diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_AirDataFusion.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_AirDataFusion.cpp
index 2fef831ffe..c0ea29f1dd 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_AirDataFusion.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_AirDataFusion.cpp
@@ -94,9 +94,14 @@ void NavEKF3_core::FuseAirspeed()
         }
 
         if (!inhibitDelVelBiasStates && !airDataFusionWindOnly) {
-            Kfusion[13] = SK_TAS[0]*(P[13][4]*SH_TAS[2] - P[13][22]*SH_TAS[2] + P[13][5]*SK_TAS[1] - P[13][23]*SK_TAS[1] + P[13][6]*vd*SH_TAS[0]);
-            Kfusion[14] = SK_TAS[0]*(P[14][4]*SH_TAS[2] - P[14][22]*SH_TAS[2] + P[14][5]*SK_TAS[1] - P[14][23]*SK_TAS[1] + P[14][6]*vd*SH_TAS[0]);
-            Kfusion[15] = SK_TAS[0]*(P[15][4]*SH_TAS[2] - P[15][22]*SH_TAS[2] + P[15][5]*SK_TAS[1] - P[15][23]*SK_TAS[1] + P[15][6]*vd*SH_TAS[0]);
+            for (uint8_t index = 0; index < 3; index++) {
+                uint8_t stateIndex = index + 13;
+                if (!dvelBiasAxisInhibit[index]) {
+                    Kfusion[stateIndex] = SK_TAS[0]*(P[stateIndex][4]*SH_TAS[2] - P[stateIndex][22]*SH_TAS[2] + P[stateIndex][5]*SK_TAS[1] - P[stateIndex][23]*SK_TAS[1] + P[stateIndex][6]*vd*SH_TAS[0]);
+                } else {
+                    Kfusion[stateIndex] = 0.0f;
+                }
+            }
         } else {
             // zero indexes 13 to 15 = 3*4 bytes
             memset(&Kfusion[13], 0, 12);
@@ -388,9 +393,14 @@ void NavEKF3_core::FuseSideslip()
         }
 
         if (!inhibitDelVelBiasStates && !airDataFusionWindOnly) {
-            Kfusion[13] = SK_BETA[0]*(P[13][0]*SK_BETA[5] + P[13][1]*SK_BETA[4] - P[13][4]*SK_BETA[1] + P[13][5]*SK_BETA[2] + P[13][2]*SK_BETA[6] + P[13][6]*SK_BETA[3] - P[13][3]*SK_BETA[7] + P[13][22]*SK_BETA[1] - P[13][23]*SK_BETA[2]);
-            Kfusion[14] = SK_BETA[0]*(P[14][0]*SK_BETA[5] + P[14][1]*SK_BETA[4] - P[14][4]*SK_BETA[1] + P[14][5]*SK_BETA[2] + P[14][2]*SK_BETA[6] + P[14][6]*SK_BETA[3] - P[14][3]*SK_BETA[7] + P[14][22]*SK_BETA[1] - P[14][23]*SK_BETA[2]);
-            Kfusion[15] = SK_BETA[0]*(P[15][0]*SK_BETA[5] + P[15][1]*SK_BETA[4] - P[15][4]*SK_BETA[1] + P[15][5]*SK_BETA[2] + P[15][2]*SK_BETA[6] + P[15][6]*SK_BETA[3] - P[15][3]*SK_BETA[7] + P[15][22]*SK_BETA[1] - P[15][23]*SK_BETA[2]);
+            for (uint8_t index = 0; index < 3; index++) {
+                uint8_t stateIndex = index + 13;
+                if (!dvelBiasAxisInhibit[index]) {
+                    Kfusion[stateIndex] = SK_BETA[0]*(P[stateIndex][0]*SK_BETA[5] + P[stateIndex][1]*SK_BETA[4] - P[stateIndex][4]*SK_BETA[1] + P[stateIndex][5]*SK_BETA[2] + P[stateIndex][2]*SK_BETA[6] + P[stateIndex][6]*SK_BETA[3] - P[stateIndex][3]*SK_BETA[7] + P[stateIndex][22]*SK_BETA[1] - P[stateIndex][23]*SK_BETA[2]);
+                } else {
+                    Kfusion[stateIndex] = 0.0f;
+                }
+            }
         } else {
             // zero indexes 13 to 15 = 3*4 bytes
             memset(&Kfusion[13], 0, 12);
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_MagFusion.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_MagFusion.cpp
index ace96cd72e..8659348d1b 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_MagFusion.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_MagFusion.cpp
@@ -602,9 +602,14 @@ void NavEKF3_core::FuseMagnetometer()
             }
 
