diff --git a/src/features/online-board/components/OnlineBoardFilter.tsx b/src/features/online-board/components/OnlineBoardFilter.tsx
index c8dbc35c..54e3adf9 100644
--- a/src/features/online-board/components/OnlineBoardFilter.tsx
+++ b/src/features/online-board/components/OnlineBoardFilter.tsx
@@ -336,6 +336,7 @@ export const OnlineBoardFilter: FC<OnlineBoardFilterProps> = ({
                           placeholder={t("SHARED.FLIGHT_NUMBER_PLACEHOLDER")}
                           value={flightNumber}
                           maxLength={5}
+                          aria-invalid={Boolean(flightNumberError)}
                           onChange={(e) => {
                             setFlightNumber(e.target.value);
                             if (flightNumberError) setFlightNumberError(null);