diff --git a/src/blackcore/context/contextsimulatorimpl.cpp b/src/blackcore/context/contextsimulatorimpl.cpp
index e426b2945..132f21d9f 100644
--- a/src/blackcore/context/contextsimulatorimpl.cpp
+++ b/src/blackcore/context/contextsimulatorimpl.cpp
@@ -203,8 +203,7 @@ namespace BlackCore
             {
                 // ever used with XPlane
                 const QString pluginDir = CXPlaneUtil::pluginDirFromRootDir(m_simulatorSettings.getSimulatorDirectoryOrDefault(CSimulatorInfo::XPLANE));
-                const QDir dir(pluginDir);
-                if (dir.exists())
+                if (CDirectoryUtils::isDirExisting(pluginDir))
                 {
                     // only check if we are on a XP machine
                     const QStringList conflicts = CXPlaneUtil::findConflictingPlugins(pluginDir);
diff --git a/src/blackcore/simulatorcommon.cpp b/src/blackcore/simulatorcommon.cpp
index 87d4464ab..8f8b02586 100644
--- a/src/blackcore/simulatorcommon.cpp
+++ b/src/blackcore/simulatorcommon.cpp
@@ -479,7 +479,7 @@ namespace BlackCore
             if (part2 == "show")
             {
                 const QDir dir(CInterpolationLogger::getLogDirectory());
-                if (dir.exists())
+                if (CDirectoryUtils::isDirExisting(dir))
                 {
                     const QUrl dirUrl = QUrl::fromLocalFile(dir.absolutePath());
                     QDesktopServices::openUrl(dirUrl); // show dir in browser
diff --git a/src/blackmisc/directoryutils.cpp b/src/blackmisc/directoryutils.cpp
index e76ea349d..9d1f14ece 100644
--- a/src/blackmisc/directoryutils.cpp
+++ b/src/blackmisc/directoryutils.cpp
@@ -9,9 +9,9 @@
 
 //! \cond PRIVATE
 
-#include "blackmisc/directoryutils.h"
-#include "blackmisc/fileutils.h"
-#include "blackmisc/range.h"
+#include "directoryutils.h"
+#include "fileutils.h"
+#include "range.h"
 #include "blackconfig/buildconfig.h"
 #include <QCoreApplication>
 #include <QDir>
@@ -416,7 +416,7 @@ namespace BlackMisc
     {
         if (testDir.isEmpty()) { return false; }
         const QDir dir(testDir);
-        if (!dir.exists()) { return false; }
+        if (!CDirectoryUtils::isDirExisting(dir)) { return false; }
         return !dir.isEmpty();
     }
 
@@ -438,6 +438,33 @@ namespace BlackMisc
         return dirs;
     }
 
+    bool CDirectoryUtils::isDirExisting(const QString &path)
+    {
+        if (!CBuildConfig::isRunningOnWindowsNtPlatform())
+        {
+            const QDir dir(path);
+            return dir.exists();
+        }
+
+        // Windows
+        if (!CFileUtils::isWindowsUncPath(path))
+        {
+            const QDir dir(path);
+            return dir.exists();
+        }
+        const QString machine(CFileUtils::windowsUncMachine(path));
+        if (!CFileUtils::canPingUncMachine(machine)) { return false; }
+
+        const QDir dir(path);
+        return dir.exists();
+    }
+
+    bool CDirectoryUtils::isDirExisting(const QDir &dir)
+    {
+        if (!CFileUtils::isWindowsUncPath(dir.absolutePath())) { return dir.exists(); }
+        return CDirectoryUtils::isDirExisting(dir.absolutePath());
+    }
+
     QSet<QString> CDirectoryUtils::fileNamesToQSet(const QFileInfoList &fileInfoList)
     {
         QSet<QString> sl;
diff --git a/src/blackmisc/directoryutils.h b/src/blackmisc/directoryutils.h
index 673a105e4..469a39ef5 100644
--- a/src/blackmisc/directoryutils.h
+++ b/src/blackmisc/directoryutils.h
@@ -18,6 +18,7 @@
 #include <QSet>
 #include <QString>
 #include <QDateTime>
+#include <QDir>
 #include <QFileInfoList>
 
 namespace BlackMisc
@@ -144,6 +145,14 @@ namespace BlackMisc
         //! Get the existing directories
         static QStringList getExistingUnemptyDirectories(const QStringList &directories);
 
