 @@
       <set value="TRUE" var="h_ctl_disabled"/>
       <set value="(-0.6*MAX_PPRZ)" var="h_ctl_aileron_setpoint"/>
       <set value="(0.9*MAX_PPRZ)" var="h_ctl_elevator_setpoint"/>
-      <while cond="GetPosAlt() > ground_alt + 220"/>
+      <while cond="GetPosAlt() > GetAltRef() + 220"/>
       <set value="0" var="h_ctl_aileron_setpoint"/>
       <set value="0" var="h_ctl_elevator_setpoint"/>
     </block>
@@ -78,7 +78,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 20 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/hsif.xml b/conf/flight_plans/hsif.xml
index 19eb10dfb3..39808c6349 100644
--- a/conf/flight_plans/hsif.xml
+++ b/conf/flight_plans/hsif.xml
@@ -18,7 +18,7 @@
       <call fun="NavSetGroundReferenceHere()"/>
     </block>
     <block name="Takeoff">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="HSIF"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="HSIF"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" pitch="15" throttle="1.0" vmode="throttle" wp="CLIMB"/>
diff --git a/conf/flight_plans/ingolfsskali.xml b/conf/flight_plans/ingolfsskali.xml
index f980b7a2cb..8cb378e8f1 100644
--- a/conf/flight_plans/ingolfsskali.xml
+++ b/conf/flight_plans/ingolfsskali.xml
@@ -58,22 +58,22 @@
     </block>
     <block name="profile">
       <for from="1" to="5" var="i">
-        <circle alt="ground_alt+50* $i" radius="nav_radius" until="stage_time>120" wp="1"/>
+        <circle alt="GetAltRef()+50* $i" radius="nav_radius" until="stage_time>120" wp="1"/>
       </for>
     </block>
     <block name="climb">
       <circle radius="nav_radius" wp="CLIMB"/>
     </block>
     <block name="descent">
-      <circle radius="nav_radius" wp="CLIMB" vmode="throttle" throttle="0" pitch="RadOfDeg(my_nav_pitch)"  until="(ground_alt+150 > GetPosAlt())"/>
+      <circle radius="nav_radius" wp="CLIMB" vmode="throttle" throttle="0" pitch="RadOfDeg(my_nav_pitch)"  until="(GetAltRef()+150 > GetPosAlt())"/>
     <deroute block="wait"/>
     </block>
     <block name="wind">
-      <attitude pitch="RadOfDeg(my_nav_pitch)" roll="my_nav_roll" throttle="0.0" until="(ground_alt+150 > GetPosAlt())" vmode="throttle"/>
+      <attitude pitch="RadOfDeg(my_nav_pitch)" roll="my_nav_roll" throttle="0.0" until="(GetAltRef()+150 > GetPosAlt())" vmode="throttle"/>
       <deroute block="wait"/>
     </block>
     <block name="wait" strip_button="Wait">
-      <circle radius="nav_radius" wp="CLIMB" alt="ground_alt+200"/>
+      <circle radius="nav_radius" wp="CLIMB" alt="GetAltRef()+200"/>
     </block>
     <block name="roll">
       <set value="TRUE" var="h_ctl_disabled"/>
diff --git a/conf/flight_plans/joystick.xml b/conf/flight_plans/joystick.xml
index 6969aeb403..5e979f785e 100644
--- a/conf/flight_plans/joystick.xml
+++ b/conf/flight_plans/joystick.xml
@@ -33,7 +33,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" throttle="1.0" vmode="throttle" wp="CLIMB" pitch="15"/>
@@ -82,7 +82,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/kalscott.xml b/conf/flight_plans/kalscott.xml
index 49d59220b2..c9540c1192 100644
--- a/conf/flight_plans/kalscott.xml
+++ b/conf/flight_plans/kalscott.xml
@@ -26,48 +26,48 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Circle"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Circle"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" throttle="1.0" vmode="throttle" wp="CLIMB" pitch="15"/>
     </block>
     <block name="Circle" strip_button="Circle" strip_icon="home.png">
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+200" until="GetPosAlt() > ground_alt+195"/>
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+200" until="NavCircleCount() > 2"/>
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+300" until="GetPosAlt() > ground_alt+295"/>
