diff --git a/src/blackmisc/simulation/interpolatorlinear.cpp b/src/blackmisc/simulation/interpolatorlinear.cpp
index 3cd959306..a1e0372fa 100644
--- a/src/blackmisc/simulation/interpolatorlinear.cpp
+++ b/src/blackmisc/simulation/interpolatorlinear.cpp
@@ -19,11 +19,13 @@
 #include "blackmisc/range.h"
 #include "blackmisc/sequence.h"
 #include "blackmisc/statusmessage.h"
+#include "blackconfig/buildconfig.h"
 
 #include <QDateTime>
 #include <QList>
 #include <array>
 
+using namespace BlackConfig;
 using namespace BlackMisc::Aviation;
 using namespace BlackMisc::Geo;
 using namespace BlackMisc::Math;
@@ -90,7 +92,7 @@ namespace BlackMisc
         CInterpolatorLinear::Interpolant CInterpolatorLinear::getInterpolant(
             qint64 currentTimeMsSinceEpoc,
             const CInterpolationAndRenderingSetupPerCallsign &setup,
-            CInterpolationStatus &status, SituationLog &log) const
+            CInterpolationStatus &status, SituationLog &log)
         {
             Q_UNUSED(setup);
             status.reset();
@@ -98,8 +100,14 @@ namespace BlackMisc
             // with the latest updates of T243 the order and the offsets are supposed to be correct
             // so even mixing fast/slow updates shall work
             const CAircraftSituationList validSituations = this->remoteAircraftSituations(m_callsign); // if needed, we could also copy here
-            BLACK_VERIFY_X(validSituations.isSortedAdjustedLatestFirst(), Q_FUNC_INFO, "Wrong sort order");
-            Q_ASSERT_X(validSituations.size() <= IRemoteAircraftProvider::MaxSituationsPerCallsign, Q_FUNC_INFO, "Wrong size");
+            m_situationsLastModifiedUsed = this->situationsLastModified(m_callsign);
+
+            // checks
+            if (!CBuildConfig::isReleaseBuild())
+            {
+                BLACK_VERIFY_X(validSituations.isSortedAdjustedLatestFirst(), Q_FUNC_INFO, "Wrong sort order");
+                Q_ASSERT_X(validSituations.size() <= IRemoteAircraftProvider::MaxSituationsPerCallsign, Q_FUNC_INFO, "Wrong size");
+            }
 
             // find the first situation earlier than the current time
             const auto pivot = std::partition_point(validSituations.begin(), validSituations.end(), [ = ](auto &&s) { return s.getAdjustedMSecsSinceEpoch() > currentTimeMsSinceEpoc; });
@@ -150,17 +158,22 @@ namespace BlackMisc
                 Q_ASSERT(oldSituation.getAdjustedMSecsSinceEpoch() < newSituation.getAdjustedMSecsSinceEpoch());
             }
 
-            // take hint into account to calculate elevation and above ground level
-            // do not call for XP (lazy init)
-            const CElevationPlane planeOld = this->findClosestElevationWithinRange(oldSituation, CElevationPlane::singlePointRadius());
-            const CElevationPlane planeNew = this->findClosestElevationWithinRange(newSituation, CElevationPlane::singlePointRadius());
-            oldSituation.setGroundElevationChecked(planeOld);
-            newSituation.setGroundElevationChecked(planeNew);
+            // adjust ground if required
+            if (!oldSituation.canLikelySkipNearGroundInterpolation() && !oldSituation.hasGroundElevation())
+            {
+                const CElevationPlane planeOld = this->findClosestElevationWithinRange(oldSituation, CElevationPlane::singlePointRadius());
+                oldSituation.setGroundElevationChecked(planeOld);
+            }
+            if (!newSituation.canLikelySkipNearGroundInterpolation() && !newSituation.hasGroundElevation())
+            {
+                const CElevationPlane planeNew = this->findClosestElevationWithinRange(newSituation, CElevationPlane::singlePointRadius());
+                newSituation.setGroundElevationChecked(planeNew);
+            }
 
             CAircraftSituation currentSituation(oldSituation); // also sets ground elevation if available
 
             // Time between start and end packet
-            const double sampleDeltaTimeMs = newSituation.getAdjustedMSecsSinceEpoch() - oldSituation.getAdjustedMSecsSinceEpoch();
+            const qint64 sampleDeltaTimeMs = newSituation.getAdjustedMSecsSinceEpoch() - oldSituation.getAdjustedMSecsSinceEpoch();
             Q_ASSERT_X(sampleDeltaTimeMs >= 0, Q_FUNC_INFO, "Negative delta time");
             log.interpolator = 'l';
 
diff --git a/src/blackmisc/simulation/interpolatorlinear.h b/src/blackmisc/simulation/interpolatorlinear.h
index c251d876a..9332b9a6d 100644
--- a/src/blackmisc/simulation/interpolatorlinear.h
+++ b/src/blackmisc/simulation/interpolatorlinear.h
@@ -32,9 +32,9 @@ namespace BlackMisc
         public:
             //! Constructor
             CInterpolatorLinear(const Aviation::CCallsign &callsign,
-                                ISimulationEnvironmentProvider *p1, IInterpolationSetupProvider *p2, IRemoteAircraftProvider *p3,
+                                ISimulationEnvironmentProvider *simEnvProvider, IInterpolationSetupProvider *setupProvider, IRemoteAircraftProvider *remoteAircraftProvider,
                                 CInterpolationLogger *logger = nullptr) :
-                CInterpolator(callsign, p1, p2, p3, logger) {}
+                CInterpolator(callsign, simEnvProvider, setupProvider, remoteAircraftProvider, logger) {}
 
             //! Linear function that performs the actual interpolation
             class Interpolant
@@ -71,7 +71,7 @@ namespace BlackMisc
             };
 
             //! Get the interpolant for the given time point
-            Interpolant getInterpolant(qint64 currentTimeMsSinceEpoc, const CInterpolationAndRenderingSetupPerCallsign &setup, CInterpolationStatus &status, SituationLog &log) const;
+            Interpolant getInterpolant(qint64 currentTimeMsSinceEpoc, const CInterpolationAndRenderingSetupPerCallsign &setup, CInterpolationStatus &status, SituationLog &log);
         };
     } // ns
 } // ns
diff --git a/src/blackmisc/simulation/remoteaircraftprovider.cpp b/src/blackmisc/simulation/remoteaircraftprovider.cpp
index 2a67e73e7..70b25076c 100644
--- a/src/blackmisc/simulation/remoteaircraftprovider.cpp
+++ b/src/blackmisc/simulation/remoteaircraftprovider.cpp
@@ -345,9 +345,12 @@ namespace BlackMisc
             CAircraftSituationList situations = this->remoteAircraftSituations(callsign);
             const int updated = situations.setGroundElevationChecked(elevation);
             if (updated < 1) { return false; }
+            const qint64 ts = QDateTime::currentMSecsSinceEpoch();
+
             {
                 QWriteLocker l(&m_lockSituations);
                 m_situationsByCallsign[callsign] = situations;
+                m_situationsLastModified[callsign] = ts;
             }
 
             // aircraft updates