             if (!inhibitDelVelBiasStates) {
-                Kfusion[13] = SK_MX[0]*(P[13][19] + P[13][1]*SH_MAG[0] - P[13][2]*SH_MAG[1] + P[13][3]*SH_MAG[2] + P[13][0]*SK_MX[2] - P[13][16]*SK_MX[1] + P[13][17]*SK_MX[4] - P[13][18]*SK_MX[3]);
-                Kfusion[14] = SK_MX[0]*(P[14][19] + P[14][1]*SH_MAG[0] - P[14][2]*SH_MAG[1] + P[14][3]*SH_MAG[2] + P[14][0]*SK_MX[2] - P[14][16]*SK_MX[1] + P[14][17]*SK_MX[4] - P[14][18]*SK_MX[3]);
-                Kfusion[15] = SK_MX[0]*(P[15][19] + P[15][1]*SH_MAG[0] - P[15][2]*SH_MAG[1] + P[15][3]*SH_MAG[2] + P[15][0]*SK_MX[2] - P[15][16]*SK_MX[1] + P[15][17]*SK_MX[4] - P[15][18]*SK_MX[3]);
+                for (uint8_t index = 0; index < 3; index++) {
+                    uint8_t stateIndex = index + 13;
+                    if (!dvelBiasAxisInhibit[index]) {
+                        Kfusion[stateIndex] = SK_MX[0]*(P[stateIndex][19] + P[stateIndex][1]*SH_MAG[0] - P[stateIndex][2]*SH_MAG[1] + P[stateIndex][3]*SH_MAG[2] + P[stateIndex][0]*SK_MX[2] - P[stateIndex][16]*SK_MX[1] + P[stateIndex][17]*SK_MX[4] - P[stateIndex][18]*SK_MX[3]);
+                    } else {
+                        Kfusion[stateIndex] = 0.0f;
+                    }
+                }
             } else {
                 // zero indexes 13 to 15 = 3*4 bytes
                 memset(&Kfusion[13], 0, 12);
@@ -677,9 +682,14 @@ void NavEKF3_core::FuseMagnetometer()
             }
 
             if (!inhibitDelVelBiasStates) {
-                Kfusion[13] = SK_MY[0]*(P[13][20] + P[13][0]*SH_MAG[2] + P[13][1]*SH_MAG[1] + P[13][2]*SH_MAG[0] - P[13][3]*SK_MY[2] - P[13][17]*SK_MY[1] - P[13][16]*SK_MY[3] + P[13][18]*SK_MY[4]);
-                Kfusion[14] = SK_MY[0]*(P[14][20] + P[14][0]*SH_MAG[2] + P[14][1]*SH_MAG[1] + P[14][2]*SH_MAG[0] - P[14][3]*SK_MY[2] - P[14][17]*SK_MY[1] - P[14][16]*SK_MY[3] + P[14][18]*SK_MY[4]);
-                Kfusion[15] = SK_MY[0]*(P[15][20] + P[15][0]*SH_MAG[2] + P[15][1]*SH_MAG[1] + P[15][2]*SH_MAG[0] - P[15][3]*SK_MY[2] - P[15][17]*SK_MY[1] - P[15][16]*SK_MY[3] + P[15][18]*SK_MY[4]);
+                for (uint8_t index = 0; index < 3; index++) {
+                    uint8_t stateIndex = index + 13;
+                    if (!dvelBiasAxisInhibit[index]) {
+                        Kfusion[stateIndex] = SK_MY[0]*(P[stateIndex][20] + P[stateIndex][0]*SH_MAG[2] + P[stateIndex][1]*SH_MAG[1] + P[stateIndex][2]*SH_MAG[0] - P[stateIndex][3]*SK_MY[2] - P[stateIndex][17]*SK_MY[1] - P[stateIndex][16]*SK_MY[3] + P[stateIndex][18]*SK_MY[4]);
+                    } else {
+                        Kfusion[stateIndex] = 0.0f;
+                    }
+                }
             } else {
                 // zero indexes 13 to 15 = 3*4 bytes
                 memset(&Kfusion[13], 0, 12);
@@ -754,9 +764,14 @@ void NavEKF3_core::FuseMagnetometer()
             }
 
