diff --git a/track.c b/track.c
index dd1b0d0..22eba28 100644
--- a/track.c
+++ b/track.c
@@ -940,8 +940,15 @@ struct aircraft *trackUpdateFromMessage(struct modesMessage *mm)
         a->geom_rate = mm->geom_rate;
     }
 
-    if (mm->airground != AG_INVALID && accept_data(&a->airground_valid, mm->source)) {
-        a->airground = mm->airground;
+    if (mm->airground != AG_INVALID) {
+        // If our current state is UNCERTAIN, accept new data as normal
+        // If our current state is certain but new data is not, only accept the uncertain state if the certain data has gone stale
+        if (mm->airground != AG_UNCERTAIN ||
+            (mm->airground == AG_UNCERTAIN && !trackDataFresh(&a->airground_valid))) {
+            if (accept_data(&a->airground_valid, mm->source)) {
+                a->airground = mm->airground;
+            }
+        }
     }
 
     if (mm->callsign_valid && accept_data(&a->callsign_valid, mm->source)) {
diff --git a/track.h b/track.h
index 3d7475c..e52fefc 100644
--- a/track.h
+++ b/track.h
@@ -259,6 +259,12 @@ static inline int trackDataValid(const data_validity *v)
     return (v->source != SOURCE_INVALID && messageNow() < v->expires);
 }
 
+/* is this bit of data fresh? */
+static inline int trackDataFresh(const data_validity *v)
+{
+    return (v->source != SOURCE_INVALID && messageNow() < v->stale);
+}
+
 /* what's the age of this data, in milliseconds? */
 static inline uint64_t trackDataAge(const data_validity *v)
 {