diff --git a/Common/Source/Comm/LKFlarm.cpp b/Common/Source/Comm/LKFlarm.cpp
index 58ffa9ac3..5296e269a 100755
--- a/Common/Source/Comm/LKFlarm.cpp
+++ b/Common/Source/Comm/LKFlarm.cpp
@@ -251,6 +251,8 @@ BOOL NMEAParser::PFLAV(const char *String, char **params, size_t nparams, NMEA_I
 
 */
 	if(nparams > 3) {
+		ScopeLock lock(CritSec_FlightData);
+
 		pGPS->FLARM_HW_Version = strtod(params[1], nullptr);
 		pGPS->FLARM_SW_Version = strtod(params[2], nullptr);
 
@@ -365,6 +367,8 @@ BOOL NMEAParser::PFLAU(const char *String, char **params, size_t nparams, NMEA_I
 		return FALSE;
 	}
 
+	ScopeLock lock(CritSec_FlightData);
+
 	setFlarmAvailable(pGPS);
 
 	pGPS->FLARM_RX = strtoul(params[0], nullptr, 10); // number of received FLARM devices
@@ -574,6 +578,8 @@ BOOL NMEAParser::PFLAA(const char *String, char **params, size_t nparams, NMEA_I
 		return FALSE;
 	}
 
+	ScopeLock lock(CritSec_FlightData);
+
 	setFlarmAvailable(pGPS);
 
 	// 5 id, 6 digit hex
diff --git a/Common/Source/Comm/Parser.cpp b/Common/Source/Comm/Parser.cpp
index df8347f1e..bb3d1392b 100755
--- a/Common/Source/Comm/Parser.cpp
+++ b/Common/Source/Comm/Parser.cpp
@@ -232,27 +232,21 @@ BOOL NMEAParser::ParseNMEAString_Internal(DeviceDescriptor_t& d, const char* Str
     std::string_view token = params[0] + 2;
     // Proprietary String
     if (token == "TAS1"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return PTAS1(d, &String[7], params + 1, n_params - 1, pGPS);
     }
     if (token == "FLAV"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return PFLAV(&String[7], params + 1, n_params - 1, pGPS);
     }
     if (token == "FLAA"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return PFLAA(&String[7], params + 1, n_params - 1, pGPS);
     }
     if (token == "FLAU"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return PFLAU(&String[7], params + 1, n_params - 1, pGPS);
     }
     if (token == "GRMZ"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return RMZ(d, &String[7], params + 1, n_params - 1, pGPS);
     }
     if (token == "LKAS"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return PLKAS(&String[7], params + 1, n_params - 1, pGPS);
     }
     return FALSE;
@@ -262,39 +256,32 @@ BOOL NMEAParser::ParseNMEAString_Internal(DeviceDescriptor_t& d, const char* Str
     // GNSS String
     std::string_view token = params[0] + 3;
     if (token == "GSA"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return GSA(&String[7], params + 1, n_params - 1, pGPS);
     }
     if (token == "GLL"sv) {
       /*
-      ScopeLock lock(CritSec_FlightData);
       return GLL(&String[7], params + 1, n_params-1, pGPS);
       */
       return FALSE;
     }
     if (token == "RMB"sv) {
       /*
-      ScopeLock lock(CritSec_FlightData);
       return RMB(&String[7], params + 1, n_params-1, pGPS);
       */
       return FALSE;
     }
     if (token == "RMC"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return RMC(&String[7], params + 1, n_params - 1, pGPS);
     }
     if (token == "GGA"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return GGA(&String[7], params + 1, n_params - 1, pGPS);
     }
     if (token == "VTG"sv) {
-      ScopeLock lock(CritSec_FlightData);
       return VTG(&String[7], params + 1, n_params - 1, pGPS);
     }
   }
 
   if (std::string_view(params[0] + 1) == "HCHDG"sv) {
-    ScopeLock lock(CritSec_FlightData);
     return HCHDG(&String[7], params + 1, n_params - 1, pGPS);
   }
 
@@ -428,6 +415,8 @@ BOOL NMEAParser::GLL(const char* String, char** params, size_t nparams, NMEA_INF
 
   if (!activeGPS) return TRUE;
 
+  ScopeLock lock(CritSec_FlightData);
+
   pGPS->NAVWarning = !gpsValid;
   
   // use valid time with invalid fix
@@ -482,6 +471,9 @@ BOOL NMEAParser::VTG(const char* String, char** params, size_t nparams, NMEA_INF
   // if no valid fix, we dont get speed either!
   if (gpsValid) {
     double speed = StrToDouble(params[4], NULL);
+
+    ScopeLock lock(CritSec_FlightData);
+
     pGPS->Speed = Units::From(unKnots, speed);
 
     if (ISCAR) {
@@ -524,6 +516,7 @@ BOOL NMEAParser::RMC(const char* String, char** params, size_t nparams, NMEA_INF
     double ps = GM130BarPressure();
     double Altitude = (1 - pow(fabs(ps / QNH),  0.190284)) * 44307.69;
 