             if (!inhibitDelVelBiasStates) {
-                Kfusion[13] = SK_MZ[0]*(P[13][21] + P[13][0]*SH_MAG[1] - P[13][1]*SH_MAG[2] + P[13][3]*SH_MAG[0] + P[13][2]*SK_MZ[2] + P[13][18]*SK_MZ[1] + P[13][16]*SK_MZ[4] - P[13][17]*SK_MZ[3]);
-                Kfusion[14] = SK_MZ[0]*(P[14][21] + P[14][0]*SH_MAG[1] - P[14][1]*SH_MAG[2] + P[14][3]*SH_MAG[0] + P[14][2]*SK_MZ[2] + P[14][18]*SK_MZ[1] + P[14][16]*SK_MZ[4] - P[14][17]*SK_MZ[3]);
-                Kfusion[15] = SK_MZ[0]*(P[15][21] + P[15][0]*SH_MAG[1] - P[15][1]*SH_MAG[2] + P[15][3]*SH_MAG[0] + P[15][2]*SK_MZ[2] + P[15][18]*SK_MZ[1] + P[15][16]*SK_MZ[4] - P[15][17]*SK_MZ[3]);
+                for (uint8_t index = 0; index < 3; index++) {
+                    uint8_t stateIndex = index + 13;
+                    if (!dvelBiasAxisInhibit[index]) {
+                        Kfusion[stateIndex] = SK_MZ[0]*(P[stateIndex][21] + P[stateIndex][0]*SH_MAG[1] - P[stateIndex][1]*SH_MAG[2] + P[stateIndex][3]*SH_MAG[0] + P[stateIndex][2]*SK_MZ[2] + P[stateIndex][18]*SK_MZ[1] + P[stateIndex][16]*SK_MZ[4] - P[stateIndex][17]*SK_MZ[3]);
+                    } else {
+                        Kfusion[stateIndex] = 0.0f;
+                    }
+                }
             } else {
                 // zero indexes 13 to 15 = 3*4 bytes
                 memset(&Kfusion[13], 0, 12);
@@ -1287,9 +1302,14 @@ void NavEKF3_core::FuseDeclination(float declErr)
     }
 
     if (!inhibitDelVelBiasStates) {
-        Kfusion[13] = -t4*t13*(P[13][16]*magE-P[13][17]*magN);
-        Kfusion[14] = -t4*t13*(P[14][16]*magE-P[14][17]*magN);
-        Kfusion[15] = -t4*t13*(P[15][16]*magE-P[15][17]*magN);
+        for (uint8_t index = 0; index < 3; index++) {
+            uint8_t stateIndex = index + 13;
+            if (!dvelBiasAxisInhibit[index]) {
+                Kfusion[stateIndex] = -t4*t13*(P[stateIndex][16]*magE-P[stateIndex][17]*magN);
+            } else {
+                Kfusion[stateIndex] = 0.0f;
+            }
+        }
     } else {
         // zero indexes 13 to 15 = 3*4 bytes
         memset(&Kfusion[13], 0, 12);
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_OptFlowFusion.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_OptFlowFusion.cpp
index b09e737e05..8c55f8028a 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_OptFlowFusion.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_OptFlowFusion.cpp
@@ -466,9 +466,14 @@ void NavEKF3_core::FuseOptFlow()
             }
 
