diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp
index 17dbc15d78..41bcb31354 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp
@@ -193,8 +193,6 @@ void NavEKF3_core::writeOptFlowMeas(const uint8_t rawFlowQuality, const Vector2f
     // need to run the optical flow takeoff detection
     detectOptFlowTakeoff();
 
-    // calculate rotation matrices at mid sample time for flow observations
-    stateStruct.quat.rotation_matrix(Tbn_flow);
     // don't use data with a low quality indicator or extreme rates (helps catch corrupt sensor data)
     if ((rawFlowQuality > 0) && rawFlowRates.length() < 4.2f && rawGyroRates.length() < 4.2f) {
         // correct flow sensor body rates for bias and write
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_core.h b/libraries/AP_NavEKF3/AP_NavEKF3_core.h
index b0c6da6aec..673d804840 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_core.h
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_core.h
@@ -1170,7 +1170,6 @@ private:
     uint32_t rngValidMeaTime_ms;    // time stamp from latest valid range measurement (msec)
     uint32_t flowMeaTime_ms;        // time stamp from latest flow measurement (msec)
     uint32_t gndHgtValidTime_ms;    // time stamp from last terrain offset state update (msec)
-    Matrix3F Tbn_flow;              // transformation matrix from body to nav axes at the middle of the optical flow sample period
     Vector2 varInnovOptFlow;        // optical flow innovations variances (rad/sec)^2
     Vector2 innovOptFlow;           // optical flow LOS innovations (rad/sec)
     ftype Popt;                     // Optical flow terrain height state covariance (m^2)