diff --git a/src/blackcore/db/airportdatareader.cpp b/src/blackcore/db/airportdatareader.cpp
index 899b947ca..72da6315a 100644
--- a/src/blackcore/db/airportdatareader.cpp
+++ b/src/blackcore/db/airportdatareader.cpp
@@ -152,7 +152,7 @@ namespace BlackCore
 
         void CAirportDataReader::synchronizeCaches(CEntityFlags::Entity entities)
         {
-            if (entities.testFlag(CEntityFlags::AirportEntity)) { m_airportCache.synchronize(); }
+            if (entities.testFlag(CEntityFlags::AirportEntity)) { if (m_syncedAirportCache) { return; } m_syncedAirportCache = true; m_airportCache.synchronize(); }
         }
 
         void CAirportDataReader::admitCaches(CEntityFlags::Entity entities)
diff --git a/src/blackcore/db/airportdatareader.h b/src/blackcore/db/airportdatareader.h
index ce62edce8..775ad0e65 100644
--- a/src/blackcore/db/airportdatareader.h
+++ b/src/blackcore/db/airportdatareader.h
@@ -17,7 +17,9 @@
 #include "blackcore/db/databasereader.h"
 #include "blackmisc/aviation/airportlist.h"
 #include "blackmisc/network/entityflags.h"
+
 #include <QNetworkAccessManager>
+#include <atomic>
 
 namespace BlackCore
 {
@@ -73,7 +75,8 @@ namespace BlackCore
                          BlackMisc::Db::CDbFlags::DataRetrievalModeFlag mode = BlackMisc::Db::CDbFlags::DbReading, const QDateTime &newerThan = QDateTime());
 
         private:
-            BlackMisc::CData<BlackCore::Data::TDbAirportCache> m_airportCache {this, &CAirportDataReader::airportCacheChanged};
+            BlackMisc::CData<BlackCore::Data::TDbAirportCache> m_airportCache {this, &CAirportDataReader::airportCacheChanged}; //!< cache file
+            std::atomic_bool m_syncedAirportCache { false }; //!< already synchronized?
 
             //! Reader URL (we read from where?) used to detect changes of location
             BlackMisc::CData<BlackCore::Data::TDbModelReaderBaseUrl> m_readerUrlCache {this, &CAirportDataReader::baseUrlCacheChanged };
diff --git a/src/blackcore/db/icaodatareader.cpp b/src/blackcore/db/icaodatareader.cpp
index b0c7bb9dd..5bb244942 100644
--- a/src/blackcore/db/icaodatareader.cpp
+++ b/src/blackcore/db/icaodatareader.cpp
@@ -576,9 +576,9 @@ namespace BlackCore
 
         void CIcaoDataReader::synchronizeCaches(CEntityFlags::Entity entities)
         {
-            if (entities.testFlag(CEntityFlags::AircraftIcaoEntity)) { m_aircraftIcaoCache.synchronize(); }
-            if (entities.testFlag(CEntityFlags::AirlineIcaoEntity)) { m_airlineIcaoCache.synchronize(); }
-            if (entities.testFlag(CEntityFlags::CountryEntity)) { m_countryCache.synchronize(); }
+            if (entities.testFlag(CEntityFlags::AircraftIcaoEntity)) { if (m_syncedAircraftIcaoCache) { return; } m_syncedAircraftIcaoCache = true; m_aircraftIcaoCache.synchronize(); }
+            if (entities.testFlag(CEntityFlags::AirlineIcaoEntity))  { if (m_syncedAirlineIcaoCache) { return; } m_syncedAirlineIcaoCache = true; m_airlineIcaoCache.synchronize(); }
+            if (entities.testFlag(CEntityFlags::CountryEntity)) { if (m_syncedCountryCache) { return; } m_syncedCountryCache = true; m_countryCache.synchronize(); }
         }
 
         void CIcaoDataReader::admitCaches(CEntityFlags::Entity entities)
diff --git a/src/blackcore/db/icaodatareader.h b/src/blackcore/db/icaodatareader.h
index 969be511b..43c7cee56 100644
--- a/src/blackcore/db/icaodatareader.h
+++ b/src/blackcore/db/icaodatareader.h
@@ -26,6 +26,7 @@
 #include <QObject>
 #include <QReadWriteLock>
 #include <QString>
+#include <atomic>
 
