diff --git a/libraries/AP_TECS/AP_TECS.cpp b/libraries/AP_TECS/AP_TECS.cpp
index ae01d87e75..71ddf6cabd 100644
--- a/libraries/AP_TECS/AP_TECS.cpp
+++ b/libraries/AP_TECS/AP_TECS.cpp
@@ -536,6 +536,9 @@ void AP_TECS::_detect_underspeed(void)
     }
     else
     {
+        // this clears underspeed if we reach our demanded height and
+        // we are either below 95% throttle or we above 90% of min
+        // airspeed
         _flags.underspeed = false;
     }
 }