diff --git a/src/features/online-board/types.ts b/src/features/online-board/types.ts
index 6f77abb2..787aa70b 100644
--- a/src/features/online-board/types.ts
+++ b/src/features/online-board/types.ts
@@ -237,7 +237,11 @@ export interface IOperatingBy {
   actual?: string;
   /** @deprecated use `scheduled` / `actual`; retained for old consumers */
   carrier?: string;
-  /** @deprecated code-share flight number; unused in React */
+  /**
+   * Code-share flight number (e.g. "0100"). Used in DetailsHeaderBadge
+   * to render the secondary `KL 1234, AF 5678` line under the primary
+   * flight number for multi-leg flights with different operating carriers.
+   */
   flightNumber?: string;
 }