| When the traffic situation at an airport allows the transmission of information which does not need to be acknowledged by the ground station |
| When a pilot has flown into cloud or fog unintentionally and therefore would like to request navigational assistance from a ground unit |
| When no radio communication can be established with the appropriate aeronautical station, but when evidence exists that transmissions are received at that ground unit |
| When a transmission containing important navigational or technical information is to be sent to several stations at the same time |
EN 