diff --git a/src/FDM/YASim/FGFDM.cpp b/src/FDM/YASim/FGFDM.cpp
index e0249222c..9b5128c62 100644
--- a/src/FDM/YASim/FGFDM.cpp
+++ b/src/FDM/YASim/FGFDM.cpp
@@ -601,7 +601,12 @@ void FGFDM::parseWing(const XMLAttributes* a, const char* type, Airplane* airpla
         const char* flowregime = a->getValue("flow");
         if (!strcmp(flowregime,"TRANSONIC")) {
             w->setFlowRegime(FLOW_TRANSONIC);
-            w->setCriticalMachNumber(attrf(a, "mcrit", 0.6f));
+            const float mcrit = attrf(a,"mcrit", 0.6f);
+            if ( (mcrit > 0.0f) && (mcrit <= 1.0f)) {
+                w->setCriticalMachNumber(mcrit);
+            } else {
+                SG_LOG(SG_FLIGHT, SG_ALERT, "YASim warning: invalid input for critical mach number. Defaulting to mcrit=0.6.");
+            }
         }
     } else {
         w->setFlowRegime(FLOW_SUBSONIC);
diff --git a/src/FDM/YASim/Surface.cpp b/src/FDM/YASim/Surface.cpp
index a4a4e13aa..7566d57b4 100644
--- a/src/FDM/YASim/Surface.cpp
+++ b/src/FDM/YASim/Surface.cpp
@@ -182,12 +182,20 @@ void Surface::calcForce(const float* v, const float rho, float mach, float* out,
     float pg_correction {1};
     float wavedrag {0};
     if (_flow == FLOW_TRANSONIC) {
-        pg_correction = Math::polynomial(pg_coefficients, mach);
+        if (mach < 0.8f) {
+            pg_correction = 1.0f/sqrt(1.0f-(mach*mach));
+        }
+        if ((mach >= 0.8f) && (mach < 1.2f)) {
+            pg_correction = Math::polynomial(pg_coefficients, mach);
+        }
+        if (mach >= 1.2f) {
+            pg_correction = 2.0f/(((mach*mach)-1.0f)*YASIM_PI);
+        }
         out[2] *= pg_correction;
 
         // Add mach dependent wave drag (Perkins and Hage)
         if (mach > _Mcrit) {
-            wavedrag = 9.5f * Math::pow(mach-_Mcrit, 2.8f) + 0.00193f;
+            wavedrag = 9.5f * Math::pow((mach > 1.0f ? 1.0f : mach)-_Mcrit, 2.8f) + 0.00193f;
             out[0] += wavedrag;
         } 
     }
diff --git a/src/FDM/YASim/Surface.hpp b/src/FDM/YASim/Surface.hpp
index c3b771416..a6dd14c2f 100644
--- a/src/FDM/YASim/Surface.hpp
+++ b/src/FDM/YASim/Surface.hpp
@@ -135,10 +135,9 @@ private:
     float _alpha {0};
 
     FlowRegime _flow{FLOW_SUBSONIC};
-    float _Mcrit {1.0f};
+    float _Mcrit {0.6f};
 
-    std::vector<float> pg_coefficients {1, -0.163f, 5.877f, -39.157f, 104.694f,
-        -111.838f, 46.749f, -5.313f};
+    std::vector<float> pg_coefficients {-1.7671f, 0.4495f, 10.3423f, -6.9237f};
     
     SGPropertyNode* _fxN;
     SGPropertyNode* _fyN;