diff --git a/src/features/schedule/components/ScheduleFilter.tsx b/src/features/schedule/components/ScheduleFilter.tsx
index 3fac2286..424a6931 100644
--- a/src/features/schedule/components/ScheduleFilter.tsx
+++ b/src/features/schedule/components/ScheduleFilter.tsx
@@ -111,6 +111,10 @@ export const ScheduleFilter: FC<ScheduleFilterProps> = ({
   ]);
   const [directOnly, setDirectOnly] = useState(initialDirectOnly);
   const [returnFlights, setReturnFlights] = useState(initialReturnFlights);
+  // Mirrors Angular ScheduleFilterValidationService: a single inline
+  // error shown below the arrival input when the user submits with
+  // departure === arrival. Cleared whenever either city changes.
+  const [sameCitiesError, setSameCitiesError] = useState<string | null>(null);
 
   const scheduleMinDate = useRef(getScheduleMinDate()).current;
   const scheduleMaxDate = useRef(getScheduleMaxDate()).current;
@@ -127,6 +131,13 @@ export const ScheduleFilter: FC<ScheduleFilterProps> = ({
       const arr = arrival.trim().toUpperCase();
       if (!dep || !arr) return;
 
+      // Angular rejects same-code routes with SHARED.ARRIVAL-EQUALS-DEPARTURE-ERROR.
+      if (dep === arr) {
+        setSameCitiesError("SHARED.ARRIVAL-EQUALS-DEPARTURE-ERROR");
+        return;
+      }
+      setSameCitiesError(null);
+
       // Default to current week if no range provided.
       const now = new Date();
       const day = now.getDay();
@@ -175,7 +186,10 @@ export const ScheduleFilter: FC<ScheduleFilterProps> = ({
               label={t("SHARED.DEPARTURE_CITY")}
               placeholder={t("SHARED.CITY_PLACEHOLDER")}
               value={departure}
-              onChange={setDeparture}
+              onChange={(code) => {
+                setDeparture(code);
+                if (sameCitiesError) setSameCitiesError(null);
+              }}
               dictionaries={dictionaries}
               testIdPrefix="schedule-departure"
             />
@@ -198,10 +212,21 @@ export const ScheduleFilter: FC<ScheduleFilterProps> = ({
               label={t("SHARED.ARRIVAL_CITY")}
               placeholder={t("SHARED.CITY_PLACEHOLDER")}
               value={arrival}
-              onChange={setArrival}
+              onChange={(code) => {
+                setArrival(code);
+                if (sameCitiesError) setSameCitiesError(null);
+              }}
               dictionaries={dictionaries}
               testIdPrefix="schedule-arrival"
             />
+            {sameCitiesError && (
+              <div
+                className="validation-tooltip"
+                data-testid="schedule-same-cities-error"
+              >
+                {t(sameCitiesError)}
+              </div>
+            )}
 
             <div className="calendar">
               <label className="label--filter">