diff --git a/ArduPlane/ArduPlane.pde b/ArduPlane/ArduPlane.pde
index dd372790f2..5fba076be7 100644
--- a/ArduPlane/ArduPlane.pde
+++ b/ArduPlane/ArduPlane.pde
@@ -343,7 +343,6 @@ static bool have_position;
 ////////////////////////////////////////////////////////////////////////////////
 // Constants
 const float radius_of_earth   = 6378100;        // meters
-const float gravity                   = 9.81;           // meters/ sec^2
 
 // This is the currently calculated direction to fly.
 // deg * 100 : 0 to 360
diff --git a/ArduPlane/Attitude.pde b/ArduPlane/Attitude.pde
index ff612cec36..3a0f176721 100644
--- a/ArduPlane/Attitude.pde
+++ b/ArduPlane/Attitude.pde
@@ -328,7 +328,7 @@ static void calc_nav_roll()
     }
 
     // Bank angle = V*R/g, where V is airspeed, R is turn rate, and g is gravity.
-    nav_roll = ToDeg(atan(speed*turn_rate/9.81)*100);
+    nav_roll = ToDeg(atan(speed*turn_rate/GRAVITY_MSS)*100);
 
 #else
     // this is the old nav_roll calculation. We will use this for 2.50
diff --git a/ArduPlane/GCS_Mavlink.pde b/ArduPlane/GCS_Mavlink.pde
index c77af7cc90..24b4602ff7 100644
--- a/ArduPlane/GCS_Mavlink.pde
+++ b/ArduPlane/GCS_Mavlink.pde
@@ -235,7 +235,7 @@ static NOINLINE void send_extended_status1(mavlink_channel_t chan, uint16_t pack
 
 static void NOINLINE send_meminfo(mavlink_channel_t chan)
 {
-#if CONFIG_HAL_BOARD != HAL_BOARD_AVR_SITL
+#if CONFIG_HAL_BOARD == HAL_BOARD_APM1 || CONFIG_HAL_BOARD == HAL_BOARD_APM2
     extern unsigned __brkval;
     mavlink_msg_meminfo_send(chan, __brkval, memcheck_available_memory());
 #endif
@@ -401,9 +401,9 @@ static void NOINLINE send_raw_imu1(mavlink_channel_t chan)
     mavlink_msg_raw_imu_send(
         chan,
         micros(),
-        accel.x * 1000.0 / gravity,
-        accel.y * 1000.0 / gravity,
-        accel.z * 1000.0 / gravity,
+        accel.x * 1000.0 / GRAVITY_MSS,
+        accel.y * 1000.0 / GRAVITY_MSS,
+        accel.z * 1000.0 / GRAVITY_MSS,
         gyro.x * 1000.0,
         gyro.y * 1000.0,
         gyro.z * 1000.0,
@@ -1814,9 +1814,9 @@ mission_failed:
 
         // m/s/s
         Vector3f accels;
-        accels.x = packet.xacc * (gravity/1000.0);
-        accels.y = packet.yacc * (gravity/1000.0);
-        accels.z = packet.zacc * (gravity/1000.0);
+        accels.x = packet.xacc * (GRAVITY_MSS/1000.0);
+        accels.y = packet.yacc * (GRAVITY_MSS/1000.0);
+        accels.z = packet.zacc * (GRAVITY_MSS/1000.0);
 
         ins.set_gyro(gyros);
         ins.set_accel(accels);