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+300" until="NavCircleCount() > 2"/>
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+400" until="GetPosAlt() > ground_alt+395"/>
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+400" until="NavCircleCount() > 2"/>
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+300" until="ground_alt+305 > GetPosAlt()"/>
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+300" until="NavCircleCount() > 2"/>
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+200" until="ground_alt+205 > GetPosAlt()"/>
-      <circle radius="nav_radius" wp="CIRCLE" alt="ground_alt+200" until="NavCircleCount() > 2"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+200" until="GetPosAlt() > GetAltRef()+195"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+200" until="NavCircleCount() > 2"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+300" until="GetPosAlt() > GetAltRef()+295"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+300" until="NavCircleCount() > 2"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+400" until="GetPosAlt() > GetAltRef()+395"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+400" until="NavCircleCount() > 2"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+300" until="GetAltRef()+305 > GetPosAlt()"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+300" until="NavCircleCount() > 2"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+200" until="GetAltRef()+205 > GetPosAlt()"/>
+      <circle radius="nav_radius" wp="CIRCLE" alt="GetAltRef()+200" until="NavCircleCount() > 2"/>
       <deroute block="Circle"/>
     </block>
    <block name="Racetrack E-W" strip_button="Racetrack E-W" strip_icon="oval.png">
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+200" until="GetPosAlt() > ground_alt+195"/>
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+200" until="nav_oval_count > 2"/>
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+300" until="GetPosAlt() > ground_alt+295"/>
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+300" until="nav_oval_count > 2"/>
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+400" until="GetPosAlt() > ground_alt+395"/>
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+400" until="nav_oval_count > 2"/>
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+300" until="ground_alt+305 > GetPosAlt()"/>
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+300" until="nav_oval_count > 2"/>
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+200" until="ground_alt+205 > GetPosAlt()"/>
-      <oval p1="1" p2="2" radius="nav_radius" alt="ground_alt+200" until="nav_oval_count > 2"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+200" until="GetPosAlt() > GetAltRef()+195"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+200" until="nav_oval_count > 2"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+300" until="GetPosAlt() > GetAltRef()+295"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+300" until="nav_oval_count > 2"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+400" until="GetPosAlt() > GetAltRef()+395"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+400" until="nav_oval_count > 2"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+300" until="GetAltRef()+305 > GetPosAlt()"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+300" until="nav_oval_count > 2"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+200" until="GetAltRef()+205 > GetPosAlt()"/>
+      <oval p1="1" p2="2" radius="nav_radius" alt="GetAltRef()+200" until="nav_oval_count > 2"/>
       <deroute block="Racetrack E-W"/>
     </block>
     <block name="Racetrack N-S" strip_button="Racetrack N-S" strip_icon="oval.png">
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+200" until="GetPosAlt() > ground_alt+195"/>
