diff --git a/src/blackmisc/aviation/transponder.cpp b/src/blackmisc/aviation/transponder.cpp
index dbe8d94d0..5d5223294 100644
--- a/src/blackmisc/aviation/transponder.cpp
+++ b/src/blackmisc/aviation/transponder.cpp
@@ -108,6 +108,14 @@ namespace BlackMisc
             return StateStandby;
         }
 
+        bool CTransponder::setTransponderMode(CTransponder::TransponderMode mode)
+        {
+            const int m = static_cast<int>(mode);
+            if (m == m_transponderMode) { return false; }
+            m_transponderMode = m;
+            return true;
+        }
+
         QString CTransponder::getTransponderCodeFormatted() const
         {
             QString f("0000");
diff --git a/src/blackmisc/aviation/transponder.h b/src/blackmisc/aviation/transponder.h
index 3a0416e00..09e2bfc2c 100644
--- a/src/blackmisc/aviation/transponder.h
+++ b/src/blackmisc/aviation/transponder.h
@@ -114,11 +114,11 @@ namespace BlackMisc
             //! Set transponder code
             void setTransponderCode(const QString &transponderCode);
 
-             //! Mode from string
+            //! Mode from string
             static TransponderMode modeFromString(const QString &modeString);
 
             //! Set transponder mode
-            void setTransponderMode(TransponderMode mode) { m_transponderMode = static_cast<int>(mode); }
+            bool setTransponderMode(TransponderMode mode);
 
             //! Set emergency
             void setEmergency() { m_transponderCode = 7700; }
diff --git a/src/blackmisc/simulation/simulatedaircraft.cpp b/src/blackmisc/simulation/simulatedaircraft.cpp
index 664391efa..bce9a9880 100644
--- a/src/blackmisc/simulation/simulatedaircraft.cpp
+++ b/src/blackmisc/simulation/simulatedaircraft.cpp
@@ -567,6 +567,11 @@ namespace BlackMisc
                    m_com2system.isActiveFrequencyWithin25kHzChannel(comFrequency);
         }
 
+        bool CSimulatedAircraft::setTransponderMode(CTransponder::TransponderMode mode)
+        {
+            return (m_transponder.setTransponderMode(mode));
+        }
+
         QString CSimulatedAircraft::convertToQString(bool i18n) const
         {
             const QString s = m_callsign.toQString(i18n) %
diff --git a/src/blackmisc/simulation/simulatedaircraft.h b/src/blackmisc/simulation/simulatedaircraft.h
index f96bda744..74b546200 100644
--- a/src/blackmisc/simulation/simulatedaircraft.h
+++ b/src/blackmisc/simulation/simulatedaircraft.h
@@ -298,7 +298,7 @@ namespace BlackMisc
             void setTransponder(const Aviation::CTransponder &transponder) { m_transponder = transponder; }
 
             //! Set transponder mode
-            void setTransponderMode(Aviation::CTransponder::TransponderMode mode) { m_transponder.setTransponderMode(mode); }
+            bool setTransponderMode(Aviation::CTransponder::TransponderMode mode);
 
             //! Set transponder code
             void setTransponderCode(int code) { m_transponder.setTransponderCode(code); }