             if (!inhibitDelVelBiasStates) {
-                Kfusion[13] = t78*(P[13][0]*t2*t5-P[13][4]*t2*t7+P[13][1]*t2*t15+P[13][6]*t2*t10+P[13][2]*t2*t19-P[13][3]*t2*t22+P[13][5]*t2*t27);
-                Kfusion[14] = t78*(P[14][0]*t2*t5-P[14][4]*t2*t7+P[14][1]*t2*t15+P[14][6]*t2*t10+P[14][2]*t2*t19-P[14][3]*t2*t22+P[14][5]*t2*t27);
-                Kfusion[15] = t78*(P[15][0]*t2*t5-P[15][4]*t2*t7+P[15][1]*t2*t15+P[15][6]*t2*t10+P[15][2]*t2*t19-P[15][3]*t2*t22+P[15][5]*t2*t27);
+                for (uint8_t index = 0; index < 3; index++) {
+                    uint8_t stateIndex = index + 13;
+                    if (!dvelBiasAxisInhibit[index]) {
+                        Kfusion[stateIndex] = t78*(P[stateIndex][0]*t2*t5-P[stateIndex][4]*t2*t7+P[stateIndex][1]*t2*t15+P[stateIndex][6]*t2*t10+P[stateIndex][2]*t2*t19-P[stateIndex][3]*t2*t22+P[stateIndex][5]*t2*t27);
+                    } else {
+                        Kfusion[stateIndex] = 0.0f;
+                    }
+                }
             } else {
                 // zero indexes 13 to 15 = 3*4 bytes
                 memset(&Kfusion[13], 0, 12);
@@ -637,9 +642,14 @@ void NavEKF3_core::FuseOptFlow()
             }
 
             if (!inhibitDelVelBiasStates) {
-                Kfusion[13] = -t78*(P[13][0]*t2*t5+P[13][5]*t2*t8-P[13][6]*t2*t10+P[13][1]*t2*t16-P[13][2]*t2*t19+P[13][3]*t2*t22+P[13][4]*t2*t27);
-                Kfusion[14] = -t78*(P[14][0]*t2*t5+P[14][5]*t2*t8-P[14][6]*t2*t10+P[14][1]*t2*t16-P[14][2]*t2*t19+P[14][3]*t2*t22+P[14][4]*t2*t27);
-                Kfusion[15] = -t78*(P[15][0]*t2*t5+P[15][5]*t2*t8-P[15][6]*t2*t10+P[15][1]*t2*t16-P[15][2]*t2*t19+P[15][3]*t2*t22+P[15][4]*t2*t27);
+                for (uint8_t index = 0; index < 3; index++) {
+                    uint8_t stateIndex = index + 13;
+                    if (!dvelBiasAxisInhibit[index]) {
+                        Kfusion[stateIndex] = -t78*(P[stateIndex][0]*t2*t5+P[stateIndex][5]*t2*t8-P[stateIndex][6]*t2*t10+P[stateIndex][1]*t2*t16-P[stateIndex][2]*t2*t19+P[stateIndex][3]*t2*t22+P[stateIndex][4]*t2*t27);
+                    } else {
+                        Kfusion[stateIndex] = 0.0f;
+                    }
+                }
             } else {
                 // zero indexes 13 to 15 = 3*4 bytes
                 memset(&Kfusion[13], 0, 12);
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_PosVelFusion.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_PosVelFusion.cpp
index ea6e749ff4..8041688188 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_PosVelFusion.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_PosVelFusion.cpp
@@ -1363,9 +1363,14 @@ void NavEKF3_core::FuseBodyVel()
             }
 