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+200" until="nav_oval_count > 2"/>
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+300" until="GetPosAlt() > ground_alt+295"/>
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+300" until="nav_oval_count > 2"/>
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+400" until="GetPosAlt() > ground_alt+395"/>
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+400" until="nav_oval_count > 2"/>
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+300" until="ground_alt+305 > GetPosAlt()"/>
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+300" until="nav_oval_count > 2"/>
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+200" until="ground_alt+305 > GetPosAlt()"/>
-      <oval p1="2" p2="3" radius="nav_radius" alt="ground_alt+200" until="nav_oval_count > 2"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+200" until="GetPosAlt() > GetAltRef()+195"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+200" until="nav_oval_count > 2"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+300" until="GetPosAlt() > GetAltRef()+295"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+300" until="nav_oval_count > 2"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+400" until="GetPosAlt() > GetAltRef()+395"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+400" until="nav_oval_count > 2"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+300" until="GetAltRef()+305 > GetPosAlt()"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+300" until="nav_oval_count > 2"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+200" until="GetAltRef()+305 > GetPosAlt()"/>
+      <oval p1="2" p2="3" radius="nav_radius" alt="GetAltRef()+200" until="nav_oval_count > 2"/>
       <deroute block="Racetrack N-S"/>
     </block>
   </blocks>
diff --git a/conf/flight_plans/kv_svalbard.xml b/conf/flight_plans/kv_svalbard.xml
index 2831ac9162..7dcfa2ba9b 100644
--- a/conf/flight_plans/kv_svalbard.xml
+++ b/conf/flight_plans/kv_svalbard.xml
@@ -35,7 +35,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" throttle="1.0" vmode="throttle" wp="CLIMB"/>
@@ -47,7 +47,7 @@
       <circle radius="nav_radius" wp="PROFILE"/>
     </block>
     <block name="profile_down" strip_button="Profile Down" strip_icon="down_profile.png">
-      <circle radius="nav_radius" wp="PROFILE" vmode="throttle" throttle="0" pitch="RadOfDeg(-10)"  until="(ground_alt+150 > GetPosAlt())"/>
+      <circle radius="nav_radius" wp="PROFILE" vmode="throttle" throttle="0" pitch="RadOfDeg(-10)"  until="(GetAltRef()+150 > GetPosAlt())"/>
     <deroute block="Standby"/>
     </block>
     <block name="MOB" strip_button="Circle around here" strip_icon="mob.png">
diff --git a/conf/flight_plans/landing.xml b/conf/flight_plans/landing.xml
index f1f2aed593..b38a4de861 100644
--- a/conf/flight_plans/landing.xml
+++ b/conf/flight_plans/landing.xml
@@ -21,8 +21,8 @@
       <circle radius="nav_radius" until="And(NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10), 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG)))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
-      <go from="AF" hmode="route" vmode="glide" wp="TD" alt="ground_alt"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
+      <go from="AF" hmode="route" vmode="glide" wp="TD" alt="GetAltRef()"/>
     </block>
     <block name="flare">
       <go approaching_time="0" from="AF" hmode="route" throttle="0.0" vmode="throttle" wp="TD"/>
diff --git a/conf/flight_plans/mav06.xml b/conf/flight_plans/mav06.xml
index 746dd37c1f..69bf4e8212 100644
--- a/conf/flight_plans/mav06.xml
+++ b/conf/flight_plans/mav06.xml
@@ -32,7 +32,7 @@
     </block>
 
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go alt="baseleg_alt" approaching_time="16" from="AF" hmode="route" wp="TD"/>
