From 16bf10b333d6dbeefdeb2fe6782db8088ee75f79 Mon Sep 17 00:00:00 2001
From: James Turner <james@flightgear.org>
Date: Mon, 28 Jun 2021 12:13:56 +0100
Subject: [PATCH] Avoid Marker-beacon spam on FDM NaN case

Check and bail out of marker beacon search if we are in NaN-land; this
should making it easier to trace the cause of the NaNs.
---
 src/Instrumentation/marker_beacon.cxx | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/Instrumentation/marker_beacon.cxx b/src/Instrumentation/marker_beacon.cxx
index 816017a46..902ae20ad 100644
--- a/src/Instrumentation/marker_beacon.cxx
+++ b/src/Instrumentation/marker_beacon.cxx
@@ -297,6 +297,10 @@ void FGMarkerBeacon::search()
     _time_before_search_sec = 0.5;
 
     const SGGeod pos = globals->get_aircraft_position();
+    if (!pos.isValid()) {
+        // avoid error flood when core positions goes wrong
+        return;
+    }
 
     // get closest marker beacon - within a 1nm cutoff
     BeaconFilter filter;