             if (!inhibitDelVelBiasStates) {
-                Kfusion[13] = t77*(P[13][5]*t4+P[13][4]*t9+P[13][0]*t14-P[13][6]*t11+P[13][1]*t18-P[13][2]*t21+P[13][3]*t24);
-                Kfusion[14] = t77*(P[14][5]*t4+P[14][4]*t9+P[14][0]*t14-P[14][6]*t11+P[14][1]*t18-P[14][2]*t21+P[14][3]*t24);
-                Kfusion[15] = t77*(P[15][5]*t4+P[15][4]*t9+P[15][0]*t14-P[15][6]*t11+P[15][1]*t18-P[15][2]*t21+P[15][3]*t24);
+                for (uint8_t index = 0; index < 3; index++) {
+                    uint8_t stateIndex = index + 13;
+                    if (!dvelBiasAxisInhibit[index]) {
+                        Kfusion[stateIndex] = t77*(P[stateIndex][5]*t4+P[stateIndex][4]*t9+P[stateIndex][0]*t14-P[stateIndex][6]*t11+P[stateIndex][1]*t18-P[stateIndex][2]*t21+P[stateIndex][3]*t24);
+                    } else {
+                        Kfusion[stateIndex] = 0.0f;
+                    }
+                }
             } else {
                 // zero indexes 13 to 15 = 3*4 bytes
                 memset(&Kfusion[13], 0, 12);
@@ -1535,9 +1540,14 @@ void NavEKF3_core::FuseBodyVel()
             }
 
             if (!inhibitDelVelBiasStates) {
-                Kfusion[13] = t77*(-P[13][4]*t3+P[13][5]*t8+P[13][0]*t15+P[13][6]*t12+P[13][1]*t18+P[13][2]*t22-P[13][3]*t25);
-                Kfusion[14] = t77*(-P[14][4]*t3+P[14][5]*t8+P[14][0]*t15+P[14][6]*t12+P[14][1]*t18+P[14][2]*t22-P[14][3]*t25);
-                Kfusion[15] = t77*(-P[15][4]*t3+P[15][5]*t8+P[15][0]*t15+P[15][6]*t12+P[15][1]*t18+P[15][2]*t22-P[15][3]*t25);
+                for (uint8_t index = 0; index < 3; index++) {
+                    uint8_t stateIndex = index + 13;
+                    if (!dvelBiasAxisInhibit[index]) {
+                        Kfusion[stateIndex] = t77*(-P[stateIndex][4]*t3+P[stateIndex][5]*t8+P[stateIndex][0]*t15+P[stateIndex][6]*t12+P[stateIndex][1]*t18+P[stateIndex][2]*t22-P[stateIndex][3]*t25);
+                    } else {
+                        Kfusion[stateIndex] = 0.0f;
+                    }
+                }
             } else {
                 // zero indexes 13 to 15 = 3*4 bytes
                 memset(&Kfusion[13], 0, 12);
@@ -1708,9 +1718,14 @@ void NavEKF3_core::FuseBodyVel()
             }
 