+        //! Directory existing? Also checking UNC paths upfront.
+        //! \remark Motivation: if an UNC cannot be accessed (e.g. machine is down) it can take very long before functions like QDir respond
+        //! \remark for non-UNC paths it is the same as the QDir checks
+        //! @{
+        static bool isDirExisting(const QString &path);
+        static bool isDirExisting(const QDir &dir);
+        //! @}
+
         //! Result of directory comparison
         struct DirComparison
         {
diff --git a/src/blackmisc/fileutils.cpp b/src/blackmisc/fileutils.cpp
index d330ba156..aadf9d948 100644
--- a/src/blackmisc/fileutils.cpp
+++ b/src/blackmisc/fileutils.cpp
@@ -7,9 +7,10 @@
  * contained in the LICENSE file.
  */
 
+#include "blackmisc/network/networkutils.h"
+#include "blackmisc/math/mathutils.h"
 #include "blackmisc/worker.h"
 #include "blackmisc/fileutils.h"
-#include "blackmisc/math/mathutils.h"
 #include "blackconfig/buildconfig.h"
 
 #include <QCoreApplication>
@@ -21,10 +22,12 @@
 #include <QLockFile>
 #include <QTextStream>
 #include <QtGlobal>
+#include <QMap>
 #include <algorithm>
 
 using namespace BlackConfig;
 using namespace BlackMisc::Math;
+using namespace BlackMisc::Network;
 
 namespace BlackMisc
 {
@@ -383,6 +386,59 @@ namespace BlackMisc
         return fixedPaths;
     }
 
+    bool CFileUtils::isWindowsUncPath(const QString &filePath)
+    {
+        if (filePath.startsWith("//") || filePath.startsWith("\\\\")) { return true; }
+        if (!CBuildConfig::isRunningOnWindowsNtPlatform()) { return false; } // "/tmp" is valid on Unix/Mac
+
+        // Windows here
+        const QString fp = fixWindowsUncPath(filePath);
+        return (fp.startsWith("//") || fp.startsWith("\\\\"));
+    }
+
+    QString CFileUtils::windowsUncMachine(const QString &filePath)
+    {
+        if (!CFileUtils::isWindowsUncPath(filePath)) { return QStringLiteral(""); }
+        QString f = filePath;
+        f.replace("\\", "/");
+        f.replace("//", "");
+        if (f.startsWith("/")) { f = f.mid(1); }
+        const int i = f.indexOf('/');
+        if (i < 0) { return f; }
+        return f.left(i);
+    }
+
+    bool CFileUtils::canPingUncMachine(const QString &machine)
+    {
+        static QMap<QString, qint64> good;
+        static QMap<QString, qint64> bad;
+
+        if (machine.isEmpty()) { return false; }
+        const QString m = machine.toLower();
+        if (good.contains(m)) { return true; } // good ones we only test once
+        if (bad.contains(m))
+        {
+            const qint64 ts = bad.value(m);
+            const qint64 dt = QDateTime::currentSecsSinceEpoch() - ts;
+            if (dt < 1000 * 60) { return false; } // still bad
+
+            // outdated, test again
+        }
+
+        const bool p = CNetworkUtils::canPing(m);
+        if (p)
+        {
+            good.insert(m, QDateTime::currentSecsSinceEpoch());
+            bad.remove(m);
+        }
+        else
+        {
+            bad.insert(m, QDateTime::currentSecsSinceEpoch());
+            good.remove(m);
+        }
+        return p;
+    }
+
     QString CFileUtils::toWindowsLocalPath(const QString &path)
     {
         QString p = CFileUtils::fixWindowsUncPath(path);
diff --git a/src/blackmisc/fileutils.h b/src/blackmisc/fileutils.h
index 41d02fc28..901e73607 100644
--- a/src/blackmisc/fileutils.h
+++ b/src/blackmisc/fileutils.h
@@ -147,6 +147,15 @@ namespace BlackMisc
         //! Fix UNC file paths
         static QStringList fixWindowsUncPaths(const QStringList &filePaths);
 