       <go approaching_time="2" from="AF" hmode="route" throttle="0.1" vmode="throttle" wp="TD"/>
     </block>
@@ -48,7 +48,7 @@
     </block>
 
     <block name="climb">
-      <exception cond=" GetPosAlt() > ground_alt +30" deroute="wait"/>
+      <exception cond=" GetPosAlt() > GetAltRef() +30" deroute="wait"/>
       <attitude pitch="15" roll="0" throttle="0.8" until="10> stage_time" vmode="throttle"/>
     </block>-->
     <block name="wait" strip_button="Wait">
diff --git a/conf/flight_plans/mav07.xml b/conf/flight_plans/mav07.xml
index 83c5ce09bb..7433aac8f2 100644
--- a/conf/flight_plans/mav07.xml
+++ b/conf/flight_plans/mav07.xml
@@ -72,7 +72,7 @@
       </while>
     </block>
     <block name="takeoff">
-      <exception cond="GetPosAlt() > ground_alt + 25" deroute="standby"/>
+      <exception cond="GetPosAlt() > GetAltRef() + 25" deroute="standby"/>
       <set value="0" var="kill_throttle"/>
       <go wp="TAKEOFF"/>
     </block>
@@ -132,7 +132,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 10 > fabs(GetPosAlt() - WaypointAlt(WP_BASELEG))" wp="BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <call fun="compute_TOD(WP_AF, WP_TD, WP_TOD, GLIDE_AIRSPEED, GLIDE_VSPEED)"/>
       <go approaching_time="0" from="AF" hmode="route" wp="TOD"/>
       <go from="TOD" hmode="route" pitch="stage_time*(GLIDE_PITCH/3)" throttle="0" vmode="throttle" wp="TD"/>
diff --git a/conf/flight_plans/mav08.xml b/conf/flight_plans/mav08.xml
index 700b08d8a7..5ce3f7ae2c 100644
--- a/conf/flight_plans/mav08.xml
+++ b/conf/flight_plans/mav08.xml
@@ -41,7 +41,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" pitch="15" throttle="1.0" vmode="throttle" wp="CLIMB"/>
@@ -100,7 +100,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/mission_fw.xml b/conf/flight_plans/mission_fw.xml
index 8359db5d26..5c53485f74 100644
--- a/conf/flight_plans/mission_fw.xml
+++ b/conf/flight_plans/mission_fw.xml
@@ -26,7 +26,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block key="t" name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png" group="home">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" throttle="1.0" vmode="throttle" wp="CLIMB" pitch="15"/>
@@ -52,7 +52,7 @@
       <circle radius="nav_radius" until="And(NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10), 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG)))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/muret_demo_1.xml b/conf/flight_plans/muret_demo_1.xml
index 439ed05688..d0271dafe1 100644
--- a/conf/flight_plans/muret_demo_1.xml
+++ b/conf/flight_plans/muret_demo_1.xml
@@ -19,7 +19,7 @@
       </while>
     </block>
     <block name="circle">
-      <circle wp="road_end" ALT="ground_alt+50" radius="75"/>
+      <circle wp="road_end" ALT="GetAltRef()+50" radius="75"/>
     </block>
     <block name="go too far">
       <go wp="too far"/>
diff --git a/conf/flight_plans/muret_for.xml b/conf/flight_plans/muret_for.xml
index 961a2816c4..1837fd6b7f 100644
--- a/conf/flight_plans/muret_for.xml
+++ b/conf/flight_plans/muret_for.xml
@@ -14,7 +14,7 @@
     </block>
     <block name="for">
       <for from="0" to="3" var="i">
-        <circle alt="ground_alt+50+50*$i" radius="75" until="stage_time>10" wp="HOME"/>
+        <circle alt="GetAltRef()+50+50*$i" radius="75" until="stage_time>10" wp="HOME"/>
       </for>
       <circle wp="HOME" radius="50"/>
     </block>
diff --git a/conf/flight_plans/nav_modules.xml b/conf/flight_plans/nav_modules.xml
index 3f142d3d55..b527228872 100644
--- a/conf/flight_plans/nav_modules.xml
+++ b/conf/flight_plans/nav_modules.xml
@@ -50,7 +50,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block group="home" key="t" name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" pitch="15" throttle="1.0" vmode="throttle" wp="CLIMB"/>
@@ -82,7 +82,7 @@
       <call fun="nav_bungee_takeoff_run()"/>
     </block>
     <block group="nav_pattern" name="Poly Survey" strip_button="Poly Survey">
-      <call fun="nav_survey_polygon_setup(WP_S1,5,80,30,10,50,ground_alt+60)"/>
+      <call fun="nav_survey_polygon_setup(WP_S1,5,80,30,10,50,GetAltRef()+60)"/>
       <call fun="nav_survey_polygon_run()"/>
     </block>
     <block group="nav_pattern" name="Border line 1-2" strip_button="Border Line">
@@ -130,7 +130,7 @@
       <circle radius="nav_radius" until="And(NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10), 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG)))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/nordlys.xml b/conf/flight_plans/nordlys.xml
index f7778a7820..e526b31724 100644
--- a/conf/flight_plans/nordlys.xml
+++ b/conf/flight_plans/nordlys.xml
@@ -37,7 +37,7 @@
       <set value="TRUE" var="h_ctl_disabled"/>
       <set value="(-0.6*MAX_PPRZ)" var="h_ctl_aileron_setpoint"/>
       <set value="(0.9*MAX_PPRZ)" var="h_ctl_elevator_setpoint"/>
-      <while cond="GetPosAlt() > ground_alt + 220"/>
+      <while cond="GetPosAlt() > GetAltRef() + 220"/>
       <set value="0" var="h_ctl_aileron_setpoint"/>
       <set value="0" var="h_ctl_elevator_setpoint"/>
     </block>
@@ -70,7 +70,7 @@
       <circle radius="nav_radius" wp="PROF_LAND"/>
     </block>
     <block name="profile_down land" strip_button="Profile Down Land" strip_icon="down_profile.png">
-      <circle pitch="RadOfDeg(-10)" radius="nav_radius" throttle="0" until="(ground_alt+100 > GetPosAlt())" vmode="throttle" wp="PROF_LAND"/>
+      <circle pitch="RadOfDeg(-10)" radius="nav_radius" throttle="0" until="(GetAltRef()+100 > GetPosAlt())" vmode="throttle" wp="PROF_LAND"/>
       <deroute block="wait"/>
     </block>
     <block name="Land Right AF-TD" strip_button="Land right (wp AF-TD)" strip_icon="land-right.png">
@@ -87,7 +87,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 20 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/poles.xml b/conf/flight_plans/poles.xml
index 7241254523..ccf1487b8c 100644
--- a/conf/flight_plans/poles.xml
+++ b/conf/flight_plans/poles.xml
@@ -32,7 +32,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block key="t" name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" pitch="15" throttle="1.0" vmode="throttle" wp="CLIMB"/>
@@ -73,7 +73,7 @@
       <circle radius="nav_radius" until="And(NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10), 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG)))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/rotorcraft_basic_superbitrf.xml b/conf/flight_plans/rotorcraft_basic_superbitrf.xml
index 635610b6ae..aae3d4b9ce 100644
--- a/conf/flight_plans/rotorcraft_basic_superbitrf.xml
+++ b/conf/flight_plans/rotorcraft_basic_superbitrf.xml
@@ -39,7 +39,7 @@
   </sectors>
   <exceptions>
     <!-- Check inside small flight area, then goto Center(Standby) -->
-    <exception cond="Or(! InsideFlight_Area(GetPosX(), GetPosY()), GetPosAlt() > ground_alt + 50) && !(nav_block == BLOCK_Init) && !(nav_block == BLOCK_Geo_init) && !(nav_block == BLOCK_Landed)" deroute="Standby"/>
+    <exception cond="Or(! InsideFlight_Area(GetPosX(), GetPosY()), GetPosAlt() > GetAltRef() + 50) && !(nav_block == BLOCK_Init) && !(nav_block == BLOCK_Geo_init) && !(nav_block == BLOCK_Landed)" deroute="Standby"/>
     <!-- Check if battery is empty, then Land Here -->
     <exception cond="electrical.bat_low && !(nav_block == BLOCK_Land) && !(nav_block == BLOCK_Flare) && !(nav_block == BLOCK_Landed)" deroute="Land_Here"/>
     <!-- Check if time is up(10 seconds range), then Land Here -->
diff --git a/conf/flight_plans/slayer_training.xml b/conf/flight_plans/slayer_training.xml
index 794ec94e96..ab416079d4 100644
