| A transmission of information relating to air navigation that is not addressed to a specific station or stations. |
| A transmission from one station to another station in circumstances where two-way communication cannot be established but it is believed that the called station is able to receive the transmission. |
| A transmission where no reply is required from the receiving station. |
| A transmission of messages relating to en-route weather information which may affect the safety of aircraft operations that is not addressed to a specific station or stations. |
EN 