diff --git a/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp b/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp
index ae5fe84f3d..1ad45f68b5 100644
--- a/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp
+++ b/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp
@@ -33,6 +33,9 @@ AP_AHRS_NavEKF::AP_AHRS_NavEKF(AP_InertialSensor &ins, AP_Baro &baro, AP_GPS &gp
     AP_AHRS_DCM(ins, baro, gps),
     EKF2(_EKF2),
     EKF3(_EKF3),
+    _ekf2_started(false),
+    _ekf3_started(false),
+    _force_ekf(false),
     _ekf_flags(flags)
 {
     _dcm_matrix.identity();
@@ -116,19 +119,19 @@ void AP_AHRS_NavEKF::update_DCM(void)
 
 void AP_AHRS_NavEKF::update_EKF2(void)
 {
-    if (!ekf2_started) {
+    if (!_ekf2_started) {
         // wait 1 second for DCM to output a valid tilt error estimate
         if (start_time_ms == 0) {
             start_time_ms = AP_HAL::millis();
         }
-        if (AP_HAL::millis() - start_time_ms > startup_delay_ms || force_ekf) {
-            ekf2_started = EKF2.InitialiseFilter();
-            if (force_ekf) {
+        if (AP_HAL::millis() - start_time_ms > startup_delay_ms || _force_ekf) {
+            _ekf2_started = EKF2.InitialiseFilter();
+            if (_force_ekf) {
                 return;
             }
         }
     }
-    if (ekf2_started) {
+    if (_ekf2_started) {
         EKF2.UpdateFilter();
         if (active_EKF_type() == EKF_TYPE2) {
             Vector3f eulers;
@@ -181,19 +184,19 @@ void AP_AHRS_NavEKF::update_EKF2(void)
 
 void AP_AHRS_NavEKF::update_EKF3(void)
 {
-    if (!ekf3_started) {
+    if (!_ekf3_started) {
         // wait 1 second for DCM to output a valid tilt error estimate
         if (start_time_ms == 0) {
             start_time_ms = AP_HAL::millis();
         }
-        if (AP_HAL::millis() - start_time_ms > startup_delay_ms || force_ekf) {
-            ekf3_started = EKF3.InitialiseFilter();
-            if (force_ekf) {
+        if (AP_HAL::millis() - start_time_ms > startup_delay_ms || _force_ekf) {
+            _ekf3_started = EKF3.InitialiseFilter();
+            if (_force_ekf) {
                 return;
             }
         }
     }
-    if (ekf3_started) {
+    if (_ekf3_started) {
         EKF3.UpdateFilter();
         if (active_EKF_type() == EKF_TYPE3) {
             Vector3f eulers;
@@ -301,11 +304,11 @@ void AP_AHRS_NavEKF::reset(bool recover_eulers)
 {
     AP_AHRS_DCM::reset(recover_eulers);
     _dcm_attitude(roll, pitch, yaw);
-    if (ekf2_started) {
-        ekf2_started = EKF2.InitialiseFilter();
+    if (_ekf2_started) {
+        _ekf2_started = EKF2.InitialiseFilter();
     }
-    if (ekf3_started) {
-        ekf3_started = EKF3.InitialiseFilter();
+    if (_ekf3_started) {
+        _ekf3_started = EKF3.InitialiseFilter();
     }
 }
 
@@ -314,11 +317,11 @@ void AP_AHRS_NavEKF::reset_attitude(const float &_roll, const float &_pitch, con
 {
     AP_AHRS_DCM::reset_attitude(_roll, _pitch, _yaw);
     _dcm_attitude(roll, pitch, yaw);
-    if (ekf2_started) {
-        ekf2_started = EKF2.InitialiseFilter();
+    if (_ekf2_started) {
+        _ekf2_started = EKF2.InitialiseFilter();
     }
-    if (ekf3_started) {
-        ekf3_started = EKF3.InitialiseFilter();
+    if (_ekf3_started) {
+        _ekf3_started = EKF3.InitialiseFilter();
     }
 }
 