--- a/conf/flight_plans/slayer_training.xml
+++ b/conf/flight_plans/slayer_training.xml
@@ -35,7 +35,7 @@
       <deroute block="climb"/>
     </block>
     <block name="climb">
-      <attitude pitch="10" roll="0" throttle="0.9" until="GetPosAlt() > ground_alt+30" vmode="throttle"/>
+      <attitude pitch="10" roll="0" throttle="0.9" until="GetPosAlt() > GetAltRef()+30" vmode="throttle"/>
     </block>
     <block name="standby" strip_button="STDBY">
       <circle radius="nav_radius" wp="STDBY"/>
@@ -77,7 +77,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 10 > fabs(GetPosAlt() - WaypointAlt(WP_BASELEG))" wp="BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/tcas.xml b/conf/flight_plans/tcas.xml
index c5eeda466c..e3612c132d 100644
--- a/conf/flight_plans/tcas.xml
+++ b/conf/flight_plans/tcas.xml
@@ -33,7 +33,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" throttle="1.0" vmode="throttle" wp="CLIMB"/>
@@ -74,7 +74,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/versatile.xml b/conf/flight_plans/versatile.xml
index 5e4023afba..0887a889cf 100644
--- a/conf/flight_plans/versatile.xml
+++ b/conf/flight_plans/versatile.xml
@@ -45,7 +45,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_icon="takeoff.png" strip_button="Takeoff (wp CLIMB)">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <go wp="CLIMB"/>
     </block>
@@ -70,25 +70,25 @@
       <circle pitch="auto" radius="75" throttle="0.7" wp="1"/>
     </block>
     <block name="Climb 75% throttle">
-      <circle pitch="10" radius="50+(GetPosAlt()-ground_alt)/2" throttle="0.75" until="(10 > PowerVoltage()) || (GetPosAlt() > ground_alt+ 1350)" vmode="throttle" wp="1"/>
+      <circle pitch="10" radius="50+(GetPosAlt()-GetAltRef())/2" throttle="0.75" until="(10 > PowerVoltage()) || (GetPosAlt() > GetAltRef()+ 1350)" vmode="throttle" wp="1"/>
     </block>
     <block name="Climb 0m/s">
       <circle climb="0" radius="nav_radius" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
     </block>
     <block name="Climb 1m/s">
-      <circle climb="1" pitch="5" radius="50+(GetPosAlt()-ground_alt)/2" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
+      <circle climb="1" pitch="5" radius="50+(GetPosAlt()-GetAltRef())/2" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
     </block>
     <block name="Climb nav_climb m/s">
-      <circle climb="nav_climb" radius="nav_radius" until="(10 > PowerVoltage()) || (GetPosAlt() > ground_alt+ 1350)" vmode="climb" wp="1"/>
+      <circle climb="nav_climb" radius="nav_radius" until="(10 > PowerVoltage()) || (GetPosAlt() > GetAltRef()+ 1350)" vmode="climb" wp="1"/>
     </block>
 
     <block name="Circle 0% throttle">
-      <circle pitch="fp_pitch" radius="nav_radius" throttle="0.0" until="ground_alt+50 > GetPosAlt()" vmode="throttle" wp="1"/>
+      <circle pitch="fp_pitch" radius="nav_radius" throttle="0.0" until="GetAltRef()+50 > GetPosAlt()" vmode="throttle" wp="1"/>
       <deroute block="Standby"/>
     </block>
 
     <block name="Oval 0% throttle">
-      <oval p1="1" p2="2" pitch="fp_pitch" radius="nav_radius" throttle="0.0" until="ground_alt+50 > GetPosAlt()" vmode="throttle"/>
+      <oval p1="1" p2="2" pitch="fp_pitch" radius="nav_radius" throttle="0.0" until="GetAltRef()+50 > GetPosAlt()" vmode="throttle"/>
       <deroute block="Standby"/>
     </block>
 
@@ -127,7 +127,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 10 > fabs(GetPosAlt() - WaypointAlt(WP_BASELEG))" wp="BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
@@ -153,7 +153,7 @@
       </while>
     </block>
     <block name="Heading 30">
-      <heading alt="ground_alt+50" course="30" until="FALSE"/>
+      <heading alt="GetAltRef()+50" course="30" until="FALSE"/>
     </block>
     <block name="For loop (circles wp 1)">
       <for from="0" to="3" var="i">
@@ -168,7 +168,7 @@
     </block>
     <block name="Fly in Square">
       <exception cond="! InsideSquare(GetPosX(), GetPosY())" deroute="Come back wp 1"/>
-      <attitude alt="ground_alt+75" roll="0" vmode="alt"/>
+      <attitude alt="GetAltRef()+75" roll="0" vmode="alt"/>
     </block>
     <block name="Come back wp 1">
       <exception cond="InsideSquare(GetPosX(), GetPosY())" deroute="Fly in Square"/>
diff --git a/conf/flight_plans/versatile_airspeed.xml b/conf/flight_plans/versatile_airspeed.xml
index 3b9525bd00..ec1b0d3fdc 100644
--- a/conf/flight_plans/versatile_airspeed.xml
+++ b/conf/flight_plans/versatile_airspeed.xml
@@ -45,7 +45,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block name="Takeoff" strip_icon="takeoff.png" strip_button="Takeoff (wp CLIMB)">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="CLIMB_AIRSPEED" var="v_ctl_auto_airspeed_setpoint" />
       <go wp="CLIMB"/>
@@ -69,25 +69,25 @@
       <circle pitch="auto" radius="75" throttle="0.7" wp="1"/>
     </block>
     <block name="Climb 75% throttle">
-      <circle pitch="10" radius="50+(GetPosAlt()-ground_alt)/2" throttle="0.75" until="(10 > PowerVoltage()) || (GetPosAlt() > ground_alt+ 1350)" vmode="throttle" wp="1"/>
+      <circle pitch="10" radius="50+(GetPosAlt()-GetAltRef())/2" throttle="0.75" until="(10 > PowerVoltage()) || (GetPosAlt() > GetAltRef()+ 1350)" vmode="throttle" wp="1"/>
     </block>
     <block name="Climb 0m/s">
       <circle climb="0" radius="nav_radius" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
     </block>
     <block name="Climb 1m/s">
-      <circle climb="1" pitch="5" radius="50+(GetPosAlt()-ground_alt)/2" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
+      <circle climb="1" pitch="5" radius="50+(GetPosAlt()-GetAltRef())/2" until="10 > PowerVoltage()" vmode="climb" wp="1"/>
     </block>
     <block name="Climb nav_climb m/s">
-      <circle climb="nav_climb" radius="nav_radius" until="(10 > PowerVoltage()) || (GetPosAlt() > ground_alt+ 1350)" vmode="climb" wp="1"/>
+      <circle climb="nav_climb" radius="nav_radius" until="(10 > PowerVoltage()) || (GetPosAlt() > GetAltRef()+ 1350)" vmode="climb" wp="1"/>
     </block>
 
     <block name="Circle 0% throttle">
-      <circle pitch="fp_pitch" radius="nav_radius" throttle="0.0" until="ground_alt+50 > GetPosAlt()" vmode="throttle" wp="1"/>
+      <circle pitch="fp_pitch" radius="nav_radius" throttle="0.0" until="GetAltRef()+50 > GetPosAlt()" vmode="throttle" wp="1"/>
       <deroute block="Standby"/>
     </block>
 
     <block name="Oval 0% throttle">
-      <oval p1="1" p2="2" pitch="fp_pitch" radius="nav_radius" throttle="0.0" until="ground_alt+50 > GetPosAlt()" vmode="throttle"/>
+      <oval p1="1" p2="2" pitch="fp_pitch" radius="nav_radius" throttle="0.0" until="GetAltRef()+50 > GetPosAlt()" vmode="throttle"/>
       <deroute block="Standby"/>
     </block>
 
@@ -163,7 +163,7 @@
       </while>
     </block>
     <block name="Heading 30">
-      <heading alt="ground_alt+50" course="30" until="FALSE"/>
+      <heading alt="GetAltRef()+50" course="30" until="FALSE"/>
     </block>
     <block name="For loop (circles wp 1)">
       <for from="0" to="3" var="i">
@@ -178,7 +178,7 @@
     </block>
     <block name="Fly in Square">
       <exception cond="! InsideSquare(GetPosX(), GetPosY())" deroute="Come back wp 1"/>
-      <attitude alt="ground_alt+75" roll="0" vmode="alt"/>
+      <attitude alt="GetAltRef()+75" roll="0" vmode="alt"/>
     </block>
     <block name="Come back wp 1">
       <exception cond="InsideSquare(GetPosX(), GetPosY())" deroute="Fly in Square"/>
diff --git a/conf/flight_plans/versatile_carto_fixe_muret.xml b/conf/flight_plans/versatile_carto_fixe_muret.xml
