diff --git a/ontology-generator/ontology/fta-fmea-model.ttl b/ontology-generator/ontology/fta-fmea-model.ttl
index f90958b..3dba589 100644
--- a/ontology-generator/ontology/fta-fmea-model.ttl
+++ b/ontology-generator/ontology/fta-fmea-model.ttl
@@ -540,6 +540,9 @@ fta-fmea:system-name rdf:type owl:DatatypeProperty ;
     fta-fmea:status rdf:type owl:DatatypeProperty ;
                       rdfs:label "status" .
 
+###  http://onto.fel.cvut.cz/ontologies/fta-fmea-application/auxiliary
+    fta-fmea:auxiliary rdf:type owl:DatatypeProperty ;
+                      rdfs:label "auxiliary" .
 
 #################################################################
 #    Classes
diff --git a/src/main/java/cz/cvut/kbss/analysis/dao/FaultTreeDao.java b/src/main/java/cz/cvut/kbss/analysis/dao/FaultTreeDao.java
index 4235081..410a633 100755
--- a/src/main/java/cz/cvut/kbss/analysis/dao/FaultTreeDao.java
+++ b/src/main/java/cz/cvut/kbss/analysis/dao/FaultTreeDao.java
@@ -118,6 +118,9 @@ public Query getSummariesQuery() {
                                     OPTIONAL{
                                         ?rootEvent fta:probability ?calculatedFailureRate.
                                     }
+                                    OPTIONAL{
+                                        ?rootEventType fta:auxiliary ?auxiliary.
+                                    }
                                     OPTIONAL{
                                         ?rootEventType fta:has-failure-rate ?failureRate.
                                         ?failureRate fta:has-requirement ?failureRateRequirement.
diff --git a/src/main/java/cz/cvut/kbss/analysis/model/FaultEventType.java b/src/main/java/cz/cvut/kbss/analysis/model/FaultEventType.java
index 0ee6f83..a3dd62f 100644
--- a/src/main/java/cz/cvut/kbss/analysis/model/FaultEventType.java
+++ b/src/main/java/cz/cvut/kbss/analysis/model/FaultEventType.java
@@ -21,6 +21,9 @@ public class FaultEventType extends Event{
     @OWLDataProperty(iri = Vocabulary.s_p_fault_event_type)
     private String eventType;
 
+    @OWLDataProperty(iri = Vocabulary.s_p_auxiliary)
+    private Boolean auxiliary;
+
     @Override
     public void setAs(NamedEntity namedEntity) {
         if(namedEntity instanceof FaultEventTypeSummary)
diff --git a/src/main/java/cz/cvut/kbss/analysis/model/FaultTreeSummary.java b/src/main/java/cz/cvut/kbss/analysis/model/FaultTreeSummary.java
index 8696b77..6544776 100644
--- a/src/main/java/cz/cvut/kbss/analysis/model/FaultTreeSummary.java
+++ b/src/main/java/cz/cvut/kbss/analysis/model/FaultTreeSummary.java
@@ -51,6 +51,8 @@ public class FaultTreeSummary extends ManagedEntity{
     @OWLDataProperty(iri = Vocabulary.s_p_fha_based_failure_rate)
     protected Double fhaBasedFailureRate;
 
+    @OWLDataProperty(iri = Vocabulary.s_p_auxiliary)
+    protected Boolean auxiliary;
 
     public void copyTo(FaultTree faultTree){
         super.copyTo(faultTree);
@@ -63,6 +65,7 @@ public void copyTo(FaultTree faultTree){
                 rootType.setUri(this.getRootEventType());
                 root.setSupertypes(new HashSet<>());
                 root.getSupertypes().add(rootType);
+                rootType.setAuxiliary(auxiliary);
             }
         }
         if(this.getSystemUri() != null){
diff --git a/src/main/java/cz/cvut/kbss/analysis/service/FaultTreeRepositoryService.java b/src/main/java/cz/cvut/kbss/analysis/service/FaultTreeRepositoryService.java
index b67119e..a7609db 100755
--- a/src/main/java/cz/cvut/kbss/analysis/service/FaultTreeRepositoryService.java
+++ b/src/main/java/cz/cvut/kbss/analysis/service/FaultTreeRepositoryService.java
@@ -101,6 +101,7 @@ public void createTree(FaultTree faultTree){
         // load and persist supertypes
         if(faultTree.getManifestingEvent().getSupertypes() == null || faultTree.getManifestingEvent().getSupertypes().isEmpty()) {
             FHAEventType evt = new FHAEventType();
+            evt.setAuxiliary(true);
             evt.setName(faultTree.getManifestingEvent().getName());
             faultTree.getManifestingEvent().setSupertypes(Collections.singleton(evt));
         }
@@ -202,14 +203,19 @@ public Status getInferedStatus(FaultTree faultTree ){
     }
 
     public FaultTree update(FaultTree instance) {
-        if(instance.getManifestingEvent() == null && instance.getUri() != null){
-            FaultTree managedInstance = getPrimaryDao().find(instance.getUri()).orElse(null);
-            if(managedInstance == null)
-                throw EntityNotFoundException.create("Could find instance to update", instance.getUri());
-            managedInstance.setName(instance.getName());
-            instance = managedInstance;
-        }
-        return super.update(instance);
+        if(instance.getUri() == null)
+            throw new IllegalArgumentException("Cannot updated fault tree, fault tree uri is not set.");
+        if(!Optional.ofNullable(instance.getManifestingEvent())
+                .map(e -> e.getSupertypes())
+                .filter(s -> !s.isEmpty()).map(s -> s.iterator().next()).map(et -> ((FaultEventType)et).getAuxiliary()).orElse(false))
+            throw new IllegalArgumentException("Cannot updated name of fault tree connected to FHA event type.");
+        
+        FaultTree managedInstance = getPrimaryDao().find(instance.getUri()).orElse(null);
+        if(managedInstance == null)
+            throw EntityNotFoundException.create("Could find instance to update", instance.getUri());
+        managedInstance.setName(instance.getName());
+
+        return super.update(managedInstance);
     }
 
     @Override