 class QDateTime;
 class QNetworkReply;
@@ -162,6 +163,9 @@ namespace BlackCore
             BlackMisc::CData<BlackCore::Data::TDbAircraftIcaoCache> m_aircraftIcaoCache {this, &CIcaoDataReader::aircraftIcaoCacheChanged };
             BlackMisc::CData<BlackCore::Data::TDbAirlineIcaoCache>  m_airlineIcaoCache  {this, &CIcaoDataReader::airlineIcaoCacheChanged };
             BlackMisc::CData<BlackCore::Data::TDbCountryCache>      m_countryCache      {this, &CIcaoDataReader::countryCacheChanged };
+            std::atomic_bool m_syncedAircraftIcaoCache { false }; //!< already synchronized?
+            std::atomic_bool m_syncedAirlineIcaoCache  { false }; //!< already synchronized?
+            std::atomic_bool m_syncedCountryCache      { false }; //!< already synchronized?
 
             //! Reader URL (we read from where?) used to detect changes of location
             BlackMisc::CData<BlackCore::Data::TDbIcaoReaderBaseUrl> m_readerUrlCache {this, &CIcaoDataReader::baseUrlCacheChanged };
diff --git a/src/blackcore/db/modeldatareader.cpp b/src/blackcore/db/modeldatareader.cpp
index 0507b1341..c0a10adcf 100644
--- a/src/blackcore/db/modeldatareader.cpp
+++ b/src/blackcore/db/modeldatareader.cpp
@@ -579,9 +579,9 @@ namespace BlackCore
 
         void CModelDataReader::synchronizeCaches(CEntityFlags::Entity entities)
         {
-            if (entities.testFlag(CEntityFlags::LiveryEntity)) { m_liveryCache.synchronize(); }
-            if (entities.testFlag(CEntityFlags::ModelEntity))  { m_modelCache.synchronize(); }
-            if (entities.testFlag(CEntityFlags::DistributorEntity)) { m_distributorCache.synchronize(); }
+            if (entities.testFlag(CEntityFlags::LiveryEntity)) { if (m_syncedLiveryCache) { return; } m_syncedLiveryCache = true; m_liveryCache.synchronize(); }
+            if (entities.testFlag(CEntityFlags::ModelEntity))  { if (m_syncedModelCache) { return; } m_syncedModelCache = true;  m_modelCache.synchronize(); }
+            if (entities.testFlag(CEntityFlags::DistributorEntity)) { if (m_syncedDistributorCache) { return; } m_syncedDistributorCache = true; m_distributorCache.synchronize(); }
         }
 
         void CModelDataReader::admitCaches(CEntityFlags::Entity entities)
diff --git a/src/blackcore/db/modeldatareader.h b/src/blackcore/db/modeldatareader.h
index 3067c0c51..fb5be60cd 100644
--- a/src/blackcore/db/modeldatareader.h
+++ b/src/blackcore/db/modeldatareader.h
@@ -165,6 +165,9 @@ namespace BlackCore
             BlackMisc::CData<BlackCore::Data::TDbLiveryCache>      m_liveryCache { this, &CModelDataReader::liveryCacheChanged };
             BlackMisc::CData<BlackCore::Data::TDbModelCache>       m_modelCache  { this, &CModelDataReader::modelCacheChanged };
             BlackMisc::CData<BlackCore::Data::TDbDistributorCache> m_distributorCache { this, &CModelDataReader::distributorCacheChanged };
+            std::atomic_bool m_syncedLiveryCache { false }; //!< already synchronized?
+            std::atomic_bool m_syncedModelCache  { false }; //!< already synchronized?
+            std::atomic_bool m_syncedDistributorCache { false }; //!< already synchronized?
 
             //! Reader URL (we read from where?) used to detect changes of location
             BlackMisc::CData<BlackCore::Data::TDbModelReaderBaseUrl> m_readerUrlCache { this, &CModelDataReader::baseUrlCacheChanged };