diff --git a/libraries/AP_NavEKF2/AP_NavEKF2.cpp b/libraries/AP_NavEKF2/AP_NavEKF2.cpp
index d9af5e271f..4645b8f75f 100644
--- a/libraries/AP_NavEKF2/AP_NavEKF2.cpp
+++ b/libraries/AP_NavEKF2/AP_NavEKF2.cpp
@@ -751,6 +751,18 @@ void NavEKF2::UpdateFilter(void)
         }
     }
 
+    if (primary != 0 && core[0].healthy() && !hal.util->get_soft_armed()) {
+        // when on the ground and disarmed force the first lane. This
+        // avoids us ending with with a lottery for which IMU is used
+        // in each flight. Otherwise the alignment of the timing of
+        // the lane updates with the timing of GPS updates can lead to
+        // a lane other than the first one being used as primary for
+        // some flights. As different IMUs may have quite different
+        // noise characteristics this leads to inconsistent
+        // performance
+        primary = 0;
+    }
+
     check_log_write();
 }