diff --git a/ArduCopter/Attitude.cpp b/ArduCopter/Attitude.cpp
index 469d12e14d..fd4a116a53 100644
--- a/ArduCopter/Attitude.cpp
+++ b/ArduCopter/Attitude.cpp
@@ -135,7 +135,7 @@ void Copter::rotate_body_frame_to_NE(float &x, float &y)
 }
 
 // It will return the PILOT_SPEED_DN value if non zero, otherwise if zero it returns the PILOT_SPEED_UP value.
-uint16_t Copter::get_pilot_speed_dn()
+uint16_t Copter::get_pilot_speed_dn() const
 {
     if (g2.pilot_speed_dn == 0) {
         return abs(g.pilot_speed_up);
diff --git a/ArduCopter/Copter.h b/ArduCopter/Copter.h
index 6eb55165d4..0a2c539cae 100644
--- a/ArduCopter/Copter.h
+++ b/ArduCopter/Copter.h
@@ -662,7 +662,7 @@ private:
     float get_non_takeoff_throttle();
     void set_accel_throttle_I_from_pilot_throttle();
     void rotate_body_frame_to_NE(float &x, float &y);
-    uint16_t get_pilot_speed_dn();
+    uint16_t get_pilot_speed_dn() const;
 
 #if HAL_ADSB_ENABLED
     // avoidance_adsb.cpp
@@ -816,8 +816,8 @@ private:
     void load_parameters(void) override;
     void convert_pid_parameters(void);
     void convert_lgr_parameters(void);
-    void convert_tradheli_parameters(void);
-    void convert_fs_options_params(void);
+    void convert_tradheli_parameters(void) const;
+    void convert_fs_options_params(void) const;
 
     // precision_landing.cpp
     void init_precland();
@@ -838,8 +838,8 @@ private:
     void read_barometer(void);
     void init_rangefinder(void);
     void read_rangefinder(void);
-    bool rangefinder_alt_ok();
-    bool rangefinder_up_ok();
+    bool rangefinder_alt_ok() const;
+    bool rangefinder_up_ok() const;
     void rpm_update();
     void init_optflow();
     void update_optical_flow(void);
@@ -863,7 +863,7 @@ private:
     bool ekf_alt_ok() const;
     void update_auto_armed();
     bool should_log(uint32_t mask);
-    const char* get_frame_string();
+    const char* get_frame_string() const;
     void allocate_motors(void);
     bool is_tradheli() const;
 
diff --git a/ArduCopter/Parameters.cpp b/ArduCopter/Parameters.cpp
index e6bb2265fe..c8f1dfc6bc 100644
--- a/ArduCopter/Parameters.cpp
+++ b/ArduCopter/Parameters.cpp
@@ -1411,7 +1411,7 @@ void Copter::convert_lgr_parameters(void)
 
 #if FRAME_CONFIG == HELI_FRAME
 // handle conversion of tradheli parameters from Copter-3.6 to Copter-3.7
-void Copter::convert_tradheli_parameters(void)
+void Copter::convert_tradheli_parameters(void) const
 {
     if (g2.frame_class.get() == AP_Motors::MOTOR_FRAME_HELI) {
         // single heli conversion info
@@ -1585,7 +1585,7 @@ void Copter::convert_tradheli_parameters(void)
 }
 #endif
 
-void Copter::convert_fs_options_params(void)
+void Copter::convert_fs_options_params(void) const
 {
     // If FS_OPTIONS has already been configured and we don't change it.
     enum ap_var_type ptype;
diff --git a/ArduCopter/mode.h b/ArduCopter/mode.h
index c921812667..34098b64d0 100644
--- a/ArduCopter/mode.h
+++ b/ArduCopter/mode.h
@@ -474,7 +474,7 @@ private:
     bool verify_payload_place();
     bool verify_loiter_unlimited();
     bool verify_loiter_time(const AP_Mission::Mission_Command& cmd);
-    bool verify_loiter_to_alt();
+    bool verify_loiter_to_alt() const;
     bool verify_RTL();
     bool verify_wait_delay();
     bool verify_within_distance();
@@ -1068,7 +1068,7 @@ public:
     RTLState state() { return _state; }
 
     // this should probably not be exposed
-    bool state_complete() { return _state_complete; }
+    bool state_complete() const { return _state_complete; }
 
     virtual bool is_landing() const override;
 
@@ -1278,7 +1278,7 @@ protected:
 
 private:
 
-    void log_data();
+    void log_data() const;
     float waveform(float time);
 
     enum class AxisType {
diff --git a/ArduCopter/mode_auto.cpp b/ArduCopter/mode_auto.cpp
index e3bb22675d..a17c18d720 100644
--- a/ArduCopter/mode_auto.cpp
+++ b/ArduCopter/mode_auto.cpp
@@ -1757,7 +1757,7 @@ bool ModeAuto::verify_loiter_time(const AP_Mission::Mission_Command& cmd)
 
 // verify_loiter_to_alt - check if we have reached both destination
 // (roughly) and altitude (precisely)
-bool ModeAuto::verify_loiter_to_alt()
+bool ModeAuto::verify_loiter_to_alt() const
 {
     if (loiter_to_alt.reached_destination_xy &&
         loiter_to_alt.reached_alt) {
diff --git a/ArduCopter/mode_systemid.cpp b/ArduCopter/mode_systemid.cpp
index e3ea17f024..0db0eee754 100644
--- a/ArduCopter/mode_systemid.cpp
+++ b/ArduCopter/mode_systemid.cpp
@@ -273,7 +273,7 @@ void ModeSystemId::run()
 }
 
 // log system id and attitude
-void ModeSystemId::log_data()
+void ModeSystemId::log_data() const
 {
     uint8_t index = copter.ahrs.get_primary_gyro_index();
     Vector3f delta_angle;
diff --git a/ArduCopter/sensors.cpp b/ArduCopter/sensors.cpp
index 682b5a4333..aeafed1177 100644
--- a/ArduCopter/sensors.cpp
+++ b/ArduCopter/sensors.cpp
@@ -115,13 +115,13 @@ void Copter::read_rangefinder(void)
 }
 
 // return true if rangefinder_alt can be used
-bool Copter::rangefinder_alt_ok()
+bool Copter::rangefinder_alt_ok() const
 {
     return (rangefinder_state.enabled && rangefinder_state.alt_healthy);
 }
 
 // return true if rangefinder_alt can be used
-bool Copter::rangefinder_up_ok()
+bool Copter::rangefinder_up_ok() const
 {
     return (rangefinder_up_state.enabled && rangefinder_up_state.alt_healthy);
 }
diff --git a/ArduCopter/system.cpp b/ArduCopter/system.cpp
index be46000a79..7023c62c72 100644
--- a/ArduCopter/system.cpp
+++ b/ArduCopter/system.cpp
@@ -449,7 +449,7 @@ bool Copter::should_log(uint32_t mask)
 }
 
 // return string corresponding to frame_class
-const char* Copter::get_frame_string()
+const char* Copter::get_frame_string() const
 {
     switch ((AP_Motors::motor_frame_class)g2.frame_class.get()) {
         case AP_Motors::MOTOR_FRAME_QUAD: