diff --git a/AntennaTracker/GCS_Mavlink.cpp b/AntennaTracker/GCS_Mavlink.cpp
index f8a9be27c4..3cfba0da21 100644
--- a/AntennaTracker/GCS_Mavlink.cpp
+++ b/AntennaTracker/GCS_Mavlink.cpp
@@ -569,7 +569,7 @@ void GCS_MAVLINK_Tracker::handleMessage(mavlink_message_t* msg)
 
                 // mavproxy/mavutil sends this when auto command is entered 
             case MAV_CMD_MISSION_START:
-                tracker.set_mode(AUTO);
+                tracker.set_mode(AUTO, MODE_REASON_GCS_COMMAND);
                 result = MAV_RESULT_ACCEPTED;
                 break;
 
@@ -816,7 +816,7 @@ bool GCS_MAVLINK_Tracker::set_mode(uint8_t mode)
     case SCAN:
     case SERVO_TEST:
     case STOP:
-        tracker.set_mode((enum ControlMode)mode);
+        tracker.set_mode((enum ControlMode)mode, MODE_REASON_GCS_COMMAND);
         return true;
     }
     return false;
diff --git a/AntennaTracker/Log.cpp b/AntennaTracker/Log.cpp
index 587c00ed17..f905d42186 100644
--- a/AntennaTracker/Log.cpp
+++ b/AntennaTracker/Log.cpp
@@ -83,7 +83,7 @@ const struct LogStructure Tracker::log_structure[] = {
 
 void Tracker::Log_Write_Vehicle_Startup_Messages()
 {
-    DataFlash.Log_Write_Mode(control_mode);
+    DataFlash.Log_Write_Mode(control_mode, MODE_REASON_INITIALISED);
     gps.Write_DataFlash_Log_Startup_messages();
 }
 
diff --git a/AntennaTracker/Tracker.h b/AntennaTracker/Tracker.h
index a95e85f4f6..7b6ea50a86 100644
--- a/AntennaTracker/Tracker.h
+++ b/AntennaTracker/Tracker.h
@@ -244,7 +244,7 @@ private:
     void arm_servos();
     void disarm_servos();
     void prepare_servos();
-    void set_mode(enum ControlMode mode);
+    void set_mode(enum ControlMode mode, mode_reason_t reason);
     void check_usb_mux(void);
     void update_vehicle_pos_estimate();
     void update_tracker_position();
diff --git a/AntennaTracker/control_servo_test.cpp b/AntennaTracker/control_servo_test.cpp
index d8f4deb009..c99ffe10fa 100644
--- a/AntennaTracker/control_servo_test.cpp
+++ b/AntennaTracker/control_servo_test.cpp
@@ -20,7 +20,7 @@ bool Tracker::servo_test_set_servo(uint8_t servo_num, uint16_t pwm)
 
     // ensure we are in servo test mode
     if (control_mode != SERVO_TEST) {
-        set_mode(SERVO_TEST);
+        set_mode(SERVO_TEST, MODE_REASON_SERVOTEST);
     }
 
     // set yaw servo pwm and send output to servo
diff --git a/AntennaTracker/defines.h b/AntennaTracker/defines.h
index 6f9dc67ec2..234cec0f84 100644
--- a/AntennaTracker/defines.h
+++ b/AntennaTracker/defines.h
@@ -29,6 +29,13 @@ enum AltSource {
 	ALT_SOURCE_GPS_VEH_ONLY=2
 };
 
+enum mode_reason_t {
+    MODE_REASON_INITIALISED = 0,
+    MODE_REASON_STARTUP,
+    MODE_REASON_SERVOTEST,
+    MODE_REASON_GCS_COMMAND,
+};
+
 //  Filter
 #define SERVO_OUT_FILT_HZ               0.1f
 #define G_Dt                            0.02f
diff --git a/AntennaTracker/system.cpp b/AntennaTracker/system.cpp
index 284416ac72..82f24f3e70 100644
--- a/AntennaTracker/system.cpp
+++ b/AntennaTracker/system.cpp
@@ -110,7 +110,7 @@ void Tracker::init_tracker()
     gcs().send_text(MAV_SEVERITY_INFO,"Ready to track");
     hal.scheduler->delay(1000); // Why????
 
-    set_mode(AUTO); // tracking
+    set_mode(AUTO, MODE_REASON_STARTUP); // tracking
 
     if (g.startup_delay > 0) {
         // arm servos with trim value to allow them to start up (required
@@ -211,7 +211,7 @@ void Tracker::prepare_servos()
     SRV_Channels::output_ch_all();
 }
 
-void Tracker::set_mode(enum ControlMode mode)
+void Tracker::set_mode(enum ControlMode mode, mode_reason_t reason)
 {
     if (control_mode == mode) {
         // don't switch modes if we are already in the correct mode.
@@ -234,7 +234,7 @@ void Tracker::set_mode(enum ControlMode mode)
     }
 
 	// log mode change
-	DataFlash.Log_Write_Mode(control_mode);
+	DataFlash.Log_Write_Mode(control_mode, reason);
 }
 
 void Tracker::check_usb_mux(void)