             if (!inhibitDelVelBiasStates) {
-                Kfusion[13] = t77*(P[13][4]*t4+P[13][0]*t14+P[13][6]*t9-P[13][5]*t11-P[13][1]*t17+P[13][2]*t20+P[13][3]*t24);
-                Kfusion[14] = t77*(P[14][4]*t4+P[14][0]*t14+P[14][6]*t9-P[14][5]*t11-P[14][1]*t17+P[14][2]*t20+P[14][3]*t24);
-                Kfusion[15] = t77*(P[15][4]*t4+P[15][0]*t14+P[15][6]*t9-P[15][5]*t11-P[15][1]*t17+P[15][2]*t20+P[15][3]*t24);
+                for (uint8_t index = 0; index < 3; index++) {
+                    uint8_t stateIndex = index + 13;
+                    if (!dvelBiasAxisInhibit[index]) {
+                        Kfusion[stateIndex] = t77*(P[stateIndex][4]*t4+P[stateIndex][0]*t14+P[stateIndex][6]*t9-P[stateIndex][5]*t11-P[stateIndex][1]*t17+P[stateIndex][2]*t20+P[stateIndex][3]*t24);
+                    } else {
+                        Kfusion[stateIndex] = 0.0f;
+                    }
+                }
             } else {
                 // zero indexes 13 to 15 = 3*4 bytes
                 memset(&Kfusion[13], 0, 12);
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_RngBcnFusion.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_RngBcnFusion.cpp
index 4bb037032d..4abc2ef5a2 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_RngBcnFusion.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_RngBcnFusion.cpp
@@ -149,9 +149,14 @@ void NavEKF3_core::FuseRngBcn()
         }
 
         if (!inhibitDelVelBiasStates) {
-            Kfusion[13] = -t26*(P[13][7]*t4*t9+P[13][8]*t3*t9+P[13][9]*t2*t9);
-            Kfusion[14] = -t26*(P[14][7]*t4*t9+P[14][8]*t3*t9+P[14][9]*t2*t9);
-            Kfusion[15] = -t26*(P[15][7]*t4*t9+P[15][8]*t3*t9+P[15][9]*t2*t9);
+            for (uint8_t index = 0; index < 3; index++) {
+                uint8_t stateIndex = index + 13;
+                if (!dvelBiasAxisInhibit[index]) {
+                    Kfusion[stateIndex] = -t26*(P[stateIndex][7]*t4*t9+P[stateIndex][8]*t3*t9+P[stateIndex][9]*t2*t9);
+                } else {
+                    Kfusion[stateIndex] = 0.0f;
+                }
+            }
         } else {
             // zero indexes 13 to 15 = 3*4 bytes
             memset(&Kfusion[13], 0, 12);
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp
index 68a849a325..e341b8cd79 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp
@@ -226,6 +226,8 @@ void NavEKF3_core::InitialiseVariables()
     lastRngMeasTime_ms = 0;
 
     // initialise other variables
+    memset(&dvelBiasAxisInhibit, 0, sizeof(dvelBiasAxisInhibit));
+	dvelBiasAxisVarPrev.zero();
     gpsNoiseScaler = 1.0f;
     hgtTimeout = true;
     tasTimeout = true;
@@ -1131,6 +1133,24 @@ void NavEKF3_core::CovariancePrediction(Vector3f *rotVarVecPtr)
     float _accNoise = constrain_float(frontend->_accNoise, 0.0f, 10.0f);
     dvxVar = dvyVar = dvzVar = sq(dt*_accNoise);
 
+    if (!inhibitDelVelBiasStates) {
+        for (unsigned stateIndex = 13; stateIndex <= 15; stateIndex++) {
+            const unsigned index = stateIndex - 13;
+
+            // Don't attempt learning of IMU delta velocty bias if on ground and not aligned with the gravity vector
+            const bool is_bias_observable = (fabsf(prevTnb[index][2]) > 0.8f) && onGround;
+
+            if (!is_bias_observable && !dvelBiasAxisInhibit[index]) {
+                // store variances to be reinstated wben learnign can commence later
+                dvelBiasAxisVarPrev[index] = P[stateIndex][stateIndex];
+                dvelBiasAxisInhibit[index] = true;
+            } else if (is_bias_observable && dvelBiasAxisInhibit[index]) {
+                P[stateIndex][stateIndex] = dvelBiasAxisVarPrev[index];
+                dvelBiasAxisInhibit[index] = false;
+            }
+        }
+    }
+
     // calculate the predicted covariance due to inertial sensor error propagation
     // we calculate the lower diagonal and copy to take advantage of symmetry
 