@@ -437,7 +440,7 @@ bool AP_AHRS_NavEKF::get_secondary_attitude(Vector3f &eulers)
     case EKF_TYPE_NONE:
         // EKF is secondary
         EKF2.getEulerAngles(-1, eulers);
-        return ekf2_started;
+        return _ekf2_started;
 
     case EKF_TYPE2:
 
@@ -457,7 +460,7 @@ bool AP_AHRS_NavEKF::get_secondary_position(struct Location &loc)
     case EKF_TYPE_NONE:
         // EKF is secondary
         EKF2.getLLH(loc);
-        return ekf2_started;
+        return _ekf2_started;
 
     case EKF_TYPE2:
 
@@ -767,7 +770,7 @@ AP_AHRS_NavEKF::EKF_TYPE AP_AHRS_NavEKF::active_EKF_type(void) const
 
     case 2: {
         // do we have an EKF2 yet?
-        if (!ekf2_started) {
+        if (!_ekf2_started) {
             return EKF_TYPE_NONE;
         }
         if (always_use_EKF()) {
@@ -784,7 +787,7 @@ AP_AHRS_NavEKF::EKF_TYPE AP_AHRS_NavEKF::active_EKF_type(void) const
 
     case 3: {
         // do we have an EKF3 yet?
-        if (!ekf3_started) {
+        if (!_ekf3_started) {
             return EKF_TYPE_NONE;
         }
         if (always_use_EKF()) {
@@ -878,7 +881,7 @@ bool AP_AHRS_NavEKF::healthy(void) const
         return AP_AHRS_DCM::healthy();
 
     case 2: {
-        bool ret = ekf2_started && EKF2.healthy();
+        bool ret = _ekf2_started && EKF2.healthy();
         if (!ret) {
             return false;
         }
@@ -893,7 +896,7 @@ bool AP_AHRS_NavEKF::healthy(void) const
     }
 
     case 3: {
-        bool ret = ekf3_started && EKF3.healthy();
+        bool ret = _ekf3_started && EKF3.healthy();
         if (!ret) {
             return false;
         }
@@ -931,11 +934,11 @@ bool AP_AHRS_NavEKF::initialised(void) const
     case 2:
     default:
         // initialisation complete 10sec after ekf has started
-        return (ekf2_started && (AP_HAL::millis() - start_time_ms > AP_AHRS_NAVEKF_SETTLE_TIME_MS));
+        return (_ekf2_started && (AP_HAL::millis() - start_time_ms > AP_AHRS_NAVEKF_SETTLE_TIME_MS));
 
     case 3:
         // initialisation complete 10sec after ekf has started
-        return (ekf3_started && (AP_HAL::millis() - start_time_ms > AP_AHRS_NAVEKF_SETTLE_TIME_MS));
+        return (_ekf3_started && (AP_HAL::millis() - start_time_ms > AP_AHRS_NAVEKF_SETTLE_TIME_MS));
 
 #if CONFIG_HAL_BOARD == HAL_BOARD_SITL
     case EKF_TYPE_SITL:
diff --git a/libraries/AP_AHRS/AP_AHRS_NavEKF.h b/libraries/AP_AHRS/AP_AHRS_NavEKF.h
index f2a9789217..cdba902262 100644
--- a/libraries/AP_AHRS/AP_AHRS_NavEKF.h
+++ b/libraries/AP_AHRS/AP_AHRS_NavEKF.h
@@ -221,7 +221,7 @@ public:
     bool getGpsGlitchStatus();
 
     // used by Replay to force start at right timestamp
-    void force_ekf_start(void) { force_ekf = true; }
+    void force_ekf_start(void) { _force_ekf = true; }
 
     // is the EKF backend doing its own sensor logging?
     bool have_ekf_logging(void) const override;
@@ -248,10 +248,9 @@ private:
 
     NavEKF2 &EKF2;
     NavEKF3 &EKF3;
-    bool ekf1_started:1;
-    bool ekf2_started:1;
-    bool ekf3_started:1;
-    bool force_ekf:1;
+    bool _ekf2_started;
+    bool _ekf3_started;
+    bool _force_ekf;
     Matrix3f _dcm_matrix;
     Vector3f _dcm_attitude;
     Vector3f _gyro_bias;