diff --git a/sw/airborne/arch/sim/sim_ap.c b/sw/airborne/arch/sim/sim_ap.c
index 76a89ae2ed..a4ab8da5b8 100644
--- a/sw/airborne/arch/sim/sim_ap.c
+++ b/sw/airborne/arch/sim/sim_ap.c
@@ -47,10 +47,8 @@ uint8_t ac_id;
 
 value sim_periodic_task(value unit) {
   sensors_task();
-  navigation_task(); // FIXME, should run at 4Hz
   attitude_loop();
   reporting_task();
-  monitor_task();   // FIXME, should run at 1Hz
   periodic_task_ap();
   periodic_task_fbw();
   event_task_ap();
@@ -58,6 +56,16 @@ value sim_periodic_task(value unit) {
   return unit;
 }
 
+value sim_monitor_task(value unit) {
+  monitor_task();
+  return unit;
+}
+
+value sim_nav_task(value unit) {
+  navigation_task();
+  return unit;
+}
+
 
 float ftimeofday(void) {
   struct timeval t;
diff --git a/sw/simulator/sitl.ml b/sw/simulator/sitl.ml
index baea8733c8..f001556da9 100644
--- a/sw/simulator/sitl.ml
+++ b/sw/simulator/sitl.ml
@@ -43,6 +43,8 @@ module Make (A:Data.MISSION) (FM: FlightModel.SIG) = struct
 
   let servos_period = 1./.40. (* s *)
   let periodic_period = 1./.60. (* s *)
+  let nav_period = 1./.4. (* s *)
+  let monitor_period = 1. (* s *)
   let rc_period = 1./.40. (* s *)
 
   let msg = fun name ->
@@ -125,6 +127,8 @@ module Make (A:Data.MISSION) (FM: FlightModel.SIG) = struct
     window#show ()
 
   external periodic_task : unit -> unit = "sim_periodic_task"
+  external nav_task : unit -> unit = "sim_nav_task"
+  external monitor_task : unit -> unit = "sim_monitor_task"
   external sim_init : unit -> unit = "sim_init"
   external update_bat : int -> unit = "update_bat"
   external update_adc1 : int -> unit = "update_adc1"
@@ -177,6 +181,8 @@ module Make (A:Data.MISSION) (FM: FlightModel.SIG) = struct
   let boot = fun time_scale ->
     Stdlib.timer ~scale:time_scale servos_period (update_servos bat_button);
     Stdlib.timer ~scale:time_scale periodic_period periodic_task;
+    Stdlib.timer ~scale:time_scale nav_period nav_task;
+    Stdlib.timer ~scale:time_scale monitor_period monitor_task;
 
     (* Forward or broacast messages according to "link" mode *)
     Hashtbl.iter