Do not check turn angle when aircraft is not turning

Author: Douglasdc3

src/main/java/aero/t2s/modes/decoder/df/bds/Bds50.java

@@ -208,7 +208,7 @@ public Bds50(short[] data) {
         // Formula from SkyBrary TurnRate (1) = (TAS / 10) => Roll Angle
         // Which we can rewrite to Roll Angle * 10 * Turn Rate = TAS
         // When TAS is not known we can use GS instead allow for bigger margin
-        if (statusTrackAngle && statusRollAngle) {
+        if (statusTrackAngle && statusRollAngle && trackAngleRate != 0) {
             double expectedTAS = Math.abs(rollAngle * 10d * (trackAngleRate / 3d));
             if (statusTas) {
                 if (Math.abs(expectedTAS - tas) > 50) {

src/test/java/aero/t2s/modes/decoder/df/DfRealMessageTest.java

@@ -264,6 +264,30 @@ public void test_df21_bds40_4CA6F8() throws UnknownDownlinkFormatException {
         assertFalse(bds.isAutopilotAltitudeHold());
     }
 
+    @Test
+    public void test_df21_bds50_485209() throws UnknownDownlinkFormatException {
+        DownlinkFormat df = testMessage("A000093BFFF16B276004997B748F");
+
+        assertInstanceOf(DF20.class, df);
+        DF20 df20 = (DF20) df;
+        assertEquals("485209", df.getIcao()); // Military / corrupt transponder
+        assertEquals(14075, df20.getAltitude().getAltitude());
+
+        assertTrue(df20.isValid());
+        assertInstanceOf(Bds50.class, df20.getBds());
+
+        Bds50 bds = (Bds50) df20.getBds();
+        assertTrue(bds.isStatusGs());
+        assertEquals(314, bds.getGs(), 0.1);
+        assertTrue(bds.isStatusTas());
+        assertEquals(306, bds.getTas(), 0.1);
+        assertTrue(bds.isStatusRollAngle());
+        assertEquals(-0.1, bds.getRollAngle(), 0.1);
+        assertTrue(bds.isStatusTrueAngleRate());
+        assertEquals(0, bds.getTrackAngleRate(), 0.1);
+        assertTrue(bds.isStatusTrackAngle());
+        assertEquals(31.8, bds.getTrueTrack(), 0.1);
+    }
 
 
     private DownlinkFormat testMessage(String message) throws UnknownDownlinkFormatException {