diff --git a/aman/sys/aco/Node.py b/aman/sys/aco/Node.py
index 50d0364..312c984 100644
--- a/aman/sys/aco/Node.py
+++ b/aman/sys/aco/Node.py
@@ -147,6 +147,9 @@ class Node:
         self.ArrivalCandidates = {}
         self.Inbound = inbound
 
+        if None == referenceTime or None == sequencingConfig:
+            return
+
         # predict the distance to IAF
         timePrediction = (referenceTime - inbound.ReportTime).total_seconds()
         if 0 != timePrediction and 0 != len(sequencingConfig.ActiveArrivalRunways):