index dfd522ded7..fe9a0eb356 100644
--- a/conf/flight_plans/versatile_carto_fixe_muret.xml
+++ b/conf/flight_plans/versatile_carto_fixe_muret.xml
@@ -61,7 +61,7 @@ float varsweepsize=110;
     </block>
 
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <go wp="CLIMB"/>
     </block>
@@ -111,8 +111,8 @@ float varsweepsize=110;
     <block name="Monter">
       <call fun="NavSetWaypointHere(WP_MOB)"/>
       <set value="DEFAULT_CIRCLE_RADIUS" var="nav_radius"/>
-      <circle alt="ground_alt+105" radius="nav_radius" wp="MOB"/>
-      <exception cond="GetPosAlt() > ground_alt+100" deroute="Carto survey S1-S2-S3"/>
+      <circle alt="GetAltRef()+105" radius="nav_radius" wp="MOB"/>
+      <exception cond="GetPosAlt() > GetAltRef()+100" deroute="Carto survey S1-S2-S3"/>
     </block>
 
 
@@ -139,8 +139,8 @@ float varsweepsize=110;
     <block name="Descendre">
       <call fun="NavSetWaypointHere(WP_MOB)"/>
       <set value="DEFAULT_CIRCLE_RADIUS" var="nav_radius"/>
-      <circle alt="ground_alt+35" radius="nav_radius" wp="MOB"/>
-      <exception cond="ground_alt+40 > GetPosAlt()   " deroute="Carto survey SP1-SP2-SP3 fin"/>
+      <circle alt="GetAltRef()+35" radius="nav_radius" wp="MOB"/>
+      <exception cond="GetAltRef()+40 > GetPosAlt()   " deroute="Carto survey SP1-SP2-SP3 fin"/>
     </block>
 
     <block name="Carto survey SP1-SP2-SP3 fin" strip_button="Survey (wp S1-S2)" strip_icon="survey.png">
diff --git a/conf/flight_plans/xsens_cachejunction.xml b/conf/flight_plans/xsens_cachejunction.xml
index 3d2fd30938..fca2f69c32 100644
--- a/conf/flight_plans/xsens_cachejunction.xml
+++ b/conf/flight_plans/xsens_cachejunction.xml
@@ -23,7 +23,7 @@
   <exceptions/>
   <blocks>
     <block name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" pitch="15" throttle="1.0" vmode="throttle" wp="CLIMB"/>
@@ -91,7 +91,7 @@
       <circle radius="nav_radius" until="NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10) && 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
     <block name="flare">
diff --git a/conf/flight_plans/zamboni_survey_test.xml b/conf/flight_plans/zamboni_survey_test.xml
index 810c6a779d..9e43f0bb35 100644
--- a/conf/flight_plans/zamboni_survey_test.xml
+++ b/conf/flight_plans/zamboni_survey_test.xml
@@ -34,7 +34,7 @@
       <attitude roll="0" throttle="0" vmode="throttle"/>
     </block>
     <block key="t" name="Takeoff" strip_button="Takeoff (wp CLIMB)" strip_icon="takeoff.png" group="home">
-      <exception cond="GetPosAlt() > ground_alt+25" deroute="Standby"/>
+      <exception cond="GetPosAlt() > GetAltRef()+25" deroute="Standby"/>
       <set value="0" var="kill_throttle"/>
       <set value="0" var="autopilot_flight_time"/>
       <go from="HOME" throttle="1.0" vmode="throttle" wp="CLIMB" pitch="15"/>
@@ -66,7 +66,7 @@
       <circle radius="nav_radius" until="And(NavQdrCloseTo(DegOfRad(baseleg_out_qdr)-(nav_radius/fabs(nav_radius))*10), 10 > fabs(GetPosAlt() - WaypointAlt(WP__BASELEG)))" wp="_BASELEG"/>
     </block>
     <block name="final">
-      <exception cond="ground_alt + 10 > GetPosAlt()" deroute="flare"/>
+      <exception cond="GetAltRef() + 10 > GetPosAlt()" deroute="flare"/>
       <go from="AF" hmode="route" vmode="glide" wp="TD"/>
     </block>
 
diff --git a/sw/airborne/subsystems/nav.h b/sw/airborne/subsystems/nav.h
index 74ce373275..e10999510b 100644
--- a/sw/airborne/subsystems/nav.h
+++ b/sw/airborne/subsystems/nav.h
@@ -199,6 +199,7 @@ bool_t nav_approaching_xy(float x, float y, float from_x, float from_y, float ap
 #define GetPosX() (stateGetPositionEnu_f()->x)
 #define GetPosY() (stateGetPositionEnu_f()->y)
 #define GetPosAlt() (stateGetPositionUtm_f()->alt)
+#define GetAltRef() (ground_alt)
 
 #define SEND_NAVIGATION(_trans, _dev) { \
     uint8_t _circle_count = NavCircleCount(); \