@@ -1659,6 +1679,18 @@ void NavEKF3_core::CovariancePrediction(Vector3f *rotVarVecPtr)
         }
     }
 
+    // inactive delta velocity bias states have all covariances zeroed to prevent
+    // interacton with other states
+    if (!inhibitDelVelBiasStates) {
+        for (uint8_t index=0; index<3; index++) {
+            uint8_t stateIndex = index + 13;
+            if (dvelBiasAxisInhibit[index]) {
+                zeroCols(nextP,stateIndex,stateIndex);
+                nextP[stateIndex][stateIndex] = dvelBiasAxisVarPrev[index];
+            }
+        }
+    }
+
     // if the total position variance exceeds 1e4 (100m), then stop covariance
     // growth by setting the predicted to the previous values
     // This prevent an ill conditioned matrix from occurring for long periods
@@ -1783,6 +1815,7 @@ void NavEKF3_core::ConstrainVariances()
         zeroRows(P,10,12);
     }
 
+    const float minStateVarTarget = 1E-8f;
     if (!inhibitDelVelBiasStates) {
 
         // Find the maximum delta velocity bias state variance and request a covariance reset if any variance is below the safe minimum
@@ -1799,7 +1832,6 @@ void NavEKF3_core::ConstrainVariances()
 
         // To ensure stability of the covariance matrix operations, the ratio of a max and min variance must
         // not exceed 100 and the minimum variance must not fall below the target minimum
-        const float minStateVarTarget = 1E-8f;
         float minAllowedStateVar = fmaxf(0.01f * maxStateVar, minStateVarTarget);
         for (uint8_t stateIndex=13; stateIndex<=15; stateIndex++) {
             P[stateIndex][stateIndex] = constrain_float(P[stateIndex][stateIndex], minAllowedStateVar, sq(10.0f * dtEkfAvg));
@@ -1823,6 +1855,10 @@ void NavEKF3_core::ConstrainVariances()
     } else {
         zeroCols(P,13,15);
         zeroRows(P,13,15);
+        for (uint8_t i=0; i<=2; i++) {
+            const uint8_t stateIndex = 1 + 13;
+            P[stateIndex][stateIndex] = fmaxf(P[stateIndex][stateIndex], minStateVarTarget);
+        }
     }
 
     if (!inhibitMagStates) {
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_core.h b/libraries/AP_NavEKF3/AP_NavEKF3_core.h
index b4f7f0a58f..3b31ef0699 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_core.h
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_core.h
@@ -1029,7 +1029,6 @@ private:
     bool lastInhibitMagStates;      // previous inhibitMagStates
     bool needMagBodyVarReset;       // we need to reset mag body variances at next CovariancePrediction
     bool needEarthBodyVarReset;     // we need to reset mag earth variances at next CovariancePrediction
-    bool inhibitDelVelBiasStates;   // true when IMU delta velocity bias states are inactive
     bool inhibitDelAngBiasStates;   // true when IMU delta angle bias states are inactive
     bool gpsNotAvailable;           // bool true when valid GPS data is not available
     struct Location EKF_origin;     // LLH origin of the NED axis system
@@ -1325,6 +1324,11 @@ private:
     bool onGroundNotMoving;             // true when on the ground and not moving
     uint32_t lastMoveCheckLogTime_ms;   // last time the movement check data was logged (msec)
 
+	// variables used to inhibit accel bias learning
+    bool inhibitDelVelBiasStates;       // true when all IMU delta velocity bias states are de-activated
+	bool dvelBiasAxisInhibit[3] {};		// true when IMU delta velocity bias states for a specific axis is de-activated
+	Vector3f dvelBiasAxisVarPrev;		// saved delta velocity XYZ bias variances (m/sec)**2
+
 #if EK3_FEATURE_EXTERNAL_NAV
     // external navigation fusion
     EKF_obs_buffer_t<ext_nav_elements> storedExtNav; // external navigation data buffer