diff --git a/src/models/AirShippingMethod.ts b/src/models/AirShippingMethod.ts
index 47e52a4..805855c 100644
--- a/src/models/AirShippingMethod.ts
+++ b/src/models/AirShippingMethod.ts
@@ -13,6 +13,9 @@
 export type AirShippingMethod = {
     /**
      * Flight number in either ICAO or IATA format.
+     *
+     * For generic airfreight emissions without flight number, use Simple Shipping Method.
+     *
      */
     flightNumber: string
     /**