+        //! Windows UNC path?
+        static bool isWindowsUncPath(const QString &filePath);
+
+        //! Machine in Windows UNC path
+        static QString windowsUncMachine(const QString &filePath);
+
+        //! Can connect the UNC machine
+        static bool canPingUncMachine(const QString &machine);
+
         //! To Windows path using "\" delimiter
         static QString toWindowsLocalPath(const QString &path);
 
diff --git a/src/blackmisc/network/networkutils.cpp b/src/blackmisc/network/networkutils.cpp
index bab88e80d..aa8d3bae1 100644
--- a/src/blackmisc/network/networkutils.cpp
+++ b/src/blackmisc/network/networkutils.cpp
@@ -74,7 +74,14 @@ namespace BlackMisc
             }
             process.start();
             process.waitForFinished();
-            return process.exitCode() == 0;
+            const int rc = process.exitCode();
+            if (rc != 0) { return false; }
+
+            const QString std = process.readAllStandardOutput();
+            const QString err = process.readAllStandardError();
+            if (std.contains("unreachable", Qt::CaseInsensitive)) { return false; }
+            if (err.contains("unreachable", Qt::CaseInsensitive)) { return false; }
+            return true;
         }
 
         bool CNetworkUtils::canPing(const CUrl &url)
@@ -92,7 +99,7 @@ namespace BlackMisc
                 if (address.isNull()) { continue; }
                 if (address.protocol() == QAbstractSocket::IPv4Protocol)
                 {
-                    QString a = address.toString();
+                    const QString a = address.toString();
                     ips.append(a);
                 }
             }
diff --git a/src/blackmisc/simulation/xplane/xplaneutil.cpp b/src/blackmisc/simulation/xplane/xplaneutil.cpp
index a37693bca..acc8626ef 100644
--- a/src/blackmisc/simulation/xplane/xplaneutil.cpp
+++ b/src/blackmisc/simulation/xplane/xplaneutil.cpp
@@ -157,8 +157,8 @@ namespace BlackMisc
             QStringList CXPlaneUtil::pluginSubdirectories(const QString &pluginDir)
             {
                 const QString dirName = pluginDir.isEmpty() ? xplaneRootDir() : pluginDir;
+                if (!CDirectoryUtils::isDirExisting(dirName)) { return QStringList(); }
                 const QDir dir(dirName);
-                if (!dir.exists()) { return QStringList(); }
                 return dir.entryList(QDir::Dirs, QDir::Name | QDir::IgnoreCase);
             }
 
@@ -180,7 +180,7 @@ namespace BlackMisc
                 if (!rootDir.isEmpty())
                 {
                     const QString xswiftbusDir = CFileUtils::appendFilePathsAndFixUnc(CXPlaneUtil::pluginDirFromRootDir(xplaneRootDir), CXPlaneUtil::xswiftbusPathName());
-                    if (QDir(xswiftbusDir).exists())
+                    if (CDirectoryUtils::isDirExisting(xswiftbusDir))
                     {
                         return xswiftbusDir;
                     }
@@ -197,7 +197,7 @@ namespace BlackMisc
                 if (!rootDir.isEmpty())
                 {
                     const QString xswiftbusLegacy = CFileUtils::appendFilePathsAndFixUnc(xplaneRootDir, legacyPath);
-                    if (QDir(xswiftbusLegacy).exists())
+                    if (CDirectoryUtils::isDirExisting(xswiftbusLegacy))
                     {
                         return xswiftbusLegacy;
                     }