+    ScopeLock lock(CritSec_FlightData);
     UpdateBaroSource(pGPS, nullptr, Altitude);
   }
 
@@ -532,12 +525,8 @@ BOOL NMEAParser::RMC(const char* String, char** params, size_t nparams, NMEA_INF
       double ps = Royaltek3200_GetPressure();
       double Altitude = (1 - pow(fabs(ps / QNH),  0.190284)) * 44307.69;
 
+      ScopeLock lock(CritSec_FlightData);
       UpdateBaroSource(pGPS, nullptr,  Altitude);
-
-      #if 0
-      pGPS->TemperatureAvailable=true;
-      pGPS->OutsideAirTemperature = Royaltek3200_GetTemperature();
-      #endif
     }
   }
 
@@ -553,6 +542,8 @@ BOOL NMEAParser::RMC(const char* String, char** params, size_t nparams, NMEA_INF
     speed = StrToDouble(params[6], NULL);
   }
   
+  ScopeLock lock(CritSec_FlightData);
+
   pGPS->NAVWarning = !gpsValid;
 
   // say we are updated every time we get this,
@@ -733,6 +724,9 @@ BOOL NMEAParser::GGA(const char* String, char** params, size_t nparams, NMEA_INF
   if(gpsValid && (nSatellites == 0)) {
     nSatellites = -1; // unknown count but valid fix !
   }
+
+  ScopeLock lock(CritSec_FlightData);
+
   pGPS->SatellitesUsed = nSatellites; // 091208
   pGPS->NAVWarning = !gpsValid; // 091208
 
@@ -833,8 +827,6 @@ BOOL NMEAParser::GGA(const char* String, char** params, size_t nparams, NMEA_INF
 // LK8000 IAS , in m/s*10  example: 346 for 34.6 m/s  which is = 124.56 km/h
 BOOL NMEAParser::PLKAS(const char* String, char** params, size_t nparams, NMEA_INFO *pGPS)
 {
-  (void)pGPS;
-
   if(nparams < 1) {
     TESTBENCH_DO_ONLY(10,StartupStore(_T(". NMEAParser invalid PLKAS sentence, nparams=%u%s"),(unsigned)nparams,NEWLINE));
     // max index used is 0...
@@ -842,6 +834,8 @@ BOOL NMEAParser::PLKAS(const char* String, char** params, size_t nparams, NMEA_I
   }
   
   double vias=StrToDouble(params[0],NULL)/10.0;
+
+  ScopeLock lock(CritSec_FlightData);
   if (vias > 1) {
     double qne_altitude = QNHAltitudeToQNEAltitude(pGPS->Altitude);
     pGPS->TrueAirspeed = TrueAirSpeed(vias, qne_altitude);
@@ -859,8 +853,6 @@ BOOL NMEAParser::PLKAS(const char* String, char** params, size_t nparams, NMEA_I
 
 BOOL NMEAParser::RMZ(DeviceDescriptor_t& d, const char* String, char **params, size_t nparams, NMEA_INFO *pGPS)
 {
-  (void)pGPS;
-
   if(nparams < 2) {
     TESTBENCH_DO_ONLY(10,StartupStore(_T(". NMEAParser invalid RMZ sentence, nparams=%u%s"),(unsigned)nparams,NEWLINE));
     // max index used is 1...
@@ -877,6 +869,8 @@ BOOL NMEAParser::RMZ(DeviceDescriptor_t& d, const char* String, char **params, s
   LastRMZHB = LKHearthBeats;
 
   double Altitude = ParseAltitude(params[0], params[1]);
+
+  ScopeLock lock(CritSec_FlightData);
   UpdateBaroSource(pGPS, &d, QNEAltitudeToQNHAltitude(Altitude));
 
   return FALSE;
@@ -892,6 +886,8 @@ BOOL NMEAParser::PTAS1(DeviceDescriptor_t& d, const char* String, char **params,
     return FALSE;
   }
 
+  ScopeLock lock(CritSec_FlightData);
+
   if(*params[0] != _T('\0')) {
     const double wnet = Units::From(unKnots, (StrToDouble(params[0],NULL) - 200.0) / 10);
     UpdateVarioSource(*pGPS, d, wnet);
@@ -923,14 +919,13 @@ BOOL NMEAParser::HCHDG(const char* String, char** params, size_t nparams, NMEA_I
     return FALSE;
   }
   
-  (void)pGPS;
-  double mag=0;
-  mag=StrToDouble(params[0],NULL);
+  double mag = StrToDouble(params[0],NULL);
   if (mag>=0 && mag<=360) {
+      ScopeLock lock(CritSec_FlightData);
       pGPS->MagneticHeading=mag;
       pGPS->MagneticHeadingAvailable=TRUE;
   }
-  return FALSE;
+  return TRUE;
 }